Phase Locked Loops: Coherent vs Non-Coherent Detection, PLL & 2*pi Rotation

In summary, coherent detection involves phase locking an oscillator to the carrier of a received signal to effectively detect modulated information, while non-coherent detection does not track the signal carrier's phase. A PLL is a circuit that allows for this phase locking process. A 2*pi phase rotation is equivalent to a 360° rotation, and is often used to describe the directional vector of a modulation signal.
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janu203
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what is difference between coherent and non-coherent detection? and what is a PLL? secondly what is meant by 2*pi phase rotation? is it same as 2*pi phase shift? thanks in advance
 
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PLL. By measuring the difference in phase between an oscillator and a signal carrier, the oscillator can be adjusted to lock onto the phase of the signal. http://en.wikipedia.org/wiki/Phase-locked_loop

A coherent detector phase locks an oscillator to the carrier of the received signal. It then effectively multiplies the received signal by the oscillator to detect the modulated information. It retains the absolute phase of the modulation.

A non-coherent detector does not track the signal carrier's phase. One example is an envelope detector for AM.

Phase shift and phase rotation are effectively the same.
A 2*Pi radian rotation is a 360° rotation, so it has no net effect.
Modulation is often described as a “phasor” which is a directional vector. http://en.wikipedia.org/wiki/Phasor
 
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janu203 said:
what is difference between coherent and non-coherent detection? and what is a PLL? secondly what is meant by 2*pi phase rotation? is it same as 2*pi phase shift? thanks in advance

Please check your PMs.

Please do some reading on your own before asking overly broad questions here. We expect to see that you have put some effort into answering your questions. You have been given some great resources by Baluncore -- please read through the links, and then ask specific questions about that reading if you still have questions.
 

1. What is a phase locked loop (PLL)?

A phase locked loop is an electronic circuit that is used to generate a signal that is coherent with a reference signal. It compares the phase of the reference signal with the phase of the generated signal and adjusts the frequency of the generated signal to match that of the reference signal.

2. What is the difference between coherent and non-coherent detection in phase locked loops?

Coherent detection in a phase locked loop involves comparing the phase of the reference signal with the phase of the generated signal using a phase detector. Non-coherent detection, on the other hand, uses a frequency detector to compare the frequency of the reference signal with the frequency of the generated signal.

3. What is the role of 2*pi rotation in phase locked loops?

2*pi rotation, also known as phase shifting, is an important component in phase locked loops. It is used to adjust the phase of the generated signal to match that of the reference signal. This ensures that the generated signal remains coherent with the reference signal.

4. How does a phase locked loop maintain lock between the reference and generated signals?

A phase locked loop maintains lock between the reference and generated signals by continuously comparing the phase/frequency of the two signals and making adjustments as needed. This ensures that the generated signal stays in sync with the reference signal.

5. What are some common applications of phase locked loops?

Phase locked loops are commonly used in communication systems, such as radio and television, to maintain a stable carrier frequency. They are also used in clock recovery circuits, frequency synthesizers, and frequency modulation systems. Additionally, they are used in various control systems, such as servo motor control and phase-locked loop filters in power supplies.

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