Slight overclock ADF4350 (Analog Devices 4.4 GHz) vco/pll synthesizer? - Page 1
Forum section: electronics / rf-microwave

author: wb0gaz
author_rank: Frequent Contributor
timestamp: March 14, 2023, 05:09:19 pm
content: I'm looking at LO options for Transverter to take 1296 MHz up to 5760 MHz. The LO would nominally be 5760-1296=4464 MHz.I'm considering trying Analog Devices ADF4350 which has max spec at 4400 MHz. Have you seen any discussion of actual ceiling frequency?As this is for ham use, it need not meet all specs (at all temperatures), but should generally lock.I'd like to avoid the MAX2870/2871 which are rated to ~6 GHz, but is more costly (I have a few ADF4350 from years-gone-by, so would like to start there first.)Grateful for any advice or general comments,Dave

author: geggi1
author_rank: Frequent Contributor
timestamp: March 14, 2023, 07:01:09 pm
content: You can use a frequency dubler and run your LO on 2232MHz.https://www.ebay.com/itm/121924121318?hash=item1c633e72e6:g:1-oAAOSwoBtW5nfB&amdata=enc%3AAQAHAAAA4HY0mv9WsU9nfSbuOvFmzqrFPebM4zksj2PCfzBvhMwEL%2BjoAQMH683aPxqOuwH01g5lKRB1gil%2FryEgsh3JWc01YL09wamSPR5XSO5CFYI5AGBNNmWxhc7ZiSGd86kV7TMtBCBZAhS6dye6UmkN2ZxoQhwXoOmfc3pBanPM1QIRmCqsdakyrNNbk5cZRkeTL3lwbnEDj9su8f3w6KeNa2HzyAm7iWVxEvze3YU8rMH%2B8ccsox3WwL00%2F3qcycvL5H9tTA9TuwXZWK7KmqAiib%2Fg1GbfwIi76BOpi7ABDvEB%7Ctkp%3ABk9SR-j47ZfcYQ

author: wb0gaz
author_rank: Frequent Contributor
timestamp: March 14, 2023, 07:06:13 pm
content: That (a doubler) was my first thought as well (and avoids the whole overclock scenario), but it's got insertion loss that would entail another gain stage to make up for that.May need to try experimental approach (I believe the 4350 has several - maybe four? - VCO cores, so overclock range probably very limited at best.Thanks for the input!Dave

author: geggi1
author_rank: Frequent Contributor
timestamp: March 14, 2023, 09:27:25 pm
content: You could try a gilbert cell frequency doubler.These will have gain because it is transistor based.You can find some information about this in a NE602 or SA612 application note.

author: wb0gaz
author_rank: Frequent Contributor
timestamp: March 14, 2023, 10:16:14 pm
content: Thanks --- an active doubler is a different possibility; it will be called on to accept ~2 GHz and generate ~4 GHz, so that gets into microwave parts, but will do some searching...

author: buta
author_rank: Contributor
timestamp: March 16, 2023, 04:52:15 am
content: As you have have a few ADF4350s and it is ham use, you can try to slightly increase the ref frequency or adjust the divider to check if it works beyond 4400 MHz.

author: nctnico
author_rank: Super Contributor
timestamp: March 16, 2023, 09:27:41 am
content: Quote from: buta on March 16, 2023, 04:52:15 amI agree. This is something you just have to try. 46MHz extra is ballpark 1% of the entire range of the chip.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 16, 2023, 10:05:01 am
content: Due to the segmented ranges for the VCO the 60 MHz extra are only 1% of the full frequency, but already some 30% of the tune range for the last segment. One could still give it a try.In the DS figure 21 give the tunig sensitivey and that curve does extend to about the planed 4460 MHz. So there is a chance it may work with some units, but it can very well fail with others.A more limited temperature range can help a little.

author: wb0gaz
author_rank: Frequent Contributor
timestamp: March 16, 2023, 11:41:06 am
content: Thanks very much for the discussion - very helpful. I understand that ADF4350 etc. has several VCO cores, so agree it's not really a "1%" overrange, but rather an overrange imposed on the highest frequency core only.Experimentation is certainly the brute force solution for my question; my original posting was mainly intended to see if this had been discussed previously (as I'd rather not expend time on learning curve on the part just to discover the overrange idea isn't going to be workable.)

author: nctnico
author_rank: Super Contributor
timestamp: March 16, 2023, 12:31:53 pm
content: Quote from: wb0gaz on March 16, 2023, 11:41:06 amYes and no. The whole VCO core needs some margin due to process variations; I doubt that every chip is going to switch bands at the exact same point. If you look at the VCO tuning graph (which ofcourse shows the typical values), you'll see it starts well below 2.2GHz and extends to over 4.5GHz. IOW: there is plenty of margin in the chip. Especially when you are not going to operate it at the temperature extremes.

author: mawyatt
author_rank: Super Contributor
timestamp: March 21, 2023, 01:01:01 pm
content: As mentioned , experiment with a few samples.Usually VCOs will show a slight increase in upper frequency limit with higher supply voltages, so try a slightly higher supply voltage.Also, figures 20 and 21 in the data sheet show performance beyond 4.4GHz, so chances are good you'll be able to reach 4.464GHz!!Best,