Amplifiers – With semiconductor amplifying device – Including differential amplifier
Patent
1990-06-18
1991-06-11
Laroche, Eugene R.
Amplifiers
With semiconductor amplifying device
Including differential amplifier
330259, H03F 345
Patent
active
050235680
ABSTRACT:
A combined current difference and operational amplifier circuit (10) for use either as or in a filter embodied in an integrated receiver includes inputs (I.sub.A and I.sub.B) for oppositely phased current signals which are applied to a current mirror circuit formed by first and second NPN transistors (Q1,Q2) having their bases connected to a junction (20). Equal value resistors (R1,R2) are serially connected in the emitter circuits of the first and second transistors, respectively and the current inputs are coupled to the free ends of the resistors. The base-collector path of a third NPN transistor (Q3) is connected between the free end of one of the resistors (R1) and the junction (20). A current difference signal (i.sub.b -i.sub.a) derived from the free end of the other one of the resistors is applied to the virtual ground input of an operational amplifier formed by a common emitter stage (Q4) coupled to an emitter follower (Q5). The operational amplifier has a capacitive (C1) feedback between its output and virtual ground input so that the d.c. potential at said input has no effect on the d.c. operating point of the output.
As an alternative, resistive (Rf) feedback may be used instead of the capacitive feedback.
Another embodiment (FIG. 2) enables the input and output voltage swings to be increased without unduly degrading the bandwidth.
REFERENCES:
patent: 3852679 (1974-12-01), Schade, Jr.
patent: 4723110 (1988-02-01), Voorman
Moore Paul A.
Perry Colin L.
Voorman Johannes O.
Dinh Tan Xuan
Franzblau Bernard
LaRoche Eugene R.
U.S. Philips Corporation
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