Capacitor-Free AGC Circuit With Digital Offset Compensation
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Solution Overview
Problem
Conventional AGC circuits require large capacitors for integrating circuits, making them unsuitable for integration and causing issues with response time and multi-channelization, especially in audio systems where DC offset affects performance.
Innovation Solution
An AGC circuit design that replaces integrating circuits with A/D conversion and digital signal processing, eliminating the need for capacitors and allowing for a more compact, multi-channel solution by using A/D conversion for gain control and offset compensation, and employing digital filters and counters for offset detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an integrating circuit using a capacitor is utilized to detect amplitude level of output signal, then the AGC operation can be performed, but the capacitance value becomes so large that the capacitor cannot be mounted in the integrated circuit
Solution Approach 1:
The patent replaces the analog integrating circuit with a capacitor with a digital signal processing system consisting of an A/D conversion circuit, level detection circuit, and gain control circuit. This substitution eliminates the need for large capacitors while maintaining the AGC functionality through digital amplitude detection and control.
2Loss of time
If a large capacitance value capacitor is used for integrating circuit, then the AGC response time can be controlled, but the circuit scale increases and multi-channelization becomes difficult
Solution Approach 1:
The patent substitutes the analog integrating circuit with large capacitor with a digital processing system that uses an A/D conversion circuit to convert the output signal to digital, a level detection circuit to detect amplitude, and a gain control circuit to adjust gain. This digital approach eliminates the need for large capacitors while enabling precise control of response time through digital processing.
3Reliability
If DC offset voltage is present in input signal, then the AGC operation is adversely affected, but adding offset compensation circuit increases circuit complexity
Solution Approach 1:
The patent combines the offset compensation function with the existing A/D conversion and level detection circuits. The digital signal processing system simultaneously performs both offset compensation and amplitude detection, eliminating the need for separate analog offset compensation circuits and reducing overall circuit complexity.
Data Source
AI summary
There is provided an AGC circuit that has a very small offset voltage and is easy for integration, without using any of external capacities. For that reason, a variable gain amplifying circuit (GCA1) which has a gain controlled by a gain control signal, and whose output DC offset is controlled by an offset compensation signal, an A/D conversion circuit (AD1) for A/D converting an output signal of this variable gain amplifying circuit (GCA1), a level detection circuit (Det1) for performing peak detection of an output signal of this A/D conversion circuit (AD1) to thereby detect an amplitude level, a gain control circuit (Gctrl1) for outputting a gain control signal according to an output signal of this level detection circuit (Det1), an offset detection circuit (Det2) provided with a lowpass filter for taking out a DC component from the output signal of the A/D conversion circuit (AD1), and a D/A conversion circuit (DA1) for D/A converting an output signal of the offset detection circuit (Det2) to thereby output the offset compensation signal are provided.