WO2018186540A1 - Active noise canceling earphone using 3-level digital signal - Google Patents

Abstract

The present invention relates an active noise canceling earphone using a 3-level digital signal, the earphone reducing a loop delay time by using a 3-level pulse width modulation (PWM) signal or a 3-level pulse density modulation (PDM) signal, thereby enabling a frequency range capable of active noise canceling in the earphone receiving a digital audio signal to be increased. The active noise canceling earphone using the 3-level digital signal, according to the present invention, allows a loop delay time to be reduced in a digital active noise canceling earphone by using the 3-level PWM signal or the 3-level PDM signal, thereby enabling the attenuable maximum frequency of the noise sound signal to be increased to 500 Hz to 2,500 Hz.

Description

Active Noise Reduction Earphones with 3-Level Digital Signal

The present invention reduces the loop delay time using a three-level digital signal, in particular a three-level pulse width modulation (PWM) signal or a three-level pulse density modulation (PDM) signal, thereby reducing An active noise reduction earphone using a three-level digital signal capable of increasing the frequency range where active noise canceling is possible.

Recently, many people listen to digital audio signals supplied from smart phones using wired or wireless earphones in subways, buses, or airplanes. In this case, using earphones with Active Noise Canceling (ANC) can eliminate ambient noise and only listen to the desired audio signal.

1 is a conceptual diagram of a conventional analog active noise reduction (ANC) earphone.

Referring to FIG. 1, a conventional analog active noise reduction earphone 100 includes an analog subtractor 110, a first analog amplifier A1 and 120, an acoustic signal generator 130, and a second analog amplifier A2 and 140. It is provided.

When the analog audio signal A _IN desired by the user is input to the analog active noise reduction earphone 100, the analog subtractor 110 subtracts the analog feedback signal A _FB from the analog audio signal A _IN . Generates the analog difference signal A _ER . The first analog amplifiers A1 and 120 receive the analog difference signal A _ER as an input and amplify the analog difference signal A _ER to output the amplified difference signal.

The acoustic signal generator 130 includes an earphone speaker SP, 131, an adder 132, and a microphone MIC 133, and is located in an ear canal of the user.

The earphone speaker SP 131 receives the difference signal amplified by the first analog amplifiers A1 and 120 and outputs a speaker output sound signal S _ER .

The adder 132 combines the speaker output sound signal S _ER and the noise sound signal N introduced from the outside into the ear and outputs the synthesized sound signal S _O to the microphone MIC 133.

The microphone (MIC, 133) are converts the synthesized sound signal (S _O) to an electrical signal.

The second analog amplifiers A2 and 140 amplify an electric signal converted by the microphone MIC 133 and output the amplified electrical signal as the analog feedback signal A _FB .

Since the microphone MIC 133 is located in the user's ear, it is assumed that the sound signal detected by the microphone MIC 133 is substantially the same as the sound signal input to the ear drum of the user.

2 is a conceptual diagram for calculating a transfer function in the conventional analog active noise reduction (ANC) earphone shown in FIG.

The analog difference signal A _ER is an electrical signal of the speaker output sound signal S _ER , which is an acoustic signal generated by sequentially passing through the first analog amplifiers A1 and 120 and the earphone speaker SP and 131. A transfer function for the analog difference signal A _ER is called A ₁₁ (s), and the synthesized acoustic signal SO, which is an acoustic signal, is the microphone MIC and the second analog amplifier A2, Speaking 140) for the transfer function for the electrical signals of the said composite acoustic signal of the analog feedback signal (a _FB) (s _O) is generated through a ₂₂ turn (s), the acoustic signal delivered to the user's ear drum synthesizing a sound signal (S _O) is expressed by equation 1 below.

The transfer functions A ₁₁ (s) and A ₂₂ (s) are both configured to have a positive value at DC (s = 0), so that the microphone (MIC) and the second analog amplifier (A2) 140, a feedback loop formed by the analog subtractor 110, the first analog amplifiers A1 and 120, and the earphone speaker SP performs a negative feedback operation.

<Equation 1>

In Equation 1, if the product of loop gain A ₁₁ (s) and A ₂₂ (s) is sufficiently larger than 1, the noise acoustic signal N is 1 / {A ₁₁ (s) * A ₂₂ (s )} Is multiplied and greatly attenuated to the user's eardrum.The analog audio input signal (A _IN ) that you want to listen to is delivered relatively multiplied by the gain of 1 / A ₂₂ (s). do.

Prior to applying the gain attenuation phenomena (1 / A ₂₂ (s)) is, the analog audio input signal (A _IN) analog subtractor 110 in FIG. 1 with respect to the analog audio input signal (A _IN) A ₂₂ After passing through the analog amplifier having a gain of (s) or greater, the analog subtractor 110 can be compensated for. If the loop gain is much smaller than 1 (~ 0), the noise acoustic signal N is multiplied by 1 and transmitted to the user's eardrum so that the noise acoustic signal is not attenuated.

The conventional analog active noise reduction (ANC) earphone shown in FIG. 1 has an advantage that the loop latency is short and thus attenuates noise noise signals in a relatively high frequency band. The loop delay time is a time required for a signal starting from one point of the feedback loop to reach the same point by turning around the feedback loop.

