Dual-Loop Radio Receiver AGC for DC Transient Control
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Solution Overview
Problem
Radio receivers, especially zero-IF receivers, face issues with DC current transients due to gain step transitions in automatic gain control (AGC) systems, leading to system performance degradation and increased noise, which existing compensation circuits struggle to fully mitigate.
Innovation Solution
Implementing a dual-AGC loop system where one loop controls gain in the analogue domain with a slower cycle time and another in the digital domain with a shorter cycle time, significantly reducing DC transients by decoupling the amplification adjustments and minimizing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If gain control is implemented by changing the gain of amplifiers in discrete gain steps, then the AGC system can control signal amplification effectively, but DC transients occur at gain step transitions which degrade system performance
Solution Approach 1:
The patent divides the AGC system into two separate loops: a first AGC loop for controlling analogue signal amplification and a second AGC loop for controlling digital signal amplification. This segmentation allows each loop to operate independently with different cycle times, preventing DC transients from propagating through the entire signal chain while maintaining effective gain control.
2Device complexity
If a single AGC loop controls both analogue and digital amplification, then the system structure is simple, but gain adjustments cause DC transients that cannot be filtered by compensation circuits
Solution Approach 1:
The patent segments the AGC control function into two distinct loops operating at different stages of the signal processing chain. The first loop controls analogue amplifiers with a longer cycle time, while the second loop controls digital amplification with a shorter cycle time. This segmentation isolates DC transient generation to specific stages where they can be managed without affecting the entire system.
3Object-generated harmful factors
If DC offset compensation circuits are used to block DC signals, then DC offsets are reduced, but they cannot eliminate DC transients caused by gain step transitions
Solution Approach 1:
The patent implements preliminary action by controlling the timing and rate of gain adjustments through the two-loop AGC system. The first AGC loop with its longer cycle time pre-regulates analogue gain changes, preventing large DC transients from occurring in the first place, rather than attempting to compensate for them after they occur.
Data Source
AI summary
An automatic gain control (AGC) method and system for a radio receiver are proposed in which the ACG comprises two AGC loops; a first loop controlling signal gain in the analog portion of the radio receiver, a second loop controlling gain in the digital domain after digitization of the received signal. The analog AGC loop has a slower response time than the digital AGC loop. When applied to a multi-branch diversity receiver, each branch has its own digital AGC loop, but the analog gain can be common to all branches, based on measurement of the analog signal in each branch.