DC Offset Cancellation Circuit with Overlapped Feedback Loops
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Solution Overview
Problem
Direct conversion of RF signals to baseband in mobile telecommunication systems results in high DC offset levels due to circuit mismatch, LO self-mixing, and interferer self-mixing, degrading signal quality and increasing power consumption, with existing methods like ac-coupling and low-pass filters being either inefficient or power-hungry.
Innovation Solution
A circuit with multiple overlapped feedback loops, comprising a multistage amplifier or filter configuration with variable gain amplifiers and a low-pass filter, which adjusts gain to stabilize loop operation and provides additional feedback paths for effective DC offset cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If ac-coupling is used to cancel DC offsets, then the circuit is simple and cost-effective, but large off-chip capacitors are required and response time is slow
Solution Approach 1:
The patent replaces the mechanical/ac-coupling method with an electronic feedback-based DC offset cancellation system. The system uses multiple feedback loops with adjustable gain amplifiers and low-pass filters to electronically cancel DC offsets, eliminating the need for large physical capacitors and achieving faster response times through electronic control mechanisms.
Solution Approach 2:
The patent implements multiple feedback loops where the output signal is fed back through low-pass filters and adjustable gain amplifiers to detect and cancel DC offsets. The feedback mechanism continuously monitors and corrects DC offsets, enabling fast response times without requiring large capacitors, thus resolving the contradiction between circuit simplicity and response speed.
2Reliability
If low-pass filters are used via negative feedback to cancel DC offsets, then DC offset cancellation is achieved, but the implementation causes larger area and higher power consumption
Solution Approach 1:
The patent divides the DC offset cancellation function into multiple segmented feedback loops, each handling specific frequency ranges or offset components. By segmenting the cancellation task across multiple loops with adjustable gain amplifiers, the system achieves effective DC offset cancellation while optimizing power consumption compared to using a single high-power low-pass filter.
Solution Approach 2:
The patent employs dynamically adjustable gain amplifiers in each feedback loop that can adapt their gain settings based on the detected DC offset levels. This dynamic adjustment allows the system to maintain effective DC offset cancellation while consuming minimal power, resolving the contradiction between reliability and power consumption.
3Reliability
If multiple low-pass filters are used in multistage amplifier configuration, then DC offset cancellation is improved, but the circuit area increases
Solution Approach 1:
The patent designs feedback loops that serve multiple functions: DC offset detection, filtering, and cancellation. The same feedback infrastructure is used across multiple amplifier stages, allowing the system to achieve improved DC offset cancellation performance without proportionally increasing circuit area, as each feedback loop serves multiple purposes rather than requiring dedicated components for each function.
Solution Approach 2:
The patent merges the DC offset cancellation function with the existing multistage amplifier structure by integrating feedback loops into the amplifier stages. This merging approach allows the system to achieve enhanced DC offset cancellation performance while utilizing the existing circuit infrastructure, thereby minimizing the additional circuit area required.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution reduces circuit area and power consumption while enhancing stability and efficiency in DC offset cancellation, maintaining signal quality and reducing power consumption.
Implementation Method 1
a low-pass filter, the input thereof coupled to the output of multistage amplifier, and the output thereof coupled to the input of variable gain amplifier
Implementation Method 2
a plurality of variable gain amplifiers, the outputs of the variable gain amplifier coupled to the seriated contact between each stage amplifier of the multistage amplifier
Data Source
AI summary
A circuit having multiple overlapped feedback loops for DC offset cancellation is provided with applying in one of multistage amplifier, multistage filter, and the combination thereof. The circuit includes a plurality of negative feedback variable bandwidth switches coupled to each stage of the above mentioned multistage devices, the output of the last stage is coupled to an input of a low-pass filter loop. The circuit includes a plurality of variable gain amplifiers, output of each variable gain amplifier is coupled to the series contact of each stage respectively, and input of each variable gain amplifier is thereof coupled to an output of the low-pass filter loop. Therefore, the circuit achieves to cancel the DC offset for multistage overlapped feedback path with less area and low power consumption.