In addition, the analog active noise reduction (ANC) earphone has a wide frequency range capable of attenuating noise sound by keeping the loop gain (A ₁₁ (s) * A ₂₂ (s)) large because the loop delay time is short. There is this. For noise sound of very low frequency around 20 Hz, the gain of the microphone MIC and the earphone speaker SP is small so that the loop gain value is very small (~ 0), so that the analog active noise reduction (ANC) earphone Does not attenuate the noise sound.

In general, the analog active noise reduction (ANC) earphone works well with respect to a noise acoustic signal having a frequency included in a band from 50 Hz to a maximum frequency to attenuate the noise acoustic signal. The maximum frequency is determined by the loop delay time and the frequency stability of the loop.

However, in recent years, as the digital audio technology having excellent sound quality has been popularized, many earphones accepting digital audio inputs have been used. In this case, the analog active noise reduction (ANC) earphones cannot be used.

3 is a conceptual diagram of a conventional digital active noise reduction (ANC) earphone.

Referring to FIG. 3, the conventional digital active noise reduction earphone 300 includes a digital subtractor 310, a digital-to-analog converter DAC1 and 320, a first analog amplifier A1 and 330, and an acoustic signal generator 340. And second analog amplifiers A2 and 350 and analog to digital converters ADC 360.

Comparing the digital active noise reduction (ANC) earphone of FIG. 3 to the analog active noise reduction (ANC) earphone of FIG. 1, the analog audio input signal A _IN and the analog subtractor 110 are respectively the digital audio input signal D. _IN ) and the digital subtractor 310, the first analog amplifier A1 of FIG. 1 is replaced by a series connection of the digital-to-analog converters DAC1 and 320 and the first analog amplifiers A1 and 330. The second analog amplifier A2 of FIG. 1 has been replaced by a series connection of the second analog amplifiers A2 and 350 and the analog-to-digital converters ADC 360.

In the digital active noise reduction (ANC) earphone, a series connection between the digital-to-analog converters DAC1 and 320 and the first analog amplifiers A1 and 330 is performed in order to increase the efficiency of converting an electrical signal into an acoustic signal. It can be replaced by a series connection of -D amplifier and LC lowpass filter.

The analog-to-digital converter (ADC, 360) is usually delta to convert the analog feedback signal (A _FB ), which is the output signal of the second analog amplifier (A2, 350) into a pulse code modulation (PCM) two-level digital code. Implemented in series with a sigma modulator and a decimation filter. The decimation filter, also called a date rate converter, receives a high speed data output from the delta-sigma modulator and outputs a low speed PCM two-level digital code, from input to output. The latency of the signal is about 0.5ms, which occupies most of the loop delay time of the digital ANC earphone shown in FIG.

In FIG. 3, a microphone MIC, the second analog amplifier A2, the analog-to-digital converter ADC, the digital subtractor, the digital-to-analog converter DAC1, and the first analog amplifier A1 may be used. The feedback loop composed of earphone speaker SP is configured to perform negative feedback operation at DC (s = 0).

When the loop delay time of the feedback loop is 0.5 ms (1 / 2,000 seconds), a sine wave signal of 1,000 Hz is applied to the feedback loop to return the feedback loop one half cycle. Since the phase is changed by 180 degrees due to the time required, the negative feedback operation is changed to a positive feedback operation, so that the digital active noise reduction (ANC) earphone circuit of FIG. 3 oscillates.

When the loop delay time of the feedback loop is 0.5 ms (1 / 2,000 seconds), a quarter wave is applied when a 500 Hz sine wave signal is applied to the feedback loop to return the feedback loop once. Since the phase is changed by 90 degrees due to the time period, the digital active noise reduction (ANC) earphone circuit performs a stable operation with a phase margin of 90 degrees without oscillation.

As described above, when the loop delay time is 0.5 ms, the loop gain value is increased only for the frequency band of 50 Hz to 500 Hz, and the loop gain value is smaller than 1 for the frequency band of 500 Hz or more to ensure frequency stability. The rash can be prevented. Therefore, in such a case, the noise noise belonging to the frequency band of 50Hz to 500Hz is generally attenuated well and transmitted to the user's eardrum, and the high frequency noise sound of 500Hz or more is not attenuated and transmitted to the user's eardrum.

However, since the acoustic noise encountered in daily life is distributed in the frequency band of 50 Hz to 5,000 Hz, it is necessary to increase the maximum frequency that can attenuate the acoustic noise to 500 Hz or more.

The technical problem to be solved by the present invention is to reduce the loop delay time by using a three-level pulse width modulation (PWM) signal or a three-level pulse density modulation (PDM) signal, thereby enabling active in earphones that receive digital audio signals. It is to provide an active noise reduction earphone using a three-level digital signal that can increase the frequency range that can be active noise canceling.

The active noise reduction earphone using a three-level digital signal according to an embodiment of the present invention receives one digital audio input signal D _IN and receives a first two-level digital signal P _{IN that} is a PWM signal. A digital-input PWM signal converter for outputting; A three-level PWM signal generator that receives the first two-level digital signal P _IN and the second two-level digital signal P _FB , which are PWM signals, and outputs one single-level digital signal P _ER . ; An amplifier A3 receiving the 3-level digital signal and amplifying the 3-level digital signal; A low pass filter for performing low pass filtering on the output signal of the amplifier; It is connected to the output terminal of the low pass filter and converts the output signal of the low pass filter to an acoustic signal (S _ER ) and adds it with the noise acoustic signal (N) to output a synthesized acoustic signal (S _O ), which is then converted into an electrical signal. A synthesized sound signal generation unit for converting the signal into a signal; An analog amplifier (A2) for amplifying an electrical signal output from the synthesized acoustic signal generator and outputting the analog signal as an analog feedback signal (A _FB ); And an analog-input PWM signal converter configured to receive the analog feedback signal and output the second two-level digital signal, wherein the three-level PWM signal generator, the amplifier, the low pass filter, and the synthesized sound signal. The feedback loop composed of the generation unit, the analog amplifier, and the analog-input PWM signal converter may perform a negative feedback operation.

