USB Switch Circuit Leakage Reduction via Local Rail Clamping
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Solution Overview
Problem
Switch circuits in USB devices face challenges in reducing leakage currents, particularly Ion leakage current and Ion off leakage current, which interfere with moisture detection and are not adequately protected against high voltage direct current (DC) surges, affecting signal integrity and device suitability for moisture detection applications.
Innovation Solution
A switch circuit design incorporating a main transistor, voltage generator circuits, clamp circuits, and a driver circuit that activates and deactivates the main transistor in response to overvoltage events, generating local rails to protect the transistor and reduce leakage currents, including the use of diodes and transistors to manage voltage and current during normal and overvoltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high voltage protection circuit is added to protect against DC surges, then reliability is improved, but device complexity increases
Solution Approach 1:
The protection circuit is segmented into distinct functional blocks: overvoltage detection circuit, control circuit, and clamp circuit. Each block performs a specific function, allowing independent optimization and simplifying the overall design while maintaining comprehensive protection capability.
Solution Approach 2:
The overvoltage detection circuit continuously monitors the voltage level before damage occurs. When overvoltage is detected, the control circuit preemptively activates the clamp circuit to prevent damage, rather than reacting after damage has occurred. This preliminary action ensures protection while minimizing circuit complexity.
2Measurement precision
If leakage current is reduced for moisture detection, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The protection circuit and leakage current reduction function are merged into a single integrated design. The clamp circuit not only provides overvoltage protection but also inherently reduces leakage current by controlling the voltage levels across the switch transistor, eliminating the need for separate circuits for each function.
Solution Approach 2:
The clamp circuit serves multiple functions simultaneously: it clamps overvoltage to protect the switch transistor, reduces leakage current for accurate moisture detection, and maintains signal integrity. This multi-functionality reduces overall device complexity while achieving both protection and measurement precision goals.
3Reliability
If clamp circuit is added to reduce leakage current, then signal integrity is improved, but device complexity increases
Solution Approach 1:
The clamp circuit is applied locally at the gate terminal of the switch transistor, precisely where voltage control is needed. By clamping the voltage between the gate and source terminals, the circuit locally improves signal integrity and reduces leakage current without requiring global circuit redesign, thus minimizing added complexity.
4Reliability
If voltage generator circuits are added to generate local rails, then protection capability is improved, but manufacturing cost increases
Solution Approach 1:
The voltage generator circuits generate the necessary local voltage rails using the existing power supply and circuit elements. The overvoltage detection circuit uses the same power supply to generate reference voltages, and the clamp circuit uses available transistors and diodes to create the clamping function. This self-service approach provides robust protection capability while avoiding additional expensive external components, thereby reducing manufacturing cost.
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
The solution effectively reduces or eliminates Ion leakage and Ion off leakage currents, enhancing signal integrity and enabling the switch circuit to protect against high voltage DC surges, thus improving the device's suitability for moisture detection and reducing manufacturing costs and die size.
Implementation Method 1
a clamp circuit connected to the high local rail between the first voltage generator circuit and a gate of the main transistor, where the clamp circuit is configured to clamp the voltage between the high local rail and the gate of the main transistor during the overvoltage event
Implementation Method 2
The clamp circuit may include a first diode and a second diode. The first voltage generator circuit is configured to provide either a drain voltage of the main transistor or a source voltage of the main transistor as the voltage on the high local rail
Implementation Method 3
a main transistor configured to be activated during a normal operation of the switch circuit, where the main transistor is configured to be deactivated during an overvoltage event
Data Source
AI summary
According to an aspect, a switch circuit for a Universal Serial Bus (USB) connector device includes a main transistor configured to be activated during a normal operation of the switch circuit, a first voltage generator circuit configured to generate a voltage on a high local rail during an overvoltage event, a second voltage generator circuit configured to generate a voltage on a low local rail during the overvoltage event, where the low local rail is connected to a bulk of the main transistor, and a clamp circuit connected to the high local rail between the first voltage generator circuit and a gate of the main transistor, where the clamp circuit is configured to clamp the voltage between the high local rail and the gate of the main transistor during the overvoltage event.