Frequency tripler  - Page 1
Forum section: electronics / projects

author: TV-Repairman
author_rank: Newbie
timestamp: July 15, 2018, 07:54:07 am
content: Hi,I want to maker a stand alone marker for a spectrum analyser, or DSO, and have a 33.333 crystal oscillator,the plan is I want to make it 100 ish MHz's, does anyone have any ideas on a frequency tripler circuit.Paul

author: hendorog
author_rank: Super Contributor
timestamp: July 15, 2018, 08:02:01 am
content: I learned heaps from this doc about multiplers when making a doubler. There is a very clever tripler by Charles Wenzel which might be of interest:http://www.qsl.net/va3iul/Frequency_Multipliers/Frequency_Multipliers.pdfAlso some other links with info in case you haven't found them yourself.http://www.crystek.com/documents/appnotes/Frequency_Multiplication_Techniques.pdfhttps://www.markimicrowave.com/blog/marki-microwave-multipliers/Can buy one of course:https://www.minicircuits.com/WebStore/Multipliers.html

author: TV-Repairman
author_rank: Newbie
timestamp: July 15, 2018, 08:10:00 am
content: Hi Thank you for replying,I won't buy its the fun of making, I'll take a look at the sites you mentioned

author: TV-Repairman
author_rank: Newbie
timestamp: July 15, 2018, 08:11:35 am
content: That has crossed my mind

author: hendorog
author_rank: Super Contributor
timestamp: July 15, 2018, 08:30:25 am
content: Quote from: TV-Repairman on July 15, 2018, 08:10:00 am

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 15, 2018, 08:54:58 am
content: Couple a 100MHz bandpass onto the output, then amplify and bandpass and buffer it a bit more. Probably fine to use a pair of 1st or 2nd order bandpasses, and choose a modest impedance (~200Ω?) so the crystal oscillator isn't heavily loaded at the 3rd harmonic, and a topology (i.e., series-first) so that it isn't loaded at the other harmonics.That's basically it. Filters can be designed with calculator tools, and a few transformations if necessary (particularly beneficial for high Q resonators, e.g.https://www.jrmagnetics.com/rf/doubtune/doubccl_c.php). The characteristic impedance is sqrt(L/C), the (system) Q is this impedance over or under the system impedance (i.e., around 200Ω, don't forget the terminator!) and the resonant frequency is 1 / (2*pi*sqrt(L*C)).The amplifiers can be anything, but I'd prefer a:- Grounded base/gate: low reverse feedback, good gain, downside: input impedance a bit too low here.- Cascode: low reverse feedback, high gain, modest input impedance. Good choice.- Diff pair, especially with input to one side, ground to the other input, output from the far collector/drain -- noninverting, good gain, no Miller effect (low reverse feedback).- Emitter follower: low reverse feedback, low voltage gain, low output impedance. Good output buffer. Add a series terminating resistor (and also a coupling cap), to drive 50 ohm transmission line, or, whatever you're connecting to.You can get away with 2N3904s, or whatever JFETs (say, MMBF4393, J309, etc.), but preferably a somewhat faster type like MMBTH10 or better. Biasing is textbook. To find input and output impedances, you're probably better off setting it up in SPICE, then tweaking the real circuit and going back and forth between SPICE and reality until you've got a reasonably correct model of the real deal, including actual part values and parasitics. It's a process, but it's not at all insurmountable, even if you aren't very experienced in tuning RF circuits.Tim

author: Benta
author_rank: Super Contributor
timestamp: July 15, 2018, 09:38:35 am
content: Set it up as a third overtone oscillator. This is normal practice at these frequencies. Here's a short article on the subject:http://jaunty-electronics.com/blog/2012/08/overtone-crystal-oscillator/EDIT: scratch this, I missed that it's an oscillator, not just a crystal.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 15, 2018, 11:14:03 am
content: Also, overtones are not exact harmonics, so you'll get a different frequency -- and tempco -- doing that. Beware!Tim

author: TV-Repairman
author_rank: Newbie
timestamp: July 15, 2018, 12:08:23 pm
content: Tim ,Thanks understood every word,makes so much sense, thanks for your time, putting into practice at the moment in the workshop.Paul

author: vk6zgo
author_rank: Super Contributor
timestamp: July 15, 2018, 01:09:33 pm
content: The retro way was to take a lower frequency signal, distort it using a class "c" amplifier then as the anode/collector load of that amplifier, use an LC circuit tuned for three times the initial frequency.

author: Wolfgang
author_rank: Super Contributor
timestamp: July 18, 2018, 11:02:07 pm
content: If the signal should have low phase noise, the circuits of choice are the odd-order frequency multipliers by Charles Wenzel.I made one from 5MHz to 15MHz, but an equivalent circuit would work for 33MHz with changed filter component values.https://electronicprojectsforfun.wordpress.com/an-noninteger-frequency-divider-with-sinewave-output/and something from 28MHz to 144MHz:https://electronicprojectsforfun.wordpress.com/a-clean-23cm-signal-source/If phase noise is unimportant, any transistor tripler stage could be used.

author: LaserSteve
author_rank: Super Contributor
timestamp: July 19, 2018, 05:18:30 am
content: Back terminate the crystal oscillator. Then overdrive a Ebay MMIC amplifier demo board and filter out what you want. I would consider a high pass followed by a low pass, rather then a bandpass. This tends to do a better job of shunting the unwanted crap.If you have a square wave oscillator (Ttl?) Then all you need to do is back terminate and filter.If you have a sine oscillator just clip it with a pair of back to back 1n914s and a current limiting resistor.A single 1n914 driven as a varacter diode with a modest series resistance and home made scramble wound series inductor will produce plenty of 100 Mhz for your needs.Don't over think it. 100 Mhz does not require much in the way of specialized RF techniques.Steve

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: July 19, 2018, 06:35:28 am
content: You can also make an actual tripler. Most frequency multipliers use the square-law behavior of a diode, and that gives you a lot of harmonics. Using one can give you a doubler, but using two back-to-back will result in the second harmonic being canceled out. Filter out fundamental and you have yourself your third harmonic (likely needs some amplification or such).

author: DaJMasta
author_rank: Super Contributor
timestamp: July 19, 2018, 08:35:16 am
content: If you only want 100MHz..... square up the oscillator with a schmitt trigger (probably requiring a DC block cap and a resistor divider to bias the logic side) with a fairly short rise time, then make a fairly tight bandpass filter centered at 100MHz, then amplify as required An ideal square wave yields a third harmonic about 21% of the amplitude of the square, so a 5V TTL 33.333MHz square wave into your bandpass filter should give you around a 1Vpp 100MHz sine wave output, and if you need more you can try to raise the voltage of your squaring up circuit or just amplify the resulting sine wave.Probably not the simplest way, given more modern options, but it could be a neat project and would certainly be usable for your purpose.