NMOS PTAT Voltage Reference for IGZO Temperature Stability
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Solution Overview
Problem
Existing voltage reference circuits, particularly those using CMOS-based implementations, cannot be effectively implemented using an NMOS-only process, such as IGZO-based semiconductors, which limits their application in non-silicon-based semiconductor technologies like indium gallium zinc oxide (IGZO) processes.
Innovation Solution
A voltage reference circuit is developed using area-mismatched NMOS transistors with a voltage divider circuit and an operational amplifier to provide a reference output signal proportional to the temperature of the transistors, incorporating a PTAT circuit to generate a signal proportional to absolute temperature and a CTAT circuit for temperature compensation, ensuring stability across varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CMOS-based voltage reference circuits are used, then temperature stability and reference accuracy are improved, but compatibility with NMOS-only processes (such as IGZO) deteriorates
Solution Approach 1:
The invention extracts and eliminates the PMOS transistors from the traditional CMOS bandgap reference circuit, creating an NMOS-only implementation. This is achieved by using a specialized circuit topology where NMOS transistors with different aspect ratios operate in the subthreshold region to generate the PTAT current, removing the need for complementary devices while maintaining the temperature compensation mechanism
Solution Approach 2:
The invention changes the operating parameters of the NMOS transistors by operating them in the subthreshold region rather than in strong inversion. This parameter change enables the generation of PTAT current through the exponential relationship between gate-source voltage and drain current in subthreshold operation, allowing the circuit to function without PMOS devices
2Adaptability or versatility
If area-mismatched NMOS transistors are used to generate PTAT current, then process compatibility is improved, but circuit complexity increases
Solution Approach 1:
The invention merges the voltage reference generation and temperature compensation functions into a single integrated circuit block. The NMOS transistors with different aspect ratios are combined with resistors and capacitors to simultaneously generate PTAT current and produce the compensated reference voltage, reducing the need for separate circuit modules
Solution Approach 2:
The circuit achieves multi-functionality by using the same NMOS transistors and resistors to perform multiple tasks: generating PTAT current, creating voltage drops for comparison, and producing the final compensated reference output. This universal use of components reduces overall circuit complexity despite the sophisticated temperature compensation mechanism
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 solution provides a stable reference output signal that is independent of supply voltage and temperature variations, enhancing the stability and applicability of voltage reference circuits in non-silicon-based semiconductor technologies like IGZO processes.
Implementation Method 1
the reference output signal can be substantially proportional to a temperature of the first and/or second transistors
Implementation Method 2
the amplifier circuit is configured to provide a virtual ground at the intermediate node of the voltage divider circuit
Data Source
AI summary
A reference generator system can include a PTAT circuit coupled to a signal supply node and configured to provide a voltage reference signal or a current reference signal that is based on a physical characteristic of one or more components of the PTAT circuit and a correction signal. The system can include a CTAT circuit coupled to the PTAT circuit and configured to provide the correction signal to the PTAT circuit. In an example, the reference generator system can be implemented at least in part using NMOS devices that comprise a portion of an indium gallium zinc oxide (IGZO) substrate.