Patent ID: 7345543

Claim:
A transconductance amplifier comprising an input stage comprising two input terminals, wherein each input terminal is connected to a first control terminal of a first transistor, and a second control terminal of a second transistor; a current output terminal of the first transistor being connected, on the one hand, to a first terminal of a respective resistor and, on the other hand, to a reference supply rail via a variable current source having a value capable of automatically varying according to a voltage applied between the input terminals; up to a limiting value; and a current output terminal of the second transistor being connected, on the one hand, to the reference supply rail via a fixed current source and, on the other hand, to a second terminal of the respective resistor connected to the current output terminal of the first transistor, wherein the variable current source comprises: a third transistor connected between an emitter of the first transistor and ground; a resistor and a capacitor, series-connected between a low supply rail and a control terminal of the third transistor; wherein a midpoint of the series connection being connected to the current input terminal of the first transistor, and; a fourth transistor connected between a fixed current source and ground, the fixed current source being connected between the low supply rail and a current input terminal of the fourth transistor; wherein a control terminal of the fourth transistor being connected to the current input terminal of the fourth transistor and, via a resistor, to a control terminal of the third transistor.