Amplifiers – With semiconductor amplifying device – Including d.c. feedback bias control for stabilization
Patent
1998-08-03
2000-02-08
Mottola, Steven J.
Amplifiers
With semiconductor amplifying device
Including d.c. feedback bias control for stabilization
330259, H03F 130, H03F 345
Patent
active
060231963
ABSTRACT:
In low-voltage circuits, there is often insufficient voltage to use a current source to bias a transconductance amplifier stage. This is particularly true in mixers where a switching circuit must be stacked on top of the transconductance input stage. One way around this problem is to get "double-duty" out of the input differential pair, using it both for gain stage and for DC bias. This is done by AC coupling in a high-frequency input signal, while using a low-frequency, DC-coupled circuit to establish the proper bias level. One common technique is to use a simple current mirror scheme to establish the DC level. Proper biasing using this technique requires good matching of resistance. In some implementations of transconductance amplifiers, particularly those that use inductors as degeneration elements, series resistance of the inductor and interconnect resistance can cause significant errors in the bias current. This invention addresses that problem by using an operational amplifier with a current-sensing resistor and a low-frequency feedback loop to compensate automatically for any resistance errors. The operational amplifier drives the feedback voltage (generated in accordance with the sensed voltage at the current-sensing resistor and applied to one input of the operational amplifier) towards a reference voltage that is applied to the other input of the operational amplifier to bias the transistor(s) in the transconductance amplifier for desired operating conditions.
REFERENCES:
patent: 4459553 (1984-07-01), Diller
patent: 4849712 (1989-07-01), Jarrett
patent: 5008632 (1991-04-01), Sutterlin
"An Integrated Silicon Bipolar Receiver Subsystem for 900MHz ISM Band Applications", by Jeff Durec, Proceedings of the 1997 Bipolar/BiCMOS Circuits and Technology Meeting, sponsored by IEEE Electron Devices Society, Sep. 1997, 6 pages.
"TP 3.5: A 2.7-5.5V 0.2-1W BiCMOS RF Driver Amplifier IC with Closed-loop Power Control and Biasing", by S. Wong, S. Luo, and L. Hadley, 1998 IEEE International Solid-State Circuits Conference, 5 pages.
Ashby Kirk B.
Davis Paul C.
Womac Michael D.
Lucent Technologies - Inc.
Mottola Steven J.
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