Ramp ADC Calibration Using OTA Conductance Reconfiguration
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Solution Overview
Problem
Existing ramp-based analog-to-digital converters (ADCs) face precision issues due to manufacturing variability and environmental changes, requiring dedicated calibration circuits that increase circuit area, complexity, and overhead.
Innovation Solution
A system and method that uses an operational transconductance amplifier configured with conductance sets and a current source to set DC voltage and create a voltage ramp, compensating for variability without dedicated calibration circuits, utilizing in-memory MAC units and time-to-digital converters to adjust slope and offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dedicated calibration circuits are used to eliminate slope and offset effects, then ADC precision is improved, but circuit area, complexity, and overhead increase
Solution Approach 1:
The system uses the existing current source that is already part of the MAC unit to perform calibration functions. The current source is reconfigured through conductance settings to generate calibration voltages and ramps, eliminating the need for separate dedicated calibration circuits. This self-service approach reduces circuit area and complexity while maintaining ADC precision.
Solution Approach 2:
The current source is designed to perform multiple functions: it serves as the primary current source for MAC operations and simultaneously functions as a calibration device when reconfigured with different conductance sets. This multi-functionality allows the same hardware component to address both computation and precision calibration needs, reducing overall system complexity.
2Measurement precision
If the current source is reconfigured with different conductance sets, then calibration precision is improved, but device complexity increases
Solution Approach 1:
The system achieves calibration by changing the conductance parameters of the operational transconductance amplifier through switching between different conductance sets. These parameter changes allow the same amplifier to operate in different modes (normal operation vs. calibration) with appropriate precision characteristics, improving calibration precision without adding complex hardware.
Solution Approach 2:
The amplifier configuration is made dynamic through time-multiplexed reconfiguration. The system switches between different conductance sets at different times - using the first conductance set for normal MAC operations and the second conductance set for calibration operations. This dynamic reconfiguration enables precision calibration while maintaining simple static hardware design.
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
Enhances ADC precision by reducing variability impact, minimizing circuit area, complexity, and overhead, especially beneficial for computing systems with many ADCs, such as deep neural networks.
Implementation Method 1
The current source includes an operational transconductance amplifier. The controller is configured to configure the operational transconductance amplifier with a first set of conductances
Implementation Method 2
use the reconfigured amplifier to create a voltage ramp at the second input
Data Source
AI summary
A system includes an analog-to-digital converter (ADC), a current source, and a controller. The ADC includes a comparator having a first input and a second input, and the current source includes an operational transconductance amplifier. The controller is configured to configure the operational transconductance amplifier with a first set of conductances; and use the current source to set a DC voltage at the first input. The controller is further configured to reconfigure the amplifier with a second set of conductances; and enable the comparator and use the current source to create a voltage ramp at the second input.