Reply
Posts: 2
Registered: ‎08-21-2015

What are the phase noise implications of the Si5351A%3F

[ Edited ]

I have been using the Si5351A as a combined variable frequency oscillator and beat frequency oscillator in amateur radio Single Sideband Transceivers. The results have been very satisfactory and I have published several articles and you tube videos that demonstrate the application. BUT there are those who only read spec sheets and typically pooh pooh the Si5351 for this application claiming poor phase noise characteristics (as compared to the Si-570). I have not found phase noise to be a problem. But lacking an elaborate laboratory with costly spectrum analyzers, tracking oscillators, 500 MHz scopes and on and on, I am reaching out to any one who has made those measurements and what are the results.

Posts: 2
Registered: ‎07-29-2015

Re: What are the phase noise implications of the Si5351A%3F

please give me a call to discuss your case,thanks, my cell phone number is 13794454530

 

Best Regards,

 

Leo Luo

Silicon Labs

 

Mobile +86 13794454530

Office  +86 755 8618 5674

 

12F, Desay Building, Hi-Tech Park South, Shenzhen 518057, PRC

www.silabs.com


hamoperator wrote:

I have been using the Si5351A as a combined variable frequency oscillator and beat frequency oscillator in amateur radio Single Sideband Transceivers. The results have been very satisfactory and I have published several articles and you tube videos that demonstrate the application. BUT there are those who only read spec sheets and typically pooh pooh the Si5351 for this application claiming poor phase noise characteristics (as compared to the Si-570). I have not found phase noise to be a problem. But lacking an elaborate laboratory with costly spectrum analyzers, tracking oscillators, 500 MHz scopes and on and on, I am reaching out to any one who has made those measurements and what are the results.


 

Posts: 19
Registered: ‎11-21-2014

Re: What are the phase noise implications of the Si5351A%3F

Hi,

 

I took an example phase noise plot of an Si5351 at 156.25MHz and attached the plot. As you can see and already know, the phase noise performance is definitely worse than the Si570 (2.7ps vs 0.3ps). And you are right just based on these numbers, some will balk at using the Si5350/51 versus the Si570.

 

The point you bring up is very important in determining what device best suits your application and stresses the importance of really understanding your application. Do I need high phase noise performance, do I need programmablility, does this device offer some flexibility if my design requirements change, etc? These are all questions you should be asking yourself when choosing parts for your design. Also, cost is the main limiting/driving factor (depending on how you look at it) in designs, so why pay for a higher performance device when you don't need it? This is a very interesting topic for discussion.

 

Could you please share links to your articles and youtube videos? I'm very interested in taking a look at these and I'm sure others are as well.

 

Let me know if you would like anymore measurements taken.

 

Thanks,
Matt

Posts: 2
Registered: ‎08-21-2015

Re: What are the phase noise implications of the Si5351A%3F

 

 

Thanks for the phase noise data. Below is the link to the website where many Si5351's have been embedded into ham SSB transceivers. See the list specifically the Lets Build Something, the ZIA and the LBS 2nd Generation. In one project the Belthorn III the LO is generated at 4X and then externally divided down (SN74AC74) to 1X. This was suggested as means of improving phase noise by 6 DB -- [10*log(4)]

 

http://www.n6qw.com/  If you search you tube for n6qw there are many more si5351 application videos.

<a href="http://community.silabs.com/t5/Welcome-and-Announcements/Community-Ranking-System-and-Recognition-Program/m-p/140490#U140490"><font color="#000000"><font size="2">Hero</font></font> </a> jmg
Posts: 1,174
Registered: ‎04-27-2004

Re: What are the phase noise implications of the Si5351A%3F


I took an example phase noise plot of an Si5351 at 156.25MHz and attached the plot. As you can see and already know, the phase noise performance is definitely worse than the Si570 (2.7ps vs 0.3ps).

Let me know if you would like anymore measurements taken.

 


 

That seems to be a single plot, not a comparison of Si5351A vs Si570 ?

Do you have a test showing both ?

Highlighted
<a href="http://community.silabs.com/t5/Welcome-and-Announcements/Community-Ranking-System-and-Recognition-Program/m-p/140490#U140490"><font color="#000000"><font size="2">Hero</font></font> </a> jmg
Posts: 1,174
Registered: ‎04-27-2004

Re: What are the phase noise implications of the Si5351A%3F


 In one project the Belthorn III the LO is generated at 4X and then externally divided down (SN74AC74) to 1X. This was suggested as means of improving phase noise by 6 DB -- [10*log(4)].

 I'm not quite following that logic - if the external divider just mimics what the Si5351A Internal Dividers would have done, I don't think that improves phase noise at all ?

 Or, does the external divider somehow move the PFD frequency inside Si5351A ?