The active noise reduction earphone using the three-level digital signal according to another embodiment of the present invention receives one digital audio input signal D _IN and receives the first two-level digital signal P _{IN that is} a PDM signal. A digital-input PDM signal converter for outputting; A three-level PDM signal generator which receives the first two-level digital signal PIN and the second two-level digital signal P _FB which are PDM signals and outputs one three-level digital signal P _ER ; An amplifier A3 receiving the 3-level digital signal and amplifying the 3-level digital signal; A low pass filter for performing low pass filtering on the output signal of the amplifier; A synthesized acoustic signal generation unit connected to the output terminal of the low pass filter and converting the output signal of the low pass filter into an acoustic signal and then adding the noise acoustic signal and outputting a synthesized acoustic signal to convert it into an electrical signal; An analog amplifier (A2) for amplifying an electrical signal output from the synthesized acoustic signal generator and outputting the analog signal as an analog feedback signal (A _FB ); And an analog-input delta-sigma modulator that receives the analog feedback signal and outputs the second two-level digital signal, wherein the three-level PDM signal generator, the amplifier, the lowpass filter, and the synthesized sound The feedback loop composed of the signal generator, the analog amplifier, and the analog-input delta-sigma modulator is characterized by performing a negative feedback operation.

In an active noise reduction earphone using a three-level digital signal according to the present invention, the synthesized sound signal generation unit is connected to an output terminal of the low pass filter and converts an output signal of the low pass filter to output a speaker output sound signal. A speaker for outputting; An adder for synthesizing the speaker output sound signal and the noise sound signal N introduced from the outside and outputting a synthesized sound signal; And a microphone for converting the synthesized acoustic signal into an electrical signal and outputting the converted electrical signal.

In active noise reduction earphones using a three-level digital signal according to the invention, the amplifier is preferably a class-D type amplifier. In this case, the class-D amplifier receives a three-level digital signal P _ER and outputs two analog signals through a first output terminal OP1 and a second output terminal OM1, respectively, and the three-level amplifier. The digital signal P _ER has three kinds of values of +1, 0, and -1, and the first to sixth two-level digital intermediate signals GP1, from the one three-level digital signal P _ER . GN2, GP3, GN4, GP5, GN6).

The class-D amplifier may include the first to sixth two-level digital intermediate signals GP1, GN2, GP3, GN4, GP5, and GN6 when the three-level digital signal P _ER is +1. Has a value of logic levels '0', '0', '1', '1', '1', and '0', respectively, and when the three-level digital signal P _ER is 0, the first To sixth two-level digital intermediate signals GP1, GN2, GP3, GN4, GP5, and GN6, respectively, of the logic levels '1', '0', '1', '0', '0', and '1'. Value, and when the three-level digital signal P _ER is -1, the first to sixth two-level digital intermediate signals GP1, GN2, GP3, GN4, GP5, and GN6 each have a logic level '. It has the values 1 ',' 1 ',' 0 ',' 0 ',' 1 'and' 0 '.

In the class-D amplifier, a drain, a source, a gate, and a substrate node may include the first output terminal OP1, the positive voltage supply terminal VDD, the first two-level digital intermediate signal GP1, and A first PMOS transistor MP1 connected to the positive voltage supply terminal VDD; A drain, a source, a gate, and a substrate node are respectively connected to the first output terminal OP1, the negative voltage supply terminal VSS, the second two-level digital intermediate signal GN2, and the negative voltage supply terminal VSS. One second NMOS transistor MN2; A drain, a source, a gate, and a substrate node are respectively connected to the second output terminal OM1, the positive voltage supply terminal VDD, the third two-level digital intermediate signal GP3, and the positive voltage supply terminal VDD. Another third PMOS transistor MP3 coupled thereto; A drain, a source, a gate, and a substrate node are respectively connected to the second output terminal OM1, the negative voltage supply terminal VSS, the fourth two-level digital intermediate signal GN4, and the negative supply voltage terminal VSS. One fourth NMOS transistor MN4 connected; A drain, a source, a gate, and a substrate node are respectively connected to the second output terminal OM1, the first output terminal OP1, the fifth two-level digital intermediate signal GP5, and the positive voltage supply terminal VDD. One fifth PMOS transistor MP5; And a drain, a source, a gate, and a substrate node, respectively, the second output terminal OM1, the first output terminal OP1, the sixth two-level digital intermediate signal GN6, and the negative voltage supply terminal VSS. And one sixth NMOS transistor MN6 coupled to it.

In active noise reduction earphones using a three-level digital signal according to the invention, the speaker and the microphone are preferably located in the ear canal of the user.

