Radar Transceiver Circuit for Chirp-Time Interference Mitigation
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Solution Overview
Problem
Millimeter-wave radar systems face interference and jamming issues due to cross-coupling between transmitter and receiver paths, leading to saturation of analog-to-digital converters (ADCs) and reduced ability to detect targets, especially in automotive applications where shorter pulse repetition times are desirable for accurate target velocity detection.
Innovation Solution
A transimpedance amplifier with variable resistance and feedback amplifier circuitry is controlled by a controller to temporarily increase transconductance and decrease resistance during chirp transmission, mitigating jamming effects by enhancing the 1 dB compression point (P1 dB) of the amplifier, thereby reducing ADC saturation and improving system performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pulse repetition time is shortened to improve velocity detection accuracy, then the maximum unambiguous velocity detection is improved, but the system becomes more susceptible to ADC saturation due to transmitter-receiver cross-coupling interference
Solution Approach 1:
The transimpedance amplifier's transconductance is made dynamically adjustable through a controller that modifies the bias current based on the chirp transmission state. During chirp transmission, the transconductance is increased to raise the 1 dB compression point and prevent ADC saturation. Between chirps, the transconductance returns to normal levels, maintaining measurement precision while avoiding interference-related saturation
Solution Approach 2:
The system changes the operating parameters of the transimpedance amplifier by adjusting its transconductance value. The controller increases the transconductance parameter during chirp transmission to elevate the 1 dB compression point, thereby increasing the amplifier's tolerance to interference signals and preventing ADC saturation when using short pulse repetition times
2Reliability
If the transconductance of the transimpedance amplifier is increased to mitigate jamming effects, then the 1 dB compression point is improved, but the power consumption increases
Solution Approach 1:
The transconductance of the transimpedance amplifier is adjusted periodically in sync with the chirp transmission cycle. The controller increases transconductance only during the brief chirp transmission intervals when interference is present, then reduces it during the longer intervals between chirps. This periodic adjustment provides jamming resistance when needed while minimizing power consumption during non-transmission periods
Solution Approach 2:
The controller proactively increases the transconductance before or at the start of each chirp transmission, anticipating the interference that will occur. This preliminary adjustment ensures the amplifier is ready to handle the incoming interference signals, preventing ADC saturation before it occurs, while limiting the duration of high power consumption to only when necessary
3Productivity
If the resistance of the feedback amplifier circuitry is decreased to increase bandwidth, then the operating bandwidth is improved, but the stability of the amplifier may be compromised
Solution Approach 1:
The feedback amplifier circuitry's resistance is made dynamically controllable, allowing the system to adjust the resistance value based on operational requirements. During chirp transmission, the resistance is decreased to expand the operating bandwidth and capture wider frequency ranges. Between chirps, the resistance returns to higher values to maintain amplifier stability and prevent oscillations, thus achieving both wide bandwidth and stability at different times
Data Source
AI summary
An example radar system includes a controller coupled to a transimpedance amplifier in a forward path of receiver circuitry and to variable resistance circuitry in a feedback path of the receiver circuitry. The variable resistance circuitry is coupled to an input of a high-pass filter in the feedback path. The controller is operable to increase transconductance of the transimpedance amplifier and decrease resistance provided by the variable resistance circuitry to the high-pass filter for a programmable duration for each chirp transmitted by the radar system. The programmable duration begins before the start of transmission of the corresponding chirp and ends during transmission of the corresponding chirp.