Output Stage Bias Control at Zero Crossing in Class-AB Amplifiers
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Solution Overview
Problem
In Class-AB output stages, there is a trade-off between crossover distortion and quiescent current, where reducing crossover distortion requires a larger quiescent current, leading to increased power consumption, and existing solutions like dual output stages can cause signal glitches.
Innovation Solution
An amplifier circuit that adjusts the quiescent current at the zero-crossing point of the output signal based on the input signal strength using a digital-to-analog converter, delay circuit, and detector to generate control signals, allowing for precise management of quiescent current without glitches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the quiescent current is increased to reduce crossover distortion, then the crossover distortion is reduced, but the power consumption increases
Solution Approach 1:
The patent applies dynamics by making the quiescent current adjustable rather than fixed. The output stage transitions from a static bias configuration to a dynamic one where the quiescent current can be modified in real-time based on signal conditions, allowing the system to adapt between low-power and low-distortion modes
Solution Approach 2:
The patent changes the parameter of quiescent current from a constant value to a variable parameter. By controlling the quiescent current based on the absolute value of the output signal, the system can adjust this critical parameter to achieve optimal performance across different operating conditions, resolving the trade-off between distortion and power consumption
2Reliability
If two different output stages are used to handle different signal strengths, then the performance is improved across different signal levels, but the chip area increases and switching operations cause output signal glitches
Solution Approach 1:
The patent segments the operation of the output stage into different modes based on signal strength. Instead of using two complete output stages, it divides the operational range and applies different quiescent current levels to the same output stage, achieving the benefits of multiple stages without the area penalty
Solution Approach 2:
The patent makes the single output stage universal by enabling it to handle both low-signal and high-signal conditions through dynamic quiescent current adjustment. The same output stage circuit performs multiple functions by changing its bias conditions, eliminating the need for separate dedicated circuits for different signal ranges
3Use of energy by moving object
If the quiescent current is adjusted based on input signal strength, then the power consumption is optimized, but the adjustment may cause signal glitches if not timed properly
Solution Approach 1:
The patent takes preliminary action by detecting the zero-crossing point of the output signal before adjusting the quiescent current. This timing ensures that the current adjustment occurs at the most favorable moment (when the signal is crossing zero), minimizing the risk of introducing glitches while still achieving power optimization
Data Source
AI summary
The present invention provides an amplifier circuit, wherein the amplifier circuit includes a DAC, an output stage and a detector. In the operations of the amplifier circuit, the DAC is arranged for performing a digital-to-analog converting operation upon a digital input signal to generate an analog signal, the output stage is arranged for receiving the analog signal to generate an output signal, and the detector is arranged for detecting a characteristic of the input signal, and referring to the characteristic of the input signal to generate at least one control signal to adjust the output stage at a zero-crossing point of the output signal.