To prevent overdriving of an amplifier that receives the output of a preamplifier by adjusting a variable resistor of a gain control circuit after an input signal is compared with a reference signal and making the corresponding variable resistor contained in the preamplifier follow up the variable resistor of the gain control circuit.
Variable resistors 312 and 316 can be electrically adjusted and gates of these resistors are connected to a voltage source. Resistance values of both resistors are determined by a voltage applied to the gates of the resistors. Resistors 324 and 328 connect the outputs of a preamplifier/operational amplifier 320 to each corresponding input, and resistance values of these resistors are usually kept constant. Two other constant resistors 332 and 336 connect the inputs of the amplifier 320 to each corresponding microphone input. The positive input 304 of a microphone is connected to the negative input of the amplifier 320 via the resistor 336. Meanwhile, the negative input 308 of the microphone is connected to the positive input of the amplifier 320 via the resistor 332.
HOEI JUNG SHENG
SARIN VISHAL
