P-MOS Differential Pair Voltage Reference with Asymmetric Gate Doping
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Solution Overview
Problem
Existing voltage references, such as bandgap voltage references, suffer from noise generation, high power consumption, significant die real estate usage, and temperature instability, with initial output voltage distribution being unstable until a certain time passes.
Innovation Solution
A voltage reference is created using an operational amplifier circuit with two substantially identical P-channel metal oxide semiconductor (P-MOS) transistors having different gate dopants, configured as a differential pair, which minimizes temperature dependence and noise susceptibility by selecting appropriate gains for the P-MOS and N-MOS transistors, allowing for quick startup and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bandgap voltage reference is used, then voltage reference function is achieved, but noise is generated and power consumption increases
Solution Approach 1:
The patent changes the fundamental operating parameters by using P-MOS transistors with different gate dopants (N-type and P-type polysilicon) instead of diodes. This parameter change in the device type and doping configuration enables the generation of threshold voltage differences while inherently reducing noise generation and power consumption compared to traditional bandgap reference circuits
Solution Approach 2:
The patent substitutes the diode-based mechanism with a P-MOS transistor-based mechanism. By replacing diodes with P-MOS transistors configured as a differential pair, the system achieves voltage reference functionality through transistor threshold voltage differences rather than diode voltage drops, resulting in lower noise and power consumption
2Reliability
If bandgap voltage reference is used, then voltage reference function is achieved, but die real estate usage increases
Solution Approach 1:
The patent extracts and eliminates unnecessary support circuits from the voltage reference implementation. By using a simplified P-MOS differential pair configuration with N-MOS load transistors, the design removes redundant components required in traditional bandgap references, thereby reducing die area while maintaining voltage reference functionality
Solution Approach 2:
The patent uses a simplified circuit topology that copies only the essential functionality needed for voltage reference. The P-MOS differential pair with different gate dopants directly generates the reference voltage without requiring complex additional circuits, reducing the overall die area compared to full bandgap reference implementations
3Reliability
If bandgap voltage reference is used, then voltage reference function is achieved, but temperature stability deteriorates
Solution Approach 1:
The patent changes the device configuration to P-MOS transistors with different gate dopants, which exhibit different threshold voltage temperature coefficients. By selecting appropriate width-to-length ratios for the P-MOS and N-MOS transistors, the circuit achieves temperature compensation where the temperature drift of one transistor compensates for the other, resulting in a stable reference voltage over temperature
Solution Approach 2:
The patent introduces asymmetry through different gate dopants (N-type and P-type polysilicon) in the P-MOS transistors. This asymmetric doping creates threshold voltage differences with opposite temperature dependencies, enabling temperature compensation when the transistors are configured in a differential pair with appropriate sizing ratios
4Reliability
If bandgap voltage reference is used, then voltage reference function is achieved, but startup stability is poor
Solution Approach 1:
The patent incorporates positive feedback through the N-MOS load transistors configured in a feedback arrangement with the P-MOS differential pair. This positive feedback mechanism accelerates the startup process by reinforcing the voltage difference between the P-MOS transistors, enabling quick establishment of the reference voltage and improving startup stability without requiring extended warm-up time
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 low-noise, low-temperature drift voltage reference that consumes less power, requires less integrated circuit die real estate, and achieves stability upon startup, with temperature compensation ensuring output voltage stability better than 50 parts per million.
Implementation Method 1
The present disclosure relates to voltage references, and more particularly, to a voltage reference based upon the work function difference between two P-channel metal oxide semiconductor (P-MOS) transistors having differently doped gates
Implementation Method 2
Temperature compensation of this voltage reference may be achieved by selecting appropriate gains during the design of the P-MOS transistors and/or their N-channel metal oxide semiconductor (N-MOS) load transistors that make up the operational amplifier circuit voltage reference
Data Source
AI summary
A temperature compensated voltage reference is created from an operational amplifier circuit having two substantially identical P-channel metal oxide semiconductor (P-MOS) transistors with each one having a different gate dopant. The different gate dopants result in different threshold voltages for each of the two otherwise substantially identical P-MOS transistors. The difference between these two threshold voltages is then used to create the voltage reference equal to the difference. The two P-MOS transistors are configured as a differential pair in the operational amplifier circuit and the output of the operational amplifier is used as the voltage reference. The transistor widths of two P-MOS transistors are adjusted to minimize voltage variation over a temperature range.