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Very High Gain Frequency Selector

IP.com Disclosure Number: IPCOM000095335D
Original Publication Date: 1965-Nov-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Clapper, GL: AUTHOR

Abstract

This circuit is a narrow band-pass filter having a very high gain. The circuit comprises two transistors T1 and T2. These are supplied with DC operating and biasing voltages via the resistors R1... R4 and constitutes a conventional amplifier stage with its output connected to a conventional emitter-follower. The output of emitter-follower T2 connects to output terminal Eo and also connects to the base of T1 via an RC network including resistors R5, R6 and R7 and capacitors C1 and C2. This RC network is tuned to the frequency for which the amplifier is to provide maximum response.

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Very High Gain Frequency Selector

This circuit is a narrow band-pass filter having a very high gain. The circuit comprises two transistors T1 and T2. These are supplied with DC operating and biasing voltages via the resistors R1... R4 and constitutes a conventional amplifier stage with its output connected to a conventional emitter-follower. The output of emitter-follower T2 connects to output terminal Eo and also connects to the base of T1 via an RC network including resistors R5, R6 and R7 and capacitors C1 and C2. This RC network is tuned to the frequency for which the amplifier is to provide maximum response.

Input signals supplied to terminal Ei are supplied to the base of T1 via capacitor C3. Variable resistor R1 is adjusted so that the loop gain of the circuit including the RC network is just below that required for oscillation. When an input signal in the proper frequency is supplied at terminal Ei, the loop gain is increased to slightly over unity for in-phase signals. The controlled oscillation tendency, therefore, increases the gain in a manner similar to superregeneration with the input signal controlling the squelching action.

Alternatively, the input signal from terminal Ei can be supplied to the circuit via either C1 or C2 in the RC network. Supplying the input signal to the circuit in the latter manner reduces the gain somewhat but eliminates noise problems arising in the DC supply circuits.

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