Switched-Capacitor Amplifier Hold Circuit for Leakage Suppression
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Solution Overview
Problem
Switched-capacitor amplifiers face challenges in maintaining accurate output voltage during extended hold periods due to charge leakage through switches, leading to decreased accuracy and potential differences that cumulatively increase over time.
Innovation Solution
Incorporating a series circuit of MOS transistors with a potential holding capacitor between the common connection point and ground, ensuring the source, drain, and back gate of the MOS transistors are held at a reference voltage, preventing sub-threshold and junction leakage, and using a controller to manage switch states during sampling and holding phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional switch is used to connect the sampling capacitor to ground, then the circuit structure is simple, but charge leakage occurs through the switch during the hold period, causing output voltage accuracy to deteriorate over time
Solution Approach 1:
The second switch is segmented into a series circuit of first and second MOS transistors. This segmentation allows independent control of each transistor's gate and back gate, enabling precise control of charge leakage paths. The first MOS transistor's back gate is connected to the node between the two transistors, creating isolated control regions that prevent charge leakage while maintaining circuit functionality.
Solution Approach 2:
The invention changes the electrical parameters of the switch by applying different voltages to the gates and back gates of the MOS transistors. During the hold period, the back gate voltage is adjusted to create a potential barrier that prevents charge leakage through the transistor, while the gate voltage maintains the switching function. This parameter control allows the switch to remain open without charge leakage.
2Duration of action of stationary object
If the hold period is extended to maintain voltage stability, then output accuracy improves, but charge leakage through the switch accumulates over time, causing potential differences to increase and accuracy to decrease
Solution Approach 1:
The potential holding capacitor is pre-charged to the reference voltage before the hold period begins. During the hold period, this pre-charged capacitor actively compensates for any charge leakage by maintaining the node voltage at the reference level. The preliminary charging action ensures that even as charge leaks over extended hold periods, the voltage reference is continuously restored.
Solution Approach 2:
The circuit implements a feedback mechanism where the back gate of the first MOS transistor is connected to the node between the two transistors. This creates a feedback loop that automatically adjusts the back gate voltage in response to any voltage deviations, preventing charge leakage and maintaining the node voltage at the reference level throughout the hold period.
3Reliability
If a single MOS transistor is used as the second switch, then the circuit is simpler, but sub-threshold leakage and junction leakage occur, preventing accurate voltage holding
Solution Approach 1:
The single MOS transistor is segmented into two series-connected MOS transistors with independent back gate control. This segmentation creates two separate leakage paths that can be independently controlled, allowing the circuit to block both sub-threshold leakage and junction leakage by appropriately biasing the back gates of each transistor.
Solution Approach 2:
The potential holding capacitor acts as an intermediary element between the two MOS transistors. It maintains the voltage at the intermediate node, preventing charge leakage from propagating through either transistor. The capacitor serves as a buffer that isolates the leakage paths while maintaining the reference voltage level.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively restricts charge leakage, maintaining accurate output voltage without significant changes during the hold period, reducing errors and maintaining voltage stability over time.
Implementation Method 1
a potential holding capacitor connected between a node that is a common connection point of the first and second MOS transistors and a ground
Implementation Method 2
ensuring the source, drain, and back gate of the MOS transistors are held at a reference voltage, preventing sub-threshold and junction leakage
Implementation Method 3
ensuring the source, drain, and back gate of the MOS transistors are held at a reference voltage, preventing sub-threshold and junction leakage
Data Source
AI summary
A switched-capacitor amplifier includes a sampling capacitor, a first switch, a differential amplifier, a reference power supply, a second switch, a third switch, and a controller configured to execute on and off control of the first to third switches. The second switch includes a series circuit of first and second metal oxide semiconductor (MOS) transistors and a potential holding capacitor connected between a node that is a common connection point of the first and second MOS transistors and a ground.