Patent ID: 7551005

Claim:
An output circuit for converting an input signal to an output signal having a voltage within a predetermined voltage range, the output circuit comprising: an input terminal that receives the input signal; an output terminal that outputs the output signal; a current source circuit that generates a control current based on which the input signal is converted to the output signal; an amplifier circuit that amplifies the input signal; a filter circuit connected between the amplifier circuit and the output terminal to prevent a noise signal within a predetermined frequency range from entering through the output terminal; and a first resistor through which both an output current of the filter circuit and the control current flow, wherein the current source circuit supplying the control current to the output terminal, wherein the output signal is fed back to the current source circuit, the current source circuit changes the amount of the control current in accordance with the voltage of the output signal such that the control current increases with an increase in the voltage of the output signal and becomes zero when the voltage of the output signal decreases to or below a predetermined threshold voltage, and the output signal is a voltage drop across the first resistor.