In an active noise reduction earphone using a three-level digital signal according to the present invention, the low pass filter LPF comprises: a first input terminal connected to a first output terminal OP1 of the class-D amplifier; A second input terminal connected to a second output terminal OM1 of the class-D amplifier; A first output terminal OP2 connected to the positive input terminal of the speaker; A second output terminal OM2 connected to a negative input terminal of the speaker; A first inductor LP connected between the first input terminal and the first output terminal OP2; A second inductor LM connected between the second input terminal and the second output terminal OM2; A first storage battery CP connected between the first output terminal OP2 and a negative voltage supply terminal VSS; And a second storage battery CM connected between the second output terminal OM2 and the negative voltage supply terminal VSS.

In this case, the first storage battery CP and the second storage battery CM may be replaced with one storage battery connected between the first output terminal OP2 and the second output terminal OM2.

In an active noise reduction earphone using a three-level digital signal according to the present invention, the analog-input PWM signal converter converts the differential signal of the analog feedback signal A _FB and the differential signal of the reference analog signal A _REF . It may be configured as a comparator that receives the input and outputs the second two-level digital signal (P _FB ). In this case, when the value of the analog feedback signal A _FB is greater than the value of the reference analog signal A _REF , the second two-level digital signal P _FB becomes a logic level '1'. When the value of the analog feedback signal A _FB is less than or equal to the value of the reference analog signal A _REF , the second two-level digital signal P _FB becomes a logic level '0'.

Active noise reduction earphones using a three-level digital signal according to the invention can also be used in hearing aids or personal acoustic amplifiers.

In an active noise reduction earphone using a three-level digital signal according to the present invention, the loop delay time, which is the time taken for the signal to travel one cycle along the feedback loop, is less than 0.0001 sec. It is preferable.

In an active noise reduction earphone using a three-level digital signal according to the present invention, the three-level PWM signal generator and the three-level PDM signal generator are configured for the second two-level digital signal in the first two-level digital signal. The result of subtracting the signal is output as the 3-level digital signal P _ER .

In an active noise reduction earphone using a three-level digital signal according to the present invention, the electrical signal output by the microphone is preferably a differential signal.

According to an active noise reduction earphone using a three-level digital signal according to the present invention, in a digital active noise reduction earphone, a loop using a three-level pulse width modulation (PWM) signal or a three-level pulse density modulation (PDM) signal is used. By reducing the delay time, the maximum frequency of the noise acoustic signal that can be attenuated can be increased from 500 Hz to 2,500 Hz in existing active noise reduction earphones.

1 is a conceptual diagram of a conventional analog active noise reduction earphone.

2 is a conceptual diagram for calculating a transfer function in a conventional analog active noise reduction earphone.

3 is a conceptual diagram of a conventional digital active noise reduction earphone.

4 is a diagram illustrating an embodiment of an active noise reduction earphone using a three-level digital signal according to the present invention.

5 is a diagram illustrating another embodiment of an active noise reduction earphone using a three-level digital signal according to the present invention.

FIG. 6 is a diagram for describing an operation of the 3-level PWM signal generator of FIG. 4 and the PDM signal generator of FIG. 5.

FIG. 7 is a circuit diagram illustrating a connection relationship between a class-D type amplifier, a low pass filter, and a speaker in an active noise reduction earphone using a three-level digital signal according to the present invention shown in FIGS. 4 and 5.

FIG. 8 is a circuit diagram illustrating a connection relationship between a microphone and a second analog amplifier in an active noise reduction earphone using a three-level digital signal according to the present invention shown in FIGS. 4 and 5.

FIG. 9 is a diagram illustrating an analog-input PWM signal converter of an active noise reduction earphone using a three-level digital signal according to the present invention shown in FIG. 4.

FIG. 10 is a diagram illustrating waveforms of a reference analog signal shown in FIG. 9.

FIG. 11 is a diagram illustrating a digital-input PWM signal converter and a reference analog signal generating circuit of an active noise reduction earphone using a three-level digital signal according to the present invention shown in FIG. 4.

12 is a diagram illustrating a digital-input PDM signal converter of an active noise reduction earphone using a three-level digital signal according to the present invention shown in FIG.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

4 is a diagram illustrating an embodiment of an active noise reduction earphone using a three-level digital signal according to the present invention.

Referring to FIG. 4, the active noise reduction earphone 400 using a three-level digital signal according to the present invention includes a digital-input PWM signal converter 410, a three-level PWM signal generator 420, an amplifier A3, 430, a low pass filter 440, an acoustic signal generator 450, analog amplifiers A2 and 460, and an analog-input PWM signal converter 470.

The digital-input PWM signal converter 410 receives one digital audio input signal D _IN and outputs a first two-level digital signal P _{IN that} is a PWM signal.

The three-level PWM signal generator 420 receives the first two-level digital signal P _IN and the second two-level digital signal P _FB which are PWM signals and receive one three-level digital signal P _ER. ) Amplifiers A3 and 430 receive the three-level digital signal and amplify and output the digital signal. The low pass filter 440 performs low pass filtering on the output signal of the amplifier.

Acoustic signal generator 450 is connected to the output terminal of the low pass filter and converts the output signal of the low pass filter into an acoustic signal, and then adds it with the noise acoustic signal to output a synthetic sound signal and converts it into an electrical signal and outputs do.

The analog amplifiers A2 and 460 amplify the electric signals output from the synthesized acoustic signal generator 450 and output the amplified electrical signals as analog feedback signals A _FB . The analog-input PWM signal converter 470 receives the analog feedback signal A _FB and outputs the second two-level digital signal P _FB .

In this case, the three-level PWM signal generator 420, the amplifier 430, the low pass filter 440, the synthesized acoustic signal generator 450, the analog amplifier 460 and the analog-input PWM signal The feedback loop consisting of the transducer 470 performs a negative feedback operation.

