Recommendation for a VCO/PLL IC for a DIY GPSDO/OCXO 10MHz lab reference.  - Page 1
Forum section: electronics / projects

author: t1d
author_rank: Super Contributor
timestamp: February 04, 2024, 03:48:18 pm
content: Recommendation for a VCO/PLL IC for a DIY GPSDO/OCXO 10MHz lab reference.Arduino 328P MCU. Ublox M8N.Maybe something in the 4046 series, but I can't tell if it is a discontinued chip? Finding the data sheet is not so easy? Mouser and Digikey have the 4046AM, but not the data sheet? Maybe I am just having a bad day?If a 4046, which particular model? What else might I need to consider.I would rather build the device, so as to learn, than buy a $100 Ebay model. I think I have most everything, except this IC.Thanks for your help.

author: edavid
author_rank: Super Contributor
timestamp: February 04, 2024, 04:38:07 pm
content: Quote from: t1d on February 04, 2024, 03:48:18 pmSuggestion: look at some of the many existing designs and see what they use. You might even find that you could build one of those designs instead of starting from scratch.QuoteOpen findchips.com and search for 4046 with "In Stock Only". If the distributors have thousands in stock, it's not discontinued.https://www.findchips.com/search/4046QuoteIf you do a Google search for "4046 datasheet", it works fine.Quote74HC4046 is the obvious choice for a 10MHz, 5V design.

author: jbb
author_rank: Super Contributor
timestamp: February 04, 2024, 09:08:21 pm
content: I may be about to get rotten fruit thrown at me… how about the LMK series from Texas Instruments? They seem to integrate a lot of what you need; given an XO input and 1 pulse per second input they run a fancy super low jitter internal 2.5 GHz oscillator and can spit out 3 or more derived clocks.https://www.ti.com/product/LMK5B12204https://www.ti.com/product/LMK05318BNote: apparently if you want to do a GPSDO thing, they recommend that the XO should not be 10 MHz but instead 14.something MHz; see data sheet for details.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: February 04, 2024, 09:54:14 pm
content: Quote from: jbb on February 04, 2024, 09:08:21 pmInteresting parts, completely the opposite end from a simple logic device like 12c 4046, that can work without any MCU needed.The price is high, but not totally nuts, and it is single sourced. Needs quite a lot of mA when running too... running at 2.5GHz does thatI wonder how well they can work, and how they cope with the 1/48MHz jitter seen on typical GPS references signals.They can be configured with FINC/FDEC pins, and do need a companion MCU.

author: edavid
author_rank: Super Contributor
timestamp: February 04, 2024, 10:42:47 pm
content: Quote from: jbb on February 04, 2024, 09:08:21 pmHow does a hobbyist mount a VQFN48 package

author: jbb
author_rank: Super Contributor
timestamp: February 04, 2024, 11:06:31 pm
content: Quote from: edavid on February 04, 2024, 10:42:47 pmWell, that is a bit tricky. Thankfully it’s a 0.5mm pitch, rather than something smaller. I’d use solder paste and hot air reflow. Given the high power consumption - looks like a whole 1 Watt! - you’d need to solder the center pad to a nice big ground plane as well. So I’d recommend using a 4 layer (or more) board & solder paste stencil too.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: February 05, 2024, 10:05:14 am
content: Quote from: t1d on February 04, 2024, 03:48:18 pmJust recently been there, used a 74HC4046 "new old stock" from eBay.See:https://www.qsl.net/g4aon/gpsdo/SJ

author: jonpaul
author_rank: Super Contributor
timestamp: February 05, 2024, 11:00:44 am
content: Great reference example, \https://www.leobodnar.com/shop/index.php?main_page=index&cPath=107Leo can answer questiuonsj

author: raftronik
author_rank: Contributor
timestamp: February 05, 2024, 06:48:41 pm
content: Hello,I made my GPSDO from few projects,one part from thishttps://www.dl4zao.de/projekte/index.html#a1968changed PLL dividercontroler from thishttps://dl6gl.de/gps-diszipliniertes-10mhz-normal.htmland few more changes for my needs.

