Bootstrapped Sampling Switch for Beyond-Rail Input Handling
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Solution Overview
Problem
Existing bootstrapped switch circuits fail to function when input signals exceed the voltage supply rails, leading to issues such as forward-biased drain-bulk diode voltage and potential short circuits.
Innovation Solution
A bootstrapped switch circuit design that includes a p-type field effect transistor configured to decouple the bootstrap capacitor during a bootstrap phase, with its bulk coupled to the node of highest potential, enabling the signal switch to handle input signals beyond the supply rails and providing over-voltage protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional bootstrapped switch circuit is used, then power consumption is minimized and low voltage operation is achieved, but the circuit fails to function when input signals exceed the voltage supply rails
Solution Approach 1:
The patent introduces a bulk voltage coupling mechanism that acts as an intermediary between the input signal and the transistor operation. By coupling the bulk terminal to the input signal voltage, the circuit creates a moving reference potential that allows the transistor to operate reliably even when the input signal exceeds the supply rails. This intermediary coupling resolves the contradiction by enabling both extended voltage range and maintained circuit functionality.
2Adaptability or versatility
If the bulk of transistors is coupled to rail voltage VDD, then gate-drain voltage is limited to rail voltage, but the drain-bulk diode becomes forward-biased when input signals exceed supply rails
Solution Approach 1:
The patent dynamically changes the bulk voltage parameter from a fixed rail voltage to a signal-dependent voltage. By coupling the bulk terminal to the input signal, the bulk voltage tracks with the input signal voltage, maintaining an appropriate reverse bias on the drain-bulk diode even when input signals exceed the supply rails. This parameter change eliminates the harmful forward-biased condition while enabling extended voltage range operation.
3Adaptability or versatility
If additional transistors are added to extend switch operation from rail-to-rail, then device complexity increases, but the circuit can handle higher input voltages
Solution Approach 1:
The patent extracts the voltage limiting function from the transistor gate control and relocates it to the bulk terminal coupling. By taking out the voltage reference function from the fixed rail connection and making it signal-dependent through bulk coupling, the circuit achieves extended voltage handling capability without requiring additional transistors. This extraction principle resolves the contradiction by reducing device complexity while maintaining enhanced voltage capability.
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
Enables the switch to handle input signals higher in magnitude than the supply rails while preventing gate-drain and gate-source voltage overstress, ensuring reliable operation and minimizing power consumption.
Implementation Method 1
a bootstrap capacitor 2 having a capacitance Coffset
Implementation Method 2
one of the plurality of switches comprises a p-type field effect transistor configured to decouple, by deactivating a second p-type field effect transistor, the bootstrap capacitor during a bootstrap phase
Data Source
AI summary
A bootstrapped switch circuit may include a signal switch configured to, when enabled via a gate terminal of the signal switch during a sampling phase of the bootstrapped switch circuit, pass an input signal received at its input to its output. The bootstrapped switch circuit may also include a bootstrap circuit coupled to the signal switch comprising a bootstrap capacitor and a plurality of switches coupled to the bootstrap capacitor, wherein one of the plurality of switches comprises a p-type field effect transistor configured to decouple, by deactivating a second p-type field effect transistor, the bootstrap capacitor during a bootstrap phase of the bootstrapped switch circuit in which the signal switch is disabled, and further wherein the p-type field effect transistor is coupled to other of the plurality of switches and the bootstrap capacitor such that the signal switch is able to pass the input signal having a magnitude greater than voltage supply rails of the bootstrapped switch circuit from the input to the output.