Texas Instruments Corporation

Texas Instruments Incorporated Deutschland, Gmbh

Martin Braier

Karlheinz Muth

Gerd Schuppener

Lothar Schmidt

An integrated preamplifier circuit for detecting a signal current from a photodiode and converting the signal current into an output voltage is provided. The circuit includes a signal amplifier and a dummy amplifier, the dummy amplifier being matched to the signal amplifier. Each of these amplifiers includes an input transistor and an output transistor, the input transistor of the signal amplifier receiving an input signal derived from the signal current and the input transistor of the dummy amplifier receiving no input signal. The signal and dummy amplifiers provide the desired differential output signal. The input transistors of the signal and dummy amplifiers each have a biasing current source forced to follow a reference current source implemented within the integrated circuit.

Integrated preamplifier circuit for detecting a signal current from a photodiode

A transimpedance amplifier circuit comprising transistors, a constant current source, a load resistor, and the feedback resistor with a shunt circuitry consisting of the additional transistors, which are driven for example with electrically adjustable voltage sources. In a bipolar npn implementation the amplifier stage consists of a common emitter input transistor Q, a transistor Qwith its base connected to the collector of the first transistor operates as an emitter follower. A resistor RF connected between the emitter of said second transistor and the base of said first transistor provides a voltage controlled current feedback from the amplifier output to its input. The output voltage VOUT is generated at the emitter node of said second transistor. A shunt circuitry consists of a third and a fourth transistor Qand Qconnected in shunt across resistor RF. In an embodiment, the base node voltages of the transistors Qand Qare adjusted by control voltage sources. By means of an appropriate implementation of these voltage sources the maximum and minimum limits of the output voltage VOUT is defined, which can easily be implemented with arbitrary temperature or supply voltage dependency.

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Hannover, Germany

Martin Braier