How to use network resistors in a feedback circuit?

In the realm of electronic circuits, feedback loops play a pivotal role in ensuring stability, accuracy, and performance. Network resistors, a specialized type of resistor configuration, are often employed within these feedback circuits to fine - tune and optimize their operation. As a leading supplier of network resistors, I am well - versed in the ins and outs of using these components effectively in feedback circuits. In this blog, I'll share insights on how to harness the power of network resistors in feedback applications.

Understanding Feedback Circuits

Before delving into the use of network resistors, it's crucial to understand the basic concept of feedback circuits. A feedback circuit is a configuration where a portion of the output signal is fed back to the input. There are two main types of feedback: positive and negative.

Positive feedback amplifies the input signal, leading to an increase in the output. It is commonly used in oscillators, where the goal is to generate a continuous output signal. Negative feedback, on the other hand, reduces the difference between the input and the output. It is widely used in amplifiers to improve linearity, reduce distortion, and increase stability.

The Role of Network Resistors in Feedback Circuits

Network resistors are groups of resistors that are fabricated on a single substrate. They offer several advantages in feedback circuits. Firstly, they provide matched resistance values. In a feedback loop, having well - matched resistors is essential for accurate signal processing. For example, in an operational amplifier (op - amp) circuit with negative feedback, the ratio of the resistors in the feedback path determines the gain of the amplifier. If the resistors are not well - matched, the gain will deviate from the desired value, leading to inaccurate output.

Secondly, network resistors offer good temperature tracking. Since they are fabricated on the same substrate, they experience similar temperature changes, which means that their resistance values change in a correlated manner. This is particularly important in applications where the circuit is exposed to varying temperatures, as it helps maintain the stability of the feedback loop.

Selecting the Right Network Resistors for Feedback Circuits

When choosing network resistors for a feedback circuit, several factors need to be considered.

Precision

The precision of the network resistors is of utmost importance. High - precision resistors are required when accurate gain settings or signal processing is needed. For ultra - precise applications, you might want to consider our Ultra Precision Network Resistor. These resistors offer extremely low tolerance values, ensuring that the resistance values are very close to the specified nominal values.

Temperature Coefficient

The temperature coefficient of resistance (TCR) indicates how much the resistance of a resistor changes with temperature. In a feedback circuit, a low TCR is desirable to maintain stability over a wide temperature range. Our Low Temperature Drift Foil Network Resistance is an excellent choice for applications where temperature stability is critical.

Power Rating

The power rating of the network resistors should be sufficient to handle the power dissipated in the circuit. If the power rating is too low, the resistors may overheat, leading to changes in their resistance values and potentially damaging the circuit.

Package Type

The package type of the network resistors should be compatible with the circuit board layout and the assembly process. Different package types offer different levels of thermal performance, mechanical stability, and ease of handling.

Practical Applications of Network Resistors in Feedback Circuits

Op - Amp Amplifier Circuits

Operational amplifiers are widely used in electronic circuits, and network resistors are commonly used in their feedback paths. For example, in an inverting amplifier circuit, the gain is determined by the ratio of the feedback resistor ($R_f$) to the input resistor ($R_{in}$). By using a network resistor with well - matched values, the gain can be accurately set.

The formula for the gain of an inverting amplifier is $A_v=-\frac{R_f}{R_{in}}$. If $R_f$ and $R_{in}$ are part of a network resistor with a high degree of matching, the gain will be very close to the calculated value.

Voltage Dividers in Feedback Loops

Voltage dividers are often used in feedback loops to provide a reference voltage or to scale the output signal. Network resistors can be used to construct voltage dividers with precise voltage division ratios. For example, in a power supply regulation circuit, a voltage divider in the feedback loop is used to compare the output voltage with a reference voltage. By using network resistors with accurate resistance values, the voltage regulation can be more precise.

Design Considerations for Using Network Resistors in Feedback Circuits

PCB Layout

The printed circuit board (PCB) layout is crucial when using network resistors in feedback circuits. The traces connecting the network resistors should be as short as possible to minimize parasitic capacitance and inductance. Additionally, the resistors should be placed close to the relevant components in the feedback loop to reduce signal interference.

Signal Integrity

In high - frequency applications, signal integrity is a major concern. Network resistors can affect the signal integrity in a feedback circuit. For example, the parasitic capacitance and inductance of the resistors can cause signal distortion. Therefore, it is important to choose network resistors with low parasitic effects and to optimize the PCB layout accordingly.

Troubleshooting Common Issues

When using network resistors in feedback circuits, several issues may arise.

Gain Error

If the gain of the feedback circuit deviates from the expected value, it could be due to resistor tolerance. In this case, using higher - precision network resistors, such as our Precision Metal Foil Network Resistor, can help reduce the gain error.

Temperature - related Instability

If the circuit performance changes with temperature, it may be due to the temperature coefficient of the resistors. Using network resistors with low TCR values can mitigate this issue.

Conclusion

Network resistors are invaluable components in feedback circuits, offering matched resistance values, good temperature tracking, and other benefits. By carefully selecting the right network resistors based on factors such as precision, temperature coefficient, and power rating, and by considering design aspects like PCB layout and signal integrity, you can optimize the performance of your feedback circuits.

If you are looking for high - quality network resistors for your feedback circuit applications, we are here to help. Our extensive range of network resistors, including Ultra Precision Network Resistor, Precision Metal Foil Network Resistor, and Low Temperature Drift Foil Network Resistance, can meet the diverse needs of your projects. Contact us to discuss your specific requirements and start a procurement negotiation.

References

• Horowitz, P., & Hill, W. (1989). The Art of Electronics. Cambridge University Press.
• Sedra, A. S., & Smith, K. C. (2015). Microelectronic Circuits. Oxford University Press.