Temperature-Independent Oscillation Circuit Using Depletion MOS Transistors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional oscillation circuits are large in scale and have significant temperature fluctuations affecting their oscillation frequency, requiring multiple current sources and a band gap reference circuit, which increases complexity and sensitivity to temperature variations.
Innovation Solution
An oscillation circuit design utilizing a constant current circuit with depletion MOS transistors, a charge/discharge circuit with matching threshold voltage and temperature characteristics, and an RS latch circuit to produce a waveform that is independent of temperature, reducing circuit scale and temperature influence on oscillation frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional oscillation circuit configuration with multiple current sources and band gap reference is used, then temperature independence of oscillation frequency is achieved, but circuit scale becomes large
Solution Approach 1:
The invention extracts and eliminates unnecessary components from the conventional oscillation circuit. Specifically, it removes the band gap reference circuit and one of the current sources by using a single current source that directly charges both capacitors through switching mechanisms, thereby reducing circuit scale while maintaining temperature independence through the use of depletion MOS transistors with complementary threshold voltage characteristics
Solution Approach 2:
The single current source in the invention serves multiple functions: it charges both the first and second capacitors, and its current is modulated by both the first and second depletion MOS transistors to achieve temperature compensation. This multi-functionality reduces the number of components while maintaining the temperature independence characteristic
2Speed
If conventional oscillation circuit with resistor and multiple current sources is used, then oscillation frequency can be controlled, but circuit becomes sensitive to temperature variations due to resistor temperature characteristics
Solution Approach 1:
The invention converts the harmful temperature sensitivity into a beneficial temperature compensation mechanism. By using depletion MOS transistors with complementary threshold voltage temperature characteristics (one with positive temperature coefficient and one with negative), the circuit automatically compensates for temperature variations. The threshold voltage changes of these transistors counterbalance each other, maintaining stable oscillation frequency across temperature ranges
Solution Approach 2:
The invention changes the operating parameters of the MOS transistors to achieve temperature independence. Specifically, it uses depletion MOS transistors whose threshold voltages have opposite temperature coefficients, and by carefully selecting their dimensions and bias conditions, the temperature-dependent parameters cancel each other out, resulting in temperature-independent oscillation frequency
3Reliability
If band gap reference circuit is used for temperature compensation, then oscillation frequency stability is improved, but circuit scale and complexity increase
Solution Approach 1:
Instead of using a complex band gap reference circuit, the invention creates a simplified copy of the temperature compensation function using depletion MOS transistors. The threshold voltage characteristics of these transistors replicate the temperature compensation effect of a band gap reference, but with much fewer components and lower circuit complexity
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 proposed design results in a compact oscillation circuit with an oscillation frequency that is independent of temperature, achieved by using depletion MOS transistors with matching threshold voltage and temperature characteristics, thereby minimizing the impact of temperature changes on circuit performance.
Implementation Method 1
the second depletion MOS transistor being provided in a current path for charging the first capacitor, and having the same threshold voltage and the same temperature characteristics of the threshold voltage as a threshold voltage of the first depletion MOS transistor and temperature characteristics of the threshold voltage of the first depletion MOS transistor
Data Source
AI summary
An oscillation circuit small in circuit scale and in the influence of temperature on its oscillation frequency is provided. The oscillation circuit includes: a constant current circuit configured to supply a current based on a first depletion MOS transistor; a charge/discharge circuit having a first capacitor, a second capacitor, a second depletion MOS transistor, and a third depletion MOS transistor provided in a current path for charging the second capacitor, the first to third depletion MOS transistors having the same threshold voltage and the same temperature characteristics of the threshold voltage; and an RS latch circuit configured to output a waveform that falls by input of the reset signal and rises by input of the set signal.