Flash ADC Crossbar Calibration for Monotonic Digital Output
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Solution Overview
Problem
Non-idealities in the fabrication of electronic circuits lead to non-monotonicity in analog-to-digital converters (ADCs), causing random fluctuations in comparator reference voltages, which result in less linear and less monotonic digital output in flash ADCs.
Innovation Solution
Reordering the comparator array in flash ADCs such that reference voltages increase monotonically, utilizing a crossbar switch to effectively reorder the bits in the digital output and correct the non-idealities, ensuring a unique voltage range is converted to a unique digital code.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a flash ADC uses a comparator array with reference voltages generated by fabrication processes, then the ADC can perform high-speed conversion, but random fluctuations in feature sizes cause non-monotonicity in the digital output
Solution Approach 1:
The patent applies preliminary action by measuring the actual reference voltages of all comparators before normal operation and storing these measurements in a lookup table. During conversion, the pre-measured monotonic reference voltages are used to correct the digital output, ensuring monotonicity is achieved in advance rather than requiring perfect fabrication precision
Solution Approach 2:
The patent changes the parameter mapping between comparators by using a lookup table that maps thermometer code outputs to corrected monotonic digital codes. This parameter transformation corrects non-monotonic behavior by replacing the actual non-ideal reference voltage sequence with an ideal monotonic sequence stored in memory
2Manufacturing precision
If the comparator array is reordered to improve monotonicity, then linearity of digital output improves, but device complexity increases due to additional calibration circuitry
Solution Approach 1:
The patent creates a digital copy of the reference voltage characteristics by measuring and storing the actual reference voltages in a lookup table. This digital copy is then used to correct output errors without requiring physical reordering of comparators or complex analog calibration circuits
Solution Approach 2:
The patent replaces potential physical reordering mechanisms with a digital lookup table approach. Instead of using switches or multiplexers to physically reorder comparator outputs based on measured voltages, the system uses memory storage and digital table lookup to achieve the same monotonicity correction with simpler circuitry
Data Source
AI summary
A system includes an array of comparators configured to convert an analog input to a digital output, a switch configured to adjust output bits of the digital output, and a control logic; the control logic is configured to initialize the switch and a direct-current source coupled to the analog input; the control logic is configured to increase the direct-current source in incremental steps of a minimal voltage value corresponding to the least significant bit of the digital output; and the control input is also configured to cause the switch to adjust one or more output bits of the digital output based at least in part on a value of the output bit corresponding to the current incremental step.