Successive Approximation ADC Calibration for Capacitance Variations
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Solution Overview
Problem
In analog-to-digital converters using a successive approximation system, manufacturing errors in capacitance values can lead to inaccurate digital data due to variations in bias voltage, especially when multiple operation systems are combined.
Innovation Solution
An analog-to-digital converter design that incorporates a counter, ramp waveform signal generation, and signal conversion units with sample-and-hold circuits, successive approximation capacitance groups, and a control unit to generate and compare bias voltages, allowing for accurate digital conversion by compensating for capacitance variations through calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a successive approximation system is used to increase conversion speed, then productivity is improved, but manufacturing precision deteriorates due to capacitance value variations
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements before the actual analog-to-digital conversion. The calibration process measures the actual capacitance values of the capacitor array in advance, and these measured values are stored for use during conversion. This preliminary measurement allows the system to compensate for manufacturing variations in capacitance values during the high-speed successive approximation conversion process, thereby maintaining both high conversion speed and accurate digital output despite capacitance variations.
2Productivity
If multiple operation systems are combined to improve conversion performance, then productivity is improved, but device complexity increases
Solution Approach 1:
The patent merges the calibration function and the analog-to-digital conversion function into a single integrated device. The same capacitor array, comparator, and control logic are used for both calibration measurements and subsequent conversion operations. By combining these functions rather than implementing them as separate systems, the patent achieves high conversion speed through the successive approximation system while avoiding the complexity that would arise from having completely separate calibration and conversion hardware.
Data Source
AI summary
To obtain accurate digital data while using a successive approximation system when performing analog-to-digital conversion processing in a plurality of steps, an AD converter includes: a signal generation unit that generates a ramp voltage based on a count signal; a signal conversion unit including a circuit that holds an input signal voltage, a successive approximation capacitance group that outputs bias voltages according to a connection combination of capacitances having different capacitance values, and a unit that compares one of the ramp voltage and the bias voltage with the signal voltage; and a control unit generating a digital signal of the signal voltage based on a comparison result of the bias voltage and the comparison result of the ramp voltage while acquiring data for calibration of the capacitance group based on the connection combination and the ramp voltage.