Compensated Amplifier Switching for Higher Slew Rate ADCs

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Solution Overview

Problem

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 amplification period, reducing negative feedback and enhancing the slew rate of the operational amplifier.

Engineering Contradictions & Design Principles

VSEngineering 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

Engineering Contradiction:

Improveamplifier stabilityVSAvoidslew rate

Core Design Contradiction:

Stability of the object's compositionVSSpeed

Solution Approach 1:

The switch is closed in advance during the sampling phase to pre-establish the virtual ground condition at the inverting input terminal. This preliminary action ensures that when the amplification phase begins, the compensation capacitors are already discharged and the operational amplifier is ready to respond immediately to voltage changes, thereby achieving high slew rate without sacrificing stability

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The switch operates periodically, alternating between closed state during sampling and open state during amplification. This periodic action allows the system to cycle between two operational modes: one optimized for charging the compensation capacitors (sampling with switch closed) and one optimized for stable amplification (switch open), thus resolving the contradiction between stability and slew rate

Inventive Principle:

Principle #19Periodic action

2Measurement precision

If the switch is closed during sampling, then the virtual ground is established improving sampling accuracy, but the amplification speed is reduced

Engineering Contradiction:

Improvesampling accuracyVSAvoidamplification speed

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

The switch is closed during the sampling phase to establish virtual ground and improve sampling accuracy, then opened during the amplification phase to enable fast response. This periodic switching ensures that the system optimizes for accuracy during sampling and for speed during amplification, resolving the contradiction between measurement precision and amplification speed

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS7898337B2High slew rate amplifier, analog-to-digital converter using same, CMOS imager using the analog-to-digital converter and related methods

Publication Date: 2011.03.01 STANCHART BUSINESS CREDIT

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.