Bandgap Reference Circuit Using Dynamic Element Matching
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Solution Overview
Problem
Conventional bandgap reference voltage circuits exhibit poor long-term stability and high chip-to-chip variation due to sensitivity to random component mismatches, temperature variations, and mechanical stresses, which complicates optimization and increases noise in the generated reference voltage.
Innovation Solution
A bandgap reference voltage circuit that employs dynamic element matching techniques, rotating currents and transistors to average differential bandgap charges, reducing sensitivity to component mismatches and temperature drift, and utilizing an array of transistors to stabilize the reference voltage, rather than relying on a single unit transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If scaled components are used to generate the necessary ΔVBE voltage, then the reference voltage can be generated, but the circuit becomes highly sensitive to random component mismatches and variations
Solution Approach 1:
The patent divides the single transistor into multiple identical transistors (e.g., 8 transistors) and divides the single current source into multiple identical current sources. By successively connecting different combinations of these segmented transistors and current sources, the circuit averages out random mismatches and variations, reducing chip-to-chip variation while maintaining reference voltage accuracy.
Solution Approach 2:
The patent employs dynamic switching to successively connect different transistors and current sources in multiple cycles. This dynamic element matching technique rotates through different combinations, allowing the circuit to average the effects of random component variations over time, thereby improving reliability without sacrificing measurement precision.
2Device complexity
If a single unit transistor is used, then the circuit is simple, but the reference voltage is highly sensitive to transistor parameter variations and mechanical stress
Solution Approach 1:
Instead of using a single unit transistor, the patent segments it into multiple identical transistors connected in parallel. This segmentation distributes the sensitivity across multiple devices, so that random variations and mechanical stress effects average out, significantly improving reliability while the modular structure keeps the circuit relatively simple.
Solution Approach 2:
The patent combines multiple identical transistors and current sources into a unified circuit structure that operates through systematic switching. By merging these components and using dynamic element matching, the circuit achieves robustness against transistor variations while maintaining manageable complexity through structured organization.
3Measurement precision
If amplifier gain is increased to amplify the small ΔVBE voltage, then the reference voltage accuracy improves, but the input offset voltage and drift are also amplified increasing noise
Solution Approach 1:
The patent segments the ΔVBE generation into multiple parallel transistor-current source combinations. By successively activating different segments and averaging their outputs, the circuit achieves the necessary voltage level without requiring high amplifier gain, thereby reducing the amplification of input offset voltage and drift.
Solution Approach 2:
The patent uses dynamic switching to rotate through different transistor-current source combinations over multiple cycles. This dynamic element matching allows the circuit to build up the ΔVBE voltage through accumulation and averaging rather than high-gain amplification, significantly reducing amplifier noise and drift effects.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves improved long-term stability and reduced temperature drift with lower noise and power consumption, making the reference voltage less dependent on individual transistor variations and more dependent on the total chip area, thus enhancing repeatability and reducing chip-to-chip variation.
Implementation Method 1
The generated reference voltage VREF is a sum of a VBE voltage (base-to-emitter voltage) which is a CTAT voltage that is inversely proportional to absolute temperature and a ΔVBE voltage which is a PTAT voltage (Proportional to Absolute Temperature) voltage that is directly proportional to absolute temperature.
Data Source
AI summary
A circuit for generating a band gap reference voltage (VREF) includes circuitry (I3×7) for supplying a first current to a first conductor (NODE1) and a second current to a second conductor (NODE2). The first conductor is successively coupled to a plurality of diodes (Q0×16), respectively, in response to a digital signal (CTL-VBE) to cause the first current to successively flow into selected diodes. The second conductor is coupled to collectors of the diodes which are not presently coupled to the first conductor. The diodes are successively coupled to the first conductor so that the first current causes the diodes, respectively, to produce relatively large VBE voltages on the first conductor and the second current causes sets of the diodes not coupled to the first conductor to produce relatively small VBE voltages on the second conductor. The relatively large and small VBE voltages provide differential band gap charges (QCA-QCB) which are averaged to provide a stable band gap reference voltage (VREF).