XR2206 revived by China ? - Page 1
Forum section: electronics / general

author: rob77
author_rank: Super Contributor
timestamp: December 10, 2014, 02:04:20 pm
content: Hi Guys,just noticed that ebay is full of new XR2206 chips from China for $3-$5 a piece... but that little beast was discontinued a long time ago... (but mouser got 3 of them on stock for a mere 65 Euro a pop)does anyone here has experience with those chinese new chips ? do they work like the original exar chips ? or are those at least close enough ?R.

author: JoeO
author_rank: Frequent Contributor
timestamp: December 10, 2014, 04:16:20 pm
content: I just saw today that Tayda has them for sale:http://www.taydaelectronics.com/ic-integrated-circuits/specialized-function/xr-2206-xr2206cp-xr2206-monolithic-function-generator-ic.html

author: rob77
author_rank: Super Contributor
timestamp: December 10, 2014, 04:21:39 pm
content: i will definitely add 2-3 pieces into my next order , in worst case i will use them as decorationi doubt those are NOS, otherwise the price would be in the same ballpark as mouser.

author: amyk
author_rank: Super Contributor
timestamp: December 10, 2014, 04:25:42 pm
content: Jameco too:http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_34972_-1Maybe someone discovered a huge stock of them abandoned somewhere...

author: magetoo
author_rank: Frequent Contributor
timestamp: December 10, 2014, 11:12:45 pm
content: Quote from: JoeO on December 10, 2014, 04:16:20 pmI threw in a couple with my order from them this summer. Have they been discontinued for long? I kind of assumed there were droves of them around, so this thread has come as a surprise.

author: calexanian
author_rank: Super Contributor
timestamp: December 11, 2014, 05:54:45 am
content: Most likely old stock. Exar gave a lot of warning when they phased it out. Lots of time for people to stock up. Now that enough time has passed the bulk distributors in the east are probably letting them go. It would however be a good part for somebody like a Princeton technologies or some other niche analog company to make litho for, if the hobbyist market were there for it. Otherwise with cheap fast processing power and good low cost D/A converters you can write a piece of software to DDS that signal and have it lower in distortion than a 2206 could ever do.

author: rob77
author_rank: Super Contributor
timestamp: December 11, 2014, 07:46:14 am
content: sure there are better solutionsbut nothing can beat the simplicity of xr2206.btw it's discontinued long enough - no major distributor have them (except mouser 3pcs @ 65Eur).but anyways... ordered few of those from China - let's see in few weeks once delivered

author: dannyf
author_rank: Super Contributor
timestamp: December 11, 2014, 12:15:41 pm
content: QuoteMost likely brand new design - functional equivalent to the old design.China sports the most IC design houses in the world. If there is a demand, some smart people will fill it. That's the beauty of capitalism.

author: JoeO
author_rank: Frequent Contributor
timestamp: December 11, 2014, 02:01:43 pm
content: Quote from: magetoo on December 10, 2014, 11:12:45 pmWhat is the date code on your chips?

author: magetoo
author_rank: Frequent Contributor
timestamp: December 11, 2014, 04:52:22 pm
content: Good idea JoeO, should have checked that already. Let's see... it says 0919.Have nothing to compare with, but I would assume NOS.

author: calexanian
author_rank: Super Contributor
timestamp: December 13, 2014, 07:02:26 am
content: Quote from: dannyf on December 11, 2014, 12:15:41 pmThat would be handy for hobbyists. If that is the case they should advertise that they are new parts under their own name. Would be a good entrance to the market to introduce a chip company previously not well known in the west..

author: dannyf
author_rank: Super Contributor
timestamp: December 13, 2014, 10:42:25 am
content: QuoteSome of them do - like LDOs or specialty chips that sell for the millions.But it is much easier to market under a known name, like XR2206, than GQ420,

author: VK3DRB
author_rank: Super Contributor
timestamp: December 14, 2014, 02:01:49 am
content: Quote from: dannyf on December 11, 2014, 12:15:41 pmChina is a communist country, not capitalist. President Xi Jinping, is the General Secretary of the Communist Party of China. The country is ruled by the Communist Party of China, whose power is enshrined in China's constitution. Granted, their form of communism is perverse and corrupt.As for the XR2206, it is a great device. But with a decent microcontroller, you should be able to make a function generator than is more powerful... triangle, square, sine wave or anything you want. And you can make it triggerable, and have multiple outputs. And have a programmable pulse train. For a fraction of the price, excluding the labour to write the code. That latter point makes the XR2206 a good device if you want to get something robust up and running quickly.

