Bandgap Reference Voltage Curvature Compensation Using PMOS
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Solution Overview
Problem
Existing electronic devices face challenges in generating accurate bandgap reference voltages with low temperature drift, as the base-emitter voltage of bipolar transistors is not absolutely stable over temperature, and current trimming procedures are expensive and not always accurate.
Innovation Solution
A bandgap reference generator circuit is designed with two current paths, each containing a bipolar transistor, coupled with resistors and a common resistor node, using a curvature compensation stage that generates a non-linear compensation current to stabilize the voltage drop across the transistors, eliminating the need for NWELL resistors and reducing process sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If NWELL resistors are used for VBE curvature compensation, then curvature compensation is achieved, but process sensitivity increases and robustness decreases
Solution Approach 1:
The patent changes the type of resistor used for curvature compensation from NWELL resistors to PMOS transistors operating in the triode region. This parameter change transforms the compensation mechanism from relying on high-temperature-coefficient resistors to using the voltage-dependent resistance characteristics of MOS transistors, thereby reducing process sensitivity and improving robustness
Solution Approach 2:
The patent substitutes the physical resistor-based compensation mechanism with a transistor-based mechanism. Instead of using NWELL resistors with specific temperature coefficients, the invention uses PMOS transistors where the channel resistance varies with drain-source voltage, providing curvature compensation through electrical field effects rather than material properties
2Measurement precision
If production trimming is used to achieve accurate reference voltages, then accuracy is improved, but manufacturing cost increases
Solution Approach 1:
The patent implements self-service by designing a curvature compensation mechanism that automatically corrects VBE temperature dependence without requiring external trimming. The PMOS-based compensation circuit inherently provides the necessary correction through its voltage-dependent resistance, eliminating the need for post-fabrication trimming operations
Solution Approach 2:
The patent applies preliminary action by pre-compensating for temperature effects during the normal operation of the bandgap reference circuit. The compensation mechanism is built into the circuit topology itself, providing continuous correction across the operating temperature range without requiring separate calibration steps
3Ease of operation
If two-point temperature testing is used, then testing is simplified, but accuracy at extreme temperatures is reduced
Solution Approach 1:
The patent employs feedback mechanisms where the bandgap reference voltage and compensation currents are continuously monitored and adjusted. The circuit uses feedback loops that ensure accurate voltage reference generation across the entire operating temperature range, not just at test points, by continuously compensating for temperature drift
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
This approach provides a more accurate and less sensitive bandgap reference voltage generation method that is cost-effective and easy to implement, reducing the impact of process variations and production spread without requiring additional chip area or complex modifications.
Implementation Method 1
VBE linearization with non-linear bias currents or voltages using a temperature dependent gain for a AVBE which is added to VBE
Implementation Method 2
The most accurate approach to achieve stable reference voltages employs the bandgap of bipolar transistors in bandgap reference voltage generators
Implementation Method 3
These reference generators employ the base-emitter voltage (VBE) of bipolar transistors. The base-emitter voltage of a bipolar transistor is not absolutely stable over temperature. Thus measures to stabilize VBE over temperature are required.
Data Source
AI summary
The invention relates to an electronic device with a bandgap reference generator including a first path with series connection of a first bipolar transistor, a first resistor and a second resistor, and a second path with series connection of a second bipolar transistor and a third resistor. The first and second paths are supplied current via a common node through a fourth resistor controlled by an amplifier sensing voltage drops within the first and second paths. A curvature compensation stage compensates for a variation of base emitter voltage of the bipolar transistors by drawing a compensation current from the common resistor node.