Chopper Amplifier Offset Tracking Across Multiple Input Pairs

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Solution Overview

Problem

Chopper amplifiers face challenges in quickly compensating for input offset voltage changes when switching between different pairs of input transistors, leading to delays in suppressing chopping ripple and maintaining spectral integrity of the output signal.

Innovation Solution

A chopper amplifier with an offset correction circuit that separately tracks the input offset of each pair of input transistors, allowing for quick updates to the input offset compensation signal when switching between pairs, thereby minimizing delay and suppressing chopping ripple.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a chopper amplifier uses multiple pairs of input transistors for amplification, then the amplifier can handle different input signal ranges and operating conditions, but switching between transistor pairs causes delay in offset compensation and chopping ripple suppression

Engineering Contradiction:

Improveamplifier operation across different input signal rangesVSAvoiddelay in offset compensation when switching transistor pairs

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The offset correction circuit pre-tracks the input offset voltage of each transistor pair separately before switching occurs. When a transistor pair is selected, its offset compensation is already prepared and ready to be applied immediately, eliminating the delay that would normally occur during switching transitions.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The offset correction circuit is divided into separate tracking paths for each transistor pair. Each path independently tracks the offset of its associated transistor pair, allowing the system to quickly switch between pre-tracked offset values without requiring a new tracking period after switching.

Inventive Principle:

Principle #1Segmentation

2Device complexity

If the offset correction circuit tracks a single averaged input offset, then the circuit complexity is reduced, but switching between transistor pairs causes delays in compensating for input offset changes

Engineering Contradiction:

Improveoffset correction circuit structureVSAvoidinput offset compensation accuracy during transistor switching

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

Instead of using a single averaged offset tracking path, the circuit implements multiple separate tracking paths - one for each transistor pair. Each path independently measures and tracks the offset of its specific transistor pair, providing precise compensation data ready for immediate use when that pair is selected.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each tracking path continuously or periodically pre-tracks the offset of its associated transistor pair so that when switching occurs, the compensation value is already prepared. This eliminates the need for slow re-tracking after switching while maintaining high precision for each individual transistor pair.

Inventive Principle:

Principle #10Preliminary action

3Productivity

If the amplifier switches between different pairs of input transistors to maintain linearity, then the amplifier can operate over a wider dynamic range, but chopping ripple suppression is compromised due to tracking delays

Engineering Contradiction:

Improveamplifier dynamic range and linearity maintenanceVSAvoidchopping ripple in output signal

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The offset correction circuit pre-tracks the input offset voltage of each transistor pair before switching occurs. When a transistor pair is selected, its offset compensation is already prepared and ready to be applied immediately, eliminating the delay that would normally occur during switching transitions.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses feedback from the separately tracked offset values to quickly adjust the compensation signal when switching between transistor pairs. This feedback mechanism ensures that chopping ripple is rapidly suppressed after switching by applying the appropriate pre-tracked offset compensation for the newly selected transistor pair.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS11139789B1Chopper amplifiers with tracking of multiple input offsets

Publication Date: 2021.10.05 ANALOG DEVICES INC

AI summary

Chopper amplifiers with tracking of multiple input offsets are disclosed herein. In certain embodiments, a chopper amplifier includes chopper amplifier circuitry including an input chopping circuit, an amplification circuit, and an output chopping circuit electrically connected along a signal path. The amplification circuit includes two or more pairs of input transistors, from which a control circuit chooses a selected pair of input transistors to amplify an input signal. The chopper amplifier further incudes an offset correction circuit that senses the signal path to generate an input offset compensation signal for the amplification circuit. Furthermore, the offset correction circuit separately tracks an input offset of each of the two or more pairs of input transistors.