Bias circuit for compensating fluctuation of supply voltage
A supply voltage bias circuit includes: an output circuit which comprises a first transistor having a terminal from which output voltage or output current is supplied, the output voltage and output current having values proportional to a supply voltage at a supply line; a second transistor forming a current mirror circuit together with the first transistor, the second transistor being connected to a first connection node; a third transistor connected to the first connection node; and a current source connected between the first connection node and the supply line. Drains of the second and third transistors or sources of the second and third transistors are commonly connected to the first connection node. The drains or sources of the second and third transistors which are not connected to the first connection node are grounded or earthed. The first connection node is connected to a gate of the third transistor and is functioning as an output terminal of the bias circuit.
1. A supply voltage bias circuit, comprising:
an output circuit which comprises a first transistor having a terminal from which output voltage or output current is supplied, the output voltage and output current having values proportional to a supply voltage at a supply line;
a second transistor forming a current mirror circuit together with the first transistor, the second transistor being connected to a first connection node;
a third transistor connected to the first connection node; and
a current source connected between the first connection node and the supply line, wherein
drains of the second and third transistors or sources of the second and third transistors are commonly connected to the first connection node,
the drains or sources of the second and third transistors which are not connected to the first connection node are grounded or earthed,
the first connection node is connected to a gate of the third transistor and is functioning as an output terminal of the bias circuit.
2. A supply voltage bias circuit according to claim 1 , wherein
the current source is an absolute-temperature-proportional power source or a band-gap power source.
3. A supply voltage bias circuit according to claim 1 , wherein the output circuit comprises:
a reference voltage generation circuit, which generate a reference voltage proportional to the supply voltage;
a supply voltage output terminal outputting the supply voltage;
an operational amplifier having an inversion input terminal and a non-inversion input terminal, the non-inversion input terminal being connected to the supply voltage output terminal;
a resistive element comprising a first terminal connected to the inversion input terminal of the operational amplifier and a second terminal, which is grounded or earthed; and
a fifth transistor forming a current mirror circuit together with the fourth transistor, wherein
a source or drain of the fifth transistor is connected to a source of drain of the first transistor.
4. A supply voltage bias circuit according to claim 3 , wherein
the resistive element has a resistance-temperature coefficient which changes by temperature.
5. A supply voltage bias circuit according to claim 1 , further comprising:
an output terminal that is connected to an amplifier circuit.
6. A supply voltage bias circuit according to claim 5 , wherein
the amplifier circuit comprises a transistor of which a source is grounded or earthed.