Detailed high-gain hearing aid ASIC
Hearing aids are tools, equipment, devices, and instruments that help hearing-impaired people improve their hearing impairments and improve their ability to communicate with others. In a broad sense, all kinds of devices that can effectively transmit sound to the ear can be regarded as hearing aids. In the narrow sense, the hearing aid is an electroacoustic amplifier. By amplifying the sound, the monk hears the original and cannot hear clearly. The sound of this device is a hearing aid.
TB 505 high gain hearing aid ASIC
The TB505's internal circuitry features a low-noise, low-drift, high-stability, self-compensating, high-gain op amp. An ultra-high beta-level three-stage transistor is connected to the output of the op amp to improve the buck characteristics of the circuit, and the circuit can still operate reliably when the operating voltage is reduced from 1.55V to 1V. A negative feedback circuit can be externally connected to the pin 1 to adjust the gain of the operational amplifier to improve the sound quality of the hearing aid.
Select a resistor between pin 2 and ground to adjust the output current to about 1.3 mA. At this time, the circuit gain is the best, the current consumption is the smallest, and the noise is the lowest. The circuit has a gain of 72dB, a resonance distortion of 2%, a volume control range of 43dB, an allowable power consumption of 25mW, a noise of less than 1.2μV, and an input impedance of 8kΩ. The integrated circuit is used to assemble the hearing aid for the ear, and the sensitivity is high, the number of external circuit components is small, and the reliability is high. In Figure 103-2, BP is an electret microphone micro-pickup. The load can be used with a hearing aid earphone or other high-impedance earphone. The resistance is 100-180Ω, RP is the volume adjuster, R2 is the limit signal resistance, and C1 is the coupling. Capacitor, R3 is the power supply overload protection resistor, R1 is the transducer current regulating resistor, and C3 is the high frequency harmonic capacitor. Select components according to the circuit, carefully install them, and receive satisfactory results without adjustment.
Using LM386 audio amplifier integrated circuit
The hearing aid is mainly a micro-small amplifier composed of a micro-speaker (microphone), an amplifier and a headphone. Although the circuit structure of the hearing aid is similar in form to the general amplifier, the requirements of the two are different. The amp is designed according to the hearing range and range of the normal person, and the hearing aid is designed according to the characteristics and degree of the snoring of the deaf patient. Generally, the requirements of frequency response, harmonic distortion, noise, etc. of the hearing aid are not as high as those of the amplifier, and the number of amplifiers is less than that of the amplifier. However, there are certain requirements for the performance pointer. Generally, the sound gain of the hearing aid should be 15 to 55 dB. Left and right, the frequency response is between 100 and 600 Hz, and the distortion is less than 10% to 15%. Obviously, the LM386 integrated block can be used. The LM386's high-frequency response is up to 300kHz. When the power supply voltage ranges from 1 to 6V, its static power supply is 4mA, which is suitable for battery power supply.
The LM386 is connected as a positive phase amplifier circuit. The 1 and 8 pins are connected with a 10μF capacitor, so the circuit gain is maximized. The reason for this is that the gain of the LM386 is not too large, and the margin is not sufficient for the hearing aid, especially when the sensitivity of the microphone is poor, and the gain is often not satisfactory. The microphone signal is coupled to the 3 pin through RP1 and C1, amplified by the LM386 and output from the 5 pin, and then the headphone sounds, RP1 is used for volume adjustment, and S1 is the frequency response selection switch. When S1 is placed at 1, 2, and 3 positions, the corresponding circuit frequency response is about 3000, 4500, and 6000 Hz, respectively, and the frequency response selection circuit is actually a capacitance attenuation circuit. The purpose of setting it is to compress the frequency response of the circuit, to attenuate and eliminate the audio components and noise that are not needed by the deaf to improve clarity and reduce ear fatigue. C1 is the output coupling capacitor and C4 is the power supply decoupling capacitor. R1 is the load of the FET in the electret microphone BP.
Hearing aid circuit assembled with discrete components
The power circuit is composed of a power switch S, a battery GB, a current limiting resistor R3, and a pre-stage filter capacitor Cl. The sound pickup amplifying circuit is composed of a microphone BM, a capacitor C2, resistors R1, R2, a potentiometer RP, and transistors V1, V2. The amplification output circuit is composed of a capacitor C3, resistors R4, R5, transistors V2, V3, a socket XS, a plug XP, and an earphone BE. Turn on the power switch S, the battery GB provides 1.5V working power for the whole machine. The BM converts the picked sound signal into an electrical signal, and then reproduces the sound through the earphone BE after the two-stage audio amplification of Vl and V2 and the V3 power amplification. Adjust the resistance of the RP to change the volume.
Component selection
The Rl-R5 uses a 1/8W metal film resistor or a carbon film resistor. The RP uses an ultra-small switch (power switch S) to synthesize a carbon film potentiometer. Cl uses ultra-small aluminum electrolytic capacitors; both C2 and C3 use monolithic capacitors. Both Vl and V2 use S9014 silicon NPN transistor; V3 selects S8050 silicon NPN transistor. The BM uses a miniature high sensitivity electret microphone. The XS uses a φ3.5mm two-channel headphone jack. The BE uses a finished 30Ω two-channel earphone. GB uses the 7th battery.
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