Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Reexamination Certificate
2001-08-14
2003-07-15
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C327S344000
Reexamination Certificate
active
06593802
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to tuning circuits and, more specifically, to producing a stable, process independent RC time constant for use in automatic tuning of continuous time filters.
BACKGROUND OF THE INVENTION
Continuous-time filters, such as intermediate frequency (IF) communications filters and video processors, generally require frequency tuning within the filter to match a specified frequency. Existing on-chip automatic tuning techniques typically employ a phase-lock loop (PLL), introducing poles in the feedback loop and therefore creating stability issues.
Additionally, frequency response precision within continuous-time filters is often constrained by RC time constant variances from one circuit to another due to fabrication process tolerances, operating temperature variations, and aging.
There is, therefore, a need in the art for a stable RC time constant within automatic tuning circuits.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide, for use in on-chip automatic tuning, a stable, process independent RC time constant for precision frequency response, generated using a feedback loop employing a voltage controlled resistor to force current through the output node to equal a reference current. The only terms in the expression for the time constant affected by process variations are two resistances, which are uniformly affected by any process variations to maintain proportion. The open loop transfer function for the feedback loop contains only one pole; because no phase-locked loop or other complex circuit introducing multiple poles within the feedback loop are employed, the time constant tuning filter is intrinsically stable.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art will appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words or phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, whether such a device is implemented in hardware, firmware, software or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, and those of ordinary skill in the art will understand that such definitions apply in many, if not most, instances to prior as well as future uses of such defined words and phrases.
REFERENCES:
patent: 4851719 (1989-07-01), Hitomi
patent: 4882762 (1989-11-01), Waldhauer
patent: 5874830 (1999-02-01), Baker
patent: 5883545 (1999-03-01), Boyd
patent: 6246351 (2001-06-01), Yilmaz
“High-Frequency CMOS Continuous-Time Filters,” Haideh Khorramabadi and Paul R. Gray, IEEE Journal of Solid-State Circuits, vol. SC-19, No. 6, Dec. 1984.
“An Elliptic Continuous-Time CMOS Filter with On-Chip Automatic Tuning, ” Mihai Banu and Yannis Tsividis, IEEE Journal of Solid-State Circuits, vol. SC-20, No. 6, Dec. 1985.
Mariani Giorgio
Orlandini Valter
Callahan Timothy P.
Cox Cassandra
Jorgenson Lisa K.
Munck William A.
STMicroelectronics Inc.
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