An amplifier includes a first amplifier comprising an N-type field-effect transistor receiving a reference voltage at a gate, a P-type field-effect transistor connected between a drain of the N-type field-effect transistor and a power supply voltage line, and a constant current source connected between a source of the N-type field-effect transistor and a ground, to output a voltage from a connection of the drain of the N-type and P-type field-effect transistors; a second amplifier comprising a resistance and P-type field-effect transistors connected in series between the power supply voltage line and the ground to receive the voltage output from the first amplifier at their gate, and outputting a voltage from a connection of the P-type field-effect transistor and the resistance; and a switch between an output of the first amplifier and the power supply voltage line and comprising an N-type field-effect transistor receiving a reference voltage at a gate.
1. An amplifier comprising:
a first amplifier comprising
an N-type field-effect transistor which receives a reference voltage at a gate, a P-type field-effect transistor connected between a drain of the N-type field-effect transistor and a power supply voltage line, and a constant current source connected between a source of the N-type field-effect transistor and a ground terminal, the first amplifier outputting a voltage from a connecting point of the drain of the N-type field-effect transistor and the P-type field-effect transistor;
a second amplifier comprising a resistance, and a P-type field-effect transistor connected in series between the power supply voltage line and the ground terminal, the second amplifier receiving the voltage output from the first amplifier at a gate of the P-type field-effect transistor and outputting a voltage from a connecting point of the P-type field-effect transistor and the resistance; and
a switch provided between an output of the first amplifier and the power supply voltage line and comprising an N-type field-effect transistor which receives the reference voltage at a gate.
2. An amplifier according to claim 1 , wherein
a threshold voltage of the P-type field-effect transistor of the first amplifier is set to be higher than that of the P-type field-effect transistor of the second amplifier.
3. An amplifier according to claim 1 , wherein
sizes or threshold voltages of the P-type field-effect transistor and the N-type field-effect transistor of the first amplifier are set so that at power-on, the second amplifier starts operating at a higher voltage than the first amplifier.
4. An amplifier according to claim 1 , wherein
the N-type transistor of the first amplifier operates at a source-to-drain voltage close to 0V.
5. An amplifier according to claim 4 , wherein
the N-type transistor of the first amplifier operates at a voltage in a sub-threshold range.
6. An amplifier according to claim 1 , further comprising
a reference voltage generator circuit which generates and supplies a reference voltage and comprises a first field-effect transistor having a high density N-type gate and a second field-effect transistor having a high-density P-type gate that are connected in series between the power supply voltage line and the ground terminal, wherein:
substrate potentials of the first and second field-effect transistors are grounded;
the gate of the first field-effect transistor is grounded;
the gate of the second field-effect transistor is connected with a connecting point of the first and second field-effect transistors and receives the reference voltage output from the connecting point.