author: miguelvp
author_rank: Super Contributor
timestamp: December 14, 2014, 03:20:08 am
content: Quote from: VK3DRB on December 14, 2014, 02:01:49 amSure buthttp://en.wikipedia.org/wiki/Jack_Mais worth $29.7 billion

author: blackdog
author_rank: Frequent Contributor
timestamp: December 14, 2014, 09:40:04 am
content: Hi,I designed more than a year ago this little sinus/square wave generator for a special test setup.It is using a XR2206 and give's desend output signals, not like most of the schematics you wil find on the Internet.1eThe output is 50 Ohm independend of the output settings.2e3 overlapping ranges , 10Hz to 500Hz, 100Hz to 5Khz and 1Khz to 50Khz.3eLow cost part and high quality output signals.4eThe squarewave output is also bufferd, high quality square wave's, see the picture's5eEasy to build6eOuput range is from 0,27mV to 34mV and 27mV to 3,4V RMSUse the components in this schematic, dont ask if you can replace the NE5534a whit a uA741I used al lot of time to disign this generator the way it is now, simpel easy to build en with good quality output signals.This is the best you can get out of a XR2206 for a generator from 10Hz tot 50Khz.It is part of een testsetup for testen loopgain of power supply's and i needed a battery-powered generator. (commonmode problems)SchematicTest setup10Khz Sinus10Khz Square50Khz Sinus Max Output.50Khz Square Max Output.50Khz Sinus Max Output.3,3Khz Square wave, 40dB attunator on, no overshoot!!1Khz Sinus wave, "0" dB ouput, almost perfect sinus, about 0,5% distortion, if you look careful you can just see a smal abbaration on the topof the sinus wave...It was not "simpel" to remove this abaration without affecting the frequentie respons to much.I read the frequentie of the generator on one of my counters, on top is the generator and the bottom box is a dual 40dB wide band,low noise measuring amplifier to test the stability of power supply's.Build on a proto typing board.Build in a CISCO PIX Firewall box, battery powered.Have fun with it!Kind regarts,Blackdog

author: dannyf
author_rank: Super Contributor
timestamp: December 14, 2014, 11:00:26 am
content: -China is a communist country, not capitalist. President Xi Jinping, is the General Secretary of the Communist Party of China. The country is ruled by the Communist Party of China, whose power is enshrined in China's constitution. Granted, their form of communism is perverse and corrupt-This must be posted by someone IN the 1960s.It is sure proof that time travel is possible.

author: echen1024
author_rank: Super Contributor
timestamp: December 14, 2014, 10:58:49 pm
content: Quote from: dannyf on December 14, 2014, 11:00:26 amChina is hugely capitalist. Many former state-owned corporations are now corrupt, privately owned companies that milk money from the state in the form of subsidies.

author: Yansi
author_rank: Super Contributor
timestamp: December 14, 2014, 11:09:34 pm
content: Quote from: JoeO on December 10, 2014, 04:16:20 pmOh, fuck that crap! Maybe a year or two ago, I bought two from Tayda. They DID NOT WORK properly. It is therefore highly expected, these are reviewed or another way fucked by china, not original. I have been playing with them for a looong time, hardly getting any oscillation. Then I've found, that lowering supply voltage just under 10V or so made it working. CRAP!Better try another type of func gen. Anyone tried ICL8038? I've just come across that part a few days ago.

author: dannyf
author_rank: Super Contributor
timestamp: December 14, 2014, 11:13:08 pm
content: -They DID NOT WORK properly. -Sounded more like you couldn't make it work.

author: Yansi
author_rank: Super Contributor
timestamp: December 14, 2014, 11:19:14 pm
content: How can I make the chip workin, if it just looses oscillation above 10V and begins drawing more current? Just standard schematic, like the one in datasheet page 8. It worked, but only with a very low supply voltage. Why? Your guess is good as mine....Thrown them away and made func gen out of opamps, with sinewave beeing shaped on a JFET-diode network. Not the best concept, but worked, unlike the chinese fake chip.

author: dannyf
author_rank: Super Contributor
timestamp: December 14, 2014, 11:30:11 pm
content: -. Why?-There is more to a working circuit than the right parts or the right schematic.Otherwise, every datasheet writer would be the greatest engineer.

