Pipeline ADC Test Signal Sharing for Capacitor Error Correction
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Solution Overview
Problem
Pipeline A/D converters face challenges in achieving high accuracy due to capacitance value errors between sampling and feedback loop capacitors, which degrade analog input-output characteristics, especially in high-resolution conversions, and existing error correction methods require external test signals and additional circuitry, leading to accuracy issues and increased circuit size.
Innovation Solution
A pipeline A/D converter configuration that allows for internal generation and supply of test signals by sharing the voltage supply portion between normal and test modes, eliminating the need for a separate test signal line and external DA converter, using a control portion to manage input signal and reference voltage selection, and incorporating an auxiliary capacitor to simulate test conditions without altering the normal operation circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external test signal lines and external DA converter are used for error correction testing, then testing capability is improved, but circuit complexity and device area increase
Solution Approach 1:
The patent merges the test signal generation function into the existing voltage supply portion of the pipeline A/D converter. The voltage supply portion that normally provides reference voltages (+Vref, 0V, -Vref) to the DA conversion portion is repurposed to also generate test signals. This eliminates the need for external test signal lines and external DA converters, reducing circuit complexity while maintaining testing capability.
Solution Approach 2:
The voltage supply portion is designed to serve multiple functions: it provides reference voltages for normal DA conversion operation and generates test signals for error correction testing. By making the voltage supply portion universal, the patent eliminates dedicated test signal generation circuitry, thereby reducing device area and circuit complexity while preserving full testing capability.
2Measurement precision
If separate test signal input line is provided, then testing accuracy is improved, but device area and circuit complexity increase
Solution Approach 1:
The patent combines the test signal path with the existing reference voltage paths within the voltage supply portion. Instead of providing a separate test signal input line that would require additional routing and components, the test signals are generated internally using the same voltage supply circuitry that provides reference voltages. This approach maintains signal integrity for accurate testing while avoiding the area penalty of separate external connections.
3Device complexity
If capacitance value errors are not corrected, then circuit simplicity is maintained, but conversion accuracy deteriorates
Solution Approach 1:
The pipeline A/D converter performs self-testing and self-correction of capacitance value errors. The voltage supply portion generates test signals that are processed through the converter stages, and the digital operation portion calculates correction values based on the test results. This self-service capability allows the converter to maintain high conversion accuracy without requiring external testing equipment or complex additional correction circuitry.
Solution Approach 2:
The patent implements a feedback mechanism where the output of the converter is fed back to the digital operation portion, which calculates correction values based on the relationship between input and output signals. These correction values are then applied to compensate for capacitance value errors in subsequent conversions. This feedback-based correction maintains conversion accuracy while keeping the overall circuit relatively simple.
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
This configuration enables accurate testing and correction of capacitance value errors within the A/D converter, improving conversion accuracy and reducing circuit complexity by eliminating the need for external test signal generation and separate test lines, thus enhancing the overall performance and reliability of the pipeline A/D converter.
Implementation Method 1
an output signal Vout amplified by the operational amplifier 9 will be as follows: Vout={(Cs+Cf)/Cf}·Vin−(Cs/Cf)·Vdac
Implementation Method 2
the switches 10 and 11 are on and the switch 12 is off, resulting in the input analog signal Vin being sampled in the sampling capacitor Cs
Implementation Method 3
the switches 10 and 11 will be off and the switch 12 will be on, resulting in the charge sampled in the sampling capacitor Cs being redistributed to the sampling capacitor Cs and the feedback loop capacitor Cf
Data Source
AI summary
In each stage, a digital signal corresponding to a portion of bits is generated from an input analog signal, an analog reference signal is generated by a DA conversion portion (7, 8) based on the digital signal, and a remainder operation on the input analog signal is performed by a remainder operation portion (9). A test can be performed by supplying a test signal in place of the input analog signal. A control portion (14a) performs control, in a test mode, to stop supply of the input analog signal to the remainder operation portion and stop the reference voltage selection of the DA conversion portion based on the digital signal, while performing reference voltage selection based on a DA conversion control signal for use in testing, thereby supplying the remainder operation portion with the test signal composed of predetermined one of the reference voltages, in place of the input analog signal, and the analog reference signal. A test signal can be input with a small-scale configuration, without providing a test signal line separately from a line used for normal operation.