In the active noise reduction earphone using the three-level digital signal according to the present invention of FIG. 4, the conventional digital active noise reduction (ANC) earphone shown in FIG. 3 by using a pulse width modulation (PWM) signal instead of the PCM code. The analog-to-digital converter (ADC) and the digital-to-analog converter (DAC1) circuits can be implemented in a simple manner, so that the loop delay time can be greatly reduced compared to the conventional digital active noise reduction (ANC) earphones.

Comparing FIG. 4 with the conventional digital active noise reduction (ANC) earphone of FIG. 3, the analog-to-digital converter (ADC) is replaced with an analog-input PWM converter 470, The series connection of the digital-to-analog converter DAC1 and the first analog amplifier A1 is replaced by the series connection of one class-D type amplifier A3 and 430 and one low pass filter LPF and 440. .

In addition, the digital subtractor 310 is replaced by one three-level PWM generator 420, and the digital audio input signal D _IN is converted into one PWM signal, the first two-level digital signal P _IN . A digital-input PWM converter (410) was added.

In FIG. 4, the digital audio input signal D _IN is PCM 2-level digital data, but the PWM signal is used in the subtractor for negative feedback operation, and the decimation filter constituting the ADC 360 of FIG. 3 is removed. By using the analog-input PWM signal converter 470, the loop delay time is drastically reduced from 0.5 ms (1 / 2,000 seconds) to 0.1 ms (1 / 10,000 seconds). Thus, the maximum frequency of the noise acoustic signal that can be attenuated was increased five times from 500 Hz to 2,500 Hz.

In FIG. 4, the three-level PWM generator 420 receives two first two-level digital PWM signals P _IN and a second two-level digital signal P _FB as inputs. Outputs one 3-level digital signal P _ER , which is a signal.

The second two-level digital signal P _FB is a two-level digital PWM signal output from the analog-input PWM signal converter 470. The analog-input PWM signal converter 470 is a microphone (MIC, 453). The analog feedback signal A _FB and sawtooth wave reference analog signal A _REF generated by amplifying the electric signal converted by the second analog amplifiers A2 and 460 are received as inputs, and the analog feedback is input. When the value of the signal A _FB is greater than the value of the reference analog signal A _REF , the second two-level digital signal P _FB is output at a logic level '1'. The level digital signal P _FB is output at a logic level '0'.

5 is a diagram illustrating another embodiment of an active noise reduction earphone using a three-level digital signal according to the present invention.

In the embodiment of the present invention of FIG. 4, the PWM signal is used in FIG. 5, whereas the PWM signal is used in FIG. 5. The digital-input PWM signal converter 410 of FIG. 4, the analog-input PWM signal converter 470 and the three-level PWM signal generator 420 of FIG. 5 are respectively a digital-input PDM signal converter 510, Replaced by analog-input delta-sigma modulator 570 and three-level PDM signal generator 520.

Thus, in another embodiment according to the present invention illustrated in FIG. 5, the loop delay time is substantially the same as the embodiment illustrated in FIG. 4, but the sawtooth waveform analog reference input to the analog-input PWM signal converter 470 of FIG. 4 is used. Since the signal A _REF does not need to be generated and the analog signal is sensitive to noise, the embodiment shown in FIG. 5 has a strong advantage over noise than the embodiment shown in FIG. 4.

The three-level PWM signal generator 420 of FIG. 4 receives the two two-level digital PWM signals, the first two-level digital signal P _IN and the second two-level digital signal P _FB , as inputs. Generate one 3-level digital signal P _{ER that} is a signal. Meanwhile, the three-level PDM signal generator 520 of FIG. 5 receives two two-level digital PDM signals, a first two-level digital signal P _IN and a second two-level digital signal P _FB as inputs. And generates one 3-level digital signal P _{ER that} is a PDM signal.

The three-level PWM signal generator 420 of FIG. 4 and the three-level PDM signal generator 520 of FIG. 5 have two two-level digital signals, except that the modulation schemes of the signals are different from each other using PWM and PDM. It takes the same role to generate one 3-level signal as an input. Accordingly, the three-level PWM signal generator 420 and the three-level PDM signal generator 520 perform the same logic operation as shown in Equation 2, and thus, at the first two-level digital signal P _IN value. The result of subtracting the second two-level digital signal P _FB is output as a three-level digital signal P _ER .

<Equation 2>

P _ER = P _IN -P _FB

FIG. 6 is a diagram for describing an operation of the 3-level PWM signal generator of FIG. 4 and the 3-level PDM signal generator of FIG. 5.

The table shown in FIG. 6 is a table showing a logic operation according to equation (2). One three-level digital signal P _ER to the values of the first two-level digital signal P _IN and the second two-level digital signal P _FB , which are two two-level two-level digital digital input signals. The value is indicated. Here, one three-level (ternary) digital signal P _ER is represented as three two-level digital signals PLUS, ZERO, and MINUS.