author: Yansi
author_rank: Super Contributor
timestamp: December 15, 2014, 12:29:05 am
content: Shouldn't you do a philosopher?

author: echen1024
author_rank: Super Contributor
timestamp: December 15, 2014, 01:30:27 am
content: Quote from: dannyf on December 14, 2014, 11:30:11 pmWell, I do suppose datasheet errors are to add some spontaneity to an otherwise regulated EEs life?

author: calexanian
author_rank: Super Contributor
timestamp: December 15, 2014, 07:19:56 am
content: Quote from: Yansi on December 14, 2014, 11:09:34 pmThose and the MAX038 are all discontinued as well.

author: VK3DRB
author_rank: Super Contributor
timestamp: December 15, 2014, 09:55:30 am
content: Quote from: dannyf on December 14, 2014, 11:00:26 amhttp://geography.about.com/od/lists/tp/communistcountries.htmThe government preaches communism to keep the proletariat under control, but the ruling elite does whatever will make them money and save face. Comrade Yi XingPing is actually trying to get rid of corruption, but it is a near impossible task because it is so widespread and systemic. Make no mistake,officiallythe People's Republic of China is communist.http://www.bloomberg.com/news/2012-02-26/china-s-billionaire-lawmakers-make-u-s-peers-look-like-paupers.html

author: Zero999
author_rank: Super Contributor
timestamp: December 15, 2014, 10:48:33 am
content: Quote from: VK3DRB on December 15, 2014, 09:55:30 amSigh. It depends on why you mean by communist. No country has ever been truly communist.I think what the others here are referring to is governments with Marxist policies. Namely taking over the means of production, as in the old USSR. Private property is effectively abolish and everything is under state control, having a command economy, rather than a market economy. China did that but since the 80s they've been reversing those policies and moving towards a market economy by privatising the inefficient state companies and encouraging foreign investment. This is why China's economy has grown in the last 30 years.A command economy always results in everyone being poor because one central body tries to control all of the goods and services being exchanged and can't take account for everything. All of the countries you've listed either already have market economies or are starting to head in that direction, apart from North Korea and look at how badly they're doing.

author: janoc
author_rank: Super Contributor
timestamp: December 15, 2014, 11:16:34 am
content: Quote from: Hero999 on December 15, 2014, 10:48:33 amYup, indeed.I am originally from Slovakia and the regime used to be called "socialism" not communism. According to the theory, socialism was a stepping stone to communism, which was seen as the final evolution step of the society (capitalism was seen as more primitive than socialism, btw). We have never arrived there, for various reasons, neither did it happen anywhere in the world.So calling countries "communist" only because they were/are run by communistic parties is an incorrect "shortcut". It is a common mistake, especially in the West, though.

author: dannyf
author_rank: Super Contributor
timestamp: December 15, 2014, 11:26:36 am
content: QuoteI have no response whatsoever to your line,

author: miguelvp
author_rank: Super Contributor
timestamp: December 15, 2014, 06:49:07 pm
content: Quote from: dannyf on December 15, 2014, 11:26:36 amI do:http://en.wikipedia.org/wiki/Jack_MaHis parents were musicians and story tellers not a lot of connectivity with the communist party, and he is now the 18th richest person in the planet.And he never saw a computer until he was 30 years old (he claims he was 33, but he founded his Chinese Yellow Pages company at age 31) and later he founded Alibaba at age 35.What differentiate him was that he had the desire to learn English and will seek foreigners and guide them through his city for free in order to learn about what was outside. So he learned about that thing called the internet from foreign friends he made along the way.

author: dannyf
author_rank: Super Contributor
timestamp: December 16, 2014, 12:02:26 am
content: QuoteI respect people's right to be left behind, to live in the 1960s (or the stone age if it so suits them), to have their own facts, and to dream their own dreams, ...It is part of their human rights and no one shall violate it.

author: VK3DRB
author_rank: Super Contributor
timestamp: December 16, 2014, 11:45:10 am
content: Quote from: dannyf on December 16, 2014, 12:02:26 amRather than being patronising, or even condescending, how about some homework. For a start, go and find out the name of the regime that governs the people of the People's Republic of China.Here is what communism has degenerated to...http://www.theage.com.au/world/goldobsessed-chinese-officers-graft-case-worth-603-billion-magazine-20141208-122x9d.htmlGu or Xu... both are in deep Pu.

