A loop hearing aid circuit based on current feedback compensation frequency response

Abstract

The utility model discloses a kind of loop hearing aid circuit based on current feedback compensation frequency response, audio input signal TO_AMP series capacitor C29 and resistance R25 are connected to the INPUT_A positive phase input pin of power amplifier chip U9 after, the one end of the connection of sampling resistance R27 and power amplifier chip U9 is connected to the input positive terminal of audio operational amplifier U2A‌;The one end of the connection of sampling resistance R27 and loop coil L7 is connected to the input negative terminal of audio operational amplifier U2A‌;The output AMP_I of audio operational amplifier U2A is connected to the INPUT_B negative phase input pin of power amplifier chip U9 after series capacitor C19 and resistance R1.The utility model significantly optimizes the frequency response characteristic of circuit, speech signal is more balanced, more accurate amplification, so that its frequency response can still keep flat under the loop coil of different length, to effectively improve the intelligibility of speech.

Description

Technical Field

[0001] This utility model relates to the field of loop hearing aid circuit technology, and in particular to a loop hearing aid circuit based on current feedback compensation frequency response. Background Technology

[0002] The working principle of existing loop hearing aid systems is to convert sound signals into electrical signals, which are then used by a power amplifier to drive the loop coil to generate alternating current, thereby generating a magnetic field. The hearing aid worn by the hearing-impaired user receives this magnetic field signal through a built-in induction coil, converts it back into an electrical signal, and then outputs the sound through the earphone.

[0003] Because of the inductive impedance of the loop coil, nonlinear distortion is unavoidable when playing ordinary audio, which directly causes the following technical drawbacks: ① Reduced speech intelligibility: Important high-frequency consonant components in speech (such as / s / , / t / , etc.) are severely attenuated, affecting speech intelligibility. ② Music signal distortion: The lack of music harmonic components leads to changes in timbre.

[0004] The main problem with the aforementioned technologies lies in the frequency response characteristics of the audio signal: due to the inductive impedance of the loop coil, its impedance increases linearly with increasing signal frequency. This leads to significant differences in the transmission efficiency of the system for different frequency audio signals. Specifically, in the low-frequency range, due to the lower coil impedance, signal transmission loss is small, and the sound pressure level is well maintained; in the high-frequency range, due to the sharp increase in impedance, signal attenuation is severe, and the sound pressure level drops significantly. Existing traditional compensation methods, such as voltage compensation, only stabilize the DC operating voltage and cannot improve the AC frequency response, thus leading to compensation failure. Moreover, due to the inductive load, there is a phase shift problem in the voltage feedback, resulting in ringing issues. Utility Model Content

[0005] The technical problem to be solved by this utility model is to provide a loop hearing aid circuit based on current feedback compensation frequency response, which effectively improves speech clarity.

[0006] The technical solution adopted by this utility model to solve the above-mentioned technical problems is: a loop hearing aid circuit based on current feedback compensation frequency response, wherein the audio input signal TO_AMP ​​is connected to the INPUT_A non-inverting input pin of the power amplifier chip U9 after being connected in series with capacitor C29 and resistor R25, the OUT_A output pin of the power amplifier chip U9 is connected to pin 1 of the loop coil L7 after being connected in series with sampling resistor R27, and pin 2 of the loop coil L7 is connected back to the OUT_D output pin of the power amplifier chip U9;

[0007] The end of the sampling resistor R27 connected to the power amplifier chip U9 is connected in series with resistor R12 and then connected to the positive input terminal of the audio operational amplifier U2A.

[0008] One end of the sampling resistor R27 connected to the loop coil L7 is connected in series with resistor R17 and then connected to the negative input terminal of the audio operational amplifier U2A.

[0009] The output terminal AMP_I of the audio operational amplifier U2A is connected in series with capacitor C19 and resistor R1 to the negative input pin INPUT_B of the power amplifier chip U9.

[0010] Preferably, the ground terminal GND is connected in series with capacitor C28 and resistor R8 and then connected to the INPUT_B negative input pin of power amplifier chip U9;

[0011] The parameters of capacitor C28 are the same as those of capacitor C19, and the parameters of resistor R8 are the same as those of resistor R1.

[0012] Preferably, pin 1 of bridge rectifier D5 is connected to the positive terminal of diode D6, the negative terminal of diode D6 is connected to pin 2 of bridge rectifier D5, pin 3 of bridge rectifier D5 is grounded, and pin 4 of bridge rectifier D5 is connected to the INPUT_A positive input pin of power amplifier chip U9 after being connected in series with capacitor C30 and resistor R26.

