Dual-Loop Common-Mode Control for Pipelined ADC Amplifiers
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Solution Overview
Problem
Pipelined analog-to-digital signal converters face efficiency degradation due to the need for substantial amplifier current in existing common-mode control structures, which are often based on capacitors and switching transistors, leading to reduced performance in high-speed, high-resolution applications.
Innovation Solution
The implementation of a two-stage amplifier with first and second common-mode control loops, where the first loop provides high gain to maintain the common-mode level at a predetermined reference voltage and the second loop offers high bandwidth to suppress transient-induced perturbations, both achieved without using capacitors and switching transistors, thereby reducing amplifier current drain and enhancing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional common-mode control structures using capacitors and switching transistors are employed, then common-mode level control is achieved, but amplifier current consumption increases significantly
Solution Approach 1:
The common-mode control function is divided into two separate control loops: a first control loop for maintaining common-mode level at a predetermined voltage level, and a second control loop for suppressing transient-induced perturbations. This segmentation allows each loop to be optimized independently, achieving reliable control without requiring substantial current consumption from a single complex control structure.
Solution Approach 2:
The invention changes the operational parameters of the control loops by configuring the first loop with high gain and the second loop with high bandwidth. This parameter differentiation enables the system to achieve accurate common-mode control and transient suppression without relying on traditional capacitor and switching transistor structures that consume substantial current.
2Productivity
If high-speed, high-resolution conversion is achieved through pipelined systems, then sampling speed and resolution are improved, but common-mode perturbations from transients increase
Solution Approach 1:
The invention implements feedback mechanisms in both control loops. The first control loop uses feedback to maintain the common-mode level at a predetermined voltage level, while the second control loop uses feedback to detect and suppress transient-induced perturbations. These feedback structures enable the system to maintain stability and accuracy even at high sampling speeds and resolutions.
3Measurement precision
If amplifier current is increased to improve common-mode control performance, then control accuracy is enhanced, but converter efficiency deteriorates
Solution Approach 1:
The invention employs dynamic control strategies by configuring the first control loop with high gain for precise steady-state common-mode level control and the second control loop with high bandwidth for rapid transient suppression. This dynamic configuration achieves accurate control without requiring continuously high current consumption, thereby maintaining converter efficiency while improving control accuracy.
Data Source
AI summary
Control structures are provided to accurately maintain amplifier common-mode levels at the predetermined level of a common-mode reference voltage Vcm. The disclosed control structures provide amplifier feedback along a first feedback path that is configured to provide high gain and low bandwidth to closely maintain amplifier common-mode level at the predetermined level of a common-mode reference voltage Vcm. They also provide amplifier feedback along a second feedback path that is configured to provide wide bandwidth to substantially reduce perturbations of the common-mode level that would have otherwise been induced by input signal transients. In an important amplifier feature, these controls are obtained without use of structures (e.g., capacitors and switching transistors) that use substantial current which reduces amplifier efficiency. Although the disclosed control structures may be used in a variety of systems, they are particularly suited for use in samplers and converter stages of pipelined analog-to-digital converters.