Input circuit having hysteresis without power supply voltage dependence
An input circuit includes a first input transistor and a second input transistor connected to an input terminal; a current source which makes a current flow in the second input transistor through a current mirror; a switch provided between the current mirror and the current source, and having a switch control terminal connected to the drain of the first input transistor; and a transistor connected to the first input transistor, on/off of the transistor being controlled by an output signal, wherein a current drivability of the second input transistor is switched by an output signal, and a threshold voltage to the input signal is determined based on the current drivability of the second input transistor and the current source.
1. An input circuit configured to output an output signal corresponding to an input signal, comprising:
an input terminal;
an output terminal;
a first input transistor having a gate connected to the input terminal and a source connected to a second power-supply terminal;
a second input transistor having a gate connected to the input terminal and a source connected to the second power-supply terminal, and configured to provide, to the output terminal, an output signal based on a voltage of a drain of the second input transistor;
a transistor having a drain connected to a drain of the first input transistor and a source connected to a first power-supply terminal, wherein turning on/off of the transistor is controlled by a signal based on the output signal;
a current source having one end connected to the second power-supply terminal;
a first switch having one end connected to an other end of the current source and a switch control terminal connected to the drain of the first input transistor; and
a current mirror having an input terminal connected to an other end of the first switch, an output terminal connected to the drain of the second input transistor, and a current-mirror control gate connected to the other end of the current source, wherein
a current drivability of the second input transistor is switched by the output signal, and
a threshold voltage to the input signal is determined based on the current drivability of the second input transistor and the current source.
2. The input circuit according to claim 1 , further comprising
a second switch provided between the first power-supply terminal and each of the first input transistor and the second input transistor,
wherein the second switch turns off in response to turning-off of the first input transistor and the second input transistor by the input signal.