Op-Amp Output Stage Biasing Without Extra Compensation Components
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Solution Overview
Problem
Existing output stage circuits for operational amplifiers require significant layout area due to the use of multiple resistors and capacitors, and are limited by the need for a folded-cascode configuration when operating at higher supply voltages, making them unsuitable for simple two-stage amplifiers.
Innovation Solution
The proposed output stage circuit includes a first and second transistor, a level shifter, a frequency compensating circuit, and a voltage generator, which eliminates the need for extra frequency compensating circuits and reduces the requirement for resistors and capacitors, allowing for a more compact design and operation without the folded-cascode configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two sets of resistors and capacitors (R10, C10) and (R11, C11) are used in the class AB output stage circuit, then the bias voltages of nodes X and Y can be controlled, but the layout area occupied in integrated circuit increases and resistance and capacitance values become inaccurate
Solution Approach 1:
The patent extracts and removes the resistors and capacitors from the output stage circuit, replacing them with a current mirror circuit that uses only transistors. This eliminates the need for external passive components while maintaining the bias control function through transistor-based current mirroring, thereby reducing layout area and improving integration accuracy.
Solution Approach 2:
The current mirror circuit serves multiple functions: it provides bias current control, performs level shifting, and enables frequency compensation all through transistor configurations. This multi-functional approach replaces what previously required separate resistors and capacitors, reducing the overall component count and layout area while maintaining circuit performance.
2Adaptability or versatility
If a folded-cascode configuration is used in the bias circuit to support higher supply voltage (5V), then the circuit can operate at higher voltages, but it cannot be applied to simple two-stage amplifier and requires complex configuration
Solution Approach 1:
The patent changes the operating parameters of the transistors, specifically utilizing the third transistor in a diode-connected configuration to generate a voltage drop that enables the output stage to handle higher supply voltages (up to 5V). This parameter change allows the simple two-stage amplifier architecture to support higher voltages without requiring the complex folded-cascode configuration.
3Power
If folded-cascode configuration is used in bias circuit for higher supply voltage, then voltage handling capability is improved, but the circuit cannot be applied to simple two-stage amplifier
Solution Approach 1:
The patent extracts the voltage handling capability from the complex folded-cascode configuration and implements it through a simpler diode-connected transistor arrangement. This extracted approach maintains the ability to handle higher supply voltages while preserving the simplicity of the two-stage amplifier structure, eliminating the need for folded-cascode complexity.
Data Source
AI summary
The present invention relates to an output stage circuit and an operational amplifier thereof. In the output stage circuit, one of a gate of a transistor is coupled to a gate of a bias transistor and a level shifter in response to a small signal outputted from an amplifying circuit in the operational amplifier. In addition, a gate voltage of the bias transistor is controlled by a voltage generating circuit to control a DC bias of the transistor of the output stage circuit. Therefore, there is no need extra frequency compensating component for compensating the transistor of the output stage circuit, and to save circuit layout area and cost can be achieved by the present invention.