Differential Integrator Circuit for Low-Noise Sigma-Delta Modulators

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Solution Overview

Problem

Sigma-delta modulators using switched capacitor circuits face challenges with noise performance and capacitor mismatch, leading to increased noise gain and reduced signal-to-noise ratio, and require a large area for implementation.

Innovation Solution

An integrator circuit with a differential operational amplifier and controllable switches, including noise reset switches, is designed to reduce noise correlation and area consumption, utilizing a fully-floating double-sampling switched capacitor configuration with specific switching signal control to mitigate noise and capacitor mismatch issues.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a classical switched capacitor integrator is used in a sigma-delta modulator, then the circuit can be implemented, but it suffers from noise correlation and capacitor mismatch issues leading to increased noise gain and reduced signal-to-noise ratio

Engineering Contradiction:

Improvenoise performanceVSAvoidnoise gain

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The integrator circuit is divided into two separate current paths (first current path and second current path) that are differentially processed. This segmentation allows independent handling of noise and signal components, reducing noise correlation and improving noise performance while maintaining circuit functionality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent inverts the conventional approach by using a differential operational amplifier with switched current paths instead of a single-ended switched capacitor integrator. This inversion of the traditional architecture enables differential signaling that naturally rejects common-mode noise and reduces the impact of capacitor mismatch.

Inventive Principle:

Principle #13The other way round (Inversion)

2Device complexity

If a conventional integrator circuit is used, then the circuit design is simple, but it requires a large area for implementation

Engineering Contradiction:

Improvecircuit designVSAvoidarea consumption

Core Design Contradiction:

Device complexityVSArea of stationary object

Solution Approach 1:

The patent merges the functionality of noise reduction and integration into a single differential operational amplifier structure with integrated switched current paths. This consolidation eliminates the need for separate noise filtering circuits and classical SC integrators, reducing overall area consumption while maintaining design simplicity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The differential operational amplifier with switched current paths serves multiple functions simultaneously: it performs integration, noise reduction, and differential signaling. This multi-functionality eliminates the need for additional dedicated circuits, thereby reducing the total chip area required while keeping the design relatively simple.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Ease of manufacture

If standard switched capacitor circuits are used, then the implementation is straightforward, but the circuit is sensitive to capacitor mismatch

Engineering Contradiction:

Improveimplementation easeVSAvoidcapacitor mismatch robustness

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

By inverting to a differential architecture, the circuit transforms the single-ended switched capacitor approach into a differential switched current path configuration. This inversion makes the circuit inherently more robust to capacitor mismatch because differential signaling naturally rejects common-mode variations and mismatches in the capacitor values.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the operating parameters from voltage-based switched capacitor to current-based switched paths. This parameter change from voltage to current mode operation, combined with differential signaling, reduces sensitivity to capacitor value variations and mismatch, improving manufacturing precision robustness.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS10826522B2Integrator circuit for use in a sigma-delta modulator

Publication Date: 2020.11.03 AUSTRIAMICROSYSTEMS AG

AI summary

An integrator circuit (10) for use in a sigma-delta modulator (1) comprises a differential operational amplifier (130) with a first input node (E130a) and a second input node (E130b). The first input node (E130a) of the differential operational amplifier (130) is connected to a first current path (101) and the second input node (E130b) of the differential operational amplifier (130) is connected to a second current path (102). A first controllable switch (111) is arranged between the second input node (E130b) of the differential operational amplifier (130) and the first current path (101). A second controllable switch (112) is arranged between the first input node (E130a) of the differential operational amplifier (130) and the second current path (102). A third controllable switch (113) is arranged between a reference potential (RP) and the first current path (101). A fourth controllable switch (114) is arranged between the reference potential (RP) and the second current path (102).