Variable Bias Control Differential Pair for Linear Range Extension
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Solution Overview
Problem
Operational amplifier circuits with differential pairs face limitations in linear range, leading to degraded image quality in LCD panels due to nonlinear output when input voltage differences exceed a certain threshold, resulting in increased power consumption to extend this range.
Innovation Solution
The implementation of a variable bias control differential pair using four transistors (4T) architecture, where the third and fourth transistors operate as degeneration devices in the triode region, creating a feedback loop that extends the linear range by controlling resistance values based on input signals, thereby maintaining a stable transconductance over a wider input voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If larger bias current is provided for the differential pair to increase the linear range, then the linear range is improved, but power consumption increases
Solution Approach 1:
The patent applies dynamics by making the bias current variable rather than fixed. A control circuit dynamically adjusts the bias current based on the input voltage difference magnitude. When the input voltage difference is large, the bias current is increased to maintain linearity; when the input voltage difference is small, the bias current is reduced to save power. This dynamic adaptation resolves the contradiction between maintaining linear range and reducing power consumption.
Solution Approach 2:
The patent changes the parameter of bias current from a constant value to a variable value that adapts to operating conditions. By controlling the bias current according to the input signal characteristics, the system achieves both extended linear range and reduced power consumption. The control circuit monitors the input voltage difference and adjusts the bias current parameter accordingly, eliminating the need for consistently high bias current.
2Manufacturing precision
If the input voltage difference exceeds the linear range, then the output voltage deviates from the desired value, but increasing bias current to extend the linear range results in larger power consumption
Solution Approach 1:
The patent implements feedback by having the control circuit monitor the input voltage difference and adjust the bias current accordingly. When the input voltage difference approaches or exceeds the linear range, the feedback mechanism increases the bias current to pull the operation back into the linear region, ensuring accurate output voltage. This feedback-controlled approach maintains output voltage accuracy without requiring continuously high power consumption.
Data Source
AI summary
An operational amplifier circuit is provided. The operational amplifier circuit includes a differential input stage circuit and a loading stage circuit. The differential input stage circuit includes a first current source, a first transistor, a second transistor, a third transistor, and a fourth transistor. The control terminal of the first transistor receives a first input signal. The control terminal of the second transistor receives a second input signal. The third transistor has a first terminal coupled to the second terminal of the first transistor, a second terminal coupled to the first current source, and a control terminal coupled to the control terminal of the second transistor. The fourth transistor has a first terminal coupled to the second terminal of the second transistor, a second terminal coupled to the first current source, and a control terminal coupled to the control terminal of the first transistor.