Bootstrap Switch for Low-Voltage Signal Transfer
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Solution Overview
Problem
Existing electronic switches, particularly in low-voltage applications, face challenges with incomplete signal transfer due to insufficient overdrive voltage in N-channel and P-channel MOSFET transistors, leading to issues with area occupation, power consumption, heat dissipation, and performance in microelectronic circuits operating at low voltages.
Innovation Solution
An electronic switch design where the control terminal is driven by a signal that combines the input signal and the control signal, ensuring sufficient overdrive voltage for complete signal transfer without requiring high-voltage transistors, using a driving circuit that generates a driving signal equal to the sum of the input signal and the operative value of the control signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transmission gate configuration with nMOS and pMOS transistors is used, then complete signal transfer is achieved, but area occupation increases
Solution Approach 1:
The patent combines the control signal and input signal into a single driving signal that controls one transistor, merging the functions of two separate transistors into a single device. This reduces the area occupation while maintaining complete signal transfer capability through the bootstrap capacitor mechanism.
Solution Approach 2:
The patent introduces a bootstrap capacitor as an intermediary element that stores voltage and provides the necessary overdrive voltage to the transistor gate. This capacitor acts as a mediator that enables complete signal transfer without requiring a second transistor, thus reducing area occupation.
2Reliability
If high-voltage transistors are used to transfer full-swing signals, then signal transfer is improved, but parasitic capacitances increase limiting switching frequency
Solution Approach 1:
The patent changes the voltage parameters dynamically by using a bootstrap capacitor to provide time-varying overdrive voltage. The capacitor charges to the supply voltage and then provides an elevated gate voltage during the on-state, enabling full-swing signal transfer with low-voltage transistors that have lower parasitic capacitances and higher switching frequencies.
3Reliability
If overvoltage is applied to control terminal to ensure proper transfer, then signal transfer is improved, but power consumption increases
Solution Approach 1:
The patent employs periodic charging and discharging of the bootstrap capacitor to provide overvoltage only when needed during the transistor on-state. The capacitor is charged during the off-state and discharged during the on-state to provide the necessary gate overdrive, reducing average power consumption compared to continuous overvoltage application.
Data Source
AI summary
An electronic switch may include transfer transistor having a first conduction terminal for receiving an input signal, a second conduction terminal, and a control terminal. The transfer transistor may enable/disable a transfer of the input signal from the first conduction terminal to the second conduction terminal according to a control signal. The control signal may take a first value and a second value different from the first value, a difference between the first value and the second value defining, in absolute value, an operative value of the control signal. The electronic switch may further comprise a driving circuit for receiving the input signal and the control signal, and for providing a driving signal equal to the sum between the input signal and the operative value of the control signal to the control terminal of the transfer transistor.