Bandgap Reference Circuit Multi-Level Chopping for Flicker Noise
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Solution Overview
Problem
Current-mode bandgap reference circuits face significant challenges in reducing flicker noise, as existing techniques like dynamic element matching only partially cancel noise and do not effectively address the noise contributions from current mirror circuits.
Innovation Solution
The implementation of multi-level chopping actions in bandgap reference circuits, utilizing MOSFETs and bipolar junction transistors with chopping switches, is applied to current mirrors to significantly reduce flicker noise by periodically swapping components and changing their noise contributions, ensuring comprehensive noise cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If dynamic element matching is used to reduce flicker noise, then noise cancellation is partially achieved, but noise contributions from current mirror circuits are not effectively addressed
Solution Approach 1:
The patent divides the current mirror circuit into multiple segments (first current mirror with MOSFETs M1-M2, second current mirror with MOSFETs M3-M4) and applies chopping actions to each segment independently. This segmentation allows comprehensive noise cancellation across all branches of the current mirror circuits, addressing the limitation of dynamic element matching that only partially cancels noise.
Solution Approach 2:
The patent implements periodic chopping actions using switching circuits that periodically swap the connections of MOSFETs in the current mirrors. The chopping frequency is modulated to be higher than the flicker noise corner frequency, effectively moving the flicker noise to higher frequencies where it can be filtered out, thereby significantly reducing output reference voltage noise.
2Object-affected harmful factors
If multi-level chopping actions are applied to current mirrors, then flicker noise is significantly reduced, but device complexity increases
Solution Approach 1:
The patent designs the chopping switching circuits to perform multiple functions: they simultaneously chop both the first and second current mirrors, modulate the chopping frequency dynamically, and coordinate the switching of multiple MOSFETs. This multi-functionality reduces the need for separate noise cancellation circuits for each current mirror, thereby limiting the increase in device complexity while achieving comprehensive flicker noise reduction.
Solution Approach 2:
The patent introduces dynamic frequency modulation of the chopping signal, where the chopping frequency varies over time to optimize noise cancellation performance. This dynamic approach allows the circuit to adapt to different operating conditions and frequency ranges, achieving effective flicker noise reduction without requiring fixed-frequency chopping circuits for multiple stages.
Data Source
AI summary
The present disclosure provides bandgap reference circuits having multi-level chopping actions to current mirror circuits for the purpose of reducing the flicker noise of the output reference voltage. A bandgap reference circuit includes a first current mirror including a pair of a first MOSFET and a second MOSFET, a second current mirror comprising a third MOSFET electrically connected to the first current mirror, and configured to provide a reference voltage at a drain, a first bipolar junction transistor electrically connected to the first current mirror, a second bipolar junction transistor connected to the first current mirror via a first resistor, a third bipolar junction transistor connected to the third MOSFET via a second resistor. The bandgap reference circuit further includes an operational amplifier to control the MOSFETs and a plurality of chopping switches configured to perform chopping actions on outputs of the first current mirror and the second current mirror.