Temperature-Compensated Constant Current Circuit for Stable Oscillators
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Solution Overview
Problem
Conventional constant current circuits are temperature-dependent, leading to variations in delay time and cycle time of oscillators due to the temperature coefficient of resistance in components like polysilicon layers, which affects the reliability of semiconductor apparatus and analog circuits.
Innovation Solution
A constant current circuit design that combines a reference current generator with both negative and positive temperature coefficients, using a bandgap reference circuit and NMOS transistors to generate a temperature-compensated reference current by adding reference currents from parallel paths, allowing for adjustment of resistance values and current mirror ratios to achieve a zero or controlled temperature coefficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional constant current circuit using a variable resistor with positive temperature coefficient is used, then the circuit can generate a reference current, but the reference current has negative temperature coefficient and varies with temperature
Solution Approach 1:
The reference current generation is divided into two separate circuits: a first reference current generation circuit that generates a reference current with negative temperature coefficient, and a second reference current generation circuit that generates a reference current with positive temperature coefficient. By segmenting the current generation into distinct temperature-dependent paths, the patent enables independent control and compensation of temperature effects.
Solution Approach 2:
The patent changes the temperature coefficient parameter by combining currents from circuits with opposite temperature characteristics. The first circuit uses a variable resistor with positive temperature coefficient to generate negative temperature coefficient current, while the second circuit uses an NMOS transistor to generate positive temperature coefficient current. By adjusting the ratio of these currents, the overall temperature coefficient can be controlled.
2Temperature
If temperature compensation is implemented by combining multiple current sources, then temperature stability is improved, but circuit complexity increases
Solution Approach 1:
The patent merges two reference current generation circuits into a single unified structure where the first and second reference current generation circuits share common elements such as the operational amplifier and power supply connections. This merging approach achieves temperature compensation functionality while minimizing the increase in overall circuit complexity compared to using completely separate circuits.
Solution Approach 2:
The operational amplifier serves multiple functions: it acts as a unity gain buffer for the reference voltage, controls the gate voltage of the PMOS transistor in the first circuit, and enables the current mirror operation. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in circuit complexity while achieving temperature compensation.
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 temperature-compensated constant current that is independent of power supply voltage variations, ensuring stable operation across temperature changes, suitable for applications in semiconductor apparatus and memory technologies.
Implementation Method 1
a bandgap reference circuit, a temperature dependent current generator, and a reference current generator
Implementation Method 2
an NMOS transistor QTC...generating a reference current IREFP having a positive temperature coefficient based on the temperature dependent current IB
Implementation Method 3
A voltage VN of a node N is input to an inverting input terminal (−) through negative feedback. The operational amplifier OP controls a gate voltage of the PMOS transistor Q1 so that the voltage VN of the node N becomes equal to the reference voltage VREF
Implementation Method 4
a reference current flowing through the PMOS transistor Q1 is represented by IREF=VREF/RT
Data Source
AI summary
Provided is a constant current circuit supplying a temperature-compensated constant current. The constant current circuit includes a BGR circuit, a temperature dependent current generator, a reference current generator, and an output current generator. The BGR circuit generates a reference voltage with low voltage dependence. The temperature dependent current generator generates a temperature dependent current having a positive temperature coefficient. The reference current generator generates a temperature-compensated reference current by using the reference voltage and the temperature dependent current. The output current generator generates an output current based on the reference current generated by the reference current generator.