Bandgap Reference Circuit Drain-Source Voltage Matching
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Solution Overview
Problem
Conventional bandgap reference circuits suffer from poor power supply rejection ratio (PSRR) and temperature coefficient (TC) due to mismatched drain-source voltages of MOS transistors, which are sensitive to power source and temperature variations.
Innovation Solution
The improved bandgap reference circuit employs an additional operation amplifier to ensure identical drain-source voltages across all MOS transistors, utilizing a feedback circuit to maintain node voltage equality and reduce channel-length-modulation effects, thereby generating temperature-independent currents and improving PSRR and TC characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap reference circuit is used with current mirror and operation amplifier, then reference voltage can be generated, but drain-source voltage mismatch of MOS transistors causes poor power supply rejection ratio and unacceptable temperature coefficient
Solution Approach 1:
The patent introduces a feedback circuit that uses an additional operation amplifier to detect and correct drain-source voltage mismatches in real-time. The feedback mechanism monitors the voltages across MOS transistors in parallel branches and adjusts control signals to equalize them, thereby eliminating the root cause of poor PSRR and TC while maintaining reference voltage stability.
Solution Approach 2:
The patent implements equipotentiality by ensuring that all MOS transistors operating in parallel have identical drain-source voltages through the feedback control mechanism. This is achieved by using the additional operation amplifier to sense voltage differences and generate corrective signals that force the voltages to be equal, thus eliminating channel-length-modulation effects and improving temperature independence.
2Measurement precision
If channel-length-modulation effects are considered in MOS transistors, then more accurate circuit analysis is achieved, but drain-source voltage mismatch increases sensitivity to power source and temperature variations
Solution Approach 1:
The feedback circuit continuously monitors drain-source voltages and dynamically adjusts control signals to maintain equal voltages across all MOS transistors. This real-time correction eliminates the harmful effects of channel-length-modulation by ensuring that voltage mismatches do not occur, thereby reducing sensitivity to power source and temperature variations while maintaining accurate circuit operation.
Solution Approach 2:
The patent applies preliminary anti-action by proactively preventing drain-source voltage mismatches before they can affect circuit performance. The additional operation amplifier is configured to detect potential voltage differences and generate corrective signals in advance, counteracting the channel-length-modulation effects before they cause sensitivity issues with power source and temperature.
Data Source
AI summary
A bandgap reference circuit includes a reference current generator for respectively generating a first reference current on a first current path and a second reference current on a second current path, a current mirror for generating a third reference current on a third current path based on the first and second reference currents, an operation amplifier for rendering the first reference current substantially identical to the second reference current and a feedback circuit for rendering a node voltage on the first current path substantially identical to another node voltage on the third current path, so as to eliminate possible errors caused by a channel length modulation effect in the current mirror.