Depletion-Mode Transmit Receive Switch for Ultrasound Receiver Protection
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Solution Overview
Problem
Conventional transmit/receive switches in ultrasound imaging systems face challenges with high power consumption, complex component count, and layout issues due to the need for multiple diodes and power lines, which are exacerbated by the requirement for fast response times to protect low noise receivers from high voltage transmit pulses while allowing small analog signals to pass through during receive mode.
Innovation Solution
A two-terminal high voltage transmit and receive protection switch utilizing depletion-mode devices with a voltage detection circuit that automatically switches between constant resistance and constant current source characteristics, minimizing noise and power consumption, and featuring depletion-mode transistors and a switch block to manage high voltage signals without external biasing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high voltage diodes and biasing circuits are used to protect the receiver, then the receiver is protected from high voltage transmit pulses, but the power consumption increases and the component count increases
Solution Approach 1:
The patent extracts and eliminates the biasing power supplies and associated circuitry from the T/R switch design. By using back-to-back diodes without external biasing, the invention removes the continuous power consumption source while maintaining the protection function against high voltage transmit pulses.
Solution Approach 2:
The diodes in the invention are configured to be self-biasing through their own inherent characteristics and the circuit topology. The back-to-back diode arrangement automatically provides the necessary biasing through the high voltage transmit pulses themselves, eliminating the need for external biasing circuits and continuous power supply.
2Reliability
If multiple diodes and biasing circuits are used in the T/R switch, then the receiver protection is improved, but the component count and device complexity increase
Solution Approach 1:
The patent merges the protection function and the switching function into a single integrated circuit block. The back-to-back diode configuration combines multiple functions (protection, switching, and signal path management) into one compact arrangement, reducing the overall component count while maintaining receiver protection.
Solution Approach 2:
The T/R switch circuit in the invention performs multiple functions simultaneously: it protects the receiver from high voltage, switches between transmit and receive modes, and provides signal path routing. This multi-functionality is achieved through the back-to-back diode configuration, eliminating the need for separate dedicated components for each function.
3Ease of operation
If multiple power lines are routed to all channels for biasing, then the T/R switch operation is maintained, but the layout complexity and routing difficulty increase
Solution Approach 1:
The invention extracts and removes the external biasing power lines from the multi-channel T/R switch architecture. By using self-biasing diodes, the patent eliminates the need for routing multiple power lines to each channel, significantly simplifying the PCB layout and reducing routing complexity while maintaining full operational capability.
4Reliability
If the T/R switch response time is made very fast to protect the receiver, then the receiver protection is improved, but the circuit complexity and component requirements increase
Solution Approach 1:
The patent uses simple diode components that inherently provide fast response times without requiring complex active circuitry. The diodes' natural switching characteristics provide the necessary fast protection response, eliminating the need for complex transistor-based switches or additional control circuitry that would increase device complexity.
Data Source
AI summary
A two terminal transmit receive device passes small analog signals with a constant low resistance value to the input of a low noise, low voltage receiver amplifier and can protect the input against the high voltage transmit signals in ultrasound applications without the aid of any power supplies. The device uses depletion-mode transistors that are normally on to pass small analog signal and a voltage detection circuit that quickly turns off the depletion-mode transistors when the presence of high voltage is detected.