Switched-Capacitor DAC Offset Cancellation for Failure Bit Detection
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Solution Overview
Problem
In digital to analog converters using switched-capacitor circuits, the offset voltage can cause bit errors as the least significant bit voltage approaches or becomes less than the offset voltage, leading to inaccuracies in non-volatile semiconductor storage devices like flash memory, which require a method to detect and correct failure bits.
Innovation Solution
A parallel integrated digital to analog converter with an offset cancel circuit, comprising a second differential amplifier and feedback circuit, compensates for offset voltages by feeding back a reference voltage during the sampling period and inputting a differential voltage during the holding period, ensuring accurate conversion regardless of offset voltages in both amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the input digital voltage increases to reduce the least significant bit voltage, then the conversion precision improves, but the offset voltage causes bit errors when VLSB approaches or becomes less than VOFST
Solution Approach 1:
The patent applies preliminary action by performing offset voltage compensation before the main conversion operation. The first differential amplifier compensates for the offset voltage of the second differential amplifier in advance, ensuring that the offset does not cause bit errors during subsequent conversions. This preliminary compensation maintains both high conversion precision and reliability.
Solution Approach 2:
The patent implements feedback by having the first differential amplifier continuously monitor and compensate for the offset voltage of the second differential amplifier. This feedback mechanism ensures that any offset voltage is corrected in real-time, preventing bit errors while maintaining high conversion precision across varying input conditions.
2Reliability
If a dual differential amplifier structure with offset compensation is added, then the offset voltage compensation improves reliability, but the device complexity increases
Solution Approach 1:
The patent merges the offset compensation function with the main conversion function by integrating the first differential amplifier (for offset compensation) and the second differential amplifier (for conversion) into a unified circuit structure. This merging approach improves reliability through offset compensation while minimizing the increase in device complexity by combining functions efficiently.
Solution Approach 2:
The first differential amplifier serves multiple functions: it compensates for offset voltage and also contributes to the overall conversion process. This multi-functionality reduces the need for separate dedicated compensation circuits, thereby improving reliability without proportionally increasing device complexity.
Data Source
AI summary
An offset voltage VOFST is compensated in a digital to analog (DA) convertor using a switched-capacitor circuit, including an input circuit, a first differential amplifier, and an offset cancel circuit comprising a second differential amplifier, in a sampling period, when the second feedback circuit is short, an output voltage of the first differential amplifier is input to a first end of a first capacitor, the offset cancel circuit feeds back a reference voltage to an inverting input terminal of the second differential amplifier and a second end of the first capacitor from an output of the second differential amplifier, in a holding period, when the second feedback circuit is not short, the offset cancel circuit inputs a differential voltage between the reference voltage and the output voltage of the first differential amplifier into an inverting input terminal of the first differential amplifier via a second capacitor.