Push-Pull Amplifier Quiescent Bias Tuning via Even-Order Distortion
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Solution Overview
Problem
Signal processing arrangements with complementary transistors in CMOS technology face challenges in achieving low even-order distortion while maintaining stability and performance aspects like sensitivity and signal-to-noise ratio, especially in radiofrequency applications.
Innovation Solution
A controllable biasing circuit adjusts the quiescent operating point of the amplifier stages based on even-order distortion measurements, using a test signal with a frequency lower than typical signals to compensate for nominal differences in transistor characteristics, thereby reducing distortion without affecting stability or other performance metrics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If complementary transistors are used in CMOS technology for amplifier stages, then power consumption is reduced and structural simplicity is improved, but even-order distortion increases due to nominal differences in transistor characteristics
Solution Approach 1:
The patent implements a feedback mechanism where the output signal is fed back to the input through a feedback network. This feedback loop detects even-order distortion components and automatically adjusts the operating point of the amplifier stages to minimize distortion. The feedback continuously monitors performance and makes real-time corrections, resolving the contradiction between using simple CMOS complementary transistors and maintaining low distortion.
Solution Approach 2:
The patent changes operating parameters (bias voltages and currents) of the amplifier stages to optimize performance. By adjusting these parameters, the amplifier can operate at an optimal quiescent point that minimizes even-order distortion while maintaining the benefits of CMOS complementary transistor operation. This parameter optimization allows the system to achieve low distortion without changing the fundamental CMOS complementary transistor architecture.
2Object-generated harmful factors
If the quiescent operating point is adjusted to reduce even-order distortion, then distortion levels decrease, but stability and other performance aspects may be compromised
Solution Approach 1:
The feedback mechanism monitors not only distortion levels but also stability metrics. When distortion is high, the feedback system adjusts operating parameters to reduce distortion while simultaneously verifying that stability margins are maintained. This closed-loop control ensures that distortion reduction does not come at the expense of stability, as the system continuously balances these competing requirements.
Solution Approach 2:
The patent implements dynamic adjustment of operating parameters rather than fixed static settings. The amplifier can adapt its quiescent operating point in real-time based on signal conditions, allowing it to optimize distortion performance while maintaining stability margins. This dynamic capability enables the system to respond to changing conditions and maintain both low distortion and stability across different operating scenarios.
3Measurement precision
If a test signal with low frequency is used for measuring even-order distortion, then measurement accuracy is improved, but the measurement process takes more time
Solution Approach 1:
The patent uses a test signal with frequency specifically chosen to be lower than typical operating signals, which provides excessive measurement sensitivity for distortion detection. This lower frequency ensures that even small distortion components are clearly visible and measurable, achieving high measurement precision. The measurement time increase is acceptable because calibration is performed periodically rather than continuously, and the high precision gained justifies the occasional longer measurement cycle.
Data Source
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AI summary
A signal processing arrangement comprises an amplifier (AMP V1 ) that includes a stage with complementary transistors (MP3, MN3) of opposite conductivity type arranged in series between two supply lines (+, -). A controllable biasing circuit (CCS) is provided for changing a quiescent operating point of the stage as a function of a control signal (CS). A control arrangement measures an even order 5 distortion of the amplifier (AMP V1 ) and adjusts the control signal (CS) so that the even order distortion is below a critical level.