Amplifiers – Signal feedback – Nonlinear impedance element in loop path
Patent
1985-05-01
1986-12-09
LaRoche, Eugene R.
Amplifiers
Signal feedback
Nonlinear impedance element in loop path
324105, 324123C, 330289, H03F 134
Patent
active
046282777
ABSTRACT:
A femtoammeter is disclosed which resists noise induced reversed bias of the ammeter amplifier and avoids long time constant recovery with unusually high measurement accuracy. The amplifier ammeter has a feedback loop which is provided with paired opposingly faced log diodes in parallel across the feedback circuit. Transients of negative or positive bias are accommodated without biasing the amplifier to a reverse polarity and having unacceptably long time constant recovery. Conventional temperature compensation, not possible with the parallel reversed diode configuration, is supplied by heat sinking the ammeter components, providing a log diode temperature sensor for the heat sinked components and controlling the heat sink operating temperature with a thermoelectric cooler. The temperature sensing log diodes output to a computer lookup table. The same temperature sensing log diode outputs to a bridge circuit operating the thermoelectric cooler. The thermoelectric cooler is polarized to heat or cool the heat sink to thermally adjust the ammeter to an optimum operating temperature. Automated bootstrap calibration is disclosed with reed switching for prevention of stray currents. Accuracy includes heretofore unattainable results.
REFERENCES:
patent: 3724954 (1973-04-01), Dreyfoos, Jr.
patent: 4270090 (1981-05-01), Williams
patent: 4349788 (1982-09-01), Sondermeyer
Rao, K. G. Krishna, "Log Amp's Range Extended to lpA", Electronic Design 14, Jul. 5, 1976, p. 66.
Akers David D.
Hill William D.
General Electric Company
James, Jr. Ivor J.
LaRoche Eugene R.
Mottola Steven J.
Simkins Raymond G.
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