Will integer PLL work for WCDMA?

[dd2001]

PLL for WCDMA

I wonder that integer PLL works for WCDMA? Does integer PLL can meet the setting time requirement for WCDMA?

Please help.

 

[khouly]

Re: PLL for WCDMA

yeah as i think
if the system channel spacing is about 5Mhz and the bandwidth is about 60 Mhz from 2110 MHz to 2170 MHz
u can design an integer N type and use the reffernce oscillator to be 5MHz

this also will be the bandwidth of the loop is good enough to give u the settling time u want
the loop bamdwith is 1/20 of reffernce osc , so loop bandwidth could be 250Kz or more

but it is not the optimum solution

khouly

 

[springf2000]

Re: PLL for WCDMA

there is no problem,according to our experience,it works well,for example the Silab chip set

 

[dd2001]

Re: PLL for WCDMA

yeah as i think
if the system channel spacing is about 5Mhz and the bandwidth is about 60 Mhz from 2110 MHz to 2170 MHz
u can design an integer N type and use the reffernce oscillator to be 5MHz

this also will be the bandwidth of the loop is good enough to give u the settling time u want
the loop bamdwith is 1/20 of reffernce osc , so loop bandwidth could be 250Kz or more

but it is not the optimum solution

khouly

thanks. Here is a question again:

However, for GSM, a fraction-N PLL must be implemented for setting time, is it right?

 

[khouly]

Re: PLL for WCDMA

the main problem in GSM system that the channle spacing is very small so if u use integr N loop the bandwidth of the loop will be very narrow but i think the integr N loop can do the job


khouly

 

[djalli]

PLL for WCDMA

Yeah not only for CDMA

works for WCDMA, GSM/GPRS, EDGE, TDMA, PDC applications.

Is anything in particular you are seeking?

 

[dd2001]

Re: PLL for WCDMA

Well, GSM channel spacing is 200k, so bandwidth is about 20k, and integer-N setting time is about 200us, it is not meet most GSM requirement, so, I think switch to fractioanl-N may be necessary

 

[djalli]

PLL for WCDMA

hmmm yes!

 

[toonafishy]

Re: PLL for WCDMA

In GSM it also depends on how you do the frequency plan. If the synthesizer has to hop between TX - RX - MAHO - then a frac N is needed for the switching speed.

 

[djalli]

PLL for WCDMA

Anyone has any IEEE note for Delta-Sigma Fractional-N PLLs?

 

[Japp]

Re: PLL for WCDMA

Well, GSM channel spacing is 200k, so bandwidth is about 20k, and integer-N setting time is about 200us, it is not meet most GSM requirement, so, I think switch to fractioanl-N may be necessary

An Integer PLL can certainly do the job for GSM. As you will realize if you open the main part of the cellular phones on the market today.
The problems are as already stated that the channel spacing is 200kHz so you bandwidth should be below 20kHz but to this adds another problem; As the reference frequency is 200kHz you can expect spurs only 200kHz from the carrier. To suppress these you could attempt to decrease the bw further but you simply can't afford the increase in settling time.
So again if you do have a fractional-N pll that might help you (but be aware that hardly no commercial Frac-N pll meets the spec. in their own datasheets.. so go for one that can use a high ref.frequency)

 

[dd2001]

Re: PLL for WCDMA

So again if you do have a fractional-N pll that might help you (but be aware that hardly no commercial Frac-N pll meets the spec. in their own datasheets.. so go for one that can use a high ref.frequency) quote]

Well, it makes me confusing again. you said, "use a high ref. frequency", sure, I can use 5Mhz as refrence, however, question is how do I get 200K spacing from 5MHz?

Any comments?

 

[martinthorn]

Re: PLL for WCDMA

I wonder that integer PLL works for WCDMA? Does integer PLL can meet the setting time requirement for WCDMA?

Yes. For example Nokia WCDMA phones on the market use 2 integer-N
PLLs. One for RX and one for TX frequencies.

Well, GSM channel spacing is 200k, so bandwidth is about 20k, and integer-N setting time is about 200us, it is not meet most GSM requirement, so, I think switch to fractioanl-N may be necessary

Siemens and Nokia (perhaps others) run the GSM PLL at twice the wanted
frequency. This allows easy generation of quadrature signals for the
IQ modulators (flip-flops) and also a 400kHz reference frequency at the
integer-N PLL. This means that the loop bandwidth can be up to 40kHz
leading to acceptable settling time at least to class 10 GPRS (if I
remember correctly..)

 

[dd2001]

Re: PLL for WCDMA

Well, 400K isn't enough for GSM, sure, IQ need double clock, that is another issue.

 

[Japp]

Re: PLL for WCDMA

So again if you do have a fractional-N pll that might help you (but be aware that hardly no commercial Frac-N pll meets the spec. in their own datasheets.. so go for one that can use a high ref.frequency) quote]

Well, it makes me confusing again. you said, "use a high ref. frequency", sure, I can use 5Mhz as refrence, however, question is how do I get 200K spacing from 5MHz?

Any comments?

I said "use a high reference frequency if you have a Frac-N pll". If you use a Frac-N you can generate any frequency spacing from a higher one (that is what the name 'Fractional-N' stands for. Ie a fraction of the reference frequency(*N) in contrast to an integer-N pll.)

 

[martinthorn]

Re: PLL for WCDMA

Well, 400K isn't enough for GSM

Yes it is. I have designed integer-n PLLs for GSM handsets with
25kHz loop bandwidth with a 400khz reference. This was sufficient
to meet class 6/10 GPRS settling time requirements. Typical settling
time was <200us. Fractional-N is not necessary for GSM.