Patent ID: 7295072

Claim:
An amplifier circuit comprising: a first differential amplifier circuit including first and second resistors, first and second transistors having collectors or drains connected to a high-voltage power supply through the first and second resistors, respectively, and connected to first and second output nodes of the first differential amplifier, bases or gates connected to first and second input nodes of the first differential amplifier circuit, respectively, and emitters or sources connected in common, and a first controllable current source having a first end connected to the emitters or sources of the first and second transistors, a second end connected to a low-voltage power supply, and an input terminal for receiving a bias signal for externally adjusting the current of the first controllable current source; a second differential amplifier circuit which amplifies output signals from the first and second output nodes of the first differential amplifier circuit; and an active feedback circuit shaping waveforms of the output signals from the first and second output nodes of the first differential amplifier circuit by feeding back output signals from first and second output nodes of the second differential amplifier circuit, wherein the active feedback circuit includes third and fourth transistors having collectors or drains connected to the first and second output nodes of the first differential amplifier circuit, respectively, and connected to first and second input nodes of the second differential amplifier circuit, bases or gates connected to the first and second output nodes of the second differential amplifier circuit, respectively, and emitters or sources connected in common, and a second controllable current source having a first end connected to the emitters or sources of the third and fourth transistors, a second end connected to the low-voltage power supply, and an input terminal for receiving a bias signal for externally adjusting the current of the second controllable current source, the input terminals of the first and second controllable current sources not being connected together, whereby the currents produced by the first and second controllable current sources may be independently adjusted.