High-Voltage MOS Switch Using Series Isolation Junctions
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Solution Overview
Problem
Current high voltage switch designs using low voltage metal-oxide-semiconductor (MOS) transistors are limited by short-channel transistors' low source-drain breakdown voltages, leading to complexity and limitations in applying high supply voltages, particularly at interface sections like input/output (I/O) pads, and are susceptible to gate oxide breakdown.
Innovation Solution
A high voltage switch design utilizing multiple MOS structures with strategically controlled gate voltages to manage high input voltages without exceeding transistor breakdown voltages, ensuring all MOS structures are either fully 'off' or 'on' to prevent gate-related breakdowns, with a topology that includes series coupling of sources and drains between input and ground, and optional voltage dividers and reverse-biased diodes to manage voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If low voltage MOS transistors are used in high voltage switch designs, then device complexity is reduced and cost is lowered, but the source-drain breakdown voltage limits the ability to apply high supply voltages
Solution Approach 1:
The high voltage switch is divided into multiple low voltage MOS transistor stages (first stage transistor, second stage transistor, third stage transistor) connected in series. Each transistor handles a portion of the total voltage, allowing the use of low voltage transistors to achieve high voltage capability. The gate of each transistor is controlled by voltage dividers to ensure proper operation within their voltage ratings.
Solution Approach 2:
Voltage dividers are introduced as intermediary components to control the gate voltages of each MOS transistor stage. The voltage dividers step down the high input voltage to appropriate levels for gating the transistors, enabling the low voltage transistors to safely control high voltage switching without experiencing gate oxide breakdown.
2Power
If high supply voltages are applied to short-channel transistors, then power handling capability increases, but gate oxide breakdown susceptibility increases
Solution Approach 1:
The power handling function is segmented across multiple transistor stages, each operating at lower voltage levels appropriate for their gate oxide ratings. The series connection allows the cumulative power handling capability to exceed what a single low voltage transistor could provide, while maintaining gate oxide safety through proper voltage distribution.
Solution Approach 2:
Voltage dividers act as intermediary control elements that prevent excessive voltage from reaching the gate terminals. By controlling the gate voltage to remain within safe margins below the supply voltage, the voltage dividers protect the gate oxide while still enabling the transistors to control high voltage power switching through their source-drain channels.
3Adaptability or versatility
If level shifters are used to manage high supply voltages in core circuits, then voltage compatibility is achieved, but circuit complexity increases
Solution Approach 1:
The voltage shifting and high voltage switching functions are merged into a single integrated circuit block. The multiple transistor stages with their associated voltage dividers are combined to simultaneously achieve voltage level adaptation and high voltage switching capability, eliminating the need for separate level shifter circuits and reducing overall system complexity.
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
Enables efficient handling of voltages exceeding double the supply voltage without complex designs, ensuring all MOS structures operate within safe voltage margins, preventing gate oxide breakdown and maintaining high voltage capability while keeping the circuit design cost-effective and simplified.
Implementation Method 1
A reverse-biased diode is electrically coupled between the input and the voltage divider
Data Source
AI summary
A high voltage switch having first and second states includes an input receiving an input voltage that is greater than a supply voltage. Each of first, second, and third MOS structures of a first conductivity type has a gate, a source, and a drain. The sources and drains of each of the MOS structures are electrically coupled in series between the input and ground. An output is electrically coupled to the input. When the switch is in the first state, the gate of the first MOS structure is pulled to ground, the gate of the second MOS structure is pulled to the supply voltage, and the gate of the third MOS structure is pulled to a voltage greater than the supply voltage and less than the input voltage. When the switch is in the second state, the gates of all of the MOS structures are pulled to the supply voltage.