If the value of the first two-level digital signal (P _IN ) is +1 and the value of the second two-level digital signal (P _FB ) is -1, the value of the first two-level digital signal (P _IN ) is determined. Since the value of the second two-level digital signal P _FB is greater than that, the value of the three-level digital signal P _ER becomes +1. (PLUS = '1', ZERO = '0', MINUS = '0' ). If the value of the first two-level digital signal (P _IN ) is -1 and the value of the second two-level digital signal (P _FB ) is +1, the value of the first two-level digital signal (P _IN ) is equal to the value of the first two-level digital signal (P _IN ). Since the value of the second two-level digital signal P _FB is less than the value of the three-level digital signal P _ER is -1. (PLUS = '0', ZERO = '0', MINUS = '1' ). When the value of the first two-level digital signal P _IN and the value of the second two-level digital signal P _FB are equal to each other, the value of the three-level digital signal P _ER becomes 0. (PLUS = '0', ZERO = '1', MINUS = '0').

FIG. 7 is a circuit diagram illustrating a connection relationship between a class-D type amplifier, a low pass filter, and a speaker in an active noise reduction earphone using a three-level digital signal according to the present invention shown in FIGS. 4 and 5.

As shown in FIG. 7, the class-D type amplifier A3 receives one 3-level digital signal P _ER as an input and receives two analog signals from the first output terminal OP1 and the second output terminal ( Output to OM1). The three-level digital signal P _ER is represented by three two-level digital signals PLUS, ZERO, and MINUS.

Conventional class-D amplifier is a amplifier that receives a PWM or PDM signal as an input and drives a speaker. Therefore, the class-D amplifier has a high efficiency of converting an electrical signal into an acoustic signal and is used in an output stage of an audio amplifier. Conventional class-D amplifiers consist of two digital CMOS inverters and two LC lowpass filters, one CMOS inverter and one CMOS inverter with logic level values. It receives these different complementary two-level digital input signals.

In the case of the class-D amplifier A3 according to the present invention, the connection with the LC lowpass filter (LPF) is the same as that of the conventional class-D amplifier, but the conventional class-D amplifier is two-level digital complementary to each other. Class-D amplifiers according to the present invention differ from each other in that they receive one 3-level digital signal (P _ER ) as input.

The three-level digital signal P _ER is a three-level digital signal having three kinds of values of +1, 0, and -1, and three two-level digital signals PLUS, ZERO, and MINUS are illustrated in FIG. Is shown.

In the embodiment of the present invention, instead of using two digital CMOS (CMOS) inverters in a conventional class-D amplifier, a circuit is configured as shown in FIG.

That is, the class-D amplifier A3 includes three two-level two-level digital digital input terminals of PLUS, ZERO, and MINUS, two of a first output terminal OP1 and a second output terminal OM1. With three analog output terminals, first to sixth two-level digital intermediate signals GP1, GN2, GP3, GN4, GP5, and GN6 are generated from the three digital input terminals.

In this case, when the three-level digital signal P _ER is +1 (PULS = '1', ZERO = '0', MINUS = '0'), the first to sixth two-level digital intermediate signals GP1 may be used. , GN2, GP3, GN4, GP5, GN6) have logic levels '0', '0', '1', '1', '1' and '0'.

When the three-level digital signal P _ER is 0 (PULS = '0', ZERO = '1', MINUS = '0'), the first to sixth two-level digital intermediate signals GP1 and GN2 are used. , GP3, GN4, GP5, and GN6) have logic levels '1', '0', '1', '0', '0', and '1'.

When the three-level digital signal P _ER is -1 (PULS = '0', ZERO = '0', MINUS = '1'), the first to sixth two-level digital intermediate signals GP1, GN2, GP3, GN4, GP5, and GN6) have logic levels '1', '1', '0', '0', '1' and '0', respectively.

The class-D amplifier according to the present invention includes a first PMOS transistor MP1, a second NMOS transistor MN2, a third PMOS transistor MP3, a fourth NMOS transistor MN4, and a fifth PMOS transistor MP5. And a sixth NMOS transistor MN6.

The first PMOS transistor MP1 has a drain, a source, a gate, and a substrate node having the first output terminal OP1, a positive supply voltage terminal VDD, and the first two-level digital intermediate signal GP1. Is connected to the VDD.

In the second NMOS transistor MN2, a drain, a source, a gate, and a substrate node may respectively include the first output terminal OP1, a negative supply voltage terminal VSS, and the second two-level digital intermediate signal GN2. And the negative supply voltage terminal VSS.

In the third PMOS transistor MP3, a drain, a source, a gate, and a substrate node may respectively supply the second output terminal OM1, the positive supply voltage terminal VDD, the third two-level digital intermediate signal GP3, and a positive supply. It is connected to the voltage terminal VDD.

The fourth NMOS transistor MN4 has a drain, a source, a gate, and a substrate node having the second output terminal OM1, the negative supply voltage terminal VSS, the fourth two-level digital intermediate signal GN4, and the negative node, respectively. It is connected to the supply voltage terminal VSS.

The fifth PMOS transistor MP5 has a drain, a source, a gate, and a substrate node having the second output terminal OM1, the first output terminal OP1, the fifth two-level digital intermediate signal GP5, and the positive node, respectively. It is connected to the supply voltage terminal VDD.

In the sixth NMOS transistor MN6, a drain, a source, a gate, and a substrate node may respectively have the second output terminal OM1, the first output terminal OP1, the sixth two-level digital intermediate signal GN6, and the It is connected to the negative supply voltage terminal (VSS).

8 is a circuit diagram illustrating a connection relationship between a microphone and a second analog amplifier A2 in an active noise reduction earphone using a three-level digital signal according to the present invention shown in FIGS. 4 and 5.

