Current-controlled carrier tracking filter for improved spurious signal suppression
AssigneeIntersil Americas Inc.
InventorsBrent A. Myers, Paul J. Godfrey
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Abstract
Spurious energy suppression for a data communication system is achieved without using a large order noise suppression filter, by means of a post-mixer tracking filter that contains a current-controlled MOSFET-implemented resistance for a transconductance-capacitance filter and an associated transconductance tuning stage. The MOSFET-implemented resistance is controlled by the same control current that establishes the output frequency. As a result, the cut-off frequency of the tracking filter is linearly proportional to the carrier and independent of absolute processing parameters and temperature.
Claims20
For use with a communication device having a signal modulator that is adapted to modulate a signal in accordance with an output frequency coupled thereto by a current-controlled oscillator which is adapted to generate said output frequency in accordance with a control current applied thereto, and a frequency-tracking filter circuit coupled to the output of said signal modulator, the improvement wherein said frequency-tracking filter circuit has a cut-off frequency that is linearly proportional to said control current.
A current controlled filter circuit comprising:
- a filter stage containing a tunable transconductance that is adapted to establish a cut-off frequency of said filter stage;
- and
- a transconductance tuning stage coupled to said filter stage;
- and wherein
- said filter stage and said transconductance tuning stage are configured such that said cut-off frequency of said filter stage is linearly proportional to a control current applied to said transconductance tuning stage.
For use with a communication device having a signal modulator adapted to modulate a signal in accordance with an output frequency coupled thereto by a current-controlled oscillator, which is adapted to generate said output frequency in accordance with a control current applied thereto, a method of filtering the output of said signal modulator comprising the steps of:
- (a) coupling to the output of said signal modulator a frequency-tracking filter circuit having a cut-off frequency that is linearly proportional to said control current;
- and
- (b) controlling said cut-off frequency of said frequency-tracking filter circuit in linear proportion to said control current.
Dependencies are inferred from the claim text.