MOS Switch Bias Control for Low-Leakage Sample-and-Hold Circuits
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Solution Overview
Problem
Electronic switching devices in sample and hold applications experience instability due to leakage currents, which can discharge or charge capacitors to ground or power supply voltage, leading to voltage instability across capacitor terminals.
Innovation Solution
The method involves controlling a main MOS transistor to reduce leakage currents by applying specific bias voltages when in the on or off state, connecting the substrate and conducting electrode to the input terminal in the on state to lower the threshold voltage and resistance, and applying a second bias voltage to the substrate to minimize leakage currents during the off state, thereby reducing the size of reverse junctions and leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the main transistor is kept in a standard configuration, then the device structure is simple, but leakage currents cause capacitor discharge/charge instability during hold periods
Solution Approach 1:
The patent applies bias voltages to the substrate and conducting electrode in advance (before the hold period begins) to prepare the transistor for low-leakage operation. The first bias voltage is applied to the conducting electrode and the second bias voltage to the substrate, creating optimal conditions for minimizing leakage currents before the switching action occurs.
Solution Approach 2:
The patent changes the electrical parameters of the transistor by applying specific bias voltages to the substrate and conducting electrode. The second bias voltage applied to the substrate modifies the transistor's electrical characteristics to reduce leakage currents, while the first bias voltage optimizes the threshold voltage and on-state resistance.
2Productivity
If the transistor threshold voltage is reduced to charge the capacitor faster, then the sampling speed increases, but the leakage currents increase
Solution Approach 1:
The patent dynamically adjusts the transistor parameters by applying bias voltages only during specific phases. During the sampling period, the first bias voltage reduces the threshold voltage for fast charging. During the hold period, the bias voltages are configured to minimize leakage currents, thus dynamically optimizing performance for each operational phase.
Solution Approach 2:
The patent changes the electrical parameters of the transistor by applying specific bias voltages to the substrate and conducting electrode. The first bias voltage applied to the conducting electrode modifies the threshold voltage and on-state resistance to enable faster charging during sample periods.
3Reliability
If bias voltages are applied to reduce leakage currents, then voltage stability improves, but additional control circuitry is required
Solution Approach 1:
The patent makes the substrate and conducting electrode serve multiple functions: they are structural components of the transistor and simultaneously act as control nodes for applying bias voltages. This multi-functionality allows leakage current reduction without adding separate control structures.
Solution Approach 2:
The transistor's own substrate and conducting electrode are used to apply the necessary bias voltages for leakage reduction, rather than requiring entirely separate external control circuits. The existing transistor structures serve their primary switching function while also enabling leakage control through bias application.
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 approach effectively reduces leakage currents, allowing the capacitor to charge faster during sample periods and maintain stability during hold periods, enhancing the reliability of voltage references in low-power devices like microcontrollers.
Implementation Method 1
an application to this first conducting electrode of a first bias voltage chosen to reduce a leakage current between the two conducting electrodes of the main transistor
Implementation Method 2
a second bias voltage is applied to the substrate of the main transistor. The second bias voltage is chosen to reduce a leakage current flowing in the main transistor towards or coming from the output
Implementation Method 3
connecting the substrate and the first conducting electrode of the main transistor to the input terminal when the latter is in its on state makes it possible to reduce the threshold voltage of that transistor and consequently its resistance in the on state
Data Source
AI summary
A method is used to control an electronic device that includes a switching unit having a main MOS transistor having a substrate, a first conducting electrode and a second conducting electrode coupled to an output terminal. The method includes controlling the main transistor in such a way as to put it into an on state or an off state such that, when the main transistor is in the on state, the substrate and the first conducting electrode of the main transistor are connected to an input terminal and, when the main transistor is in the off state, the first conducting electrode of the main transistor is isolated from the input terminal and a first bias voltage is applied to the first conducting electrode and a second bias voltage is applied to the substrate of the main transistor.