CDAC Calibration for ADC Linearity and Gain Matching
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Solution Overview
Problem
Successive-approximation ADC circuitry using capacitive DACs suffers from performance issues related to linearity and gain mismatch, particularly in sub-ADC units of overall ADC circuitry.
Innovation Solution
The ADC circuitry employs a set of sub-ADC units with individually-switchable capacitors, including variable capacitors, to configure different test configurations for optimizing linearity and gain, where control circuitry measures performance in test mode and adjusts capacitances or reference voltage levels to achieve improved linearity and gain matching in operational mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If successive-approximation ADC circuitry uses capacitive DACs with fixed capacitors, then the circuit structure is simple, but linearity and gain matching performance deteriorate
Solution Approach 1:
The patent applies the Dynamics principle by making capacitors switchable between different states (connected or disconnected) based on calibration requirements. The capacitive DAC includes switchable capacitors that can be dynamically reconfigured during calibration modes to adjust capacitance values, enabling the system to transition from a simple fixed-structure mode to a dynamically adjustable mode for optimizing linearity and gain matching performance.
Solution Approach 2:
The patent implements Parameter changes by varying capacitance values of the capacitive DAC through switching mechanisms. During calibration, specific capacitors are connected or disconnected to change the effective capacitance parameters, allowing the system to optimize linearity and gain matching by adjusting these electrical parameters without changing the physical circuit topology.
2Manufacturing precision
If variable capacitors are added for calibration, then linearity and gain matching improve, but device complexity increases
Solution Approach 1:
The patent applies Segmentation by dividing the capacitive DAC into multiple independent capacitor elements that can be individually switched. Instead of using a single variable capacitor, the system uses several fixed capacitors with switchable connections, segmenting the total capacitance into controllable portions. This reduces the need for complex variable capacitor structures while achieving the same calibration functionality.
Solution Approach 2:
The patent uses Copying by implementing multiple identical capacitor units with the same nominal value that can be selectively activated. Rather than designing complex variable capacitors, the system creates copies of simple fixed capacitors and uses switching to select which copies are active, thereby achieving variable capacitance functionality through replicated simple structures.
3Manufacturing precision
If multiple test configurations are implemented for calibration, then performance optimization improves, but calibration time and complexity increase
Solution Approach 1:
The patent applies Preliminary action by pre-defining multiple test configurations with different capacitance settings that have been optimized for different operating conditions. During calibration, the system quickly switches between these pre-configured settings rather than performing gradual adjustments, reducing calibration time by eliminating iterative tuning steps while still achieving optimal performance across various conditions.
Solution Approach 2:
The patent implements Periodic action by implementing a systematic calibration sequence that cycles through multiple test configurations in a predetermined order. The calibration process periodically switches between different capacitor configurations, measuring performance at each stage, and selecting the optimal configuration based on measured results, thereby efficiently exploring the parameter space without requiring continuous adjustment.
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 approach allows for efficient identification and configuration of test settings that enhance the overall linearity and reduce gain mismatch in ADC circuitry, leading to improved performance and reduced silicon area and power consumption.
Implementation Method 1
at least one of the target capacitors per sub-set of sub-ADC units is a variable capacitor, controllable by the control circuitry to have any one of a plurality of nominal capacitances
Data Source
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AI summary
Mixed-signal circuitry comprising: a set of capacitive digital-to-analogue converter, CDAC, units for carrying out digital-to-analogue conversion operations to convert respective digital values into corresponding analogue values; and control circuitry, wherein: each CDAC unit comprises an array of capacitors at least some of which are configured to be individually-switched dependent on the digital values, the capacitors configured to have nominal capacitances; a given capacitor of the array of capacitors in each of the CDAC units is a target capacitor; the set of CDAC units comprises a plurality of sub-sets of CDAC units; at least one of the target capacitors per sub-set of CDAC units is a variable capacitor, controllable by the control circuitry to have any one of a plurality of nominal capacitances defined by the configuration of that capacitor; and the control circuitry is configured to: in a test mode, control the variable capacitors so that the set of CDAC units is configured into each of a plurality of different test configurations in turn, and measure the performance of the mixed-signal circuitry based on the analogue values in each of the test configurations, each test configuration configuring the variable capacitors so that, per sub-set of CDAC units, an average nominal capacitance of the target capacitors has a given value defined by that test configuration; and in an operational mode following the test mode, configure the set of CDAC units into one of the set of test configurations based on the measured performances.