Circuit and method for providing a generally log logarithmic tra

Details Circuit and method for providing a generally log logarithmic tra Circuit and method for providing a generally log logarithmic tra

1998-05-08

1999-11-02

Tran, Toan

Miscellaneous active electrical nonlinear devices, circuits, and

Specific input to output function

Logarithmic

327352, H03G 1108

Patent

active

059778121

ABSTRACT:
A circuit and method for generating a generally logarithmic transfer function based upon switching signals. The circuit includes a plurality of transistors and a switch operatively connected to each transistor in the programmable set. A line is in communication with each switch for carrying switching signals thereto thereby selecting which of the transistors will contribute to the generally logarithmic function. Preferably, the circuit is a portion of a programmable gain amplifier, and a digital code controls the gain. The gain can be generally logarithmic as a result of which transistors which are selected to contribute to the generally logarithmic transfer function. For example, there may be a plurality of sets of transistors where the values of the transistors in each set are such that when all the transistors of the set are selected to contribute to the generally logarithmic gain, the set of transistors provides a gain having a value approaching m. Each of the transistors in the set has a value which is generally a multiple of 1/2 m.

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A Low-Power CMOS VGA for 50 Mb/s Disk Drive Read Channels; IEEE Transactions on Circuits and Systems II: Analog and Digital Signal Processing, vol. 42, No. 6, Jun. 1995; pp. 370-376.

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