PTAT Circuit Using Feedback Amplifier and MOSFET
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Solution Overview
Problem
Existing bandgap voltage reference circuits in integrated circuits face challenges due to statistical variations in semiconductor processes, leading to part-to-part and lot-to-lot variations, and sensitivity to base currents and noise, which affect the accuracy and reliability of temperature-independent voltage generation.
Innovation Solution
A proportional to absolute temperature (PTAT) circuit design utilizing two bipolar transistors with collectors connected to a common node and a MOSFET between their bases, along with a feedback amplifier, which is insensitive to base currents and noise, allowing for low part-to-part and lot-to-lot variation and low 1/f noise, and can be implemented using substrate PNP transistors in CMOS processes without the need for high-performance bipolar transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional bandgap voltage reference circuits are implemented using standard semiconductor processes, then manufacturing cost is reduced, but part-to-part and lot-to-lot variation increases due to statistical process variation
Solution Approach 1:
The patent changes the operating parameters of the bipolar transistors by implementing a specific current mirror configuration where the collector currents are forced to be equal through the use of matched transistors Q1 and Q2. This parameter control approach eliminates the need for precise geometric matching while maintaining the PTAT voltage generation, thereby reducing part-to-part variation without increasing manufacturing complexity
Solution Approach 2:
The patent employs a feedback mechanism through the current mirror configuration that automatically compensates for process variations. The equal current condition enforced by the current mirror provides negative feedback that stabilizes the PTAT voltage output against statistical process variations, improving manufacturing precision without additional trimming steps
2Manufacturing precision
If high-performance bipolar transistors are used to reduce variation, then manufacturing precision improves, but device complexity and cost increase
Solution Approach 1:
The patent replaces the requirement for high-performance, expensive bipolar transistors with a configuration that uses standard, lower-performance devices. By relying on the current mirror principle rather than transistor geometric precision, the design allows the use of cheaper, more readily available bipolar transistors that are easier to manufacture with standard processes
Solution Approach 2:
The invention changes the critical parameter from transistor geometric dimensions (which require high manufacturing precision) to collector current equality (which is enforced by the current mirror configuration). This parameter transformation allows the use of standard bipolar transistors without requiring high-performance device characteristics, thereby reducing device complexity
3Device complexity
If traditional PTAT circuit configurations are used, then circuit simplicity is maintained, but sensitivity to base currents and noise increases
Solution Approach 1:
The current mirror configuration provides automatic feedback that equalizes the collector currents of Q1 and Q2. This feedback mechanism actively compensates for base current effects and reduces noise sensitivity, improving the signal quality without adding significant circuit complexity beyond the mirror configuration itself
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 PTAT circuit achieves a temperature-independent output with low sensitivity to base currents and noise, reducing variations and noise components, enabling accurate voltage references and temperature sensors without trimming, thus improving the reliability and cost-effectiveness of high-volume production.
Implementation Method 1
an amplifier having a first input coupled to an emitter of the first bipolar transistor, a second input coupled to an emitter of the second bipolar transistor and an output coupled to a gate of the MOSFET
Data Source
AI summary
In accordance with an embodiment, a proportional to absolute temperature (PTAT) circuit includes a first bipolar transistor having a collector coupled to a common node; a second bipolar transistor having a collector coupled to the common node; a MOSFET having a load path coupled between a base of the first bipolar transistor and a base of the second bipolar transistor; and an amplifier having a first input coupled to an emitter of the first bipolar transistor, a second input coupled to an emitter of the second bipolar transistor and an output coupled to a gate of the MOSFET.