[0013] The parameters of capacitor C30 are the same as those of capacitor C29, and the parameters of resistor R26 are the same as those of resistor R25.

[0014] Preferably, the power amplifier chip U9 uses the TPA3251D2DDVR chip, and the audio operational amplifier U2A uses the OPA1662AID chip.

[0015] Preferably, the audio input signal TO_AMP ​​is output by an analog switch and an audio attenuation circuit, which includes an analog switch chip U5 and an audio attenuation chip U10. An external analog signal is connected to the NO pin of the analog switch chip U5 after being connected in series with a resistor R19, and an external digital signal is connected to the NC pin of the analog switch chip U5 after being connected in series with a resistor R31. A low-level or high-level signal is connected to the IN pin of the analog switch chip U5.

[0016] The COM pin of analog switch chip U5 is connected in series with resistor R22 and capacitor C23 and then connected to the IN input terminal of audio attenuation chip U10.

[0017] The OUT output of the audio attenuation chip U10 is amplified by amplifier U3B to output the audio input signal TO_AMP.

[0018] Preferably, when a low-level signal is connected to the IN pin of the analog switch chip U5, the NC pin and COM pin of the analog switch chip U5 are connected, and the external analog signal is then connected to the IN input terminal of the audio attenuation chip U10.

[0019] When a high-level signal is connected to the IN pin of analog switch chip U5, the NO pin and COM pin of analog switch chip U5 are connected, and the external digital signal is then connected to the IN input terminal of audio attenuation chip U10.

[0020] Preferably, the analog switch chip U5 is a TS5A4624DCKT, and the audio attenuation chip U10 is an LM1971M.

[0021] Preferably, the OUT_A output pin of the power amplifier chip U9 is connected to the audio input signal TO_AMP ​​via inductor L3 and resistor R37 in series. One end of capacitor C40 is connected to the audio input signal TO_AMP, and the other end of capacitor C40 is connected to ground via resistor R36 in series. The other end of capacitor C40 is connected to the end of resistor R37 connected to inductor L3 via capacitor C41 in series.

[0022] Preferably, the OUT_D output pin of the power amplifier chip U9 is connected to ground via inductor L4 and resistor R39 in series. One end of capacitor C42 is grounded, and the other end of capacitor C42 is connected to ground via resistor R38 in series. The other end of capacitor C42 is connected to the end of resistor R39 connected to inductor L4 in series with capacitor C43.

[0023] The beneficial effects of this invention are as follows: Compared with the problem of uneven frequency response in existing loop hearing aid systems, the loop hearing aid circuit of this invention adopts an active current feedback adjustment method to significantly optimize the frequency response characteristics of the circuit, so that the speech signal is amplified more evenly and accurately, and the driving current voltage compensation is dynamically improved, so that the frequency response can remain flat under loop coils of different lengths, thereby effectively improving the clarity of speech. Attached Figure Description

[0024] Figure 1 This is a circuit diagram showing the specific connection between the power amplifier chip U9 and other components in the loop hearing aid circuit of this utility model.

[0025] Figure 2 This is a detailed connection circuit diagram of the audio operational amplifier U2A in the loop hearing aid circuit of this utility model;

[0026] Figure 3 This is a circuit diagram showing the specific connection between the analog switch and the audio attenuation circuit in the loop hearing aid circuit of this utility model. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and preferred embodiments. These drawings are simplified schematic diagrams, illustrating only the basic structure of the present invention, and therefore only show the components relevant to the present invention.

[0028] like Figure 1 , Figure 2 As shown, a loop hearing aid circuit based on current feedback compensation for frequency response includes an analog switch and an audio attenuation circuit, a power amplifier chip U9, and an audio operational amplifier U2A. The power amplifier chip U9 is a TPA3251D2DDVR chip, and the audio operational amplifier U2A is an OPA1662AID chip. The audio input signal TO_AMP ​​is output by the analog switch and the audio attenuation circuit.

[0029] The audio input signal TO_AMP ​​is connected to the INPUT_A non-inverting input pin of the power amplifier chip U9 after being connected in series with capacitor C29 and resistor R25. The OUT_A output pin of the power amplifier chip U9 is connected to pin 1 of the loop coil L7 after being connected in series with sampling resistor R27. Pin 2 of the loop coil L7 is connected back to the OUT_D output pin of the power amplifier chip U9.

