Audio transmission device and audio transmission system

Abstract

To provide an audio transmission device and an audio transmission system that can improve the characteristics of an AD converter compared to a conventional device.SOLUTION: An audio transmission device according to the present disclosure includes an inverting amplifier having an input node, a first input terminal connected to a microphone module, a second input terminal connected to the input node of the inverting amplifier, and an attenuator electrically connected between the first input terminal and the second input terminal.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to an audio transmission device and an audio transmission system. [Background technology]

[0002] The voice transmission system installed in a vehicle uses a microphone to perform signal processing such as hands-free calling and voice recognition, as well as noise control such as noise suppression in the vehicle cabin and ANC (active noise control). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-27991 [Patent Document 2] Japanese Patent Application Publication No. 9-294038 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, when noise is controlled in an audio transmission system, the sound pressure level input from a microphone is input to an AD (analog / digital) converter, and noise control is performed using a digital signal, but there is room for further improvement.

[0005] The present disclosure provides an audio transmission device and an audio transmission system that can improve the characteristics of an AD converter compared to conventional devices. [Means for solving the problem]

[0006] The audio transmission device of the present disclosure comprises an inverting amplifier having an input node, a first input terminal connected to a microphone module, a second input terminal connected to the input node of the inverting amplifier, and an attenuator electrically connected between the first input terminal and the second input terminal. [Effects of the Invention]

[0007] According to the voice transmission device according to the present disclosure, the characteristics of the AD converter can be improved.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

[0009] Hereinafter, embodiments of the voice transmission apparatus according to the present disclosure will be described with reference to the drawings.

[0010] (Embodiment) The voice transmission system according to the embodiment is mounted in a vehicle and has a microphone. The microphone in the vehicle is used in a wide variety of applications such as hands-free calling, voice recognition, in-vehicle noise suppression, and ANC (active noise control). The voice transmission system uses the microphone to perform signal processing in hands-free calling and voice recognition, and to perform noise control such as in-vehicle noise suppression and ANC.

[0011] For example, when performing noise control, the voice transmission system inputs the sound pressure level input from the microphone to an AD (analog / digital) converter and performs noise control with a digital signal, but there is still room for further improvement.

[0012] Therefore, in this embodiment, in order to improve the characteristics of the AD converter as compared with the prior art, there is an attenuator electrically connected between a first input terminal connected to the microphone module and a second input terminal connected to the input node of the inverting amplifier.

[0013] FIG. 1 is a circuit diagram showing an example of the configuration of a voice transmission system 100 according to the embodiment. The voice transmission system 100 includes a microphone module 1 and a voice transmission device 2. The voice transmission device 2 is a subsequent device of the microphone module 1, and an AD converter chip 3 in the subsequent device performs AD conversion on the signal input by the microphone module 1.

[0014] The audio transmission device 2 has a first resistor 201, a second resistor 202, a capacitor 203, and an AD converter chip 3. The first resistor 201 is connected between point A and the capacitor 203. The second resistor 202 is connected between the first resistor 201, the capacitor 203, and ground. The capacitor 203 is connected between the first resistor 201 and the second resistor 202 and point B. In other words, the capacitor 203 is electrically connected to the attenuator and point B.

[0015] The AD converter chip 3 includes a gain register 301 , a feedback register 302 , an inverting amplifier 303 , an ADC (analog-to-digital converter) 310 , an HPF (high-pass filter) 311 , and an audio interface 312 .

[0016] The gain register 301 is connected between point B and the inverting input of the inverting amplifier 303, and acquires the input voltage signal at point B. The gain register 301 is electrically connected to point B. The gain register 301 also outputs a signal that has been impedance-converted with respect to the acquired input voltage signal.

[0017] The feedback resistor 302 is connected between the output and inverting input of the inverting amplifier 303, and applies negative feedback from the output to the input of the inverting amplifier 303. The feedback resistor 302 is electrically connected to the gain resistor 301.

[0018] The inverting amplifier 303 is connected between the gain register 301 and the ADC 310. The inverting amplifier 303 is electrically connected to the gain register 301 and the feedback register 302. The inverting input of the inverting amplifier 303 is connected to the output of the gain register 301, and the non-inverting input is virtually grounded.