In the case of using an electret condenser microphone (ECM) as the microphone MIC, a resistor R having the same value is connected to two terminals of the microphone MIC, and among the two terminals of each resistor, to the microphone MIC. The microphone MIC outputs a differential analog signal by connecting an unconnected terminal to a positive supply voltage VDD and a negative supply voltage VSS, respectively, and through the two capacitors, the second analog amplifier A2. The second analog amplifier A2 outputs an analog feedback signal A _FB , which is a differential analog signal, in connection with a differential input terminal of. It is preferable that the second analog amplifier A2 is implemented as a fully differential amplifier and can vary the voltage gain.

FIG. 9 is a diagram illustrating an analog-input PWM signal converter of an active noise reduction earphone using a three-level digital signal according to the present invention shown in FIG. 4.

The analog-input PWM signal converter receives two differential analog signals, an analog feedback signal (A _FB ) and a reference analog signal (A _REF ) as inputs, and a two two-level digital PWM signal, a second two-level digital signal (P). _FB ) is printed. The analog feedback signal A _FB is an output signal of the second analog amplifier A2 and the reference analog signal A _REF has a triangular waveform. When the analog feedback signal A _FB is greater than the reference analog signal A _REF , the second two-level digital signal P _FB becomes a logic level '1', otherwise the second 2- The level digital signal P _FB is at logic level '0'.

FIG. 10 is a diagram illustrating a waveform of the reference analog signal A _REF illustrated in FIG. 9.

Referring to FIG. 10, it can be seen that the waveform of the reference analog signal A _REF is a triangular waveform having the same slew rate and falling slew rate with respect to time.

FIG. 11 is a diagram illustrating a digital-input PWM signal converter and a reference analog signal A _REF generation circuit of an active noise reduction earphone using a three-level digital signal according to the present invention shown in FIG. 4.

The digital-input PWM signal converter 410 of an active noise reduction earphone using a three-level digital signal according to the present invention is a digital audio input signal D _IN and an up / down counter represented by a PCM code. Compare the output of the digital audio input signal (D _IN ) is greater than the output value of the up / down counter (up / down counter), the first two-level digital signal (P _IN ) value of the logic level '1 Otherwise, the value of the first two-level digital signal P _IN becomes a logic level '0'.

Meanwhile, the reference analog signal A _REF shown in FIG. 10 is generated by applying the output value of the up / down counter to the digital-to-analog converter DAC2.

12 is a diagram illustrating a digital-input PDM signal converter of an active noise reduction earphone using a three-level digital signal according to the present invention shown in FIG.

In the delta-sigma DAC, only the low pass filter connected to the final stage is removed. The input digital audio input signal (D _IN ) is usually 16 bit 2-level digital PCM data of 44.1kS / sec, with the first stage increasing the sampling rate, the second stage performing the digital lowpass filter operation, and the third stage. In this case, the digital delta-sigma modulation operation is performed to output a first two-level digital signal P _{IN that} is a one-bit two-level digital PDM data value.

Although the preferred embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and may be implemented in various embodiments based on the basic concept of the present invention defined in the following claims. Such embodiments are also within the scope of the present invention.

Claims (17)

