Capacitive Programmable Gain Amplifier Switch for Charge Injection Suppression

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Solution Overview

Problem

Existing signal amplifiers in integrated-circuit image sensors face challenges in achieving low-noise, high-fidelity signal amplification due to charge injection and leakage issues during the transition between precharge and active phases.

Innovation Solution

The implementation of an active-leakage/injection-suppression capacitive programmable-gain amplifier (PGA) with a multi-transistor T-switch configuration, which provides a low-impedance expulsion path for residual carriers and equalizes voltage across critical leakage-path components, reducing charge injection and leakage into the amplifier input node.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional amplifier switch is used during phase transition, then the amplifier can be reset and activated, but charge injection and leakage occur at the amplifier input node

Engineering Contradiction:

Improveamplifier reset and activationVSAvoidcharge injection and leakage

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

A dedicated neutralizing transistor (X3) is introduced as an intermediary component specifically to handle charge expulsion during the phase transition. This transistor acts as a mediator between the amplifier input node and the feedback path, providing a controlled path for residual carriers to be expelled without injecting charge into the amplifier input node, thus resolving the contradiction between reliable amplifier activation and charge injection suppression

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If precharge transistors are switched off to activate the amplifier, then the amplifier enters active phase, but residual carriers are injected into the amplifier input node

Engineering Contradiction:

Improveamplifier active phase operationVSAvoidresidual carrier injection

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The neutralizing transistor (X3) is activated in advance during the transition phase, before the precharge transistors are completely switched off. This preliminary action establishes a safe discharge path for residual carriers, ensuring that when the precharge transistors turn off and the amplifier enters active phase, no charge injection occurs at the amplifier input node

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If a simple switch configuration is used, then the device structure is simple, but charge leakage occurs during active phase

Engineering Contradiction:

Improveswitch configurationVSAvoidcharge leakage

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The switch configuration is segmented into distinct functional components: precharge transistors (X1, X2) for resetting and a dedicated neutralizing transistor (X3) for charge expulsion. This segmentation allows each transistor to perform its specific function optimally, with X3 specifically tasked with preventing charge leakage during the active phase by providing a controlled expulsion path for residual carriers

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS12237817B2Programmable gain amplifier with active charge-injection/charge-leakage suppression

Publication Date: 2025.02.25 GIGAJOT TECHNOLOGY INC

AI summary

Charge leakage/injection suppression circuitry within a capacitive programmable gain amplifier provides a low-impedance expulsion path for residual carriers within a feedback-path amplifier-mode switch and equalizes a voltage across a critical-leakage-path component of that amplifier-mode switch, reducing charge injection and leakage into an otherwise isolated amplifier input node to yield a low-noise amplifier output.