Bootstrapped Switch Circuit for Linear Resistance at High Voltage
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Solution Overview
Problem
Existing switch configurations, such as those using Field Effect Transistor (FET) and Micro-Electro-Mechanical (MEM) switches, face challenges in maintaining linearity when input signals approach power supply rails, leading to increased resistance and harmonic distortions, especially in high voltage applications like ultrasound, where signals can range from 100V to 200V, and risk damaging circuitry due to voltage coupling.
Innovation Solution
A bootstrapped switch circuit incorporating a high impedance element, like diodes, connected between the switch control input and gate, along with a gate turn-off mechanism, ensures highly linearized resistance by maintaining gate voltage during transients and limiting voltage swing to prevent damage, using diodes in series or parallel configurations to manage impedance and breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a resistor is added in series with the gate to maintain gate drive during slow transients, then linearity is improved, but the gate cannot hold bootstrapped voltage and resistance changes during long period transients
Solution Approach 1:
A capacitor is introduced as an intermediary energy storage element between the gate and the bootstrapping network. This capacitor holds the bootstrapped voltage during slow transients, preventing voltage collapse while maintaining gate drive. The capacitor acts as a buffer that decouples the gate from direct resistive discharge paths, resolving the contradiction between voltage holding and linearity.
Solution Approach 2:
The impedance of the gate path is dynamically changed by switching between resistive and capacitive coupling. During fast transients, resistive coupling provides damping; during slow transients, capacitive coupling provides voltage holding. This parameter change allows the system to maintain both linearity and voltage holding capability under different transient conditions.
2Object-affected harmful factors
If high voltage coupling is allowed to protect against damage, then circuit safety is improved, but linearity deteriorates due to voltage swing limitations
Solution Approach 1:
A series capacitor is introduced as an intermediary between the high voltage input and the gate. This capacitor blocks DC voltage coupling while allowing AC signal transmission, protecting the gate from high voltage damage. The capacitor's impedance decreases with frequency, allowing full signal swing at operating frequencies while blocking damaging DC components.
Solution Approach 2:
The coupling impedance is changed from direct resistive coupling to capacitive coupling. This parameter change allows the system to block DC high voltage (protecting the circuit) while maintaining AC signal coupling (preserving linearity). The frequency-dependent impedance of the capacitor provides different behavior for different signal components.
3Device complexity
If gate drive is reduced when input signals are near power supply rails, then circuit simplicity is maintained, but resistance increases and linearity deteriorates
Solution Approach 1:
A capacitor is introduced as an intermediary to couple the gate to the input signal. This capacitor maintains gate drive voltage even when the input signal approaches the power supply rails, preventing the gate drive reduction that would otherwise occur. The capacitor blocks DC while allowing AC coupling, maintaining linearity without requiring complex active compensation circuits.
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 provides stable and linear resistance across a wide input range, preventing harmonic distortions and protecting circuitry from high voltage coupling, ensuring consistent performance in high voltage applications like ultrasound transmitters.
Implementation Method 1
a high impedance element such as one or more diodes connected from the transistor to the control input signal
Implementation Method 2
the voltage will quickly decrease to the original value as charge from the gate capacitance discharges
Data Source
AI summary
Systems and methods are disclosed for operating a highly linearized resistance for a switch through use of a bootstrapped features. In one exemplary implementation, there is provided a method and system that implements a method for operating a circuit configured to provide a highly linearized resistance including receiving a signal via a bootstrapped switch, coupling the received signal to a gate if the received signal is high, receiving a signal via a switch control input coupled to a high impedance element. Moreover, the method includes coupling the high impedance element to the gate and turning off the switch via a gate turn off when the gate turn off pulls the gate low.