High input impedance amplifier circuit

Amplifiers – With semiconductor amplifying device – Including signal feedback means

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Details

330100, 330112, 330156, 330311, H03F 138

Patent

active

045243310

ABSTRACT:
A three-stage amplifier circuit specially configured to provide a high input impedance. An initial emitter follower transistor stage amplifies the current level of an ac input signal to produce a first intermediate signal, a common-base transistor stage amplifies the voltage level of the first intermediate signal to produce a second intermediate signal, and a final emitter-follower transistor stage amplifies the current level of the second intermediate signal to produce an output signal in phase with the input signal. A feedback circuit feeds back the output signal to the input of the common-base transistor stage, to supplement the first intermediate signal input. This effectively increases the input impedance of the common-base transistor stage and, likewise, the initial emitter follower transistor stage, whereby the amplifier circuit can be used to amplify signals produced by high impedance sources.

REFERENCES:
patent: 2942200 (1960-06-01), Hanel et al.
patent: 3379987 (1968-04-01), Volkers
patent: 3720879 (1973-03-01), Reitmeyer, Jr.
patent: 3750041 (1973-07-01), Gay
patent: 4042887 (1977-08-01), Mead et al.
patent: 4218659 (1980-08-01), Arai
Aghion, "Use of Positive Feedback to Enhance the Open-Coop Gain of Fast Operational Amplifiers", Alta Frequenza, vol. XLVII, No. 11, Nov. 1978, pp. 485E-815-18.
Electronic Design, "Bootstrapping Helps Transistors Approach FET Performances", Dec. 6, 1963, p. 66.

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