Switched-Capacitor Comparator Circuit for High-Temperature Offset Cancellation
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Solution Overview
Problem
Conventional comparison circuits face errors due to offset voltages and noise components, particularly exacerbated at high temperatures, leading to inaccurate voltage comparisons.
Innovation Solution
A comparison circuit design utilizing switches, capacitors, and a comparator to cancel offset components and suppress errors from leak currents and noise, ensuring high accuracy across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional comparator is used for voltage comparison, then the comparison function is achieved, but offset voltage and noise cause errors and degrade accuracy
Solution Approach 1:
The patent applies preliminary action by performing a sample phase before the comparison phase. During the sample phase, switches S2 and S4 are turned on to pre-charge capacitors C3 and C4 with reference voltages, and switch S1 is turned on to equalize the voltages at input terminals N3 and N4. This preliminary equalization eliminates offset voltages and reduces noise influence before the actual comparison occurs in the comparison phase.
Solution Approach 2:
The patent implements periodic action through alternating sample and comparison phases. The control signal periodically switches between these two phases, turning switches S1-S4 on and off in specific sequences. This periodic switching allows the circuit to repeatedly perform voltage equalization followed by comparison, maintaining high accuracy through continuous offset cancellation.
2Measurement precision
If switches are used to control capacitor charging, then offset cancellation is achieved, but off-leak current increases at high temperatures causing errors
Solution Approach 1:
The patent addresses temperature stability by introducing asymmetry in the switch configuration. Switch S3 is connected differently from switches S2 and S4 - specifically, S3 connects the output terminal to input terminal N3 while S2 and S4 connect reference voltage terminals to capacitors C3 and C4 respectively. This asymmetric connection ensures that off-leak currents from all switches flow in consistent directions, preventing differential errors that would otherwise increase with temperature.
Solution Approach 2:
The patent compensates for temperature-induced leak current changes by ensuring symmetric charge storage conditions. Capacitors C3 and C4 are designed with equal capacitance values, and the switching时序 is optimized so that both capacitors experience identical voltage conditions during the sample phase. This parameter matching ensures that temperature-dependent leak currents affect both sides equally, canceling out in the differential comparison.
3Measurement precision
If multiple switches and capacitors are added to cancel offset, then accuracy is improved, but circuit complexity increases
Solution Approach 1:
The patent achieves high accuracy with moderate complexity by making the capacitors serve multiple functions. Capacitors C3 and C4 both store voltage differences from the sample phase and provide feedback during the comparison phase. The switches S1-S4 collectively perform voltage equalization, charge transfer, and feedback control. This multi-functionality reduces the need for additional dedicated components.
Solution Approach 2:
The patent combines multiple functions into integrated circuit blocks. The sample phase and comparison phase operations are merged into a single operational cycle controlled by timing signals. The offset cancellation and voltage comparison functions are merged through the feedback connection of capacitors C3 and C4 to the comparator input terminals, eliminating the need for separate cancellation circuitry.
Data Source
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AI summary
A comparison circuit is provided which is capable of removing the influence of an offset voltage of a comparator in the comparison circuit and obtaining a highly accurate comparison/determination result even at a high temperature. The comparison circuit includes a comparator having a first input terminal inputted with a first input voltage through a first capacitor, a second input terminal inputted with a second input voltage through a second capacitor, and an output terminal; a first switch which has one end connected to the first input terminal and is turned on in a sample phase to set a voltage of the first input terminal as a voltage of the output terminal; a second switch which has one end connected to the second input terminal and is turned on in the sample phase to set a voltage of the second input terminal as a reference voltage; and a third switch which is turned on in a comparison phase to equalize voltages of the other end of the first switch and the other end of the second switch.