Mixer Output AC Coupling for Fast Receiver DC Offset Calibration
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Solution Overview
Problem
Conventional DC offset calibration methods in communication systems are inefficient due to long response times and power consumption, and struggle to accurately calibrate offsets caused by self-mixing, LO leakage, and noise, especially in mixer circuits.
Innovation Solution
A receiving device and method that combines an AC coupling circuit with a post-stage circuit and a DC offset calibration circuit, using dynamic resistor-capacitor switching to reduce DC offset and provide compensation current, effectively addressing transistor mismatch and noise-related issues while minimizing system startup time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AC coupling is applied in each amplifying circuit or filtering circuit to filter out DC offset, then DC offset filtering is achieved, but the total response time of the receiving system becomes much longer
Solution Approach 1:
The patent extracts the DC offset removal function from multiple distributed AC coupling circuits and concentrates it into a single AC coupling circuit located after the mixer. This centralization maintains the DC offset filtering capability while eliminating the cumulative response time delay that would result from placing AC coupling circuits in each amplifying or filtering stage throughout the receiver chain.
2Reliability
If current compensation operation is used to calibrate DC offset, then DC offset calibration is achieved, but power consumption increases and the determined compensation current is easily affected by temperature and voltage changes
Solution Approach 1:
The patent implements a self-calibrating mechanism where the receiving system automatically performs DC offset calibration by detecting the DC offset level and adjusting the compensation current accordingly. The calibration process uses the system's own resources - the mixer output, AC coupling circuit, and post-stage circuit - without requiring external calibration equipment or additional power-hungry dedicated calibration hardware. The system self-adjusts to maintain accurate DC offset compensation despite temperature and voltage variations.
3Reliability
If current compensation is used, then DC offset from transistor mismatch can be calibrated, but it cannot accurately calibrate DC offset from self-mixing, LO leakage, or other noise
Solution Approach 1:
The patent introduces an AC coupling circuit as an intermediary element between the mixer and the post-stage circuit. This AC coupling circuit acts as a mediator that blocks DC components (including those from self-mixing and LO leakage) while allowing AC signal components to pass through. By placing this intermediary at a strategic point in the signal path, the system can effectively remove DC offset from multiple sources simultaneously, not just from transistor mismatch.
4Reliability
If multiple AC coupling circuits are used in different stages, then DC offset is filtered at each stage, but the system startup time becomes longer
Solution Approach 1:
The patent extracts the DC offset filtering function from multiple distributed AC coupling circuits and consolidates it into a single AC coupling circuit positioned after the mixer. This consolidation maintains effective DC offset filtering while reducing the total number of circuits that require startup time, thereby shortening the overall system startup duration.
Data Source
AI summary
A receiving device includes a mixer, an AC coupling circuit, a post-stage circuit, and a DC offset calibration circuit. The mixer is utilized for mixing an input signal with a local oscillating (LO) signal from an oscillator to generate a converted signal. The AC coupling circuit is coupled to the mixer and utilized for reducing at least one portion of DC offset of the converted signal to generate a filtered signal. The post-stage circuit is coupled to the AC coupling circuit and utilized for processing the filtered signal to generate an output signal. The DC offset calibration circuit is coupled to the post-stage circuit and utilized for providing at least a compensation current for the post-stage circuit to reduce DC offset of the output signal.