Reference Voltage Circuit Temperature Compensation
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Solution Overview
Problem
Conventional reference voltage generating circuits using MOS transistors are susceptible to variations in threshold voltage, leading to significant offset voltages and requiring trimming, while circuits operating at low voltages face challenges in maintaining stability and temperature dependency.
Innovation Solution
A reference voltage generating circuit comprising a PTAT current generating section, a voltage generating section with negative temperature coefficient, and a compensation current generating section, where the emitter size ratio of transistors is set to 1:N, and a synthesis section that outputs a voltage sum of terminal voltage and base-to-emitter voltage, with the compensation current proportional to the differential voltage, to reduce temperature dependency and offset voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional MOS transistor circuits are used for reference voltage generation, then the circuit can operate with standard components, but the threshold voltage variations cause significant offset voltages requiring trimming
Solution Approach 1:
The invention changes the operating parameters by using bipolar transistors instead of MOS transistors, exploiting the exponential relationship between base-emitter voltage and collector current. This parameter change eliminates threshold voltage variations inherent in MOS devices, thereby reducing offset voltage without requiring trimming operations
Solution Approach 2:
The invention uses a differential amplifier configuration where two bipolar transistors are arranged in a symmetric manner. By copying the transistor structure and using matched pairs, the circuit achieves immunity to threshold voltage variations, as the differential configuration cancels out common-mode offset voltages
2Use of energy by moving object
If the circuit operates at low voltages below 1.2V, then power consumption is reduced, but temperature dependency and stability deteriorate
Solution Approach 1:
The invention changes the temperature compensation mechanism by using a different ratio relationship in the differential amplifier feedback network. By adjusting the resistor ratios and transistor emitter areas, the circuit achieves temperature compensation at lower operating voltages, maintaining stability while reducing power consumption below 1.2V
Solution Approach 2:
The invention introduces dynamic temperature compensation by using bipolar transistors whose base-emitter voltage has a strong negative temperature coefficient. This dynamic characteristic is exploited to compensate for temperature drift in the reference voltage, allowing stable operation at low voltages where conventional circuits fail
3Stability of the object's composition
If bipolar transistors with emitter size ratio 1:N are used, then temperature dependency is reduced, but device complexity increases
Solution Approach 1:
The invention segments the transistor emitter area into different sized regions with a 1:N ratio between the two bipolar transistors. This segmentation allows the generation of proportional-to-absolute-temperature (PTAT) currents that can be used for temperature compensation, reducing temperature dependency while maintaining a manageable device structure
Solution Approach 2:
The differential amplifier configuration serves multiple functions simultaneously: it provides voltage amplification, temperature compensation through the bipolar transistor characteristics, and offset voltage rejection. This multi-functionality reduces the need for additional compensation circuits, thereby limiting the increase in device complexity
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 reduced temperature dependency and offset voltage multiplication, allowing for stable operation at low voltages with minimal variations, eliminating the need for trimming and ensuring low voltage dependency below 1.2V.
Implementation Method 1
the base-to-emitter voltage VBE suffers from only little process variations. Hence, if the differential amplifier is an ideal amplifier, it is possible to implement a reference voltage having extremely small variations.
Implementation Method 2
The nodes N1 and N2 become equal to each other in potential due to negative feedback of the differential amplifier A1.
Data Source
AI summary
A reference voltage generating circuit is described. The circuit includes a current generating section that generates a first current having a positive temperature coefficient, a voltage generating section that generates a voltage having a negative temperature coefficient, a synthesis section that generates a voltage which is the sum of a voltage having a positive temperature coefficient and developed across both terminals of a resistor, where the voltage has a negative temperature coefficient, and a compensation current generating section that generates a second current having a positive temperature coefficient. The current corresponding to the sum of said first and second currents is caused to flow through the resistor. The synthesis section generates a voltage which is a sum of a terminal voltage of the resistor by the sum current of the first and second currents and the voltage having a negative temperature coefficient.