[0030] The end of the sampling resistor R27 connected to the power amplifier chip U9 is connected in series with resistor R12 and then connected to the positive input terminal of the audio operational amplifier U2A.

[0031] One end of the sampling resistor R27 connected to the loop coil L7 is connected in series with resistor R17 and then connected to the negative input terminal of the audio operational amplifier U2A.

[0032] The output terminal AMP_I of the audio operational amplifier U2A is connected in series with capacitor C19 and resistor R1 to the negative input pin INPUT_B of the power amplifier chip U9.

[0033] This invention proposes a loop hearing aid circuit design based on current feedback compensation for frequency response. In the output stage of the power amplifier chip U9, a precision sampling resistor R27 is used to sample the load current (loop coil current) in real time, converting it into a proportional voltage signal. This signal is then fed back to the INPUT_B negative input pin of the power amplifier chip U9 via the audio operational amplifier U2A. The core compensation mechanism of this design is as follows: when the amplitude of the audio signal is constant but the frequency increases, the inductive impedance of the loop coil increases, leading to a decrease in the load current and a corresponding decrease in the sampling feedback voltage. This feedback voltage acts on the INPUT_B negative input pin, increasing the actual effective input signal of the power amplifier chip U9 (i.e., the difference between the positive input voltage and the negative input feedback voltage), thereby driving the output voltage to increase and compensating for the decrease in load current due to the increased inductive reactance. Conversely, when the signal frequency decreases, the inductive reactance of the loop coil decreases, causing the current to increase. The increased feedback voltage reduces the effective differential input signal, thereby suppressing the increase in output voltage and preventing excessive current increase.

[0034] Through this closed-loop negative feedback mechanism, the circuit can dynamically adjust the output voltage, significantly flatten the effective frequency response curve of the loop hearing aid circuit, effectively reduce amplitude distortion caused by changes in loop coil impedance, and improve speech clarity.

[0035] Specifically, in one alternative implementation, such as Figure 1 As shown, the ground terminal GND is connected in series with capacitor C28 and resistor R8 and then connected to the INPUT_B negative input pin of power amplifier chip U9.

[0036] The parameters of capacitor C28 are the same as those of capacitor C19, and the parameters of resistor R8 are the same as those of resistor R1.

[0037] Specifically, in one alternative implementation, such as Figure 1 As shown, pin 1 of bridge rectifier D5 is connected to the positive terminal of diode D6, the negative terminal of diode D6 is connected to pin 2 of bridge rectifier D5, pin 3 of bridge rectifier D5 is grounded, and pin 4 of bridge rectifier D5 is connected to the INPUT_A positive input pin of power amplifier chip U9 after being connected in series with capacitor C30 and resistor R26.

[0038] The parameters of capacitor C30 are the same as those of capacitor C29, and the parameters of resistor R26 are the same as those of resistor R25.

[0039] This invention's loop hearing aid circuit integrates common-mode interference suppression and DC isolation. Specifically, the audio input signal TO_AMP ​​is connected to the INPUT_A positive input pin of the power amplifier chip U9 via a series capacitor C29 and resistor R25; the output terminal AMP_I of the audio operational amplifier U2A is connected to the INPUT_B negative input pin of the power amplifier chip U9 via a series capacitor C19 and resistor R1, forming a balanced RC high-pass filter network. Further, the ground terminal (GND) corresponding to the INPUT_B negative input pin is connected to a series capacitor C28 and resistor R8, with the parameters of capacitor C28 being the same as those of capacitor C19, and the parameters of resistor R8 being the same as those of resistor R1. The ground terminal (GND) corresponding to the INPUT_A positive input pin is connected to a bridge rectifier D5, diode D6, and a series capacitor C30 and resistor R26, with the parameters of capacitor C30 being the same as those of capacitor C29, and the parameters of resistor R26 being the same as those of resistor R25. The circuit structure described above not only effectively blocks DC components, but also significantly suppresses common-mode interference and filters out high-frequency noise, thereby improving the signal-to-noise ratio of the input signal.

[0040] Specifically, in one alternative implementation, such as Figure 3 As shown, the analog switch and audio attenuation circuit includes an analog switch chip U5 and an audio attenuation chip U10. The analog switch chip U5 is a TS5A4624DCKT, and the audio attenuation chip U10 is an LM1971M.

