Switched Capacitor Amplifier Feedback Loops for Sampled Noise Reduction

Solution Overview

Problem

Noise from various sources reduces the accuracy of digital representations in sampling circuits, particularly in read out integrated circuits (ROICs) used in applications like X-ray systems, and conventional methods to reduce sampling noise, such as increasing capacitance or front end gain, incur increased circuit area and power consumption.

Innovation Solution

A second feedback loop is coupled in parallel with a first feedback loop in the amplifier, operating in a dummy phase to transfer sampling noise-related charge to the first feedback loop's capacitance, thereby reducing sampling noise without increasing circuit area or power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If capacitance or front end gain is increased to reduce sampling noise, then noise reduction is achieved, but circuit area and power consumption increase

Engineering Contradiction:

Improvesampling noiseVSAvoidcircuit area

Core Design Contradiction:

Object-affected harmful factorsVSArea of stationary object

Solution Approach 1:

The feedback mechanism is segmented into two distinct loops: a first feedback loop for signal processing and a second feedback loop specifically for noise reduction during the dummy phase. This segmentation allows the noise reduction function to be performed separately without requiring increased capacitance in the main signal path, thus reducing circuit area while maintaining noise reduction effectiveness.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The second feedback loop performs preliminary noise reduction action during the dummy phase before the actual signal processing phase. By transferring and neutralizing sampling noise-related charge during this preliminary phase, the system reduces noise without needing to increase the capacitance of the main feedback loop, thereby avoiding increased circuit area and power consumption.

Inventive Principle:

Principle #10Preliminary action

2Object-affected harmful factors

If capacitance or front end gain is increased to reduce sampling noise, then noise reduction is achieved, but power consumption increases

Engineering Contradiction:

Improvesampling noiseVSAvoidpower consumption

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by stationary object

Solution Approach 1:

The feedback mechanism is segmented into two distinct loops: a first feedback loop for signal processing and a second feedback loop specifically for noise reduction during the dummy phase. This segmentation allows the noise reduction function to be performed separately without requiring increased capacitance in the main signal path, thus reducing circuit area while maintaining noise reduction effectiveness.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The second feedback loop performs preliminary noise reduction action during the dummy phase before the actual signal processing phase. By transferring and neutralizing sampling noise-related charge during this preliminary phase, the system reduces noise without needing to increase the capacitance of the main feedback loop, thereby avoiding increased circuit area and power consumption.

Inventive Principle:

Principle #10Preliminary action

3Object-affected harmful factors

If a second feedback loop is added to reduce sampling noise, then noise reduction is achieved, but device complexity increases

Engineering Contradiction:

Improvesampling noiseVSAvoidfeedback loop structure

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The second feedback loop is merged with the existing first feedback loop structure, sharing common components such as the amplifier and capacitors. The second loop is activated only during the dummy phase and uses the same physical capacitors (Cf1 and Cf2) that are already present in the circuit, thereby adding noise reduction functionality without proportionally increasing device complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The existing capacitors Cf1 and Cf2 serve dual functions: they participate in the first feedback loop for signal processing during the signal phase and in the second feedback loop for noise reduction during the dummy phase. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in device complexity while achieving noise reduction.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS12580527B2Reducing sampled AZ noise and sampled reset noise in switched capacitor amplifiers

Publication Date: 2026.03.17 TEXAS INSTRUMENTS INC

AI summary

In at least one example, a circuit includes an amplifier, a first feedback loop, and a second feedback loop. The amplifier includes an amplifier input and an amplifier output. The first feedback loop includes a first feedback capacitor and a first switch. The first feedback loop is coupled between the amplifier input and the amplifier output. The first feedback capacitor is coupled to the amplifier output through the first switch. The second feedback loop includes a second feedback capacitor and a second switch. The second feedback loop is coupled in parallel with the first feedback loop between the amplifier input and the amplifier output. The second feedback capacitor is coupled to the amplifier input and to the first feedback capacitor through the second switch.