Bootstrapped Switch Gate Control for Linear Resistance Near Supply Rails
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Solution Overview
Problem
Existing switch configurations, such as FET and MEM switches, experience increased resistance and harmonic distortions when input signals approach power supply rails, particularly in high voltage applications like ultrasound, due to reduced gate drive and voltage leakage through resistors, leading to non-linearity and potential circuit damage from high voltage coupling.
Innovation Solution
A bootstrapped switch circuit incorporating a high impedance element, such as diodes, and a gate turn-off mechanism to maintain consistent gate drive and limit voltage, ensuring linear resistance and protecting circuitry from high voltage signals by using diodes and transistors to manage impedance and voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resistor is connected in series with the gate of the switch to maintain gate drive when input swings high, then the gate drive is maintained, but during slow transients the gate will not hold the bootstrapped voltage since charge from the gate capacitance discharges through the resistor
Solution Approach 1:
A diode is introduced as an intermediary element between the gate and the bootstrapping network. The diode acts as a one-way conductor that allows charging of the gate capacitance during fast transitions but blocks discharge during slow transients, thereby maintaining the bootstrapped voltage for extended periods while still providing the necessary gate drive enhancement.
Solution Approach 2:
The circuit dynamically adjusts its impedance characteristics based on the timescale of the input signal. During fast transitions, the circuit provides low impedance paths for rapid charging. During slow transients, the diode becomes effectively high impedance, preventing discharge and maintaining voltage. This dynamic behavior resolves the contradiction between maintaining gate drive and holding voltage over different timescales.
2Productivity
If high voltage coupling is allowed to reach the gate, then the full input signal range is transmitted, but high voltage coupling back onto the gate could damage circuitry connected to that node
Solution Approach 1:
The diode structure converts the potentially harmful high voltage coupling into a beneficial effect. By orienting the diode to conduct during high voltage conditions, the circuit allows the high voltage signal to pass through while simultaneously using the diode's forward voltage drop to protect the gate. The harmful high voltage is thus transformed into a protected state where the gate experiences only safe voltage levels.
Solution Approach 2:
The diode serves as a protective intermediary between the high voltage input signal and the gate circuitry. It allows the high voltage signal to be transmitted to the switch while blocking excessive voltage from reaching the gate, thereby enabling full signal range transmission without exposing the gate to damaging voltage levels.
3Power
If the switch is used in high voltage applications like ultrasound with input signals in the 100V to 200V range, then the switch can handle high power applications, but it is difficult to maintain linearity over this range
Solution Approach 1:
The bootstrapped configuration, enhanced by the diode, works to maintain equipotential conditions across the switch terminals by dynamically adjusting the gate voltage to match the input signal voltage. This reduces the voltage differential that causes non-linear effects, thereby maintaining resistance linearity even across the wide 100V to 200V input range required for high power ultrasound applications.
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 highly linearized resistance and protects circuitry from high voltage signals, maintaining linearity across a wide input range (100V-200V) and preventing damage, while ensuring consistent gate drive and harmonic distortion reduction.
Implementation Method 1
when the input swings high, the gate also swings high from capacitive coupling
Implementation Method 2
an element or other means to turn off the gate of the switch... using diodes and transistors to manage impedance and voltage
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.