RFPositive vs. Negative Feedback: Differences and Applications
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This article compares negative feedback and positive feedback, highlighting the differences between them, especially in the context of amplifiers. We’ll explore the advantages and disadvantages of negative feedback compared to positive feedback.
As we know, feedback is a process where a portion of the output signal is fed back to the input. This technique is used to control the dynamic behavior of a circuit or system.
There are two main types of feedback in amplifiers:
- Positive Feedback
- Negative Feedback
Positive Feedback
If the original input signal and the feedback signal are in phase, the feedback is considered positive feedback_. This type of feedback tends to _increase the output signal. Think of it like a snowball rolling down a hill – it gets bigger and bigger.
Negative Feedback
Conversely, if the original input signal and the feedback signal are out of phase (typically 180 degrees), the feedback is negative feedback_. This type of feedback tends to _reduce the output signal. It’s like a governor on an engine, preventing it from running too fast.
Types of Feedback Amplifiers
Depending on the sampling type and mixing networks, feedback amplifiers are categorized as follows:
- Voltage series feedback
- Current series feedback
- Current shunt feedback
- Voltage shunt feedback
Positive Feedback vs. Negative Feedback: A Comparison
| Parameter | Positive Feedback | Negative Feedback |
|---|---|---|
| Overall phase shift | 0 or 360 degrees | 180 degrees |
| Input/output voltage, noise | Increases due to feedback | Decreases due to feedback |
| Feedback & input signal | In phase | Out of phase |
| Gain | Increases | Decreases |
| Stability | Poor | Better |
| Applications | Oscillators | Amplifiers |
Advantages of Negative Feedback over Positive Feedback
Here are some of the advantages of using negative feedback instead of positive feedback:
- Gain Stabilization: Negative feedback stabilizes the gain of the amplifier. This is crucial for reliable and predictable performance.
- Input Resistance Control: Input resistance can be increased for certain amplifier configurations.
- Output Resistance Control: Output resistance can be decreased for certain amplifier configurations.
- Operating Point Stabilization: The operating point of the amplifier is stabilized, making it less susceptible to variations in temperature or component values.
- Wide Applicability: Negative feedback is employed in various applications such as electronic amplifiers, regulated power supplies, wideband amplifiers, etc.
Disadvantages of Negative Feedback over Positive Feedback
Despite its numerous advantages, negative feedback also has some drawbacks:
- Gain Reduction: Negative feedback reduces the overall gain of the amplifier. This might require additional amplification stages to compensate.
- Input Resistance Reduction: In current shunt and voltage shunt type amplifiers, the input resistance is reduced.
- Output Resistance Increase: In current series and current shunt feedback amplifiers, the output resistance is increased.
