Low Noise Voltage Reference Circuit Using Shunted Bipolar Transistors
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Solution Overview
Problem
Bandgap voltage reference circuits face challenges in minimizing both low band (1/f) noise and high band noise simultaneously due to opposing operational requirements, with existing solutions either increasing or decreasing collector and base currents, which are not sufficient to compensate for noise effectively.
Innovation Solution
A voltage reference circuit is designed with a pre-amplifier stage using shunted bipolar transistors with larger emitter areas to reduce base and collector currents, and a capacitor connected to the high impedance common collector node to filter high band noise, allowing for independent minimization of both noise components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If bipolar transistors with very high gain are used to reduce low band noise, then low band noise is reduced, but device complexity and manufacturing difficulty increase
Solution Approach 1:
Instead of changing the transistor gain parameter (beta) to reduce low band noise, the patent changes the bias current parameter. By operating the first bipolar transistor with an optimized bias current, low band noise is reduced without requiring transistors with exceptionally high gain, thus maintaining compatibility with standard manufacturing processes.
Solution Approach 2:
The patent segments the noise reduction function from the gain requirement. The first bipolar transistor handles the low band noise through bias current optimization, while the second bipolar transistor handles the PTAT generation. This segmentation eliminates the need for single transistors with extremely high gain, making the circuit manufacturable with standard processes.
2Device complexity
If a single bipolar transistor is used for both CTAT and PTAT generation, then device complexity is reduced, but noise performance deteriorates
Solution Approach 1:
The patent segments the single bipolar transistor into two separate bipolar transistors with distinct functions: the first bipolar transistor generates the CTAT voltage component, and the second bipolar transistor generates the PTAT voltage component. This segmentation enables independent noise optimization for each transistor, significantly improving overall noise performance while maintaining reasonable circuit complexity.
Solution Approach 2:
Each bipolar transistor serves multiple purposes: the first transistor provides both the CTAT voltage and serves as a reference for the PTAT generation, while the second transistor provides the PTAT voltage and maintains the temperature compensation relationship. This multi-functionality approach reduces the need for additional components while improving noise performance.
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 circuit achieves significant reduction in both 1/f noise and high band noise, generating a low noise voltage reference, with exemplary improvements showing three times less flicker noise and five times less wide band noise compared to conventional circuits.
Implementation Method 1
In order to reduce high band noise from the voltage reference a capacitor is connected from the high impedance common collector node of the preamplifier to ground
Implementation Method 2
the bipolar base current and in order to reduce this noise the base current has to be reduced
Data Source
AI summary
A low noise voltage reference circuit is described. The reference circuit utilizes a bandgap reference component and may include at least one of a current shunt or filter to reduce high and low noise contributions to the output. Further modifications may include a curvature correction component.