Bandgap Reference Start-Up Circuit for DC Offset Stability
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Solution Overview
Problem
The existing bandgap reference voltage generating circuits face instability in output voltage due to differences in electrical characteristics, such as DC offset, between input transistors, leading to reduced reliability and performance when switching from sleep to operation mode.
Innovation Solution
A start-up circuit design that includes specific configurations of PMOS and NMOS transistors to stabilize the bandgap output voltage, with a low pass filter to remove high-frequency noise, ensuring a stable and rapid start-up even with DC offset variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a bandgap reference voltage generating circuit is switched from sleep mode to operation mode, then the circuit should start up rapidly, but the output voltage becomes unstable due to DC offset differences between input transistors
Solution Approach 1:
The start-up circuit is activated in advance during sleep mode to pre-charge the output node and establish proper voltage levels. When transitioning to operation mode, the circuit is already primed and can rapidly stabilize without suffering from cold-start instability caused by transistor mismatches.
Solution Approach 2:
A dedicated start-up circuit acts as an intermediary between the power supply and the bandgap reference core. This intermediate circuit provides the necessary initial conditions and protects the main reference circuit from the adverse effects of mode transitions and transistor parameter variations.
2Device complexity
If the bandgap reference voltage generating circuit uses standard input transistors, then the circuit complexity is low, but the output voltage suffers from DC offset errors reducing reliability
Solution Approach 1:
The start-up circuit serves as an intermediary that compensates for the limitations of standard input transistors. Rather than requiring precision-matched transistors, the start-up circuit provides the necessary initial conditions to overcome DC offset errors, maintaining reliability without increasing device complexity.
Solution Approach 2:
The start-up circuit automatically detects and corrects its own activation needs based on the operational state of the bandgap reference. It self-activates during mode transitions and self-deactivates when the reference is stable, providing reliable operation without requiring additional control logic or increasing overall circuit complexity.
Data Source
AI summary
Disclosed is a start-up circuit that can stably and rapidly start up a bandgap reference voltage generating circuit when the bandgap reference voltage generating circuit is switched from a sleep mode to an operation mode, even if a difference in electrical characteristic, such as DC offset or the like, occurs due to, e.g, a physical difference between input transistors of an operational amplifier.