[0019] The ADC310 is connected between the inverting amplifier 303 and the HPF311. The ADC310 is electrically connected to the inverting amplifier. Also, the ADC310 acquires the analog output signal output from the inverting amplifier 303. Then, the ADC310 converts the acquired analog voltage signal into a digital voltage signal.

[0020] The HPF311 is connected between the ADC310 and the audio interface 312. The HPF311 is electrically connected to the ADC310. Also, the HPF311 acquires the digital voltage signal output from the inverting amplifier 303. Then, the HPF311 has a high-pass characteristic of attenuating the low frequency band and passing the high frequency band for the acquired digital voltage signal, and outputs a high-frequency amplified signal obtained by high-pass filtering the output signal.

[0021] The audio interface 312 is electrically connected to the HPF311. The audio interface 312 acquires the high-frequency amplified signal output from the HPF311. Also, the audio interface 312 outputs the acquired high-frequency amplified signal to the outside.

[0022] Here, as the characteristics of the AD converter chip 3, the case where the inverting amplifier 303 is built-in and the input level at point B is -29 [dBV] and the output level is -26 [dBFS] will be described. Point A is the input level when the sensitivity of the microphone module 1 is -10.5 [dBV].

[0023] The audio transmission device 2 constitutes an attenuator with the first resistor 201 and the second resistor 202 electrically connected to the first resistor 201 in order to attenuate the input level of -10.5 [dBV] at point A to the input level of -29 [dBV] at point B. That is, the attenuator has the first resistor 201 and the second resistor 202 electrically connected to the first resistor 201.

[0024] The audio transmission device 2 includes an inverting amplifier 303 having an input node, point A connected to the microphone module 1, point B connected to the input node of the inverting amplifier 303, and an attenuator electrically connected between points A and B. Point A is also called the first input terminal, and point B is also called the second input terminal. Here, the required attenuation is as shown in Equation 1.

[0025]

number

[0026] When the impedance of the capacitor 203 is negligibly small compared to the impedances of the first resistor 201, the second resistor 202, and the gain resistor 301, the relationship between the resistance values of the first resistor 201, the second resistor 202, and the gain resistor 301 and the attenuation can be expressed by Equation 2. Here, the resistance value R S , resistance value R M , resistance value R G are the resistance values of the first resistor 201, the second resistor 202, and the gain resistor 301, respectively.

[0027]

number

[0028] Also, rearranging equation 2, the resistance value R S is the resistance value R M , resistance value R G When expressed as:

[0029]

number

[0030] Here, the resistance value R G = 41 kΩ, resistance R S -Resistance value R M The characteristics are shown in Fig. 2. Fig. 2 shows the resistance R S -Resistance value R M 1 is a diagram showing an example of the characteristics of a resistance value RM R G If the resistance is sufficiently small compared to the resistance R S is the resistance value R M The region E1 shown in Figure 2 is called the linear region.

[0031]

number

[0032] On the other hand, the resistance value R G is the resistance value R M If the resistance R is sufficiently small compared to the resistance R, then Equation 3 can be transformed into Equation 5. The region E2 shown in Figure 2 is called the saturation region. M When is infinite, the resistance R S = 304 kΩ. In other words, the resistance value R G is the resistance value R M If it is smaller than the resistance R S and resistance value R M The relationship between these two is saturated.

[0033]

number

[0034] Next, we will consider the noise level including the bias circuit for the inverting amplifier 303. Fig. 3 is a circuit diagram showing an example of the configuration of the inverting amplifier 303 according to this embodiment. Fig. 3 shows a first resistor 201, a second resistor 202, a capacitor 203, a gain resistor 301, a feedback resistor 302, an inverting amplifier 303, a non-inverting bias matching resistor 304, a third resistor 305, and a fourth resistor 306.

[0035] The non-inverting bias matching resistor 304 is connected between the third resistor 305, the fourth resistor 306 and the non-inverting input of the inverting amplifier 303. The third resistor 305 is connected between the power supply voltage Vdd and the fourth resistor 306. The fourth resistor 306 is connected between the third resistor 305 and ground.

[0036] Also, the resistance value R F The resistance value R T The resistance values R3 and R4 are respectively the resistance values of the feedback register 302, the inverting amplifier 303, the non-inverting bias matching register 304, the third resistor 305, and the fourth resistor 306.

[0037] Here, the noise at the output C point of the inverting amplifier 303 with respect to the input at point A shown in FIG. 3 is obtained. The noise voltage V at point C N is given by Equation 6.

