Temperature compensated logarithmic circuit

Electrical transmission or interconnection systems – Nonlinear reactor systems – Parametrons

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Details

307491, 307492, 328145, G06G 712, G06G 724

Patent

active

046045325

ABSTRACT:
A log-amp or log-ratio circuit for producing a temperature-independent output signal corresponding to the logarithm of the ratio of a pair of input currents. The basic logarithm function is generated by a pair of opposed P-N junctions through which the respective input currents flow. Temperature compensation is effected by a circuit including a second pair of opposed P-N junctions which receive a PTAT current split between the junctions in accordance with a modulation factor proportional to the desired logarithmic function. The temperature-induced signal variations produced by the PTAT current source are equal and opposite to the temperature-induced signal variations produced in the first pair of P-N junctions, and a temperature-independent output signal is developed in accordance with the modulation factor applied to the PTAT current through the second pair of P-N junctions.

REFERENCES:
patent: 4029974 (1977-06-01), Brokaw
patent: 4454433 (1984-06-01), Welland
patent: 4475103 (1984-10-01), Brokaw et al.

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