Amplifiers – Signal feedback – Multiple feedback paths
Patent
1977-06-09
1978-11-14
Mullins, James B.
Amplifiers
Signal feedback
Multiple feedback paths
328151, 330259, 330261, 330296, H03F 108
Patent
active
041258134
ABSTRACT:
A sample and hold circuit is disclosed which employs a matched pair of operational amplifiers as a decoupling circuit to isolate the output of the sample and hold circuit from the sampling capacitor. Prior art decoupling circuits employ a simple isolation amplifier which has a tendency to charge the sampling capacitor with the isolation amplifier input bias and leakage currents. The disclosed decoupling circuit employs one of a pair of matched operational amplifiers as a self-compensating isolation amplifier which dynamically generates the bias and leakage currents found at its input while isolating the sample and hold output from the sampling capacitor. The other operational amplifier is connected in series between the isolation amplifier and the sample and hold output and functions to cancel the input bias current signal generated by the self-compensating isolation amplifier. Thus, the net quiescent current into the input of the decoupling circuit is essentially zero, thereby eliminating the capacitor charging problem of prior art isolation amplifiers.
REFERENCES:
patent: 3812383 (1974-05-01), Scheinberg
patent: 3988689 (1976-10-01), Ochi et al.
Choice, "Series-Connected Op Amps Null Offset Voltage," Electronics, Mar. 27, 1972, p. 92.
Naylur, "Digital and Analog Signal Applications of Operational Amplifiers," IEEE Spectrum, May 1971, pp. 79-87.
Bell Telephone Laboratories Incorporated
Graziano James M.
Mullins James B.
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