Temperature-Compensated MOS Current Source Without Bandgap Reference
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Solution Overview
Problem
Semiconductor devices face performance variations due to temperature-dependent current output, which is undesirable and affects stability and efficiency.
Innovation Solution
A current source is implemented using a resistor element and PMOS transistor with a gate terminal connected to a ground voltage, along with a diode-connected NMOS transistor, to provide a constant current regardless of temperature changes without a bandgap reference circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bandgap reference circuit is used to provide constant current, then temperature stability is improved, but device area increases
Solution Approach 1:
The patent extracts and eliminates the bandgap reference circuit from the semiconductor device, replacing it with a simplified current source configuration using a PMOS transistor, resistor element, and diode-connected NMOS transistor. This removal of the unnecessary bandgap reference circuit directly reduces device area while the remaining components are configured to inherently provide temperature-compensated constant current through their electrical characteristics
Solution Approach 2:
The patent utilizes parameter changes in transistor threshold voltages and resistor characteristics with temperature. The PMOS transistor threshold voltage varies inversely with temperature, and the resistor element's resistance varies with temperature in a manner that compensates for current variations, allowing the circuit to maintain constant current output across temperature ranges without requiring a bandgap reference circuit
2Area of stationary object
If circuit area is reduced by eliminating bandgap reference circuit, then integration density is improved, but temperature stability may worsen
Solution Approach 1:
The patent deliberately exploits parameter changes with temperature - specifically, the inverse temperature dependence of the PMOS transistor threshold voltage and the temperature dependence of the resistor element's resistance. These parameter variations are configured to compensate for each other, ensuring that the current remains constant across temperature ranges even without a bandgap reference circuit
Solution Approach 2:
The diode-connected NMOS transistor provides a feedback mechanism that stabilizes the current. By connecting the NMOS transistor in a diode configuration (gate connected to drain), it creates a feedback path that automatically adjusts the current flow to maintain a stable operating point, compensating for temperature-induced parameter changes in the PMOS transistor and resistor
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
This configuration maintains a stable current output, reducing the circuit area and improving integration density and performance by compensating for temperature variations.
Implementation Method 1
a resistor element having a resistance value that varies in proportion to temperature
Implementation Method 2
a PMOS transistor having a threshold voltage that varies inversely in proportion to temperature
Data Source
AI summary
A semiconductor device includes; a resistor element connected to a first power supply node providing a first power supply voltage having a first magnitude, a PMOS transistor having a gate terminal connected to a second power supply node providing a second power supply voltage having a second magnitude less than the first magnitude, a source terminal connected to the resistor element, and a drain terminal providing a first current, and a first NMOS transistor configured as a diode-connected transistor, and connected between the drain terminal of the PMOS transistor and the second power supply node.