Bootstrap Circuit for Boosted Switches in Wide Voltage Ranges
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Solution Overview
Problem
Switched capacitor circuits face challenges in operating effectively with input signals that exceed the supply voltage, particularly in industrial and automotive applications where common-mode voltage variations are significant, and there is a need for circuits that can maintain compliance over a wide range of voltages.
Innovation Solution
The implementation of a bootstrap circuit that boosts the clock phase generator and uses bootstrapped clock signals to ensure switching transistors remain compliant across a large common-mode voltage range, with protection devices to prevent gate over-voltage, allowing the circuit to operate in both high and low voltage domains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If supply voltage is reduced to prevent device breakdown and reduce power consumption, then device reliability and power efficiency are improved, but the compliance range of switching transistors is reduced
Solution Approach 1:
The bootstrap circuit performs preliminary charging of the capacitor during the first phase when the switch is off, storing energy before the switch needs to operate. This preliminary action enables the switch to achieve higher gate drive voltage during the active phase without requiring a higher overall supply voltage, thus maintaining reliability while improving compliance range.
Solution Approach 2:
The invention changes the voltage parameter dynamically by using a bootstrap capacitor to generate a time-varying gate drive voltage. During the off-phase, the capacitor charges to a higher voltage, and during the on-phase, this stored voltage is applied to the gate, effectively changing the voltage parameter to maintain adequate compliance range even with reduced supply voltage.
2Use of energy by moving object
If supply voltage is reduced to reduce power consumption, then power efficiency is improved, but the ability to handle input signals exceeding supply voltage is lost
Solution Approach 1:
The bootstrap capacitor is pre-charged to a voltage higher than the supply voltage during the phase when the switch is off. This preliminary charging action stores the necessary energy to drive the gate during the active phase, enabling the circuit to handle input signals that exceed the supply voltage while maintaining low power consumption during the off-phase.
Solution Approach 2:
The invention introduces dynamic voltage boosting through the bootstrap capacitor that operates in phases. The gate drive voltage dynamically switches between boosted voltage (when capacitor is charged) and lower voltage (when capacitor discharges), enabling the circuit to adapt to input signals with voltages exceeding the supply voltage while maintaining low average power consumption.
3Ease of operation
If boosted gate signal is used to extend compliance range, then switching transistor compliance is improved, but circuit complexity increases
Solution Approach 1:
The bootstrap capacitor is merged with the existing switch control circuitry, combining the voltage boosting function with the gate drive function. This integration allows the compliance range to be extended without adding completely separate control circuits, thereby limiting the increase in overall circuit complexity while still achieving improved compliance.
4Measurement precision
If bootstrap capacitor is decoupled from first input before second end voltage change, then charge injection errors are prevented, but switching speed is reduced
Solution Approach 1:
The decoupling of the capacitor from the first input is performed as a preliminary action before changing the voltage at the second end. This sequencing prevents charge injection errors by ensuring the capacitor is isolated from the signal path before voltage transitions occur, while the preliminary charging phase ensures the capacitor is ready to provide the necessary gate drive voltage when needed.
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
This solution enables switched capacitor circuits to operate over a wide range of common-mode input voltages, including high peaks and transients, maintaining accuracy and reducing device area requirements, while preventing charge injection errors and ensuring safe operation.
Implementation Method 1
a control node coupled to a first end of a capacitor of the bootstrap circuit. A first end of the capacitor is coupled to the first input of the bootstrap circuit and a second end of the capacitor is set to a first voltage
Data Source
AI summary
In accordance with an embodiment, a method includes activating a first semiconductor switch having a first switch node coupled to a first input of a bootstrap circuit, a second switch node, and a control node coupled to a first end of a capacitor of the bootstrap circuit. A first end of the capacitor is coupled to the first input of the bootstrap circuit and a second end of the capacitor is set to a first voltage. Next, the first end of the capacitor is decoupled from the first input of the bootstrap circuit, and the second end of the capacitor is set to a second voltage. The control node is boosted to a first activation voltage that turns on the first semiconductor switch.