Sample-and-Hold Circuit Error Compensation via Feedback
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Solution Overview
Problem
Sample-and-hold circuits suffer from inaccuracies due to charge injection and noise, leading to deviations in output voltage, which affects the accuracy of signal sampling, particularly in image sensors where pattern noise can occur.
Innovation Solution
Incorporating an error correction circuit with an error-current-accumulating capacitor and feedback loop to cancel out error voltages, ensuring the output voltage accurately represents the sampled input signal by adjusting the voltage boost based on the error-current-accumulating capacitor's voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional sample-and-hold circuit is used to sample signals, then the circuit structure is simple and operation is straightforward, but charge injection and noise cause deviations in output voltage reducing sampling accuracy
Solution Approach 1:
The patent implements a feedback mechanism where the output of the differential amplifier is fed back to its inverting input through a feedback capacitor. This feedback loop continuously compensates for charge injection errors by adjusting the inverting input voltage to counteract the charge injected by the switch, thereby improving sampling accuracy without requiring complex external correction circuits
Solution Approach 2:
The patent introduces a non-inverting input as an intermediary element that receives a compensation signal. This non-inverting input acts as a mediator that balances the charge injection effect by providing an equal and opposite voltage adjustment at the differential amplifier input, thereby canceling out the error without complicating the overall circuit topology
2Measurement precision
If the sampling window is extended to improve signal measurement accuracy, then more complete signal capture is achieved, but the input signal may change during the sampling period introducing additional errors
Solution Approach 1:
The patent employs periodic switching actions with precisely controlled timing to charge and discharge the sampling capacitor at specific moments. By using periodic clock signals to control the switching of charge injection compensation, the circuit achieves accurate signal capture during the sampling window while maintaining timing precision through the regular, predictable nature of the periodic operation
3Measurement precision
If ideal component conditions are assumed (zero switch resistance, infinite amplifier gain), then theoretical accuracy is achieved, but actual circuits with non-ideal components exhibit deviations and noise
Solution Approach 1:
The patent converts the harmful charge injection effect into a beneficial compensation mechanism. By deliberately injecting a controlled amount of charge through the feedback loop that is equal and opposite to the parasitic charge injection, the circuit transforms the harmful effect into a self-correcting feature, improving reliability under real operating conditions
Solution Approach 2:
The differential amplifier with feedback automatically compensates for its own non-ideal characteristics. The feedback mechanism uses the amplifier's own output to adjust its input, creating a self-correcting system that maintains accuracy despite non-ideal components, thereby improving reliability without requiring external calibration or adjustment
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively minimizes and eliminates errors caused by charge injection and noise, resulting in an output voltage that closely matches the input voltage, enhancing the accuracy of signal sampling and reducing pattern noise in image sensors.
Implementation Method 1
an error correction circuit with an error-current-accumulating capacitor and feedback loop
Implementation Method 2
applying, via the feedback circuit, a voltage boost to an input of the amplifier, where the magnitude of the voltage boost depends on a voltage of the error-current-accumulating capacitor
Data Source
AI summary
A sample-and-hold circuit having an error correction circuit portion that compensates for charge injection and noise. The error correction circuit portion includes an error-current-accumulating capacitor and a feedback circuit. The error-correction circuit performs error correction during a sampling operation by accumulating, at the error-current-accumulating capacitor, an error current output from an amplifier of the sample-and-hold circuit, and then applying, via the feedback circuit, a voltage boost to an input of the amplifier. The magnitude of the voltage boost depends on a voltage of the error-current-accumulating capacitor, and on various design parameters of the components of the circuit. By appropriately setting the design parameters, the magnitude of the fed-back voltage boost can be made to cancel out error due to charge injection and noise.