Bootstrap Circuit Timing Bias for Low-Amplitude Input Operation
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Solution Overview
Problem
Conventional bootstrap circuits require input signals with an amplitude at least 1.5 to 2 times larger than the threshold voltage of transistors to produce a bootstrap effect, leading to a narrow operating margin and increased power consumption, which is problematic especially when manufacturing variations of transistor threshold voltages are large.
Innovation Solution
A bootstrap circuit design that includes a first transistor connected to a power supply and a second transistor with the same conductivity type, where a second input signal, obtained by inverting the first input signal, is delayed and DC-biased to be applied to the gate node of the second transistor, allowing the circuit to operate with input signals approximately equal to or slightly above the threshold voltage, thereby reducing power consumption and increasing the operating margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bootstrap circuits are used to increase signal amplitude, then the bootstrap effect can be produced, but the input signal amplitude must be 1.5 to 2 times larger than the transistor threshold voltage, resulting in a narrow operating margin
Solution Approach 1:
A delay circuit is introduced as an intermediary component between the input signal and the bootstrap circuit. This delay circuit delays the inverted input signal, allowing the bootstrap transistor to remain conductive longer and enabling the gate potential to exceed the power supply potential. The delay circuit mediates the timing relationship between signals, resolving the contradiction by allowing the bootstrap effect to occur with smaller input signal amplitudes while maintaining a wide operating margin.
2Power
If conventional bootstrap circuits are used, then signal amplitude can be increased, but power consumption increases due to the requirement for larger input signal amplitudes
Solution Approach 1:
The delay circuit performs preliminary action by delaying the inverted input signal before it reaches the bootstrap transistor gate. This preliminary delay allows the bootstrap transistor to conduct for a longer duration, enabling the gate potential to rise above the power supply potential before the transistor turns off. This preliminary timing adjustment reduces the required input signal amplitude and consequently reduces power consumption while maintaining the desired signal amplitude increase.
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 solution enables the bootstrap circuit to operate effectively with input signals of smaller amplitude, providing a wide operating margin and reducing power consumption, while maintaining reliability even with variations in transistor characteristics.
Implementation Method 1
a coupling capacitor connecting a source electrode and the gate electrode of the first transistor
Implementation Method 2
a delay circuit delaying the inverted signal
Implementation Method 3
a DC bias circuit adding a direct current bias to the delayed signal
Data Source
AI summary
A bootstrap circuit comprises: a first transistor connecting a first power supply with an output node; and a second transistor applying a first input signal to a gate node of the first transistor and having a conductivity type identical to that of the first transistor. A second input signal obtained by inverting a level of the first input signal, delaying the inverted signal, and adding a direct current bias to the delayed signal is inputted to a gate node of the second transistor.