DC Offset Calibration in Direct Downconversion RF Receivers
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Solution Overview
Problem
Direct downconversion RF receivers face challenges in removing DC offset due to its dependence on operation frequency, signal amplification level, and temperature, which complicates calibration and gain setting, especially in frequency hopping patterns, and lack of intermediate frequency filtering limits the effectiveness of existing solutions like SAW filters.
Innovation Solution
A differential amplifier with DC offset reduction circuitry, comprising a pair of transistors and an adjustable current generator, along with a series of differential amplifiers that can selectively shunt current, allowing for dynamic calibration and reduction of DC offset through programmable gain and zeroing of input signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If SAW filters are used to filter intermediate frequency signal to reduce DC offset, then DC offset reduction is achieved, but device size increases and power consumption increases
Solution Approach 1:
The patent extracts and eliminates the SAW filter component from the receiver architecture by implementing direct downconversion, thereby removing the source of size and power consumption problems while addressing DC offset through alternative means
Solution Approach 2:
The patent replaces the mechanical SAW filter system with an electronic direct downconversion system that uses digital signal processing and electronic filtering to achieve DC offset reduction without requiring physical acoustic wave filters
2Adaptability or versatility
If frequency hopping patterns are implemented, then communication flexibility is improved, but recalibration time between frequency hops becomes insufficient
Solution Approach 1:
The patent performs DC offset calibration in advance during idle periods or transition times between frequency hops, preparing correction values before they are needed, thus ensuring calibration is complete before the next frequency hop begins without causing time loss during active communication
Solution Approach 2:
The patent maintains continuous DC offset compensation by updating calibration values during frequency transitions and applying them seamlessly, ensuring the useful action of DC offset reduction continues without interruption despite frequency hopping
3Reliability
If DC offset calibration is performed to remove DC offset, then signal processing capability is improved, but device complexity increases
Solution Approach 1:
The patent implements self-calibrating circuitry that automatically performs DC offset measurement and correction without requiring external calibration equipment or manual intervention, thereby improving signal processing capability while keeping the added complexity self-contained and automatic
Data Source
AI summary
A variable amplifier with adjustable current to correct for DC offset. The variable amplifier includes a zero function, allowing for zeroing of some amplifiers in an amplifier chain during correction for DC offset of another amplifier in an amplifier chain. In some embodiments selectable current injection is provided to an amplifier chain in conjunction with signals from selectable mixers.