Correlated Double Sampling Amplifier With Power-Down OTA

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Solution Overview

Problem

Existing signal processing circuitry for low power applications faces challenges in achieving low inactive power consumption, fast turn-on from a powered-down state, low offset voltage, and low noise while optimizing power consumption for battery-powered or implantable devices.

Innovation Solution

A signal acquisition or conditioning amplifier using correlated double sampling (CDS) with a storage capacitor in a capacitive feedback network and a low power operational transconductance amplifier (OTA) that can be powered down between samplings, allowing for efficient power scaling and reduced noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If signal processing components are powered down between signal acquisitions to save power, then inactive power consumption is reduced, but turn-on time and settling time increase

Engineering Contradiction:

Improveinactive power consumptionVSAvoidturn-on and settling time

Core Design Contradiction:

Loss of energyVSLoss of time

Solution Approach 1:

The amplifier is divided into multiple independent operational blocks (input stage, intermediate stage, output stage) that can be selectively powered down. This segmentation allows the circuit to enter different power consumption modes depending on activity level, reducing inactive power while maintaining fast wake-up capability for active blocks.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The amplifier implements preliminary biasing circuits that pre-establish operating conditions before full signal processing begins. This preliminary action reduces the settling time required after power-up by pre-configuring bias currents and voltage levels, addressing the turn-on time issue while maintaining low inactive power.

Inventive Principle:

Principle #10Preliminary action

2Object-affected harmful factors

If chopper amplifiers are used to reduce noise, then low-frequency noise is reduced, but power consumption increases and synchronization with signal measurements becomes complex

Engineering Contradiction:

Improvelow-frequency noiseVSAvoidpower consumption

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by moving object

Solution Approach 1:

The patent extracts and eliminates the chopper modulation mechanism entirely, replacing it with a direct-coupled operational transconductance amplifier design. This removes the noise modulation benefits of chopper amplifiers while eliminating their associated power consumption and synchronization complexity issues.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The mechanical switching and modulation mechanisms of chopper amplifiers are replaced with continuous analog signal paths using operational transconductance amplifiers. This substitution eliminates the need for synchronization while maintaining low noise through careful circuit design and filtering.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If amplifiers are designed for resistive loads to simplify design, then design complexity is reduced, but power consumption increases due to continuous current flow

Engineering Contradiction:

Improvedesign complexityVSAvoidpower consumption

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The amplifier design transitions from resistive load operation to capacitive load operation, fundamentally changing the impedance parameter. This allows the use of switching techniques and sleep modes that are not feasible with resistive loads, dramatically reducing inactive power consumption while maintaining design simplicity through standard operational transconductance amplifier topologies.

Inventive Principle:

Principle #35Parameter changes

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

This approach enables flexible power management, reducing inactive power consumption and noise while maintaining good performance characteristics, making it suitable for a wide range of signal acquisition and measurement applications.

Implementation Method 1

a low power operational transconductance amplifier (OTA)

Methodology Applied

Scientific EffectTransconductance:

Implementation Method 2

a storage capacitor in a capacitive feedback network

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS10809792B2Correlated double sampling amplifier for low power

Publication Date: 2020.10.20 ANALOG DEVICES INC

AI summary

A signal acquisition or conditioning amplifier can be configured and controlled to use correlated doubling sampling (CDS) of a differential input signal, and a storage capacitor in a capacitive or other feedback network, a low power operational transconductance amplifier (OTA) capable of being powered down between CDS samplings, and which can be operated in a manner that provides good performance characteristics while still providing low or efficient power consumption. The amplifier and other signal processing circuitry can allow power to be scaled down, when less signal measurement throughput is needed, and to be scaled up, when more signal measurement throughput is needed. Such flexibility can help make the present approach useful for a wide range of signal acquisition and measurement applications. Precharging via buffer amplifiers can provide improved signal acquisition circuitry effective input impedance.