crystal value for wireless transmitter 1

[Lanfeust23]

Hi,
I need to use a 13.125MHz crystal for the AT86RF401 transmitter from ATMEL and I would like to know if this value must be respected exactely or can be changed, because I only found a 13.0625 MHz crystal.
Thanks

 

[IRstuff]

Why don't you ask ATMEL's applications engineers where to get the crystal?

TTFN

 

[Lanfeust23]

There is only one company which sell the good crystal : Crystek. And the probleme is that it's the only one item I need to buy in Crystek and it will cost a lot for only one item. But I need several other items I found in Digikey (and not in Crystek), which is faster for me !

 

[nbucska]

you need
The specification of the receiver
The frequency range you may operate
Cost and space limitations

It is possible to generate an other frequency from a crystal several ways (dividing/mixing/frequency synthetizers).

<nbucska@pcperipherals.com>

 

[IRstuff]

Did you read the datasheet and app note carefully? The answer is in there.

TTFN

 

[Lanfeust23]

I read it but not enough carefully if you say the answer is in there. (and I don't know what do you speak about app note ! I only read datasheet !)

 

[IRstuff]

That's why companies like ATMEL had websites; to make easier to get data.

From page 9 of the datasheet:
The crystal oscillator circuit is designed to work with crystals with fundamental frequen-cies between 11 and 19 MHz. Forty pF of internal capacitance is connected between each of the crystal input pins and (chip) ground. Alternatively, an external clock can be used for these functions.

The app note for the evaluation board indicates that you need a 20ppm crystal.

TTFN

 

[Lanfeust23]

I've seen that but I thought it was weird to give such a range, I supposed if the value changes so much, emitting frequencie changes also and I have to change also the receiver one. Just a last question : what means 20ppm ?
Thank you for your help !

 

[melone]

Parts Per Million

 

[IRstuff]

The point was, given a 20ppm stability crystal, the transmitter would take any crystal from 11 to 19 MHz.

TTFN

 

[nbucska]

Lanfeust:
As I wrote, you must check the receiver, too and make sure
it can receive the transmitted signal.

<nbucska@pcperipherals.com>

 

[Lanfeust23]

The receiver is the one ATMEL matched with : the T5744 receiver!