Ultrasound T/R Switch Circuit Without Steady-State Current
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Solution Overview
Problem
Existing ultrasound probe switch circuits require a large area and high power consumption due to the use of multiple high-voltage MOSFETs and capacitors, which is problematic for compact ultrasonic diagnosis apparatuses that need to minimize area and power usage while preventing steady-state current flow.
Innovation Solution
A switch circuit configuration using three high-voltage MOSFETs and a shunt circuit with a high-pass filter, eliminating the need for steady-state current and reducing area requirements by incorporating a PMOSFET for gate potential pull-up and a low-voltage NMOSFET for shunting, allowing efficient switching between transmission and reception states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple high-voltage MOSFETs and capacitors are used in the switch circuit, then the electrical protection and switching performance are improved, but the circuit area and power consumption increase
Solution Approach 1:
The patent extracts and removes unnecessary capacitors from the traditional switch circuit configuration. By eliminating the capacitor that was used for gate voltage retention, the circuit area is significantly reduced while the NMOSFETs are controlled by external timing signals to maintain proper switching states without requiring energy storage elements.
Solution Approach 2:
The patent makes the NMOSFETs serve multiple functions: they act as both the main switching elements for isolating the receiver circuit during transmission and as controllable impedance elements. The gate control mechanism is integrated with the existing timing control infrastructure of the ultrasonic device, eliminating the need for separate control circuits.
2Reliability
If multiple high-voltage MOSFETs and capacitors are used in the switch circuit, then the electrical protection and switching performance are improved, but the power consumption increases due to steady-state current
Solution Approach 1:
The patent removes the capacitor from the circuit that was responsible for retaining gate-source voltage. Without this capacitor, there is no continuous charging and discharging cycle, eliminating the steady-state current that caused power consumption. The NMOSFET gates are instead controlled by external timing signals that only draw power during state transitions.
Solution Approach 2:
The switch circuit operates in periodic cycles corresponding to the transmission-reception timing of the ultrasonic device. The NMOSFETs are switched on during reception periods and off during transmission periods, with no continuous power consumption in between state changes. This periodic operation eliminates the need for continuous energy supply to maintain switch states.
3Area of stationary object
If the circuit area is reduced by using fewer high-voltage devices, then the compactness is improved, but the ability to withstand high-voltage signals and protect the receiver circuit may be compromised
Solution Approach 1:
The patent applies high-voltage capability locally only where absolutely necessary - in the drain-source path of the NMOSFETs that directly handle the high-voltage transmit signals. The gate control infrastructure can remain at lower voltages since it only needs to control switching states, not handle the full high-voltage power. This localized high-voltage design minimizes the overall high-voltage device area requirement.
Solution Approach 2:
The patent introduces a high-pass filter as an intermediary element between the switch circuit and the receiver. This filter blocks high-voltage transmit signals from reaching the receiver while allowing low-voltage receive signals to pass through, providing an additional layer of protection that enables the use of fewer high-voltage protection devices in the main switch circuit.
4Use of energy by moving object
If steady-state current is eliminated to reduce power consumption, then the energy efficiency is improved, but the mechanism for maintaining switch-on and switch-off states becomes more complex
Solution Approach 1:
The patent merges the switch control mechanism with the existing timing control infrastructure of the ultrasonic device. The same timing signals that control the transmit-receive switching are also used to control the NMOSFET gate voltages. This integration eliminates the need for separate control circuits and reduces overall system complexity despite the elimination of energy-storage capacitors.
Solution Approach 2:
The NMOSFETs are designed to be self-controlling within each half-cycle of operation. During transmission, the inherent timing signal automatically keeps them off; during reception, the timing signal automatically turns them on. The devices serve themselves by responding to the natural rhythm of the ultrasonic operation without requiring external capacitors to maintain their state.
Data Source
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AI summary
A transmit receive switch circuit described in conjunction with embodiments of the present invention is a switch circuit that has a first MOSFET (MN1) and a second MOSFET (MN2), goes into a switch-off state at the time of transmission, and goes into a switch-on state at the time of reception, the first MOSFET (MN1) and the second MOSFET (MN2) being connected between an input terminal (SWIN) and an output terminal (SWOUT). The switch circuit includes a shunt circuit (SHNT) that is connected between a common gate (COMG) and a common source (COMS), the common gate being connected to the gates of the first and second MOSFETs, and the common source being connected to the sources of the first and second MOSFETs. When a signal having a negative voltage relative to a reference voltage is applied to the input terminal, a switch that temporarily turns on causes the shunt circuit to short-circuit the common gate and the common source.