Charge-Sensitive Amplifier Switching for Low-Noise Wide Charge Range

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Solution Overview

Problem

Charge sensitive amplifiers for sensor frontends face a contradiction between requiring high dynamic range and low noise, with single transistor switches failing to optimize noise without limiting charge input range, especially in line sensors with varying pixel defects and large charge inputs.

Innovation Solution

Implementing a charge sensitive amplifier circuit with two transfer switches, where the first switch has high conductivity at the beginning and reduces to a low-conductive state at the end of charge transfer, while the second switch only activates for large charges, allowing for variable bandwidth to manage noise without compromising input charge range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single transistor switch is used to transfer charge, then the device complexity is reduced, but the bandwidth must be excessively large to remove all charges during transfer phase while fulfilling low noise requirements

Engineering Contradiction:
Improvenumber of transfer switchesVSAvoidcharge transfer completeness
Core Design Contradiction:
Device complexityVSReliability

Solution Approach 1:

The charge transfer function is segmented into two parallel paths: a first transfer switch for normal operation and a second transfer switch for large charge removal. This segmentation allows each switch to be optimized for its specific function, with the second switch providing additional transfer capability when needed without affecting the noise performance of the first switch during normal operation.

Inventive Principle:
Principle #1Segmentation

2Speed

If the bandwidth of the charge sensitive amplifier is made large, then the charge transfer speed is improved, but the noise of the input stage increases

Engineering Contradiction:
Improvecharge transfer speedVSAvoidinput stage noise
Core Design Contradiction:
SpeedVSObject-generated harmful factors

Solution Approach 1:

The circuit dynamically switches between two transfer paths based on the charge magnitude. For small charges, only the first transfer switch operates with low bandwidth to minimize noise. For large charges, the second transfer switch is activated to provide high bandwidth for fast charge removal, thus adapting the bandwidth to the actual transfer needs.

Inventive Principle:
Principle #15Dynamics

Solution Approach 2:

The effective bandwidth parameter of the charge sensitive amplifier is changed based on the charge magnitude by selectively activating different transfer switches. The first transfer switch operates with a first bandwidth parameter for noise optimization, while the second transfer switch provides a second, larger bandwidth parameter for fast charge removal when needed.

Inventive Principle:
Principle #35Parameter changes

3Object-generated harmful factors

If the bandwidth of the charge sensitive amplifier is reduced to optimize noise, then the input stage noise is minimized, but the charge transfer time increases

Engineering Contradiction:
Improveinput stage noiseVSAvoidcharge transfer time
Core Design Contradiction:
Object-generated harmful factorsVSLoss of time

Solution Approach 1:

The charge transfer function is segmented into two parallel paths: a first transfer switch for normal operation and a second transfer switch for large charge removal. This segmentation allows each switch to be optimized for its specific function, with the second switch providing additional transfer capability when needed without affecting the noise performance of the first switch during normal operation.

Inventive Principle:
Principle #1Segmentation

4Adaptability or versatility

If a high dynamic range is required for the input charge, then the charge input range is extended, but the bandwidth requirements increase excessively

Engineering Contradiction:
Improveinput charge rangeVSAvoidbandwidth requirement
Core Design Contradiction:
Adaptability or versatilityVSSpeed

Solution Approach 1:

The circuit dynamically switches between two transfer paths based on the charge magnitude. For small charges, only the first transfer switch operates with low bandwidth to minimize noise. For large charges, the second transfer switch is activated to provide high bandwidth for fast charge removal, thus adapting the bandwidth to the actual transfer needs.

Inventive Principle:
Principle #15Dynamics

Data Source

PatentUS12015395B2Charge sensitive amplifier circuit for sensor frontend
Publication Date: 2024.06.18 AMS INTERNATIONAL AG
  • US12015395B2 patent drawing

AI summary

A charge sensitive amplifier circuit for sensor frontend comprises an input node to be connected to a sensor to receive an input charge, and an output node to be connected to a charge conversion circuit. The charge sensitive amplifier circuit comprises a first transfer switch located between the input node and the output node to transfer the input charge to the output node. The charge sensitive amplifier circuit further comprises a second transfer switch located in parallel to the first transfer switch between the input node and the output node to transfer the input charge to the output node.