Bootstrapped Switch Circuit With Constant Gate-Source Voltage
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Solution Overview
Problem
Existing transistor switch embodiments face challenges in delivering optimal control signals to turn transistors on and off effectively, leading to unpredictable on-resistance and performance degradation due to varying gate-to-source voltages.
Innovation Solution
A bootstrapped switch circuit that includes a voltage-controlled voltage source to provide constant gate-to-source voltages to transistors, independent of input signals, using a differential pair and current sources to manage these voltages based on control signals, ensuring predictable on and off states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If static control signal voltages are used to turn PMOS transistors on and off, then the switch can be controlled, but the gate-to-source voltage varies during operation causing unpredictable on-resistance and performance degradation
Solution Approach 1:
The patent applies bootstrapping circuitry that dynamically adjusts the gate voltage of PMOS transistors during operation. The circuit uses a bootstrapped capacitor to maintain a constant gate-to-source voltage by dynamically charging and discharging the capacitor in sync with the switching operation, ensuring predictable on-resistance while maintaining ease of control through a simple control signal.
Solution Approach 2:
The patent changes the voltage parameter at the gate terminal dynamically during switching operation. By using bootstrapping circuitry that adjusts the gate voltage in real-time based on the source voltage changes, the gate-to-source voltage remains constant, ensuring predictable transistor behavior and performance while maintaining simple control signal delivery.
2Reliability
If the back gate is connected to the source to prevent body diode conduction, then transistor operation is improved, but the body diode still appears between drain and source causing performance issues
Solution Approach 1:
The patent applies preliminary anti-action by using bootstrapped switches that proactively prevent body diode conduction before it can occur. The bootstrapping circuitry maintains the gate voltage above the source voltage throughout the switching cycle, creating a reverse bias condition that prevents the body diode from conducting, thus eliminating the harmful effect before it can impact performance.
3Reliability
If PMOS transistors are arranged in series to prevent body diode conduction, then switching control is achieved, but the on-resistance varies with gate-to-source voltage changes
Solution Approach 1:
The patent applies dynamics by implementing bootstrapped switches that dynamically adjust the gate voltage to maintain a constant gate-to-source voltage during operation. This dynamic voltage adjustment ensures consistent on-resistance values for the series-connected PMOS transistors, achieving both reliable switching control and precise on-resistance consistency.
Solution Approach 2:
The patent changes the gate voltage parameter dynamically during switching operation to compensate for source voltage variations. By using bootstrapping circuitry that adjusts the gate voltage in real-time, the gate-to-source voltage remains constant, ensuring consistent on-resistance and predictable performance of the series-connected transistors.
Data Source
AI summary
A bootstrapped switch circuit can include at least one transistor, to receive an input signal and allow the input signal to pass through as an output signal based on a control signal, and a voltage-controlled voltage source, to provide first and second voltages between a gate and a source of the at least one transistor in response to the control signal. The voltage-controlled voltage source can include a differential pair and a current source. A gate of one of the differential pair can receive the control signal and a gate of the other of the differential pair can receive a logical inverse of the control signal. The current source can provide a current to connected sources of the differential pair. The first voltage can turn on the at least one transistor and be produced in response to a first logic state of the control signal resulting in the current of the current source flowing entirely through a first one of the differential pair. The second voltage can turn off the at least one transistor and be produced in response to a second logic state of the control signal resulting in the current of the current source flowing entirely through a second one of the differential pair.