Reference Voltage Circuit Using Highly-Doped Gates
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Solution Overview
Problem
Conventional reference voltage generating circuits using depletion-type and enhancement-type field-effect transistors suffer from large variations due to process, temperature, and power supply voltage fluctuations, leading to poor precision and temperature characteristics.
Innovation Solution
A reference voltage generating circuit is designed using a depletion-type n-channel field-effect transistor and two additional transistors with highly-doped gates, where the gate of the first transistor is connected to a joint point between the second and third transistors, and the substrate gates are coupled to ground, with specific channel width to channel length ratios to achieve improved temperature dependency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If depletion-type and enhancement-type field-effect transistors are used to generate reference voltage, then the reference voltage can be extracted from threshold voltage difference, but large variations occur due to process and temperature fluctuations
Solution Approach 1:
The patent changes the doping concentration parameter of the gate electrode from conventional levels to highly-doped levels (e.g., 1×10^20 atoms/cm³ or higher). This parameter change makes the threshold voltage less sensitive to process variations and temperature fluctuations, thereby improving both the precision and stability of the reference voltage. The highly-doped gate creates a fixed work function that reduces variability in the threshold voltage difference used for reference voltage generation.
Solution Approach 2:
The patent applies different doping concentrations to different parts of the transistor structure. Specifically, the gate electrode is highly-doped while other regions maintain conventional doping levels. This local quality differentiation ensures that the threshold voltage difference remains stable against environmental variations while maintaining proper transistor operation characteristics.
2Device complexity
If conventional field-effect transistors are used, then the circuit structure is simple, but temperature characteristics are poor with large variations
Solution Approach 1:
The patent modifies the gate doping concentration parameter to highly-doped levels, which fundamentally changes the temperature dependency characteristics of the threshold voltage. This parameter change reduces the temperature coefficient of the reference voltage from typical values (hundreds of ppm/°C) to much lower values, improving temperature characteristics while maintaining the simple two-transistor circuit structure.
3Measurement precision
If depletion-type and enhancement-type transistors are used, then reference voltage can be generated, but fluctuations due to power supply voltage changes are large
Solution Approach 1:
The highly-doped gate parameter creates a more stable threshold voltage that is less dependent on drain-source voltage variations. This parameter change reduces the sensitivity of the reference voltage to power supply fluctuations, as the threshold voltage difference becomes more fixed and less influenced by changes in operating conditions.
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 reduces reference voltage variations to ±6% and improves temperature characteristics to 40 ppm/°C, while minimizing fluctuations due to power supply voltage changes, enhancing the stability and precision of the reference voltage.
Implementation Method 1
a second field-effect transistor having one node thereof coupled to another node of the first field-effect transistor and having a highly-doped n-type gate, and a third field-effect transistor having one node thereof coupled to another node of the second field-effect transistor, another node thereof coupled to a ground voltage, and a highly-doped p-type gate
Data Source
AI summary
A reference voltage generating circuit for producing a predetermined reference voltage at an output node includes a depletion-type n-channel field-effect transistor serving as a first field-effect transistor having one node thereof coupled to a power supply voltage, a second field-effect transistor having one node thereof coupled to another node of the first field-effect transistor and having a highly-doped n-type gate, and a third field-effect transistor having one node thereof coupled to another node of the second field-effect transistor, another node thereof coupled to a ground voltage, and a highly-doped p-type gate.