In this paper, we conduct a detailed analysis and comparison of various methods used to identify and retrieve feedback in analog electronic technology courses, including positive and negative feedback, voltage and current feedback, as well as series and parallel feedback. Feedback is one of the most essential concepts in electronic circuits, widely applied across different fields of electronics. It plays a crucial role in enhancing circuit performance by adjusting the output (voltage or current) in response to changes, thereby stabilizing and improving system behavior. As such, understanding feedback is an integral part of learning analog electronics.
However, students often find it challenging to grasp the concept of feedback, especially when dealing with complex circuits that may contain multiple types of feedback. Identifying which components are responsible for feedback and determining the type of feedback can be quite confusing. This article aims to address these difficulties by discussing effective methods for identifying and classifying feedback in electronic circuits.
1. **How to Identify Feedback**
To determine whether a circuit has feedback, students should look for a connection between the input and output loops of the amplifier. If such a connection exists, it indicates the presence of feedback. For example, in the circuit shown in Figure 1, resistor Re is connected both in the input and output loops, making it a feedback component and confirming that the circuit includes feedback.
2. **How to Distinguish Between Positive and Negative Feedback**
The instantaneous polarity method is commonly used to differentiate between positive and negative feedback. In a common-emitter configuration, the collector and base are out of phase, while in a common-base configuration, the collector and emitter are in phase. For operational amplifier circuits, the inverting input and output are out of phase, whereas the non-inverting input and output are in phase. By analyzing the phase relationship of the feedback signal relative to the input, one can determine whether the feedback is positive or negative.
3. **Discriminating Voltage Feedback from Current Feedback**
Voltage feedback occurs when the feedback signal is proportional to the output voltage, while current feedback is when the feedback signal is proportional to the output current. To distinguish between the two, one can short the output and observe if the feedback signal disappears (indicating voltage feedback) or remains (indicating current feedback). Additionally, examining where the feedback signal is sampled from the output can help identify whether it's voltage or current feedback.
4. **Distinguishing Series Feedback from Parallel Feedback**
Series and parallel feedback are differentiated based on how the feedback signal interacts with the input signal. If the feedback signal is compared with the input signal in terms of voltage, it is considered series feedback. If it is compared in terms of current, it is parallel feedback. For instance, in an operational amplifier circuit, if the feedback signal is subtracted from the input voltage, it is classified as series feedback.
In summary, the process of identifying feedback involves several key steps: first, using the instantaneous polarity method to determine whether the feedback is positive or negative; second, analyzing the output to determine whether the feedback is voltage or current; and finally, evaluating how the feedback signal interacts with the input to classify it as either series or parallel feedback. These methods provide a structured approach to understanding and applying feedback in electronic circuits.
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