author: t1d
author_rank: Super Contributor
timestamp: February 06, 2024, 11:02:21 am
content: Thanks for all of your excellent responses and information!1) I may have been having some trouble with the model number... I was searching for 74HCT4046A. I rather imagine that I got this particular number from some reference project. The extra "T" was limiting things. Here's the difference with the T model:The only difference between the 74HC4046A and 74HCT4046A is the input level specification of the INH input.2) I am now able to find available stocks for the Non-T model at Mouser, where I usually shop. However, the data sheet link is tied back to TI, directly, and it fails. It fails via Digikey and TI.com, as well. I can get the Nexperia data sheet. Has the TI model changed to "CD74HC4046?" That did not seem to work, either.3) Yes, I do refer to other projects for learning and inspiration. I might even build one, fully as designed. However, I do prefer to dig down into the circuit, in order to learn. Learning and building are the fun part, to me, as opposed to buying a unit, which I probably could do for cheaper. But, what's the fun in that?Cheers!

author: PCB.Wiz
author_rank: Super Contributor
timestamp: February 06, 2024, 10:49:17 pm
content: Quote from: t1d on February 06, 2024, 11:02:21 amTI have busted something, or they plan to EOL the 74hc4046 ??nexperia data sheets are good,TI still have CD4046 data herehttps://www.ti.com/lit/an/scha002a/scha002a.pdfand lcsc have data herehttps://datasheet.lcsc.com/lcsc/2304140030_Texas-Instruments-CD74HC4046AM96_C6542.pdf

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: February 06, 2024, 11:01:02 pm
content: I used surplus Philips 74HC4046ANMouser have the datasheet, but no stock as they are obsolete.https://eu.mouser.com/datasheet/2/302/74HC_HCT4046A_CNV_2-38776.pdfSJ

author: SCSKITS
author_rank: Regular Contributor
timestamp: March 24, 2024, 05:18:05 pm
content: Look at the CD74HC7046A. It only has two detectors vs three for the 4046, but it has a lock indicator.If using an external OCXO, you will not be using the VCO on the chip.You can also just use an exclusive OR gate if the two input signals are already at the frequency you intend to use.I ended up putting the dividers and an exclusive OR gate in a small EPLD and then buffered the exclusive OR output using a non inverting gate powered from a precision reference.That drives the PLL filter (100K 100uF) which is followed by an op-amp buffer and some level shifting circuitry and another op-amp to reduce the OCXO control range.

author: t1d
author_rank: Super Contributor
timestamp: March 25, 2024, 02:47:44 pm
content: Quote from: SCSKITS on March 24, 2024, 05:18:05 pmThank you for the chip suggestion. I do have a question, though. My OCXO includes a voltage input, with which to true its frequency to the GPS. So. I do not understand why I would not need the VCO feature. Is this because the MCU will be monitoring the frequencies and doing the adjusting? (Pardon my brain fog. Rough night = back pain and no sleep.)

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: March 25, 2024, 03:06:11 pm
content: “My OCXO includes a voltage input, with which to true its frequency to the GPS. So. I do not understand why I would not need the VCO feature. Is this because the MCU will be monitoring the frequencies and doing the adjusting?“With a 10 MHz GPSDO, the crystal oscillator is usually contained within a heated case and adjusted automatically by Voltage control. It’s often just referred to as an OCXO… not quite correct, but not important.The 4046 and similar ICs are used as part of the control circuit, as in the “time interval counter” in the Lars Walenius Arduino controlled GPSDO.

author: bingo600
author_rank: Super Contributor
timestamp: March 25, 2024, 08:35:55 pm
content: Quote from: t1d on March 25, 2024, 02:47:44 pmThe "VCO" would be substituted by the (prob. downscaled) 10MHz OCXO , so you don't need/want to use the built in (unprecise) VCO in the chip.

author: kevin.gibbs
author_rank: Regular Contributor
timestamp: March 26, 2024, 03:17:55 pm
content: You will need an OCXO with good short-term stability. Which one do you have now?What accuracy do you plan to achieve? 0.1ppb, 0.01ppb