Multi-PTAT Bandgap Circuit for Flicker Noise Reduction
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Solution Overview
Problem
Bandgap circuits with single PTAT cores suffer from noise amplification due to flicker noise, which is difficult to filter, especially in MOS circuits, leading to temperature-drift-induced voltage changes that are not effectively mitigated.
Innovation Solution
A low-noise multi-PTAT-core bandgap circuit is implemented, where multiple uncorrelated PTAT cores deliver currents to a temperature-complementary load, reducing noise amplification by delivering unscaled currents that sum to match the desired amplitude, and calibration circuitry equalizes current amplitudes and temperature coefficients to produce a temperature-insensitive output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single PTAT core is used in a bandgap circuit, then the circuit structure is simple, but flicker noise is amplified and temperature stability deteriorates
Solution Approach 1:
The single PTAT core is divided into multiple PTAT cores (first PTAT core, second PTAT core, etc.), each generating uncorrelated flicker noise. By segmenting the core, the patent reduces the overall flicker noise through statistical averaging while maintaining temperature proportionality, thus improving temperature stability without significantly increasing circuit complexity
Solution Approach 2:
Each PTAT core is designed with specific local characteristics (different transistor sizes, bias conditions) to generate uncorrelated noise signals. The local quality variation among cores ensures that their flicker noise components are statistically independent, allowing noise reduction through summation while preserving the desired PTAT characteristic
2Reliability
If multiple PTAT cores are used to reduce flicker noise, then temperature stability improves, but device complexity increases
Solution Approach 1:
Multiple PTAT cores are merged into a unified bandgap circuit architecture where their output currents are summed at a common node. This merging approach allows the benefits of noise reduction from multiple cores to be achieved while sharing common circuit elements (current mirrors, bias circuits, calibration logic), thereby limiting the increase in overall device complexity
Solution Approach 2:
The circuit includes automatic calibration mechanisms that self-adjust the output currents of multiple PTAT cores to ensure they sum to the desired amplitude. The calibration circuitry automatically compensates for manufacturing variations and mismatches among cores, reducing the need for manual trimming and simplifying the overall device complexity
3Object-generated harmful factors
If current amplitudes from multiple PTAT cores are summed directly, then noise reduction is achieved, but temperature coefficient matching becomes difficult
Solution Approach 1:
The circuit incorporates feedback mechanisms through calibration circuitry that monitors the summed output current and adjusts individual core contributions. This feedback ensures that the positive and negative temperature coefficients are properly balanced, compensating for manufacturing variations and ensuring accurate temperature compensation despite the complexity of summing multiple core outputs
Data Source
AI summary
Multiple temperature-proportional cores are implemented within a bandgap circuit to deliver respective, uncorrelated temperature-proportional currents to a temperature-complementary load, reducing flicker noise in the resulting bandgap reference voltage.