Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function – Logarithmic
Reexamination Certificate
2000-04-14
2001-06-19
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
Logarithmic
C327S351000, C327S359000, C327S563000
Reexamination Certificate
active
06249170
ABSTRACT:
This invention relates, in general, to a gain control circuit for integrated circuit amplifiers, for example Radio Frequency (RF) amplifiers in telecommunication applications such as cellular and cordless telephones. Specifically this invention relates to a logarithmic gain control circuit.
In a typical RF telecommunication application, particularly a cellular phone application, it is desirable to closely monitor and control amplifier gain to avoid excessively weak or strong transmissions. A preferred method for controlling amplifier gain is to apply a gain control voltage to an amplifier such that the ratio of the output signal current to the input signal current is a logarithmic function of the gain control voltage.
Prior art implementations attenuate a signal current by cascoding the current through an amplifier using a differential transistor pair. The differential transistor pair splits the current between the two transistors, with the collector current of one transistor as the output current and the collector current of the second transistor connected to V
cc
. A differential gain control voltage applied to the bases of the transistor pair controls the attenuation of the output signal current.
The disadvantage of the prior art implementation is it fails to maintain the logarithmic relationship between the output signal current and the gain control voltage. The prior art circuits have a significant dB loss in signal output current when operated at higher gains. Therefore, a need exists to provide a gain control circuit that provides for a logarithmic relationship between the signal output current and the gain control voltage.
REFERENCES:
patent: 4004141 (1977-01-01), Curtis
patent: 4379995 (1983-04-01), Yamada et al.
patent: 4818951 (1989-04-01), Roberts
patent: 5200655 (1993-04-01), Feldt
patent: 5302868 (1994-04-01), Fergus
patent: 6104226 (2000-08-01), Weber
Coffing Danielle L.
Durec Jeffrey
Main William E.
Cunningham Terry D.
Motorola Inc.
Nguyen Long
Parker Lanny L.
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