Grounded emitter logarithmic circuit

Details Grounded emitter logarithmic circuit Grounded emitter logarithmic circuit

2008-07-01

2008-07-01

Mai, Tan V. (Department: 2193)

Electrical computers: arithmetic processing and calculating

Electrical analog calculating computer

Particular function performed

Reexamination Certificate

active

07395308

ABSTRACT:
A logarithmically-responding circuit includes a differential-input amplifier that drives the control terminal of a three-terminal device that exhibits an exponential response in its output current. This arrangement allows the third terminal to be grounded. In a preferred embodiment the three-terminal device is a bipolar junction transistor (BJT). This, and other supporting circuit features described, enable single-supply, wide-range, fully temperature-compensated operation. A compensation technique significantly reduces errors caused by the finite ohmic emitter resistance of a BJT. To support use in logarithmically compressing the current generated by a photodiode, an adaptive bias signal can provided which maintains an essentially constant bias on the photodiode's internal junction.

REFERENCES:
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patent: 6822433 (2004-11-01), Gilbert
patent: 2005/0110479 (2005-05-01), Gilbert

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