Reference Voltage Circuit Temperature Compensation
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Solution Overview
Problem
Conventional integrated circuits face significant challenges in generating stable reference voltages due to temperature dependence, leading to high power consumption and large silicon area occupancy, particularly in bandgap reference voltage circuits using bipolar junction transistors and NMOS transistors.
Innovation Solution
A reference voltage generating circuit utilizing a current source, current mirror, and transistors with different threshold voltages, where the ratio of currents between transistors is set to minimize temperature dependence by adjusting biasing voltages to achieve a complementary to absolute temperature (CTAT) behavior, reducing the temperature coefficient of the reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a first order bandgap reference voltage circuit is used to reduce temperature dependence, then the temperature coefficient is improved, but power consumption increases significantly
Solution Approach 1:
The patent changes the operating parameters of NMOS transistors by biasing them in the weak-inversion region and carefully selecting the ratio of width-to-length ratios (W/L) to achieve PTAT voltage generation. This parameter optimization allows the circuit to generate temperature-compensated reference voltages with much lower current consumption (on the order of pA) compared to conventional bandgap circuits, directly resolving the contradiction between temperature stability and power consumption
Solution Approach 2:
The patent uses current mirror circuits to replicate and scale currents through multiple transistor branches with different W/L ratios. By copying the reference current and distributing it through mirrored transistor pairs, the circuit achieves the necessary voltage differences for temperature compensation without requiring excessive bias currents, thus reducing overall power consumption while maintaining temperature independence
2Stability of the object's composition
If resistors are used in bandgap reference voltage circuit to generate stable reference voltage, then temperature independence is improved, but silicon area occupancy increases unreasonably
Solution Approach 1:
The patent extracts and eliminates resistors from the reference voltage generation circuitry, replacing them entirely with transistor-based voltage generation mechanisms. By removing the large-area resistors (which typically occupy tens to hundreds of micrometers squared) and using only transistor W/L ratios and current mirrors to generate the reference voltage, the circuit achieves temperature compensation with minimal silicon footprint
Solution Approach 2:
The patent substitutes the passive resistor-based voltage division mechanism with an active transistor-based voltage generation mechanism. Instead of using resistors to create voltage drops, the circuit uses biased transistors in weak-inversion region to generate voltages with inherent temperature dependence that can be compensated through circuit topology, replacing bulky passive components with compact active devices
3Use of energy by moving object
If NMOS transistors operating in weak-inversion region are used to reduce power consumption, then power consumption is reduced, but threshold voltage mismatch between transistors dominates performance
Solution Approach 1:
The patent intentionally introduces asymmetry by using NMOS and PMOS transistors with different threshold voltage characteristics. By combining transistors from different transistor types with complementary temperature coefficients, the circuit achieves temperature compensation that is more robust to individual transistor mismatches, as the opposing temperature behaviors of NMOS and PMOS devices provide inherent error cancellation
Solution Approach 2:
The patent employs feedback mechanisms through operational amplifiers that sense the reference voltage and adjust bias currents to maintain the desired voltage relationship between different transistor branches. This feedback loop compensates for threshold voltage mismatches and other process variations, ensuring accurate reference voltage generation even when individual transistor parameters vary, thus improving measurement precision without increasing power consumption
Data Source
AI summary
An apparatus and a method to reduce temperature dependence of a reference voltage have been presented. In one embodiment, the method includes generating a reference voltage associated with a difference between a first threshold voltage of a first transistor and a second threshold voltage of a second transistor. The method may further include biasing the first transistor and the second transistor at a predetermined ratio of currents of the first and the second transistors to reduce temperature dependence of the reference voltage.