[0038]

Equation

[0039] Here, e S e M e G e T e F e R3 e R4 C×e ni are respectively represented by Equations 7 to 14. k is the Boltzmann constant, T is the absolute temperature, and e ni is the input-referred noise voltage of the operational amplifier.

[0040]

Equation

[0041]

Equation

[0042]

Equation

[0043]

Equation

[0044]

Number

[0045]

Number

[0046]

Number

[0047]

Number

[0048] Here, the resistance value R G = resistance value R F = 41 [kΩ], resistance value R T = 11 [kΩ], resistance value R3 = resistance value R4 = 30 [kΩ], under the condition that the absolute temperature T = 300 [K], with the resistance value R M as a parameter, e S e M e G e T e F e R3 e R4 C×e ni and the characteristics of the noise voltage V N are shown in FIGS. 4 to 12.

[0049] FIG. 4 is a diagram showing an example of the characteristics of the noise voltage of the thermal noise of the first resistor 201 according to the embodiment. FIG. 5 is a diagram showing an example of the characteristics of the noise voltage of the thermal noise of the second resistor 202 according to the embodiment. FIG. 6 is a diagram showing an example of the characteristics of the noise voltage of the thermal noise of the gain register 301 according to the embodiment. FIG. 7 is a diagram showing an example of the characteristics of the noise voltage of the thermal noise of the non-inverting bias matching register 304 according to the embodiment. FIG. 8 is a diagram showing an example of the characteristics of the noise voltage of the thermal noise of the feedback register according to the embodiment.

[0050] FIG. 9 is a diagram showing an example of the characteristics of the noise voltage of the third resistor according to the embodiment. FIG. 10 is a diagram showing an example of the characteristics of the noise voltage of the fourth resistor according to the embodiment. FIG. 11 is a diagram showing an example of the characteristics of the input noise voltage of the operational amplifier according to the embodiment. FIG. 12 is a diagram showing an example of the characteristics of the output noise voltage of the inverting amplifier 303 according to the embodiment.

[0051] The horizontal axis of the graphs shown in FIGS. 4 to 12 is the resistance value R M [kΩ], and the vertical axis of the graphs shown in FIGS. 4 to 12 is the noise voltage [nV / √Hz].

[0052] Here, for the noise voltage V N when the band is limited from 10 [Hz] to 100 [kHz], the noise level is given by Equation 15, and in dB (decibel) notation, it becomes Equation 16.

[0053]

Equation

[0054]

Equation

[0055] Also, an example of the characteristics derived from Equation 16 is shown in FIG. 13. FIG. 13 is a diagram showing an example of the characteristics of the output noise voltage of the inverting amplifier according to the embodiment. The horizontal axis of the graph shown in FIG. 13 is the resistance value RM [kΩ], and the vertical axis of the graph shown in FIG. 13 is the noise voltage [dBV]. The graph shown in FIG. 13 is a diagram showing an example of the characteristics when the band is limited from 10 [Hz] to 100 [kHz]. Here, the noise levels in the linear region and the saturation region of the inverting amplifier 303 are compared from FIGS. 2 and 13.

[0056] The resistance value R in the linear region shown in FIG. 2 S = 7.5 [kΩ], the resistance value R MFor the combination of 1 [kΩ], the noise level in Figure 13 is -95.0 [dBV]. Also, for the combination of the resistance value RS = 302 [kΩ] and the resistance value RM = 6279 [kΩ] shown in Figure 2, the noise level in Figure 13 is -98.7 [dBV], indicating that the noise level has improved.

[0057] Next, the noise level of the AD converter chip 3 will be described in more detail. For the resistance value R S = 300 [kΩ], the resistance value R M = not implemented, and for the case where the resistance value R S = 51 [kΩ], the resistance value R M = 8.2 [kΩ], a measured example of the AD converter chip 3 is shown in Figure 14. Figure 14 is a table showing an example of the measured values of the AD converter chip 3 according to the embodiment.

[0058] In Figure 14, the combination of the resistance value R S = 300 [kΩ] and the resistance value R M = not implemented corresponds to the saturation region in Figure 2. Also, in Figure 14, the combination of the resistance value R S = 51 [kΩ] and the resistance value R M = 8.2 [kΩ] corresponds to the linear region.

