Temperature Compensating Circuit Using Negative Temperature Coefficient Resistors
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Solution Overview
Problem
Internal oscillators in integrated circuits experience frequency drift due to temperature changes, as components and wires exhibit temperature-dependent properties, leading to instability in oscillation frequency.
Innovation Solution
A temperature compensating circuit is developed using a combination of negative-temperature-coefficient and positive-temperature-coefficient resistors to maintain consistent charging and discharging rates across all stages of the oscillator, thereby compensating for temperature-induced frequency changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a ring oscillator is used as the internal oscillator, then the oscillator can be implemented with a simple structure, but the oscillation frequency drifts with temperature changes
Solution Approach 1:
The patent changes the parameter of resistance by introducing a negative temperature coefficient resistor to compensate for the positive temperature coefficient effect of MOS devices. This parameter change counteracts the frequency drift caused by temperature variations, maintaining frequency stability while keeping the ring oscillator structure simple.
Solution Approach 2:
The patent combines resistors with different temperature coefficients (positive and negative) to create a composite resistance network. This composite structure compensates for temperature effects on the oscillator frequency, achieving frequency stability without increasing structural complexity significantly.
2Productivity
If capacitors are added to each inverter to increase delay time and reduce the number of stages, then the oscillation frequency can be adjusted, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
Instead of adding capacitors to change the delay characteristics, the patent changes the resistance parameter by introducing negative temperature coefficient resistors. This approach adjusts the oscillation frequency while maintaining a simpler circuit structure without additional capacitive elements in each inverter stage.
3Productivity
If resistors with positive temperature coefficient are used to adjust oscillation frequency, then the frequency can be tuned, but the frequency becomes more sensitive to temperature changes
Solution Approach 1:
The patent converts the harmful effect of temperature-dependent resistance into a beneficial compensation mechanism. By using resistors with opposite temperature coefficients, the temperature sensitivity that would normally cause frequency drift is transformed into a compensating effect that stabilizes the frequency across temperature variations.
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 stabilizes the oscillation frequency by adjusting the resistance characteristics of the resistors in response to temperature changes, ensuring the oscillator's frequency remains consistent across varying temperatures.
Implementation Method 1
a negative-temperature-coefficient resistor, and at least a first portion of the reference current flows through the negative temperature coefficient resistor
Data Source
AI summary
A temperature compensating circuit including a reference circuit, a transistor and a first circuit is provided. The reference circuit has a reference current and a resistance circuit, wherein the resistance circuit includes a first terminal receiving the reference current, a second terminal and a negative-temperature-coefficient resistor. The transistor has a drain, a source and a path disposed between the drain and the source, wherein the path of the transistor is connected in series with the resistance circuit, a gate of the transistor is electrically connected to the drain of the transistor and the second terminal of the resistance circuit, and the drain of the transistor produces a bias-voltage signal. The first circuit produces an output signal having a variable frequency in response to the bias-voltage signal, wherein the temperature compensating circuit utilizes the negative-temperature-coefficient resistor to compensate the variable frequency for a temperature change in the temperature compensating circuit.