Op-Amp Offset Compensation Using Switched Load Resistance
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Solution Overview
Problem
Conventional methods for compensating offset in operational amplifiers, such as those used in liquid crystal display panels, often result in increased circuit complexity and size due to the need for multiple capacitors and comparators, and are not highly accurate.
Innovation Solution
A voltage output device with an operational amplifier that includes connection switching means between input terminals, load resistance changing means, and load resistance setting means to adjust resistance values, allowing for offset compensation without the need for alternate transistor switching or multiple capacitors, thereby maintaining a simpler circuit structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple capacitors and comparators are used for offset compensation, then offset compensation accuracy is improved, but circuit scale increases
Solution Approach 1:
The patent extracts and eliminates the comparator component from the offset compensation circuit. Instead of using a comparator to detect offset voltage, the invention uses a switching mechanism that directly connects the inverting and non-inverting input terminals, allowing offset compensation through resistance adjustment alone, thereby reducing circuit scale while maintaining compensation functionality
Solution Approach 2:
The switching means serves multiple functions: it not only switches between different resistance values but also directly connects the input terminals to enable offset detection and compensation. This multi-functionality eliminates the need for separate comparator circuits and multiple capacitors, achieving accurate offset compensation with a more compact circuit design
2Measurement precision
If alternate switching between input transistors is used, then offset compensation is achieved, but display image flicker occurs
Solution Approach 1:
The patent performs offset compensation in advance by connecting the inverting and non-inverting input terminals through the switching means before normal operation. This preliminary offset elimination allows the operational amplifier to operate without alternate transistor switching during display operation, thereby preventing display image flicker while maintaining offset compensation
Solution Approach 2:
Instead of using alternate transistor switching to compensate for offset during operation, the invention inverts the approach by directly connecting the input terminals through switching means to equalize their potentials, thereby eliminating offset without causing the harmful flicker effect in display images
3Measurement precision
If sequentially varying capacitance value is used for offset compensation, then offset compensation is achieved, but chip size increases
Solution Approach 1:
The patent changes the compensation parameter from capacitance value to resistance value. By using a variable resistor with switching means to adjust resistance values rather than sequentially varying capacitance values, the invention achieves offset compensation while reducing the number of discrete capacitor components needed, thereby minimizing chip size
Data Source
AI summary
A voltage output device capable of preventing an increase in circuit scale includes an offset compensation function and is suitably applicable to a drive circuit for display devices. The voltage output device includes an operational amplifier having an inverting input terminal and a non-inverting input terminal. Resistance values of a load resistor on the inverting input side and a load resistor on the non-inverting input side are maintained when the output voltage of the amplifier has changed while sequentially varying either one or both of the resistance values of the load resistor on the inverting input side and the load resistor on the non-inverting input side in a state that the inverting input terminal and the non-inverting input terminal are connected. The voltage output device is configured to output the output voltage of the amplifier with the inverting input terminal not connected to the non-inverting input terminal.