Logarithmic amplifier circuit using triple-tail cells

Details Logarithmic amplifier circuit using triple-tail cells Logarithmic amplifier circuit using triple-tail cells

1995-09-11

1996-05-28

Tran, Toan

Miscellaneous active electrical nonlinear devices, circuits, and

Specific input to output function

Logarithmic

327351, G06F 7556, G06G 724, H03G 1108

Patent

active

055215424

ABSTRACT:
A logarithmic amplifier circuit is provided, which contains a differential amplifier, a first rectifier for rectifying an initial input signal and for generating a first rectified output signal, a second rectifier for rectifying an amplified output signal from the differential amplifier and for generating a second rectified output signal, and an adder for adding the first and second rectified output signals to produce an output signal having a logarithmic characteristic. The first and second rectifiers each is made of a triple-tail cell. The cell contains first, second and third emitter- or source-coupled transistors and a constant current source for driving the transistors. An input signal is applied across bases or gates of the first and second transistors, and a dc voltage is applied to a base or gate of the third transistor. An output current is outputted through the coupled collectors or drains of the first and second transistors or through the collector or drain of the third transistor. The number of necessary current sources can be reduced. The logarithmic transfer characteristics can be adjusted by changing the dc voltage as required.

REFERENCES:
patent: 4990803 (1991-02-01), Gilbert
patent: 5319264 (1994-06-01), Kimura
patent: 5467046 (1995-11-01), Kimura
IEEE Transactions on Circuit and Systems, Fundamental Theory and Applications, vol. 39, No. 9, Sep., 1992, pp. 771-777.
IEE of Japan, Mar. 10, 1994, with English abstract.

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