Bootstrap Sampling Switch Circuit for Stable Gate Voltage
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Solution Overview
Problem
Designing a satisfactory bootstrap circuit for an analog-to-digital converter in wireless communications circuitry is challenging due to difficulties in maintaining a constant gate-to-source voltage, which can degrade the DC voltage level and signal gain at the input sampling switch.
Innovation Solution
A bootstrap circuit is introduced, comprising a bootstrap capacitor, transistors, and a resistive element, configured to maintain a constant voltage across the input and control terminals of the sampling switch, thereby optimizing the performance of the sampling switch and the overall analog-to-digital converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a bootstrap circuit is designed to maintain constant gate-to-source voltage across the input sampling switch, then the voltage stability is improved, but the circuit complexity increases
Solution Approach 1:
The bootstrap circuit is segmented into distinct functional blocks: a bootstrap capacitor for voltage storage, a first transistor for voltage boosting, a second transistor for discharge control, and a resistive element for impedance adjustment. Each component performs a specific function, making the overall circuit more manageable and easier to design while maintaining voltage stability.
Solution Approach 2:
The bootstrap capacitor is pre-charged to a specific voltage level before the sampling phase begins. This preliminary charging action ensures that when the sampling switch operates, the gate-to-source voltage is already established at the desired constant level, eliminating the need for complex real-time regulation mechanisms.
2Reliability
If the bootstrap circuit uses a resistive element to boost input resistance, then the input resistance increases, but the DC voltage level may be degraded
Solution Approach 1:
The resistive element's resistance value is carefully selected and adjusted to achieve the desired input resistance boost while maintaining acceptable DC voltage levels. By optimizing this parameter, the circuit achieves high input resistance without excessive voltage degradation, resolving the trade-off between these two parameters.
Solution Approach 2:
The first transistor acts as an intermediary between the bootstrap capacitor and the input terminal, providing voltage boosting that compensates for the voltage drop introduced by the resistive element. This intermediary action allows the resistive element to increase input resistance while the transistor maintains the DC voltage level.
3Reliability
If the bootstrap circuit alternates between phases with the resistive component turned on and off, then the input resistance is boosted during operation, but the circuit control complexity increases
Solution Approach 1:
The resistive component is periodically switched on and off in synchronization with the sampling and holding phases of the analog-to-digital converter. During the sampling phase, the resistive component is turned on to boost input resistance; during the holding phase, it is turned off. This periodic action aligned with the natural operating cycles of the ADC simplifies control logic while achieving the desired resistance boosting.
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 proposed bootstrap circuit effectively maintains a higher DC voltage level and enhances the input resistance, preventing degradation of signal swing across the gate and source terminals of the sampling switch, thus improving the overall performance of the analog-to-digital converter.
Implementation Method 1
The bootstrap circuitry may include a bootstrap capacitor
Implementation Method 2
a resistive element coupled between the first transistor and the bottom plate terminal of the bootstrap capacitor. The resistive element may be a resistor or a transistor that is configured to boost the input resistance of the bootstrap circuit
Data Source
AI summary
An electronic device may include wireless circuitry having analog-to-digital converter (ADC) circuitry. The ADC circuitry may include a sampling switch coupled to a bootstrap circuit. The bootstrap circuit may include a bootstrap capacitor, a first transistor coupled between an input of the sampling switch and a bottom plate terminal of the bootstrap capacitor, a second transistor coupled between the bottom plate terminal of the bootstrap capacitor and ground, and a resistor or transistor that is disposed between the first transistor and the bottom plate terminal of the bootstrap capacitor and that is configured to boost the input impedance of the bootstrap circuit.