Constant-current circuit operating in saturation region

DETAILED DESCRIPTION (1) In a first aspect of this invention, a temperature sensor circuit of a differential output type is provided which is formed of MOS transistors.
This circuit includes a differential pair circuit and a feedback circuit.
The differential pair circuit includes first and second MOS transistors whose gate-width and gate-length ratio (W/L) are different from each other, a load circuit of the first and second transistors and a constant-current source for driving the first and second transistors.
The feedback circuit is supplied from the drain of one MOS transistor of the differential pair circuit with an output voltage of the differential pair circuit thereby feedback-controlling the differential pair circuit so that the drain currents of the first and second MOS transistors can be made equal to each other.
Preferably, the gate of the first MOS transistor of the differential pair circuit is connected to one terminal of the output terminal pair of the temperature sensor circuit to be applied with the reference voltage.
The gate of the second MOS transistor is connected to the other terminal of the output terminal pair thereof thereby receiving therethrough a feedback voltage from the feedback circuit.
The load circuit is preferable to comprise a current mirror circuit.
In this case, the load circuit preferably comprises two MOS transistors equal in gate-width and gate-length ratio (W/L) to each other.
The temperature sensor circuit of the first aspect of this invention feeds back an output voltage of the feedback circuit to the differential pair circuit to control the drain currents of the first and second transistors thereof to become equal to each other, so that between the two input terminals of the differential pair circuit is obtained a voltage proportional to the temperature.
Consequently, such a temperature sensor circuit that is of a differential output type formed of MOS transistors can be obtained with superior characteristics.
The feedback circuit is not limited to that shown above, it may be any other types of circuit if operable in the same manner as above