CMOS Reference Current Source with Negative Temperature Coefficient
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Solution Overview
Problem
Conventional reference current sources for very low power applications require high-value resistors, occupying large chip area and having positive temperature coefficients, which are unsuitable for applications needing a negative temperature coefficient.
Innovation Solution
A CMOS reference current source design using only MOS transistors, with specific circuit branches connected in parallel, eliminating the need for resistors and providing a current that is inversely proportional to temperature, thus achieving a negative temperature coefficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high-value resistors are used for very low power reference current, then power consumption is reduced, but chip area increases
Solution Approach 1:
The invention extracts and eliminates the resistor component from the reference current source circuit. By using only MOS transistors in a specific configuration (two parallel branches with cross-connected gates), the design achieves very low power consumption (20 nA or less) without requiring high-value resistors, thus avoiding the large chip area that would be needed for such resistors.
2Area of stationary object
If conventional current sources without resistors are used, then chip area is reduced, but temperature coefficient becomes positive
Solution Approach 1:
The invention changes the operating parameters and configuration of MOS transistors to achieve a negative temperature coefficient. By configuring two parallel branches with cross-connected gates and utilizing the temperature-dependent characteristics of MOS transistors, the circuit generates a reference current with negative temperature coefficient, opposite to conventional designs.
3Use of energy by moving object
If high-value resistors are used to achieve very low current, then power consumption is reduced, but manufacturing complexity increases
Solution Approach 1:
The invention changes from using high-value resistors (which are difficult to manufacture with precision) to using MOS transistors in a specific configuration. This parameter change enables the circuit to achieve very low power consumption while being compatible with standard CMOS manufacturing processes, thereby improving ease of manufacture.
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 achieves a compact, low-power CMOS reference current source with a negative temperature coefficient, suitable for very low power RC oscillators, and allows for temperature compensation in alternative designs.
Implementation Method 1
the generated current is approximately proportional to the transistor threshold voltage which, in turn, is inversely proportional to temperature. Accordingly, the generated current has the desired negative temperature coefficient.
Data Source
AI summary
A CMOS reference current source comprises two circuit branches connected in parallel between supply terminals. The first circuit branch includes a series connection of a bias current source (MP1) and a first MOS transistor (MN1) of a first conductivity type. The second circuit branch includes a series connection of a diode-connected MOS transistor (MP2) of a second conductivity type, a second MOS transistor (MN2) of the first conductivity type and a third MOS transistor (MN3) of the first conductivity type. The first MOS transistor (MN 1) of the first conductivity type has its gate connected to the drain of the third MOS transistor (MN3) of the first conductivity type. The second MOS transistor (MN2) of the first conductivity type has its gate connected to the drain of the first MOS transistor (MN1) of the first conductivity type. The third MOS transistor (MN3) the first conductivity type has its gate connected to a bias source (MN4).