Reference Voltage Supply Circuit Subthreshold Operation
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Solution Overview
Problem
Conventional reference voltage supply circuits utilizing a work function difference exhibit high temperature dependency and significant variations, making them unsuitable for low power consumption applications in microcomputers.
Innovation Solution
A reference voltage supply circuit design that includes a current supply and two transistors, where the first transistor is in a shallow well within a deep well of a semiconductor layer, and the second transistor is in a well of a different conductivity type, with specific gate insulating films and impurities, operating in a subthreshold region to minimize temperature dependency and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional reference voltage supply circuit utilizing a work function difference is used, then low power consumption is achieved, but high temperature dependency occurs
Solution Approach 1:
The reference voltage supply circuit is divided into two separate transistors (first transistor in shallow well, second transistor in deep well) with different gate impurity concentrations. Each transistor contributes differently to the reference voltage generation, allowing the circuit to maintain low power consumption while compensating for temperature effects through the combined action of segmented components with distinct characteristics.
Solution Approach 2:
The first transistor is designed with a first gate impurity concentration optimized for one aspect of temperature compensation, while the second transistor has a second gate impurity concentration optimized for another aspect. This local quality differentiation allows each transistor to address specific temperature dependency issues, achieving overall low temperature dependency while maintaining the low power consumption advantage of work function difference type circuits.
2Use of energy by moving object
If a conventional reference voltage supply circuit utilizing a work function difference is used, then low power consumption is achieved, but significant variations in reference voltage occur
Solution Approach 1:
By segmenting the reference voltage generation into two transistors with different gate impurity concentrations and well structures, the circuit distributes the reference voltage generation function across multiple components. This segmentation reduces the impact of process variations on any single transistor, thereby reducing overall reference voltage variations while maintaining low power consumption.
Solution Approach 2:
The circuit uses a composite structure combining transistors with different gate impurity concentrations (first gate impurity concentration vs. second gate impurity concentration) and different well configurations (shallow well vs. deep well). This composite approach leverages the complementary characteristics of each transistor type to produce a reference voltage that is both low power and highly stable against process variations.
3Temperature
If transistors with different gate impurity concentrations are used, then temperature dependency is reduced, but device complexity increases
Solution Approach 1:
The circuit is segmented into exactly two transistors with different gate impurity concentrations, which is the minimum number needed to achieve temperature compensation while keeping the structure simple. This segmented approach reduces temperature dependency without excessive complexity by using only the necessary number of differentiated components.
Solution Approach 2:
The invention changes the gate impurity concentration parameter to create the first and second transistors with different electrical characteristics. By varying this single parameter (gate impurity concentration) while maintaining the basic transistor structure, the circuit achieves temperature compensation without significantly increasing device complexity. The parameter change approach allows temperature dependency reduction through a straightforward modification rather than a complex structural overhaul.
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 reference voltage with low temperature dependency and reduced variations, effectively lowering standby power consumption in microcomputers by adjusting the ratio of gate widths and impurity concentrations in the transistors.
Implementation Method 1
the work function difference between a p+-type gate electrode and an n+-type gate electrode is Φpn, the following equations are obtained. Idsng=β/2×(Vg—n1−Vsng−Vtng)2. Idspg=β/2×(Vg—n1−Vspg−Vtpg)2=β/2×(Vg—n1−Vtng−Φpn)2
Implementation Method 2
The first transistor and the second transistor operate in a subthreshold region when potential of the source of the first transistor is output outside as a reference voltage
Data Source
AI summary
A reference voltage generator includes a first transistor and a second transistor coupled in series between a current supply and ground. Gate insulating films of the first transistor and the second transistor are made of the same type of film with the same thickness. Impurities contained in gate electrodes of the first transistor and the second transistor have different conductivity types, or have the same conductivity type and different concentrations. The first transistor has a greater gate width than the second transistor. The first transistor and the second transistor operate in a subthreshold region when a reference voltage is output outside.