Impedance conversion circuit

Abstract

This invention provides an impedance conversion circuit designed to reduce noise voltage. [Solution] The impedance conversion circuit 1 uses the microphone's capacitor C MIC The input signal from is received, and the input signal is received with high impedance so as not to attenuate, and the load 2 is driven with a low impedance output. The gate of the PMOS transistor M1 is the input T IN Connected to the source, output T OUT It is connected to the current source 4, which supplies current to the source of the PMOS transistor M1. The back gate potential supply circuit 8 supplies the power supply voltage V DD The back gate potential of PMOS transistor M1 is generated from this and supplied to PMOS transistor M1.

Claims

1. In an impedance conversion circuit that receives a signal at high impedance to prevent attenuation of the input signal from the microphone's capacitor and outputs it at low impedance to drive the load, A first transistor with its gate connected to the input and its source connected to the output, A current source that supplies current to the source of the first transistor, The system includes a back gate potential supply circuit that generates the back gate potential of the first transistor from the power supply voltage output from the power supply and supplies it to the first transistor. Impedance conversion circuit.

2. In the impedance conversion circuit described in claim 1, The aforementioned back gate potential supply circuit is A capacitor connected between the back gate and ground of the first transistor, A second transistor connected between the capacitor and the power supply, The control circuit has a mechanism that turns on the second transistor after power is applied, and turns it off after a certain period of time has elapsed. Impedance conversion circuit.

3. In the impedance conversion circuit described in claim 1, The aforementioned power supply voltage is a voltage supplied from a power source outside the IC into which the impedance conversion circuit is integrated. Impedance conversion circuit.

4. In the impedance conversion circuit described in claim 1, The aforementioned power supply voltage is the voltage supplied from the internal power supply within the IC in which the impedance conversion circuit is integrated. Impedance conversion circuit.

5. In the impedance conversion circuit according to any one of claims 1 to 4, A current detection circuit for detecting the current flowing through the first transistor, The system includes a feedback circuit that controls the current flowing through the current source according to the detection result of the current detection circuit, Impedance conversion circuit.

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