Radar Baseband Cancellation Circuit for Self-Interference
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Solution Overview
Problem
Radar systems suffer from self-interference due to amplifier nonlinearities, leading to ghost targets and increased noise floors, which are particularly challenging for digitally coded radars and result in stringent linearity and dynamic range requirements that are impractical in terms of power dissipation and silicon area.
Innovation Solution
A radar transceiver with a digital correction module that performs self-interference cancellation in the discrete time domain using a sampling capacitor and variable cancellation capacitor, integrated with a switched capacitor architecture to sample and subtract the interference signal before amplification, reducing linearity and dynamic range requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If linear broadband amplification is used to meet dynamic range requirements, then receiver performance improves, but power dissipation and silicon area increase significantly
Solution Approach 1:
The receiver chain is segmented into multiple functional blocks (LNA, mixer, baseband amplifier, ADC) with distributed gain allocation. Instead of using a single high-gain linear amplifier, the gain is distributed across stages, allowing each component to operate within practical linearity limits while achieving the required overall dynamic range.
Solution Approach 2:
A correction signal is introduced as an intermediary element that actively cancels the nonlinear distortion products generated by the variable gain amplifier. This correction signal, generated by estimating the nonlinear behavior, mediates between the unavoidable nonlinear amplification and the requirement for linear receiver performance.
2Measurement precision
If high linearity is maintained in variable gain amplifiers, then ghost targets are reduced, but device complexity and power consumption increase
Solution Approach 1:
The nonlinear distortion products, which originally caused ghost targets and degraded performance, are converted into a beneficial correction signal. By estimating the nonlinear behavior of the VGA and generating a corresponding correction signal, the harmful nonlinear effects are transformed into a manageable parameter that can be actively compensated.
Solution Approach 2:
A feedback loop is implemented where the output of the receiver is used to estimate the nonlinear distortion, which then generates a correction signal fed back to cancel the distortion. This feedback mechanism allows the system to adaptively maintain measurement precision without requiring the amplifier to operate in a highly linear regime.
3Adaptability or versatility
If baseband bandwidth is increased to 4GHz for short range radar, then detection capability improves, but amplifier linearity requirements become more stringent
Solution Approach 1:
The system dynamically adjusts the correction signal based on the actual operating conditions and signal characteristics. The correction signal generator adapts to different bandwidth requirements and signal levels, allowing the receiver to maintain performance across varying detection scenarios without requiring fixed high-linearity amplifier design.
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 proposed solution effectively cancels self-interference, improving radar performance by simplifying timing requirements, reducing noise, and relaxing ADC dynamic range needs, while maintaining high detection accuracy and flexibility.
Implementation Method 1
a sampling capacitor, a variable cancellation capacitor controllable by the digital correction signal, an amplifier and a switching arrangement configured to sample the baseband received signal and sum a sampled charge across the sampling capacitor with a charge across the variable cancellation capacitor
Implementation Method 2
sum a sampled charge across the sampling capacitor with a charge across the variable cancellation capacitor to provide a residue signal
Implementation Method 3
the amplifier configured to amplify the residue signal to provide the corrected analog baseband signal to the ADC
Data Source
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AI summary
The disclosure relates to cancellation of self-interference in radar transceivers. Example embodiments include a radar transceiver (500) in which a correction module (510) is configured to combine an analog baseband received signal with a digital correction signal to provide a corrected analog baseband signal, the correction module (510) comprising a sampling capacitor (Cs), a variable cancellation capacitor (Cc) controllable by the digital correction signal, an amplifier (519) and a switching arrangement (520) configured to sample the baseband received signal and sum a sampled charge across the sampling capacitor (Cs) with a charge across the variable cancellation capacitor (Cc) to provide a residue signal to the amplifier (519), the amplifier (519) configured to amplify the residue signal to provide the corrected analog baseband signal to an ADC (511).