Compensated Amplifier Switching for Higher Slew Rate ADCs
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Solution Overview
Problem
Conventional operational amplifiers used in pipelined analog-to-digital converters have slow slew rates due to compensation capacitors, which reduce the speed of A/D converters and other devices.
Innovation Solution
Incorporating a switch to temporarily couple complementary nodes as virtual grounds during the initial amplification period, reducing negative feedback and enhancing the slew rate, and using a pass gate with an NMOS and PMOS transistor pair controlled by a pulse generator to manage feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If compensation capacitors are used to stabilize the operational amplifier, then stability is improved, but slew rate deteriorates
Solution Approach 1:
The switch temporarily couples the complementary nodes as virtual grounds at the beginning of the amplification period, before the compensation capacitors can exert their full stabilizing effect. This preliminary action reduces negative feedback during the critical initial phase when slew rate is most needed, allowing faster voltage changes while maintaining stability through the compensating capacitors for the remainder of the cycle.
Solution Approach 2:
The amplifier system transitions from a static feedback configuration to a dynamic one where the feedback path is selectively modified during different phases of operation. The switch dynamically alters the coupling between complementary nodes based on the amplification period timing, creating time-varying feedback characteristics that optimize both slew rate and stability performance.
2Speed
If negative feedback is reduced to enhance slew rate, then speed is improved, but stability may deteriorate
Solution Approach 1:
The switch operates periodically during the amplification period, creating time-varying feedback conditions. During the initial phase of each period, the switch couples the complementary nodes to reduce negative feedback and enhance slew rate. The periodic nature ensures that stability is maintained through the compensating capacitors for the remainder of the cycle, balancing speed and stability requirements.
Data Source
AI summary
An amplifier, which may be used in a pipelined analog-to-digital converter, includes a first amplifier stage driving a second amplifier stage. At least one compensation capacitor is coupled to provide negative feedback through the capacitor from the second amplifier stage to the first amplifier stage. The slew rate of the amplifier is enhanced by substantially reducing the negative feedback coupled through the capacitor during a period following the transition of a signal applied to an input terminal of the amplifier. If the first stage of the amplifier has complementary signal nodes, the negative feedback coupled through the capacitor may be reduced, for example, by closing a switch coupled between first and second complementary nodes of the first amplifier stage.