How to go about making a Frequency Synthesizer for GSM ??

[cyclops_steel]

mc145152 100khz

I am using MC145152-2 IC.
I have to design it for GSM Frequency (935MHz - 960MHz)
The channel spacing is 200KHz.
I am really confused !!!!!!
This is for a Receiver Application
Is there any online tutorial on how to go about designing it !!!!
Please Help !!!!!!!!
Thanks !!!!!

 

[biff44]

upb1506- rf circuit

Wow, where did you find those chips? In a museum?

You are going to have a hard time doing what you want to, since the maximum input frequency for that PLL chip is 25 MHz. The only saving grace is that programming is done with parallel bits, so you do not have to drive with a microcontroller to programm frequency, but you can use a bank of switches.

 

[cyclops_steel]

Re: How to go about making a Frequency Synthesizer for GSM ?

hehe........
I have been told to design the Frequency Synthesizer using that chip only !!!!

Heres some more information.......
There is a VCO already designed !!!!!
+ the IF is 70 MHz
I have to design the freq Synth for Receiver !!

Thanks for your reply.....could you ellaborate more......

 

[biff44]

Re: How to go about making a Frequency Synthesizer for GSM ?

I would probably talk my boss into another chip. If I had a gun to my head, I would use a NEC prescaler UPB1506, a 12.8 MHz crystal oscillator, a divide by R=8192, and divide by N=8650, 8651,...,8900.

Your phase noise is going to be poor, and there will be sidebands 1.56 KHz away from the carrier to deal with. Tuning speed will be slow.

 

[biff44]

Re: How to go about making a Frequency Synthesizer for GSM ?

Here is an excel spread sheet. The problem is that if you use any prescaler value smaller than 64, the freescale chip does not work (input frequency gets too high). Therefore you need a very low phase detector comparison frequency to get the 100 KHz step size.

 

[cyclops_steel]

Re: How to go about making a Frequency Synthesizer for GSM ?

Wow !!!!!!!!!
You are a life-saver......
Thank you so so much !!!!!!!


I ll work on it and let you know the progress...
Thanks once again !!!!

 

[biff44]

Re: How to go about making a Frequency Synthesizer for GSM ?

Hey, I just reread your orignal post and noticed that you need a 200 KHz step size, not 100 KHz that I suggested. You can use a 3.12k KHz comparison frequency, and the phase noise should get 6 dB better. New spreadsheet is attached.

 

[cyclops_steel]

Re: How to go about making a Frequency Synthesizer for GSM ?

Thanks a LOt !!!!!!!!!!
I will get back to you soon !!!

 

[cyclops_steel]

Re: How to go about making a Frequency Synthesizer for GSM ?

I am facing one problem............

The maximum R value i can get in MC145152 is 2048
Whereas you have mentioned 8192........

Added after 2 minutes:

How would this value affect the performance and the circuit !!!

 

[kspalla]

The configuration is simple.
There is no pre-scalar
You are using 12.8MHz crystal then use R to 64 which gives 200KHz step size sane as PFD frequency.
Now vary the N from 4325 to4450 to get 865MHz to 890MHz
In case of any confusion pm me.

 

[biff44]

Jeez, you are right. The data sheet I saw had 2 different part numbers on it, I was looking at the MC145151-2.

For your part, you just want to use the 2048 divisor and pick a crystal oscillator that results in the phase detector comparison frequency of 3.125 KHz. So you need a crystal oscillator of 6.4000 MHz. You can choose any divisior R that you want, and vary the crystal oscillator frequency accordingly.

Added after 58 minutes:

kspalla, this is a very old silicon part, and can only operate, on a good day, to 25 MHz input frequency.

 

[cyclops_steel]

Re: How to go about making a Frequency Synthesizer for GSM ?

Thanks people.....

Even i was thinking of the same thing, using a 6.4MHz Crystal.

One more thing will a simple OPAMP (741) suffice for a loop filter. An active filter will be better rite !!!!!!!!!

 

[biff44]

Re: How to go about making a Frequency Synthesizer for GSM ?

For a generic pll, my choice would be an op27. Fairly low noise, not too much bandwidth to cause oscillation problems.