Dual-Input Buffer Circuit for Floating Reference Startup Switching
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Solution Overview
Problem
Existing circuit designs for high-voltage applications face challenges in providing a stable floating reference signal during startup, as bandgap circuits used for generating such signals are slow to turn on, leading to potential transistor overstress.
Innovation Solution
A buffer circuit utilizing an operational amplifier with two non-inverting inputs and an inverting input, configured as a voltage follower, is used to provide a floating reference signal. This circuit buffers either the first or second input signal, depending on which is lower, allowing for early startup of transistors in high-voltage domains by using a quick-starting coarse reference signal until the bandgap circuit stabilizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a bandgap circuit is used to generate a floating reference signal, then the reference signal stability and precision are improved, but the startup time increases significantly
Solution Approach 1:
A startup circuit is added that preemptively generates a coarse reference signal before the bandgap circuit is fully operational. This preliminary action allows the system to function during startup without waiting for the slow bandgap circuit to settle, effectively solving the startup time issue while maintaining the precision benefits of the bandgap circuit during normal operation.
Solution Approach 2:
An operational amplifier is introduced as an intermediary component that can switch between two reference signals: a fast-starting coarse reference from the startup circuit and a precise reference from the bandgap circuit. This intermediary allows seamless transition during startup while maintaining precision during steady-state operation.
2Measurement precision
If a bandgap circuit is used to provide reference signal during startup, then reference signal accuracy is improved, but transistor overstress occurs due to delayed signal availability
Solution Approach 1:
The startup circuit generates a preliminary coarse reference signal immediately upon power-up, before the bandgap circuit becomes operational. This preliminary signal is sufficient to control transistors during startup, preventing overstress conditions that would occur if transistors had to wait for the slow bandgap circuit to settle.
Solution Approach 2:
The system prepares a backup reference signal path through the startup circuit that can immediately support transistor operation during startup. This cushioning mechanism ensures that transistors never experience a reference signal gap that would cause overstress, while the precise bandgap circuit takes over once stable.
3Use of energy by moving object
If a low-dropout circuit is added to reduce bandgap power consumption, then energy efficiency is improved, but a chicken-and-egg problem occurs during startup
Solution Approach 1:
The startup circuit is designed to operate independently and provide reference signal before the LDO-regulated bandgap circuit becomes operational. This preliminary action resolves the chicken-and-egg problem by ensuring that reference signal is available during startup without requiring the LDO to be fully operational, thus maintaining energy efficiency while simplifying startup sequences.
Data Source
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AI summary
In one embodiment a buffer circuit for providing a floating reference signal comprises an operational amplifier comprising a first input, a second input, a third input and an output. The first input represents a non-inverting input and is configured to receive a first input signal. The second input represents another non-inverting input and is configured to receive a second input signal. The third input represents an inverting input. The output forms an output of the buffer circuit. The operational amplifier is configured as a voltage follower. The buffer circuit is configured to provide either the first or the second input signal at its output, such that a lower one of the first and the second input signal is provided as the floating reference signal.