Automatic Gain Control DC Offset Removal
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Solution Overview
Problem
Conventional automatic gain control circuits fail to fully utilize the input range of A/D converters due to the influence of DC offsets, which are either not removed effectively or require costly external components.
Innovation Solution
An automatic gain control apparatus comprising a variable gain amplifier, A/D converter, and a feedback circuit with an amplitude level detector, range detector, and gain controller, along with a filter to remove DC offsets without external capacitors, ensuring both amplitude levels fall within a predetermined range for optimal input utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a DC offset detector and adder are used to remove DC offset after the A/D converter, then the DC offset can be removed, but the DC offset still exists at the input end of the A/D converter and influences the full utilization of input range
Solution Approach 1:
The patent applies preliminary action by removing the DC offset before the A/D converter rather than after. The DC offset removal circuit is placed in the signal path before the A/D converter, and the DC offset value is detected and compensated in advance, ensuring that the DC offset does not affect the full utilization of the A/D converter input range during the conversion process.
2Measurement precision
If a high pass filter is placed in front of the A/D converter to remove DC offset, then the DC offset can be removed, but a required off-chip capacitor is costly
Solution Approach 1:
The patent extracts the DC offset component from the signal using a DC offset detection circuit that separates the DC component from the AC signal. This extracted DC offset is then compensated by subtracting it from the original signal, eliminating the need for expensive off-chip capacitors required by traditional high pass filter approaches.
Solution Approach 2:
The patent replaces the mechanical/electrical high pass filter system with a digital signal processing approach. Instead of using physical capacitors and resistors to filter out DC offset, the system uses digital detection and subtraction methods to remove the DC component, reducing hardware cost and complexity.
3Device complexity
If DC offset is not removed, then the apparatus is simpler, but the DC offset shifts the center of the amplified analog signal from the center of the input range of the A/D converter
Solution Approach 1:
The patent implements self-service by having the system automatically detect and compensate for its own DC offset without requiring external intervention or complex additional circuits. The DC offset detection and compensation functions are integrated into the existing signal processing path, allowing the system to self-correct the offset and maintain optimal input range utilization.
Data Source
AI summary
An automatic gain control apparatus receiving an analog signal and outputting a digital signal includes a variable gain amplifier, an A/D converter, and a feedback circuit. The variable gain amplifier amplifies the analog signal with a gain. The A/D converter converts the amplified analog signal to the digital signal. The feedback circuit includes an amplitude level detector, a range detector, and a gain controller. The amplitude level detector generates a first amplitude level and a second amplitude level in response to the digital signal. The range detector generates an adjustment signal in response to the first amplitude level and the second amplitude level. The gain controller adjusts a gain control level for the variable gain amplifier in response to the adjustment signal.