Current Source Circuit Temperature Compensation Using PTC Resistor

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Solution Overview

Problem

Depletion-type MOS transistors in current source circuits exhibit a positive temperature property, leading to increased drain current with temperature, necessitating compensation to flatten the temperature property.

Innovation Solution

A current source circuit incorporating a current mirror circuit with two enhancement-type MOS transistors and a polysilicon resistor with a negative temperature property, along with an adjusting circuit featuring MOS transistors and resistors connected in series or parallel, and fuses for fine-tuning, to compensate for the temperature-dependent current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a depletion-type MOS transistor is used as a current source, then the circuit can provide a constant current, but the drain current increases with temperature (positive temperature property)

Engineering Contradiction:

Improvecurrent stabilityVSAvoidtemperature property

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent uses a resistor with positive temperature coefficient (PTC) to compensate for the negative temperature coefficient (NTC) of the depletion-type MOS transistor. The PTC resistor's property of increasing resistance with temperature is utilized to counteract the MOS transistor's tendency to increase current with temperature, thereby stabilizing the overall current output across temperature variations.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the temperature coefficient parameter by introducing a resistor with positive temperature coefficient into the current source circuit. This parameter change allows the circuit to compensate for temperature-induced current variations in the depletion-type MOS transistor, transforming the temperature-dependent current into a more stable current output.

Inventive Principle:

Principle #35Parameter changes

2Temperature

If a resistor and enhancement MOS transistor are used to compensate for temperature property, then the temperature property can be flattened, but the device complexity increases

Engineering Contradiction:

Improvetemperature propertyVSAvoidcircuit structure

Core Design Contradiction:

TemperatureVSDevice complexity

Solution Approach 1:

The patent merges the temperature compensation function with the existing current source structure by integrating a PTC resistor into the circuit. This combination allows the circuit to achieve temperature compensation without requiring entirely separate compensation circuits, thereby reducing overall complexity while still flattening the temperature property.

Inventive Principle:

Principle #5Merging (Combining)

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 effectively adjusts and stabilizes the temperature property of the current source circuit, ensuring a constant current output irrespective of temperature variations.

Implementation Method 1

a resistor configured to have a negative temperature property and be connected to a source of the one of the two enhancement-type MOS transistors

Methodology Applied

Scientific EffectNegative temperature coefficient: Thermo-resistive Effect

Data Source

PatentUS8248176B2Current source circuit and delay circuit and oscillating circuit using the same

Publication Date: 2012.08.21 MITSUMI ELECTRIC CO LTD

AI summary

A disclosed current source circuit includes a current mirror circuit having two enhancement-type MOS transistors, a depletion-type MOS transistor configured to be connected to a drain of one of the two enhancement-type MOS transistors and to function as a constant current source, and a resistor configured to have a negative temperature property and be connected to a source of the one of the two enhancement-type MOS transistors.