Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Utility Patent
1999-09-17
2001-01-02
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C327S552000
Utility Patent
active
06169447
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to stabilization of passband active filters such as may be used in radio transmitter/receivers for operating channel selection.
2. Description of the Related Art
In our co-pending application GB 9804708.7 there is described a means for frequency and channel selection for both receiver and transmitter in a radio transmitter/receiver. Included in the exemplary embodiment of the invention given in GB 9804708.7 is a passband active filter. It has been found sometimes to occur that the passband active filters of the type referred to in that embodiment suffer instability.
This instability is caused because the passband active filter consists of a negative resistance generator which acts to cancel out the losses in an associated resonator so improving the Q (Quality) of the circuit. The problem of instability arises when the negative resistance exceeds the losses in the resonator because in such a situation oscillation can occur. These oscillations may occur due to variations in manufacturing tolerances and temperature fluctuations.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a calibrator for a passband active filter to guarantee the stability of the filter while preserving the “Q” performance and to provide a method for such calibration.
In accordance with the invention there is provided a calibrator for stabilization of a passband active filter comprising means for providing a steady increase in filter supply current from a low level at which low level filter stability is assured to a high level at which high level instability occurs and means for setting said filter supply current at a level less by a pre-determined amount than the high level at which instability occurs.
In general a method of calibrating a passband active filter comprises the steps of setting a low level of filter supply current to provide filter stability, tuning the filter to the required passband, ramping up the supply current level, monitoring the filter for instability, holding the supply current level when instability is detected, reducing the supply current by a predetermined amount from the held value and re-tuning the passband active filter.
The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.
REFERENCES:
patent: 4174501 (1979-11-01), Chastagnier et al.
patent: 4426735 (1984-01-01), Kasperkovitz
patent: 5241697 (1993-08-01), Hansen
patent: 5325070 (1994-06-01), McGinn
patent: 5731694 (1998-03-01), Wilcox et al.
patent: 0 818 884 (1998-01-01), None
patent: 1 404 645 (1975-09-01), None
NEC Corporation
Nguyen Hiep
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tran Toan
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