Class AB Operational Amplifier Startup Calibration for Pop Noise Suppression
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Solution Overview
Problem
Conventional methods for reducing voltage spikes in class AB amplifiers are ineffective due to high sensitivity to process, voltage, and temperature variations, resulting in pop noise when the amplifier is turned on, despite offset calibration techniques.
Innovation Solution
An operational amplifier design that establishes a stable voltage at each node during offset calibration, using a multi-stage configuration with feedback circuits and switches to maintain a stable output common-mode voltage, preventing voltage spikes by adjusting differences between output voltages and replicating the first output stage circuit to ensure smooth transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If offset calibration technique is applied to reduce offset voltage, then offset voltage is reduced, but voltage spikes are not effectively reduced due to high sensitivity to process, voltage and temperature variations
Solution Approach 1:
The patent applies preliminary action by establishing stable voltages at all internal nodes before the amplifier is turned on. The operational amplifier performs offset calibration and voltage stabilization in advance, setting each node to its expected steady-state voltage before normal operation begins. This preliminary preparation prevents voltage spikes when the amplifier starts, as all nodes are already at their correct voltage levels rather than experiencing sudden transitions.
2Device complexity
If conventional voltage spike reduction method is used, then implementation is simple, but voltage spikes of 10 mV to 100 mV are still generated
Solution Approach 1:
The patent implements feedback mechanisms where the operational amplifier continuously monitors and adjusts the voltages at its internal nodes during the calibration phase. By comparing actual node voltages with target voltages and making real-time adjustments, the system ensures that all nodes reach their correct voltage levels before normal operation. This feedback-controlled approach achieves superior voltage spike reduction (less than 1 mV) compared to conventional methods.
3Object-generated harmful factors
If multi-stage configuration with feedback circuits is implemented, then voltage spikes are reduced to less than 1 mV, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the operational amplifier into multiple functional stages, each responsible for specific voltage stabilization tasks. The multi-stage configuration allows different parts of the circuit to be optimized independently for their specific functions, enabling precise control of voltage transitions at each node. This segmented approach achieves low voltage spikes while maintaining manageable complexity through modular design.
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AI summary
An operational amplifier is characterized by: a first amplifier stage, configured to generate first output voltages according to first input voltages; a second amplifier stage, configured to generate second output voltages according to the first output voltages; a second output stage circuit, configured to replicate an equivalent or a scaled-down version of the first output stage circuit; a first common-mode feedback circuit, configured to keep an output common-mode voltage of the second output stage circuit at a predetermined value; a logic loop circuit configured to, when the operational amplifier operates in a direct current calibration phase, adjust a difference between the first output voltages; a bias circuit, configured to generate a voltage close to a common-mode voltage of the first output voltages produced after the operational amplifier is turned on, the voltage serving as a reference voltage of a second common-mode feedback circuit.