Lookahead Pipelined ADC Using Open-Loop Residue Amplifiers
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Solution Overview
Problem
High-speed analog-to-digital converters (ADCs) face challenges in achieving both high speed and high accuracy while minimizing power consumption, particularly for 10 Gbit/s serial data transmission applications, where existing ADCs are either too power-hungry or limited in conversion rate.
Innovation Solution
The implementation of a lookahead pipelined ADC architecture using open-loop residue amplifiers with calibration, which includes a calibration unit and a sub-radix design to compensate for non-linearity, allowing for increased sampling rates with reduced power consumption and improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional closed-loop residue amplifiers are used in pipeline ADC stages, then accuracy is improved, but power consumption increases
Solution Approach 1:
The patent extracts the feedback loop from the residue amplifier configuration, transitioning from closed-loop to open-loop operation. This removes the power-consuming feedback mechanism while retaining the essential amplification function through carefully designed gain stages that achieve the required residue amplification without continuous feedback correction.
Solution Approach 2:
The patent changes the operational parameters of the residue amplifier by operating in open-loop mode with fixed gain stages rather than closed-loop mode with variable feedback. This parameter change allows the amplifier to operate at lower power consumption while maintaining sufficient accuracy through the predetermined gain architecture and redundant bit encoding.
2Productivity
If higher conversion rates are achieved in ADCs, then productivity is improved, but power consumption increases
Solution Approach 1:
The patent segments the conversion process into multiple parallel pipeline stages, each operating at a fraction of the total conversion rate. By dividing the high-speed conversion into concurrent lower-speed stages that process different portions of the signal simultaneously, the system achieves high overall throughput while each stage consumes less power, and the total power scales more efficiently than a single high-speed stage.
3Use of energy by moving object
If open-loop residue amplifiers are used to reduce power consumption, then power efficiency is improved, but measurement accuracy deteriorates due to non-linearity
Solution Approach 1:
The patent introduces feedback at the system level through a calibration mechanism that measures the non-linear characteristics of the open-loop amplifiers and compensates for them. This feedback loop operates slowly to characterize the amplifier behavior and applies correction factors to the digital output, thereby maintaining high measurement accuracy while the fast analog path remains open-loop for low power consumption.
Solution Approach 2:
The patent introduces an intermediary calibration process that acts as a mediator between the open-loop amplifier and the final digital output. This intermediary stage characterizes the amplifier's non-linear behavior and applies corrective transformations to the raw converter output, effectively decoupling the power-efficient open-loop operation from the accuracy requirement.
4Speed
If flash ADC architecture is used for high speed conversion, then conversion speed is improved, but device complexity and power consumption increase geometrically with resolution
Solution Approach 1:
The patent segments the high-resolution conversion task into multiple lower-resolution pipeline stages, each handling a portion of the total bits. Instead of using a single flash ADC with 2^N-1 comparators for N-bit resolution, the system uses multiple successive approximation register (SAR) or flash stages that each convert fewer bits, reducing the comparator count per stage from exponential to linear or constant, while the pipeline architecture maintains high overall conversion speed.
Data Source
AI summary
A lookahead pipelined ADC architecture uses open-loop residue amplifiers with calibration. This approach is able to achieve a high-speed, high-accuracy ADC with reduced power consumption. In one aspect, an ADC pipeline unit includes a plurality of lookahead pipeline stages (i.e., an ADC lookahead pipeline) coupled to a calibration unit. The ADC lookahead pipeline uses open-loop residue amplifiers. The calibration unit compensates for non-linearity in the open-loop amplifiers.