[0059] For the combination of the resistance value R S = 51 [kΩ] and the resistance value R M = 8.2 [kΩ] shown in Figure 14, and the combination of the resistance value R S = 300 [kΩ] and the resistance value R M = not implemented, the signal levels (S Level) are both approximately -26 [dBFS]. On the other hand, for the combination of the resistance value R S = 51 [kΩ] and the resistance value R M = 8.2 [kΩ] shown in Figure 14, the noise level (N Level) is -100.120 [dBFS], and for the combination of the resistance value R S = 300 [kΩ] and the resistance value R M=The noise level in the unimplemented combination was -101.760 [dBFS], which is a significant difference.

[0060] This is because the gain register 301 is virtually grounded at the inverting input of the inverting amplifier 303. When the AD converter chip 3 is viewed from point B, the resistance value R G This is because .theta..sub.R is the input impedance of the AD converter chip 3. In other words, the audio transmission device 2 has an input impedance electrically connected between point B and the input node of the inverting amplifier 303.

[0061] In summary, when the input level of the AD converter chip 3 is adjusted by the first resistor 201 and the second resistor 202, the resistance value R M The input impedance of the AD converter chip 3 is the resistance R G By making it larger than , noise can be improved.

[0062] As described above, the audio transmission device 2 of this embodiment comprises an inverting amplifier 300 having an input node, a first input terminal connected to the microphone module 1, a second input terminal connected to the input node of the inverting amplifier 303, and an attenuator electrically connected between the first input terminal and the second input terminal.

[0063] According to this configuration, the audio transmission device 2 can improve the characteristics of the AD converter.

[0064] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents. [Explanation of symbols]

[0065] 1 Microphone Module 2 Voice Transmission Device 3 AD Converter Chip 100 Voice Transmission System 201 First Resistor 202 Second Resistor 203 Capacitor 301 Gain Register 302 Feedback Register 303 Inverting Amplifier 304 Non-Inverting Bias Matching Register 305 Third Resistor 306 Fourth Resistor

Claims

1. an inverting amplifier having an input node; a first input terminal connected to a microphone module; a second input terminal connected to the input node of the inverting amplifier; an attenuator electrically connected between the first input terminal and the second input terminal; a voice transmission device.

2. having an input impedance electrically connected between the second input terminal and the input node of the inverting amplifier; The voice transmission device according to claim 1.

3. The attenuator has a first resistor and a second resistor electrically connected to the first resistor, wherein the resistance value of the second resistor is greater than the resistance value of the input impedance; The voice transmission device according to claim 2.

4. further having a capacitor between the first input terminal and the second input terminal, wherein the capacitor is electrically connected to the attenuator and the second input terminal; The voice transmission device according to claim 3.

5. The second resistor of the attenuator is connected between the first resistor of the attenuator, the capacitor connected to the first resistor, and ground; The voice transmission device according to claim 4.

6. further having an AD converter chip, wherein the AD converter chip has a gain register electrically connected to the second input terminal, a feedback register electrically connected to the gain register, the inverting amplifier electrically connected to the gain register and the feedback register, an analog / digital converter electrically connected to the inverting amplifier, a high-pass filter electrically connected to the analog / digital converter, and an audio interface electrically connected to the high-pass filter; The voice transmission device according to claim 4.

7. When the resistance value of the gain register is smaller than the resistance value of the second resistor of the attenuator, the relationship between the resistance value of the first resistor of the attenuator and the resistance value of the second resistor of the attenuator is a saturation relationship; The voice transmission device according to claim 6.

8. In a voice transmission system having a microphone module and a voice transmission device, the voice transmission device has an inverting amplifier having an input node, a first input terminal connected to the microphone module, a second input terminal connected to the input node of the inverting amplifier, A voice transmission system having an attenuator electrically connected between the first input terminal and the second input terminal. Voice transmission system. **Claim 9** A voice transmission system according to claim 8, having an input impedance electrically connected between the second input terminal and the input node of the inverting amplifier. The voice transmission system according to claim 8. **Claim 10** The attenuator has a first resistor and a second resistor electrically connected to the first resistor. The resistance value of the second resistor is larger than the resistance value of the input impedance. The voice transmission system according to claim 9. **Claim 11** The voice transmission system according to claim 10, further having a capacitor between the first input terminal and the second input terminal. The capacitor is electrically connected to the attenuator and the second input terminal. The voice transmission system according to claim 10.

Images