In electronic circuits, metal oxide film resistors are widely used due to their good stability and corrosion resistance. As a core parameter, their temperature coefficient directly determines the law of resistance value change with temperature. Temperature coefficients of different sizes and positive and negative values will have different effects on the accuracy, stability and reliability of the circuit in various scenarios such as amplifier circuits, oscillation circuits, and power supply circuits.
The temperature coefficient directly affects the resistance stability of the circuit. The temperature coefficient (TCR) of metal oxide film resistors represents the relative rate of change of resistance value per unit temperature change. A positive temperature coefficient means that the resistance value increases with increasing temperature, while a negative temperature coefficient is the opposite. In precision measurement circuits or signal processing circuits, if resistors with large TCR are used, ambient temperature fluctuations will cause significant changes in resistance value. For example, in a high-precision bridge circuit, if the resistor TCR is ±100ppm/℃, when the ambient temperature changes by 10℃, the resistance value will have a deviation of 0.1%. This error will directly affect the accuracy of the measurement result and cause distortion of the circuit output signal.
This will cause gain drift problems in the performance of the amplifier circuit. In audio amplifiers, RF amplifiers and other amplifier circuits, metal oxide film resistors are often used to set bias voltages and determine gain multiples. Due to the existence of temperature coefficients, when the operating temperature changes, the change in resistance value will break the original static operating point balance. For example, in a common emitter amplifier circuit, the change in the resistance of the base bias resistor will cause the base current of the transistor to change, thereby affecting the collector current and voltage gain. If the resistor TCR is large, in a high temperature environment, the reduction in resistance value may cause the transistor to enter the saturation region, resulting in signal distortion; at low temperatures, the transistor may operate in the cutoff region, causing the output signal to attenuate, seriously affecting the stability of the amplifier circuit and the sound quality and signal quality.
The frequency stability of the oscillation circuit is restricted by the temperature coefficient. In circuits that generate stable frequency signals such as quartz crystal oscillator circuits and RC oscillator circuits, the temperature coefficient of the resistor is crucial to the stability of the oscillation frequency. Taking the RC oscillator circuit as an example, the fluctuation of the resistance value caused by temperature changes will directly change the oscillation frequency. If a resistor with a TCR of ±200ppm/℃ is used, the oscillation frequency may deviate by up to 0.4% when the temperature changes by 20℃. This will cause serious problems such as signal transmission errors and inaccurate timing for circuits with extremely high requirements for frequency stability, such as communications and clocks.
Causes voltage output fluctuations in power supply circuits. In voltage-stabilized power supplies and DC-DC conversion circuits, metal oxide film resistors are often used in feedback loops and voltage divider circuits to adjust the output voltage. The temperature coefficient of the resistor will cause the feedback voltage to change with temperature, resulting in unstable power supply output voltage. For example, in a series voltage-stabilized circuit, when the resistance of the sampling resistor increases due to temperature increase, the voltage fed back to the adjustment tube will change, causing the output voltage to decrease; otherwise, the output voltage will increase. This voltage fluctuation will not only affect the normal operation of the load device, but may also shorten the service life of the device. For electronic devices with high requirements for voltage stability (such as servers and precision instruments), it may cause system failures.
The temperature coefficient affects the long-term reliability of the circuit. In harsh environments with high temperatures or frequent temperature changes, metal oxide film resistors with large temperature coefficients will experience repeated resistance fluctuations, which may accelerate the physical and chemical changes between the resistor film layer and the substrate, causing the film layer to crack and fall off, and then make the resistor fail. In addition, the unstable resistance value will also cause other components in the circuit to bear abnormal voltage and current, accelerating the aging of the entire circuit. For example, in circuits in the fields of automotive electronics, aerospace, etc., the ambient temperature varies widely. If resistors with excessive TCR are used, long-term operation may cause circuit failures, seriously threatening system safety.
Reduce negative effects through temperature compensation technology. In order to reduce the impact of the temperature coefficient of metal oxide film resistors on circuit performance, temperature compensation technology is often used. One method is to select high-precision resistors with a TCR close to zero, such as low TCR metal oxide film resistors manufactured using special processes, whose TCR can be controlled within ±20ppm/℃ to meet the needs of high-precision circuits. Another method is to connect resistors with different temperature coefficients in parallel or in series, and use their mutual compensation characteristics to make the temperature coefficient of the equivalent resistance after combination approach zero. In addition, introducing temperature sensors such as thermistors in circuit design, real-time monitoring of ambient temperature and feedback adjustment of circuit parameters can also effectively compensate for the impact of resistor temperature coefficients and improve circuit stability.
Future development trends will place higher demands on temperature coefficient control. With the development of technologies such as 5G communications, artificial intelligence, and the Internet of Things, the performance requirements of electronic circuits for resistors are constantly increasing, and the control of temperature coefficients is becoming more stringent. On the one hand, new metal oxide film materials and manufacturing processes are developed to further reduce the temperature coefficient of resistors and improve their stability in a wide temperature environment; on the other hand, combined with chip-level packaging technology, the temperature compensation circuit is integrated with the resistor to achieve more accurate temperature adaptive adjustment. In addition, through simulation design software, the influence of the resistor temperature coefficient is fully considered in the circuit design stage, the circuit structure is optimized, and the reliability of circuit performance is guaranteed from the source.