[0041] An external analog signal is connected to the NO pin of the analog switch chip U5 via a series resistor R19, and an external digital signal is connected to the NC pin of the analog switch chip U5 via a series resistor R31. A low-level or high-level signal is connected to the IN pin of the analog switch chip U5.

[0042] The COM pin of analog switch chip U5 is connected in series with resistor R22 and capacitor C23 and then connected to the IN input terminal of audio attenuation chip U10.

[0043] The OUT output of the audio attenuation chip U10 is amplified by amplifier U3B to output the audio input signal TO_AMP.

[0044] Specifically, in one optional implementation, when a low-level signal is connected to the IN pin of the analog switch chip U5, the NC pin and COM pin of the analog switch chip U5 are connected, and the external analog signal is then connected to the IN input terminal of the audio attenuation chip U10.

[0045] When a high-level signal is connected to the IN pin of analog switch chip U5, the NO pin and COM pin of analog switch chip U5 are connected, and the external digital signal is then connected to the IN input terminal of audio attenuation chip U10.

[0046] In this circuit, an audio attenuation chip LM1971M is added to the audio processing section to control the volume by adjusting the audio attenuation. An analog switch chip TS5A4624DCKT is also added, which is an audio selector. An external high-level or low-level signal is introduced into the IN pin of the analog switch chip U5. By controlling the high or low level of the IN pin of the analog switch chip U5, the COM pin can be switched to conduct with the NC pin or the COM pin can be switched to conduct with the NO pin, thereby switching between analog audio input and digital audio input.

[0047] Specifically, in one alternative implementation, such as Figure 1As shown, the OUT_A output pin of power amplifier chip U9 is connected to the audio input signal TO_AMP ​​via inductor L3 and resistor R37. One end of capacitor C40 is connected to the audio input signal TO_AMP, and the other end of capacitor C40 is connected to ground via resistor R36. The other end of capacitor C40 is connected to the end of resistor R37 connected to inductor L3 via capacitor C41. This part of the circuit forms a feedback network, feeding back from the output of power amplifier chip U9 to its positive input. It is mainly used for high-frequency stability compensation and phase margin improvement to prevent high-frequency oscillations and suppress overshoot or ringing. At low frequencies (f < 10kHz), the impedance of capacitors C40 and C41 is very high, and the feedback path is mainly dominated by resistor R37. At this time, the feedback network is approximately a direct resistive feedback, which helps to set the basic gain of the power amplifier. At mid-frequency (10kHz-1MHz), the interaction of capacitors and resistors causes the feedback factor to change. The circuit introduces a "notch" or "dropout" characteristic at specific frequencies, that is, the feedback signal attenuates in certain frequency bands, thereby changing the loop gain and phase response of the power amplifier. This compensates for unstable poles introduced by the power amplifier itself or the load. At high frequencies (f > 100kHz), the impedance of capacitors C40 and C41 is very low (approximately short-circuited), and the feedback path again approximates a direct connection. At high frequencies, the capacitors provide a low-impedance path, which contributes to a fast response.

[0048] Specifically, in one alternative implementation, such as Figure 1 As shown, the OUT_D output pin of power amplifier chip U9 is connected to ground via inductor L4 and resistor R39 in series. One end of capacitor C42 is grounded, and the other end of capacitor C42 is connected to ground via resistor R38 in series. The other end of capacitor C42 is connected to the end of resistor R39 connected to inductor L4 via capacitor C43 in series. The function of this part of the circuit is similar to that of the circuit composed of capacitor C40, capacitor C41, resistor R36, and resistor R37 in the previous section.

[0049] In summary, the loop hearing aid circuit of this invention adopts an active current feedback adjustment method to significantly optimize the frequency response characteristics of the circuit, resulting in a more balanced and accurate amplification of the speech signal. It dynamically improves the driving current and voltage compensation, ensuring that the frequency response remains flat under different coil lengths, making it less prone to ringing. This effectively improves the clarity of speech and greatly enhances the hearing aid effect.

[0050] The above description is only a specific embodiment of the present utility model. Various examples and illustrations do not constitute a limitation on the substantive content of the present utility model. Those skilled in the art can modify or transform the above-described specific embodiments after reading the description without departing from the essence and scope of the utility model.

