Controllable reactance circuit for an integrated circuit

Details Controllable reactance circuit for an integrated circuit Controllable reactance circuit for an integrated circuit

1998-10-20

2000-03-14

Mis, David

Oscillators

With frequency adjusting means

With voltage sensitive capacitor

331 36C, 331117FE, 331116FE, 331111, 333214, H03B 502, H03B 512, H03H 1148, H03L 708, H03L 7099

Patent

active

060378433

ABSTRACT:
A controllable reactance implemented within an integrated circuit includes a first sub-circuit (20) comprising a reactive element, for example a capacitor 12, coupled in series with a transistor (14). A controllable current source (16) injects a controllable bias current through the transistor (14) to vary the effective resistance of the transistor (14) and hence the effective complex impedance of the capacitor combination. A second transistor (18) amplifies the current to increase the effective capacitance. Preferably, a second sub-circuit (24) includes corresponding components (26, 28, 30) to mirror the real component of the current flowing in the first sub-circuit (20), and transistors (32 and 34) to reflect an inverse current to the coupling node line (22) to cancel the real component of the current at the node, to thus simulate a purely capacitive circuit. An oscillator embodying this circuit is also disclosed. The invention can provide a controllable capacitance without the need for a conventional varactor diode.

REFERENCES:
patent: 4399561 (1983-08-01), Lunn et al.
patent: 4587500 (1986-05-01), Tanaka et al.
patent: 4602224 (1986-07-01), Arimoto et al.
patent: 5510755 (1996-04-01), Kodrnja et al.
patent: 5559474 (1996-09-01), Matsumoto et al.
patent: 5745012 (1998-04-01), Oka et al.
patent: 5955929 (1999-09-01), Moon et al.

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