 And a feedback loop comprising a generator, the analog amplifier and the analog-input PWM signal converter performs a negative feedback operation. A digital-input PDM signal converter which receives one digital audio input signal D _IN and outputs a first two-level digital signal P _{IN that} is a PDM signal; A three-level PDM signal generator which receives the first two-level digital signal P _IN and the second two-level digital signal P _FB , which are PDM signals, and outputs a single three-level digital signal P _ER . ; An amplifier receiving the three-level digital signal and amplifying the three-level digital signal; A low pass filter for performing low pass filtering on the output signal of the amplifier; A synthesized sound signal generation unit connected to the output terminal of the low pass filter and converting the output signal of the low pass filter into an acoustic signal and then adding the noise sound signal to a synthesized acoustic signal to convert the signal into an electrical signal. An analog amplifier for amplifying an electrical signal output from the synthesized acoustic signal generator and outputting the analog signal as an analog feedback signal (A _FB ); And And an analog-input delta-sigma modulator that receives the analog feedback signal and outputs the second two-level digital signal. The feedback loop comprising the three-level PDM signal generator, the amplifier, the low pass filter, the synthesized acoustic signal generator, the analog amplifier, and the analog-input delta-sigma modulator performs a negative feedback operation. Active noise reduction earphones using a 3-level digital signal. The method of claim 1, wherein the synthesized sound signal generating unit A speaker connected to an output terminal of the low pass filter and converting an output signal of the low pass filter to output a speaker output sound signal; An adder for synthesizing the speaker output sound signal and a noise sound signal introduced from the outside and outputting a synthesized sound signal; And And a microphone for converting the synthesized acoustic signal into an electrical signal and outputting the synthesized audio signal. The method of claim 3, wherein the amplifier An active noise reduction earphone using a three-level digital signal characterized by a class-D type amplifier. The method of claim 3, wherein The speaker and the microphone are active noise reduction earphone using a three-level digital signal, characterized in that located in the ear canal (ear canal) of the user. The method of claim 4, wherein the class-D type amplifier, Receives a 3-level digital signal (P _ER ) and outputs two analog signals through the first output terminal OP1 and the second output terminal OM1, respectively. The three-level digital signal P _ER has three kinds of values of +1, 0, and -1, and the first to sixth two-level digital intermediate signals (P _ER ) from the three-level digital signal P _ER . Active Noise Reduction Earphones using 3-level digital signals, characterized by generating GP1, GN2, GP3, GN4, GP5, GN6). The method of claim 6, wherein the class-D type amplifier, When the three-level digital signal P _ER is +1, the first to sixth two-level digital intermediate signals GP1, GN2, GP3, GN4, GP5, and GN6 respectively have logic levels' 0 'and'. Has values of '0', '1', '1', '1', '0', When the three-level digital signal P _ER is 0, the first to sixth two-level digital intermediate signals GP1, GN2, GP3, GN4, GP5, and GN6 respectively have logic levels' 1 'and' 0. Has the values', '1', '0', '0', '1', When the three-level digital signal P _ER is -1, the first to sixth two-level digital intermediate signals GP1, GN2, GP3, GN4, GP5, and GN6 respectively have logic levels' 1 'and'. An active noise reduction earphone using a three-level digital signal characterized by having a value of '1', '0', '0', '1', and '0'. The method of claim 7, wherein the class-D type amplifier, A drain, a source, a gate, and a substrate node are respectively connected to the first output terminal OP1, the positive voltage supply terminal VDD, the first two-level digital intermediate signal GP1, and the positive voltage supply terminal VDD. One first PMOS transistor MP1; A drain, a source, a gate, and a substrate node are respectively connected to the first output terminal OP1, the negative voltage supply terminal VSS, the second two-level digital intermediate signal GN2, and the negative voltage supply terminal VSS. One second NMOS transistor MN2; A drain, a source, a gate, and a substrate node are respectively connected to the second output terminal OM1, the positive voltage supply terminal VDD, the third two-level digital intermediate signal GP3, and the positive voltage supply terminal VDD. Another third PMOS transistor MP3 coupled thereto; A drain, a source, a gate, and a substrate node are respectively connected to the second output terminal OM1, the negative voltage supply terminal VSS, the fourth two-level digital intermediate signal GN4, and the negative voltage supply terminal VSS. One fourth NMOS transistor MN4 connected; A drain, a source, a gate, and a substrate node are respectively connected to the second output terminal OM1, the first output terminal OP1, the fifth two-level digital intermediate signal GP5, and the positive voltage supply terminal VDD. One fifth PMOS transistor MP5; And A drain, a source, a gate, and a substrate node are respectively connected to the second output terminal OM1, the first output terminal OP1, the sixth two-level digital intermediate signal GN6, and the negative voltage supply terminal VSS. And a sixth NMOS transistor (MN6) connected thereto. 3. An active noise reduction earphone using a three-level digital signal. The method of claim 8, wherein the low pass filter (LPF), A first input terminal connected to a first output terminal OP1 of the class-D amplifier; A second input terminal connected to a second output terminal OM1 of the class-D amplifier; A first output terminal OP2 connected to the positive input terminal of the speaker; A second output terminal OM2 connected to a negative input terminal of the speaker; A first inductor LP connected between the first input terminal and the first output terminal OP2; A second inductor LM connected between the second input terminal and the second output terminal OM2; A first storage battery CP connected between the first output terminal OP2 and a negative voltage supply terminal VSS; And And a second storage battery (CM) connected between the second output terminal (OM2) and the negative voltage supply terminal (VSS). The method of claim 8, wherein the low pass filter (LPF), A first input terminal connected to a first output terminal OP1 of the class-D amplifier; A second input terminal connected to a second output terminal OM1 of the class-D amplifier; A first output terminal OP2 connected to the positive input terminal of the speaker; A second output terminal OM2 connected to a negative input terminal of the speaker; A first inductor LP connected between the first input terminal and the first output terminal OP2; A second inductor LM connected between the second input terminal and the second output terminal OM2; And And a storage battery connected between the first output terminal (OP2) and the second output terminal (OM2). The method of claim 1, wherein the analog-input PWM signal converter is Using a three-level digital signal comprising a comparator for receiving the analog feedback signal (A _FB ) and the reference analog signal (A _REF ) and outputs the second two-level digital signal (P _FB ) Active noise reduction earphones. 12. The apparatus of claim 11, wherein the comparator When the value of the analog feedback signal A _FB is greater than the value of the reference analog signal A _REF , the second two-level digital signal P _FB becomes a logic level '1' and the analog feedback signal When the value of A _FB is less than or equal to the value of the reference analog signal A _REF , the second two-level digital signal P _FB becomes a logic level '0'. Active noise-reduction earphones that use a digital signal at the level. The method of claim 1 or 2, wherein the earphone Active noise reduction earphones using 3-level digital signals, characterized in that they can be used in hearing aids or personal acoustic amplifiers. The method according to claim 1 or 2, An active noise reduction earphone using a three-level digital signal, characterized in that a loop delay time for the signal to travel once along the feedback loop is less than 0.0001 seconds. 2. The apparatus of claim 1, wherein the three-level PWM signal generator Active noise using a three-level digital signal, characterized in that for outputting the result value obtained by subtracting the second two-level digital signal from the first two-level digital signal as the three-level digital signal (P _ER ) Reducing earphones. 3. The apparatus of claim 2, wherein the three-level PDM signal generator is Active noise using a three-level digital signal, characterized in that for outputting the result value obtained by subtracting the second two-level digital signal from the first two-level digital signal as the three-level digital signal (P _ER ) Reducing earphones. The method of claim 3, wherein Active noise reduction earphone using a three-level digital signal, characterized in that the electrical signal output from the microphone is a differential signal.

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