Variable Gain Amplifier DC Offset Correction During Gain Changes
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Solution Overview
Problem
Existing variable gain amplifiers face challenges in correcting DC offset voltage efficiently, especially when gain is changed, due to increased current consumption and the need for large on-chip capacitors, which complicates DC offset correction during short gain setting periods.
Innovation Solution
A variable gain amplifier design with a differential amplifier circuit, feedback and input resistors, and voltage correction units that adjust resistance values and output correction voltages to attenuate DC offset voltage, allowing for simpler control and reduced power consumption, even when gain is changed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC offset cancel circuit is always driven to correct the DC offset voltage, then the DC offset correction is effective, but current consumption increases
Solution Approach 1:
The patent implements periodic DC offset correction by detecting the DC offset component only during AGC periods rather than continuously. The correction circuit is activated intermittently based on gain change detection, achieving effective DC offset correction while reducing current consumption compared to continuous correction approaches.
2Measurement precision
If a large on-chip capacitor is mounted for detecting the DC offset component, then the DC offset detection accuracy is improved, but the circuit area and current increase
Solution Approach 1:
The patent uses a small-capacitance capacitor (0.5 pF to 2 pF) that is insufficient for complete DC offset detection, but achieves adequate correction by combining it with periodic operation during AGC periods. This partial action approach avoids the need for large capacitors while maintaining practical correction effectiveness.
3Reliability
If the correction circuit operates continuously, then the DC offset voltage is corrected accurately, but the correction time increases
Solution Approach 1:
The patent performs DC offset correction in advance during AGC periods before signal processing. By detecting and correcting the DC offset component during these predetermined time windows, the system ensures correction is completed before subsequent operations require accurate signal levels, avoiding delays in the main signal processing path.
4Adaptability or versatility
If the gain of variable gain amplifier is changed during operation, then the adaptability is improved, but the DC offset correction becomes difficult to perform timely
Solution Approach 1:
The patent employs feedback mechanisms where the control unit monitors gain control signals and AGC period timing to determine when DC offset correction should be performed. This feedback-based timing synchronization ensures that correction operations are coordinated with gain changes, maintaining correction effectiveness despite dynamic operating conditions.
Data Source
AI summary
To provide a variable gain amplifier capable of correcting a DC offset voltage through simpler control even when a gain thereof is changed. A differential output type variable gain amplifier is equipped with a first voltage correction unit coupled to a preceding stage of a variable gain amplifier circuit and for outputting a first correction voltage to correct a potential difference generated between a first conductor provided with a first input resistor and a second conductor provided with a second input resistor, and a second voltage correction unit coupled to a subsequent stage of the variable gain amplifier circuit and for correcting a differential output. A control unit is configured to control the first correction voltage and a correction amount of a potential difference by the second voltage correction unit and thereby attenuate a DC offset voltage included in the differential output.