Encoder Front-End Circuit With Double Correlation Offset Cancellation
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Solution Overview
Problem
Front-end circuits in encoders amplify input offset voltages, leading to decreased position detection accuracy and a narrowed dynamic range, as these offset voltages are included in the output signal.
Innovation Solution
A front-end circuit design incorporating a preamplifier, switched capacitor circuit, and integration circuit with switching mechanisms that perform double correlation sampling, alternating the output destinations of input signals and integration capacitors between cycles to cancel out the influence of input offset voltages from the preamplifier and fully differential operational amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the front-end circuit amplifies the input signal using preamplifier and differential amplifier, then the signal amplitude is increased, but the input offset voltages are also amplified and included in the output signal, causing position detection accuracy to decrease
Solution Approach 1:
The patent implements double correlation sampling by performing sampling operations twice with different switching states. The first sampling captures the input signal plus offset, and the second sampling captures a different combination. By periodically alternating the switching states and subtracting the two samples, the offset component is eliminated while the signal is preserved and amplified.
Solution Approach 2:
The patent uses the output of the first sampling as a reference for the second sampling. The difference between the two sampling results is calculated, and this feedback mechanism allows the circuit to cancel out the offset voltage that was amplified along with the signal, thereby maintaining measurement precision despite signal amplification.
2Measurement precision
If the gains of amplifiers and amplitude of input signal are limited to reduce output offset voltages, then position detection accuracy is improved, but the dynamic range of the system is narrowed
Solution Approach 1:
By performing two sampling operations with different switching configurations and subtracting the results, the circuit can use higher amplifier gains without being constrained by offset voltage limitations. The periodic switching allows the system to maintain both high gain (for sensitivity) and large dynamic range (for adaptability) simultaneously.
Solution Approach 2:
The patent extracts and removes the offset voltage component from the amplified signal through the double correlation sampling process. By separating the offset component from the signal component and eliminating it, the system can operate with higher gains and larger input signal amplitudes without the offset limiting the dynamic range.
3Stability of the object's composition
If continuous signals are used in the encoder, then smooth position detection is achieved, but the front-end circuit requires complex switching and sampling mechanisms to handle offset cancellation
Solution Approach 1:
The patent uses periodic switching at controlled timing intervals to sample the continuous input signal. The switching occurs at specific phases of the continuous signal, and by performing the sampling twice with different switching states and subtracting the results, the circuit maintains signal continuity while systematically eliminating offset through the periodic sampling mechanism.
Solution Approach 2:
The double correlation sampling is implemented in a continuous manner where the first and second sampling operations are performed in sequence without interruption to the overall signal processing flow. The switching circuits rapidly alternate between states, maintaining continuous operation while achieving offset cancellation through the correlated sampling process.
Data Source
AI summary
A preamplifier amplifies signals input to first and second input terminals. A first switching circuit receives first and second input signals and respectively outputs those signals to the first and second input terminals. A switched capacitor circuit samples two signals amplified by the preamplifier. An integration circuit includes a fully differential operational amplifier outputting amplifying differential signals input between third and fourth input terminals between second and first output terminals, and first and second integration capacitors. A second switching circuit switches a connection relationship between the switched capacitor circuit, and the first and second integration capacitors. A third switching circuit switches a connection relationship between the first and second integration capacitors, and third and fourth output terminals. A cycle including sampling and signal integration is performed twice, and the first to third switching circuits switch the connection relationships each time the cycle changes.