Is this correct behavior from a 12MHz TCXO? - Page 1
Forum section: electronics / beginners

author: soFPG
author_rank: Frequent Contributor
timestamp: June 12, 2021, 03:53:08 pm
content: I was just connecting my TCXO and out of curiosity I turned on my oscilloscope and measured the waveform (see attachments).To be honest, I was quite surprised. I looks rather janky. This is the schematic (see attachments).I would have expected this to be a 3.3V signal, but in fact it is a 1.2V signal?!Is this behavior expected?

author: langwadt
author_rank: Super Contributor
timestamp: June 12, 2021, 04:11:31 pm
content: what scope and what is the settings?

author: soFPG
author_rank: Frequent Contributor
timestamp: June 12, 2021, 04:50:47 pm
content: 250MHz 1GS/s scope with 200MHz probe, setting 1:10These are the specs. I guess this waveform is called clipped sinewave?

author: David Hess
author_rank: Super Contributor
timestamp: June 12, 2021, 07:01:06 pm
content: It is common for the output to not be particularly clean. If you want a clean output, then there are oscillators specified to have sine wave outputs, and even they are typically not low distortion.

author: floobydust
author_rank: Super Contributor
timestamp: June 12, 2021, 08:40:50 pm
content: Yes, correct behaviour/expected signal because it's just the oscillator's raw output. Some modules have an output coupling capacitor, others do not, so it might have a DC component present as well. Usually the signal is a bit stronger but your scope (capacitance) might be loading it down.If you want a square-wave, you need to add an extra stage, some discussion about it here:https://www.eevblog.com/forum/projects/how-to-increase-tcxo-output/msg2377440/#msg2377440https://www.eevblog.com/forum/beginners/from-10mhz-sine-to-square-via-comparator-can-you-help/msg3554634/#msg3554634

author: radiolistener
author_rank: Super Contributor
timestamp: June 12, 2021, 10:07:44 pm
content: Quote from: soFPG on June 12, 2021, 03:53:08 pmWhere did you get this TCXO? Some time ago I ordered Chinese TCXO but it produce square wave about 0.8 Vpp. I'm not sure what is the reason, may be this is low voltage TCXO or may be they are defective. In any case they are unusable, because it's amplitude is too low to drive FPGA CLK input (I tested it, but it cannot see the clock), so I cannot use it. I expected 3.2 Vpp.

author: soFPG
author_rank: Frequent Contributor
timestamp: June 13, 2021, 10:44:11 am
content: QuoteOkay, good to hear. But why am I getting only 1.2V output even though the TCXO is connected to 3.3V?QuoteTaobaoQuoteIt works for me, I only had to switch the I/O type to 1.2V input (Xilinx XC3S200AN).

author: David Hess
author_rank: Super Contributor
timestamp: June 13, 2021, 10:56:18 am
content: Quote from: soFPG on June 13, 2021, 10:44:11 amDo you have a part number or datasheet?

author: Labrat101
author_rank: Unknown
timestamp: June 13, 2021, 01:12:14 pm
content: Its totally correct . the output is High Z . and your scope is probably 50.Also you need a choke on the positive feed .Check with a high impedance probe x 10 and you may have to load the output so you get a good impedance match to thescope . Try using a CRT scope and it will look much better .add a photo of the TCXO would be nice

author: langwadt
author_rank: Super Contributor
timestamp: June 13, 2021, 01:24:33 pm
content: Quote from: soFPG on June 13, 2021, 10:44:11 amswitching the IO type to a different voltage doesn't really do anything, changing the Vcco does

author: Labrat101
author_rank: Unknown
timestamp: June 13, 2021, 02:19:55 pm
content: Are sure it's a 3.3v TCXO?if you are running it at the wrong voltage will not help.Depends on the design 1v apx outIs not uncommon..Load up a picture of the TCXO.The label and serial, Ref number will give better details. If you got it as used from Ebay etc. It maybe customized . For its original usage . The guy's that sell a lot of stuff on china &co have not got a clue what they have most of the time.I picked up a customized OCXO like this for a few $s . It was 0.001 PBB . 10 -11 the voltage was also customized.So let's see what you have ..New or second hand .

author: soFPG
author_rank: Frequent Contributor
timestamp: June 13, 2021, 03:11:27 pm
content: This is the TCXO:

author: Labrat101
author_rank: Unknown
timestamp: June 13, 2021, 05:58:13 pm
content: Quote from: soFPG on June 13, 2021, 03:11:27 pmThis Not a STO-3225A for sure .Were did you fine the voltage for this ?? looking at your scope picture it looks like its running under/over voltage.I could be wrong on this as it looks more like an X Russian Mil with Ruggedized that was stuck on a different PCB.Were did you get it from ?? And where does it say 3.3v or was that what it said from the supplier ??Unless you have got some other data that is 100% accurate .PS try running it at 1.8v and see what the wave form looks like with a x10 probe

author: soFPG
author_rank: Frequent Contributor
timestamp: June 13, 2021, 06:53:12 pm
content: QuoteHow do you know?QuoteThe information below the Taobao listing lists 3.3V as supply voltage (see one of my last posts).

author: Labrat101
author_rank: Unknown
timestamp: June 13, 2021, 07:32:28 pm
content: Quote from: soFPG on June 13, 2021, 06:53:12 pmSimple this is the Date code and country of origin why would any one remove the top line . !!I would ask the supplier what was the number that has been removedIt was probably a L series the rest you have to guess .Sorry .Try running it at 1.8v and set your scope timebase so there is only 3 cycles and slowly increase the voltage on the vccWhat you are see is almost good , not knowing your setup and how you have set the scope .It should be closer to a clipped signand see what happens . if it has a better resonance @ 1.8v or 3.3 v .. Give time for it to stabilize between each adjustment.Not sure why you went for this tcxo there are so many really good New high quality tcxo's on the marketfrom reputable sources. with a spec sheet that matches . for a few $