High Voltage Transmit Receive Switch Using Enhancement-Mode Transistors
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Solution Overview
Problem
Existing two-terminal transmit/receive switches in ultrasound applications require depletion-mode devices, which are not available in all BCD process foundries, and struggle to protect low-voltage receivers from high-voltage signals without high-voltage power supplies.
Innovation Solution
An analog switch and voltage detection circuit using enhancement-mode transistors and a translinear loop, eliminating the need for depletion-mode devices by automatically switching between receive and protection modes without control signals, and utilizing a pair of low-voltage NMOS switches to minimize parasitic capacitances and harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If depletion-mode devices are used in the switch, then the switch can protect low-voltage receivers from high-voltage signals, but the switch cannot be manufactured in all BCD process foundries
Solution Approach 1:
The patent changes the operating parameters of standard enhancement-mode transistors by utilizing the body effect (substrate biasing) to create depletion-like behavior. By applying appropriate bias voltages to the substrate, the transistors can operate in a depletion region without requiring special depletion-mode devices, thus maintaining protection capability while being manufacturable in standard BCD processes
Solution Approach 2:
The patent introduces a voltage detection circuit as an intermediary that senses high-voltage conditions and automatically controls the switching action. This intermediary mechanism enables the switch to protect the receiver without requiring high-voltage power supplies or depletion-mode devices, using only standard enhancement-mode transistors available in all BCD foundries
2Reliability
If high-voltage power supplies are used to control the switch, then the switch can block high-voltage signals, but the switch requires complex high-voltage power supply infrastructure
Solution Approach 1:
The patent implements a self-service mechanism where the voltage detection circuit automatically detects high-voltage conditions and controls the switching action without external control signals or high-voltage power supplies. The circuit uses the incoming signal itself to trigger the protection mode, eliminating the need for complex power supply infrastructure
Solution Approach 2:
The patent employs feedback through the voltage detection circuit that continuously monitors the voltage level and automatically adjusts the switch state accordingly. When high voltage is detected, the feedback mechanism triggers the depletion of the enhancement-mode transistors to block the signal, creating an automatic protection response without external intervention
3Ease of manufacture
If enhancement-mode transistors are used instead of depletion-mode devices, then the switch can be manufactured in all BCD processes, but the switch loses automatic high-voltage blocking capability
Solution Approach 1:
The patent changes the operational parameters of enhancement-mode transistors by utilizing substrate biasing and body effect to create regions of high impedance that can block high-voltage signals. By dynamically adjusting the substrate voltage, the enhancement-mode transistors can transition between conducting and blocking states, achieving protection capability equivalent to depletion-mode devices
Solution Approach 2:
The voltage detection circuit acts as an intermediary that enables enhancement-mode transistors to achieve high-voltage blocking capability. The detection circuit senses high-voltage conditions and applies appropriate substrate biasing to the enhancement-mode transistors, causing them to enter a depletion-like state and block the high-voltage signal without requiring the transistors to be inherently depletion-mode devices
Data Source
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AI summary
An analog transmit/receive switch and voltage detection circuit that do not require depletion mode devices are provided. The switch may be configured to operate in a receive mode and a protection mode. The voltage detection circuit may be coupled to the switch and may be configured to measure a potential difference between two terminals of the switch. The switch and the voltage detection circuit may not include any depletion mode devices.