Bandgap Reference Start-Up Circuit for PVT-Robust Bias Voltage
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Solution Overview
Problem
Conventional start-up circuits for bandgap voltage reference circuits are affected by process, voltage, and temperature (PVT) variations, leading to erroneous states in low-temperature low-voltage conditions and improper shutdown in high-voltage conditions, which impact the bandgap voltage output.
Innovation Solution
A start-up circuit that includes series-connected P-type transistors and a P-type second transistor, with a boost current flowing through the second transistor to ensure successful startup of the bandgap voltage reference circuit across varying conditions, using a bias voltage to control the transistors and prevent excessive current in high-voltage scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional start-up circuits are used in low-temperature low-voltage conditions, then the circuit structure is simple, but the bandgap voltage remains in an erroneous state due to insufficient start-up current
Solution Approach 1:
The start-up circuit is segmented into multiple parallel paths: a first start-up path with first-type transistors for normal conditions, and a second start-up path with second-type transistors for low-temperature low-voltage conditions. This segmentation allows each path to be optimized for specific conditions, improving reliability without significantly increasing overall complexity.
Solution Approach 2:
The second-type transistors are pre-configured in the second start-up path to provide additional start-up current when needed. By having this backup path ready in advance, the circuit can immediately respond to low-temperature low-voltage conditions without requiring complex real-time detection and switching logic.
2Reliability
If conventional start-up circuits are used in high-voltage conditions, then the circuit structure is simple, but the start-up circuit cannot properly shut down and affects the bandgap voltage output
Solution Approach 1:
The start-up circuit incorporates feedback mechanisms where the bandgap voltage output is monitored and fed back to control the start-up transistors. When the bandgap voltage reaches its correct value, the feedback signal turns off the start-up transistors, ensuring proper shutdown. This feedback-based control improves shutdown reliability while maintaining relatively simple circuit structure through efficient use of existing voltage signals.
3Reliability
If the start-up circuit provides sufficient start-up current for all conditions, then start-up reliability is improved, but excessive current flows in high-voltage conditions affecting output accuracy
Solution Approach 1:
The start-up circuit uses dynamic transistor characteristics where second-type transistors with negative threshold voltage provide high start-up current when needed (low-temperature low-voltage conditions) but naturally limit current in high-voltage conditions. This dynamic behavior allows the circuit to adapt its current provision based on operating conditions, improving start-up reliability while preventing excessive current that would affect output accuracy.
Data Source
AI summary
A start-up circuit includes series-connected first-type first transistors through which a start-up current flows in a start-up period, being connected between a positive power voltage and an inner node; and a first-type second transistor through which a boost current flows in the start-up period, being connected between the positive power voltage and the inner node, and with a gate connected to an output node that provides a bias voltage.