Claims

1. A loop hearing aid circuit based on current feedback compensation frequency response, characterized in that: The audio input signal TO_AMP ​​is connected to the INPUT_A non-inverting input pin of the power amplifier chip U9 after being connected in series with capacitor C29 and resistor R25. The OUT_A output pin of the power amplifier chip U9 is connected to pin 1 of the loop coil L7 after being connected in series with sampling resistor R27. Pin 2 of the loop coil L7 is connected back to the OUT_D output pin of the power amplifier chip U9. The end of the sampling resistor R27 connected to the power amplifier chip U9 is connected in series with resistor R12 and then connected to the positive input terminal of the audio operational amplifier U2A. One end of the sampling resistor R27 connected to the loop coil L7 is connected in series with resistor R17 and then connected to the negative input terminal of the audio operational amplifier U2A. The output terminal AMP_I of the audio operational amplifier U2A is connected in series with capacitor C19 and resistor R1 to the negative input pin INPUT_B of the power amplifier chip U9.

2. The loop hearing aid circuit based on current feedback compensation frequency response according to claim 1, characterized in that: The ground terminal GND is connected in series with capacitor C28 and resistor R8 and then connected to the INPUT_B negative input pin of power amplifier chip U9; The parameters of capacitor C28 are the same as those of capacitor C19, and the parameters of resistor R8 are the same as those of resistor R1.

3. A loop hearing aid circuit based on current feedback compensation frequency response as described in claim 1 or 2, characterized in that: Pin 1 of bridge rectifier D5 is connected to the positive terminal of diode D6, the negative terminal of diode D6 is connected to pin 2 of bridge rectifier D5, pin 3 of bridge rectifier D5 is grounded, and pin 4 of bridge rectifier D5 is connected in series with capacitor C30 and resistor R26 to the INPUT_A positive input pin of power amplifier chip U9. The parameters of capacitor C30 are the same as those of capacitor C29, and the parameters of resistor R26 are the same as those of resistor R25.

4. A loop hearing aid circuit based on current feedback compensation frequency response according to claim 1, characterized in that: The power amplifier chip U9 uses the TPA3251D2DDVR chip, and the audio operational amplifier U2A uses the OPA1662AID chip.

5. A loop hearing aid circuit based on current feedback compensation frequency response according to claim 1, characterized in that: The audio input signal TO_AMP ​​is output by an analog switch and an audio attenuation circuit. The analog switch and audio attenuation circuit includes an analog switch chip U5 and an audio attenuation chip U10. An external analog signal is connected to the NO pin of the analog switch chip U5 after being connected in series with a resistor R19, and an external digital signal is connected to the NC pin of the analog switch chip U5 after being connected in series with a resistor R31. The IN pin of the analog switch chip U5 is connected to a low-level or high-level signal. The COM pin of analog switch chip U5 is connected in series with resistor R22 and capacitor C23 and then connected to the IN input terminal of audio attenuation chip U10. The OUT output of the audio attenuation chip U10 is amplified by amplifier U3B to output the audio input signal TO_AMP.

6. A loop hearing aid circuit based on current feedback compensation frequency response according to claim 5, characterized in that: When a low-level signal is connected to the IN pin of analog switch chip U5, the NC pin and COM pin of analog switch chip U5 are connected, and the external analog signal is then connected to the IN input terminal of audio attenuation chip U10. When a high-level signal is connected to the IN pin of analog switch chip U5, the NO pin and COM pin of analog switch chip U5 are connected, and the external digital signal is then connected to the IN input terminal of audio attenuation chip U10.

7. A loop hearing aid circuit based on current feedback compensation frequency response according to claim 5, characterized in that: The analog switch chip U5 uses TS5A4624DCKT, and the audio attenuation chip U10 uses LM1971M.

8. A loop hearing aid circuit based on current feedback compensation frequency response according to claim 1, characterized in that: The OUT_A output pin of the power amplifier chip U9 is connected to the audio input signal TO_AMP ​​via inductor L3 and resistor R37. One end of capacitor C40 is connected to the audio input signal TO_AMP, and the other end of capacitor C40 is connected to ground via resistor R36. The other end of capacitor C40 is connected to the end of resistor R37 connected to inductor L3 via capacitor C41.

9. A loop hearing aid circuit based on current feedback compensation frequency response according to claim 1, characterized in that: The OUT_D output pin of the power amplifier chip U9 is connected to ground via inductor L4 and resistor R39 in series. One end of capacitor C42 is grounded, and the other end of capacitor C42 is connected to ground via resistor R38 in series. The other end of capacitor C42 is connected to the end of resistor R39 connected to inductor L4 in series with capacitor C43.

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