| 摘要 |
A microphone amplifier is provided to control an amplifying gain, a consumption current, and an input capacitance by combining a junction field effect transistor and a bipolar transistor at the minimum space. A microphone amplifier includes a bias unit(23a), a voltage current conversion unit(25a), a constant current source, a current amplifying unit(27a), a second resistor(R2), and a third resistor(R3). The bias unit(23a) provides a reference potential of an input signal between a signal input terminal and a ground terminal. The voltage current conversion unit(25a) amplifies the input signal. The constant current source provides a current of a predetermined amplitude to the voltage current conversion unit(25a). The current amplifying unit(27a) amplifies a current change between the constant current source and the voltage current conversion unit(25a). The third resistor(R3) controls an amplifying gain of the input signal between the ground terminal, and the current amplifying unit(27a) and the voltage current conversion unit(27a). The second resistor(R2) controls a bias current quantity between the current amplifying unit(27a) and the third resistor(R3). |
