Chopper Op-Amp Driver Circuit for Fast Offset Cancellation
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Solution Overview
Problem
Existing operational amplifier drivers for TFT-LCD source drivers face challenges in canceling offset voltage, requiring high input signal levels and affecting response speed, especially when the input signal level is not sufficient.
Innovation Solution
An operational amplifier driver with a chopper and three switches, where the capacitor is charged or discharged through the output terminal of the operational amplifier, allowing for offset voltage cancellation without directly charging the capacitor with the input signal, enabling switching between input voltage storing and voltage outputting stages to neutralize the offset voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the input signal directly charges the capacitor to cancel offset voltage, then the offset voltage cancellation is achieved, but the input signal level must be high enough which affects response speed when input signal level is insufficient
Solution Approach 1:
The patent introduces an intermediary charging path through the operational amplifier's output terminal to charge the capacitor. Instead of directly connecting the input signal to the capacitor, the output terminal serves as an intermediary that can provide the necessary charging current regardless of input signal level, thus maintaining both offset cancellation accuracy and fast response speed
Solution Approach 2:
The patent segments the charging function from the input signal path. The offset cancellation function is separated into a distinct stage where the capacitor is charged through the output terminal independently of the input signal level, allowing the input signal processing and offset cancellation to occur in separate, optimized stages
Data Source
AI summary
An operational amplifier driver capable of canceling an offset voltage of an operational amplifier includes the operational amplifier, first to third switches and a capacitor. The operational amplifier has a chopper, first and second input terminals and an output terminal. The first switch receives an input voltage and is connected to the first input terminal. The second switch is connected to the first input terminal and the output terminal. The third switch is connected the second input terminal and the output terminal. The capacitor is connected to the second input terminal. Because the operational amplifier driver directly charges/discharges the capacitor through the output terminal, and the polarities of the first input terminal and the second input terminal may be changed, the operational amplifier driver can shorten a charge/discharge time of the capacitor and cancel the offset voltage without increasing a level of an input signal.