Automotive Radar Gain Amplifier With DC Offset Cancellation
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Solution Overview
Problem
Existing automotive radar systems face challenges in achieving improved linearity, reduced noise, and effective DC offset cancellation while maintaining full output swing matching the ADC scale, particularly in high gain operations.
Innovation Solution
A circuit design incorporating a differential amplifier with adjustable current sources and feedback circuitry to maintain constant voltage across input transistors, coupled with calibration circuitry for equalizing output voltages and adjusting current sources to enhance transconductance and cancel DC offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the current sourced by current sources is increased to increase transconductance of the differential input pair, then the linearity and operating margin are improved, but the common mode voltage at the output nodes increases which reduces the output swing range
Solution Approach 1:
The patent changes the voltage level parameter by coupling the differential amplifier output to the ADC through a voltage divider network. This transforms the output voltage levels to match the ADC's input range, resolving the contradiction between achieving high linearity through increased current and maintaining appropriate output swing for ADC conversion.
2Power
If the transconductance of the differential input pair is increased for high gain operation, then the amplification capability is improved, but the power consumption increases
Solution Approach 1:
The patent implements dynamic control of the current sources through feedback circuitry that adjusts the bias current based on the common mode voltage level. This allows the transconductance to be optimized for high gain operation when needed, while reducing power consumption when maximum amplification capability is not required, resolving the contradiction between amplification capability and power consumption.
3Reliability
If the current sources are made adjustable to maintain constant voltage across input transistors, then the operating margin is improved, but the circuit complexity increases
Solution Approach 1:
The patent employs feedback circuitry that monitors the common mode voltage at the output nodes and dynamically adjusts the current source outputs to maintain constant voltage across the input transistors. This feedback mechanism improves the operating margin and reliability while keeping the circuit design practical through the use of standard feedback techniques.
Data Source
Figure 1
Figure 2
AI summary
A differential amplifier (15) comprises a pair of input transistors (T1, T2) coupled in a differential arrangement between adjustable current sources (I1-2a, I2-2a, I2-3a, I1-2b, I2-2b, I2-3b) and receives input differential signals (Vicm+Vinp, Vicm+Vinm) from a pair of input voltage regulators (20, 21). The adjustable current sources (I1-2a, I2-2a, I2-3a, I1-2b, I2-2b, I2-3b) are configured to source more current (I2) to the pair of input transistors (T1, T2) than current (I1) that is sunk from the pair of input transistors. A first amplifier (23) has inputs coupled to receive differential output voltages from the differential amplifier (15). A second amplifier (24) has inputs coupled to receive amplified differential output voltages (Voutp, Voutm) from the first amplifier (23). A low pass filter (16) has inputs coupled to receive further amplified differential output voltages from the second amplifier (24) and produce final differential output voltages (Vipfp, Vipfm).