Method of offset voltage trim for automatic gain controls
AssigneeSilicon Systems, Inc.
InventorKiyoshi Fukahori
Life of this patent
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Abstract
A method for providing DC offset trim for automatic gain controls independent of temperature or gain. A DC trim current is added or subtracted from one side of the differential AGC circuit. The trim current balances the currents through the two halves of the differential circuit, eliminating DC offset at the AGC output. The trim current is derived from a current source that is dependent upon another current source that provides the current through the two halves of the differential circuit. Therefore, the trim current responds any changes in the current supplied to the differential AGC circuit. Thus, DC offset trim independent of temperature or gain, as well as reduction of the total harmonic distortion and direct DC coupling of signals between stages, is provided.
Claims19
A circuit comprising:
- a first transistor coupled to a first input terminal;
- a second transistor coupled to a second input terminal;
- a first current source coupled to said first transistor and to said second transistor;
- a first switch coupled to said first transistor and to said second transistor;
- a plurality of transistors coupled to said first switch;
- a second current source coupled to said plurality of transistors, said second current source dependent upon said first current source.
An apparatus for trimming the offset voltage of an automatic gain control (AGC) circuit comprising:
- a first differential pair of transistors;
- a first current source coupled to said first differential pair of transistors for providing a first current having a first current magnitude;
- a trim current source coupled to said first differential pair of transistors for controlling an offset trim current having an offset trim current magnitude, wherein said offset trim current magnitude depends upon said first current magnitude;
- programming means coupled to said trim current source for determining a nominal trim current magnitude and a trim current polarity;
- a second differential pair of transistors coupled to said first differential pair of transistors;
- a second current source coupled to said second differential pair of transistors for providing a second current, wherein a gain of said AGC circuit is dependent upon a difference between said first current and said second current;
- a first switch coupled to said first differential pair of transistors and to said offset trim current source for selecting a side of said first differential pair of transistors to which said offset trim current is to be applied.
A method of offset trim comprising the steps of:
- providing a first current source for controlling a current supplied to a differential pair;
- providing a second current source for controlling a trim current supplied to said differential pair;
- continuously adjusting said second current source in response to said first current source;
- controlling a gain of said differential pair by controlling said current supplied to said differential pair;
- digitally programming a nominal magnitude of said trim current.
Dependencies are inferred from the claim text.