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Design >> RF Design >> Coherent and noncoherent receiver
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Message started by T3N on Jul 19^th, 2010, 12:41am

Title: Coherent and noncoherent receiver
Post by T3N on Jul 19^th, 2010, 12:41am

Hi all,

I've just joined this forum a few days ago and I am a newbie in RF design. Hope that I can learn a lot from you guys. Currently, I am reading on system design topics. The book I am reading is RF microelectronics by Razavi. Based on what I learn, there are basically three types of receiver: zero-IF, low-If and heterodyne. In Razavi’s book – “Digital modulation” chapter, he classifies the receiver in to two types: coherent and non-cohenrent. Detection schemes that require phase synchronization are called “coherent”.

So this is my question. If a zero-IF or low-IF has I and Q path, does it require a phase synchronization to avoid the start-up phase uncertainty of the oscillator? And in the case it requires a phase synchronization, will it be classified as a coherent receiver as well?

Thank you.
T3N

Title: Re: Coherent and noncoherent receiver
Post by pancho_hideboo on Jul 24^th, 2010, 11:39pm

T3N wrote on Jul 19^th, 2010, 12:41am:

If a zero-IF or low-IF has I and Q path, does it require a phase synchronization to avoid the start-up phase uncertainty of the oscillator?

No.

T3N wrote on Jul 19^th, 2010, 12:41am:

And in the case it requires a phase synchronization, will it be classified as a coherent receiver as well?

Yes.

Whether it is Coherent-scheme or Noncoherent-scheme is a matter of signal detection.
It is no relation to frequency conversion scheme such as zero-IF, low-If and heterodyne.

Note : low-IF is no more than heterodyne and zero-IF is homodyne.
But sometimes there is a case where homodyne means zero-IF with coherent detection.

Title: Re: Coherent and noncoherent receiver
Post by vp1953 on Jul 26^th, 2010, 9:58am

HI T3N,

>So this is my question. If a zero-IF or low-IF has I and Q path, does it >require a phase synchronization to avoid the start-up phase uncertainty
>of the oscillator? And in the case it requires a phase synchronization,
>will it be classified as a coherent receiver as well?

What is the modulation scheme you are using? It really depends on that. FSK, ASK dont need phase synchronization. Even though ASK does not need phase synchronization, you still need I and Q paths - since depending on the distance from the transmitter, the entire received signal can be in the I channel or the Q channel (so having only one channel can result in missed signals). Even with I and Q, this does not classify as a coherent reeiver. FSK with a direct conversion architecture does not need I and Q; a low IF FSK receiver may use I and Q (for image rejection etc) but still does not classify as a coherent receiver.