Patent ID: 8154347

Claim:
A preamplifier circuit for receiving a microphone signal from a microphone to output a differential signal, comprising: an operational amplifier, having a first input end coupled to a reference voltage, a second input end, and an output end; a first voltage controlled current source, controlled by the output end of the operational amplifier to provide a first current; a first transistor first transistor, having a gate coupled to a ground voltage supply, a source coupled to the first voltage controlled current source for receiving the first current, and a drain coupled to a voltage ground; a second voltage controlled current source, controlled by the output end of the operational amplifier to provide a second current; a second transistor, having a gate for receiving the microphone signal, a source coupled to the second voltage controlled current source for receiving the second current, and a drain coupled to the voltage ground; wherein: the second input end of the operational amplifier is connected to the drain of the second transistor; the source of the first transistor is a first output end for outputting a first preamplified voltage; and the source of the second transistor is a second output end for outputting a second preamplified voltage.