Patent ID: 7683676

Claim:
A signal-level detecting apparatus that detects either one of a peak level and a bottom level of an input signal, the signal-level detecting apparatus comprising: an amplifying unit that performs a differential amplification with either one of a previous peak level and a previous bottom level of the input signal and a current input signal; a semiconductor element that includes a first terminal, a second terminal, and a third terminal, the semiconductor element transferring a signal level output from the amplifying unit from the second terminal to the third terminal by using a current that is conducted from the second terminal to the third terminal in response to a voltage applied to the first terminal; a control unit that includes: a reference semiconductor element that has a substantially same characteristic as the semiconductor element and conducts a first variable current according to a threshold voltage varying with an environmental condition, and a resistor element that is connected between the first terminal and the second terminal of the semiconductor element and conducts a second variable current corresponding to the first variable current from the second terminal to the first terminal to apply a negative bias to the voltage applied to the first terminal of the semiconductor element; and a holding unit that holds a signal level output from the third terminal of the semiconductor element, wherein the second variable current becomes lower when the threshold voltage becomes higher, while the second variable current becomes higher when the threshold voltage becomes lower.