author: Zero999
author_rank: Super Contributor
timestamp: December 16, 2014, 01:23:27 pm
content: Quote from: miguelvp on December 15, 2014, 06:49:07 pmHe's obviously very talented and gifted but he had been fortunate in that he's been given the opportunity to succeed which wouldn't have been the case if China had remained a communist country. If he'd been born 30 years earlier during the war and lived his early life under the totalitarian policies of chairman Mao, there's no way he would've been allowed to run a business and make any money.

author: vk6zgo
author_rank: Super Contributor
timestamp: December 17, 2014, 05:58:41 am
content: Quote from: janoc on December 15, 2014, 11:16:34 amAs is the habit of describing Liberal Democracies such as the USA & Australia as "Capitalist"countries.Capitalism is not a Political system at all,& can adapt itself to most forms of Government.Capitalism did quite well in Nazi Germany,& in Pinochet's Chile,but it is at its best in Liberal Democracies where it more closely resembles the Free Enterprise ideal,rather than the distorted form it assumes in Dictatorships.

author: VK3DRB
author_rank: Super Contributor
timestamp: December 17, 2014, 10:14:33 am
content: Quote from: vk6zgo on December 17, 2014, 05:58:41 amAt least capitalist countries are somewhat honest and are not knee deep in doctrinal hypocrisy. China has a wealth gap that surpasses that of the USA. That wealth gap in China between the filthy rich and forgotten impoverished is appalling. Sweden seems to have the right balance of justice and fairness... it is somewhat socialist and yet its people enjoy a high standard of living.http://www.icij.org/offshore/leaked-records-reveal-offshore-holdings-chinas-elite

author: dannyf
author_rank: Super Contributor
timestamp: December 17, 2014, 12:10:38 pm
content: QuoteObviously, for some people, it is to be taught in graduate level classes,

author: Zero999
author_rank: Super Contributor
timestamp: December 17, 2014, 12:54:21 pm
content: Quote from: VK3DRB on December 17, 2014, 10:14:33 amThat's only due to the economic reforms of the 80s. Before China moved from socialism to capitalism, everyone except a very small political elite was poor. Now China's wealth gap may be large but if it wasn't for the transistion to the market economy, there would be no rich people, everyone would remain poor, like in North Korea.

author: idpromnut
author_rank: Unknown
timestamp: December 17, 2014, 04:27:46 pm
content: Somewhat back on topic, I just ordered a few of these because I realized that I need them for a project that I'm working on (the MIT coffee can radar). I think it's just used as a convenient ramp generator for the "chirp" so this could be replaced by a discreet ramp generator built from op-amps. I will report back when I get them.

author: vinicius.jlantunes
author_rank: Regular Contributor
timestamp: December 18, 2014, 01:09:34 am
content: After building my own power supply, the classic first thing most people will do, I wanted to build a simple function generator. Well, ended up never getting to it, but I come back to it from time to time... my problem though is that all of these "easy" CI's are discontinued (MAX038, XR2206, ICL8038, etc.) and I find it difficult to judge the "crappy" designs I find when searching in google for something worth the effort. I mean, I could just build he opamp circuit, or some variations using a 555 for generating a square wave and them integrating / shaping the wave as a sine wave... but well, is that worth the effort? Then I recently found a design bases in DDS which seemed nice, but beyond my competence I am afraid...What you guys think, should I try to get one of these from tayda, or would you have a nice design to share?

author: rob77
author_rank: Super Contributor
timestamp: December 18, 2014, 02:03:03 am
content: i ordered the xr2206 ICs from China, so we'll see in few weeksbtw... the XR2206 is going up to 1 MHz, so it's definitely a good idea to build something different if you need frequency beyond that. i built myself a 2 channel DDS signal generator (2 x cheap AD9850 boards + arduino nano board + keypad + 1602 LCD) which is going up to 25Mhz , but it's still without an output amplifier (need to finish that, but i'm a bit lazy )

author: vinicius.jlantunes
author_rank: Regular Contributor
timestamp: December 18, 2014, 11:15:31 am
content: @rob77, thanks I will have a look at the AD9850 boards... well, and also buy a couple XR2206 I guess, 1 MHz would be good enough for now. In fact, even the simpler opamp designs could fit my needs for a while, but I would like to at least have a proper output stage and well, I'm a bit rusty when it comes to designing amplifiers. That, and I am lazy as well

author: John-Mike
author_rank: Newbie
timestamp: October 15, 2016, 07:19:06 pm
content: I got some of these chips a while back and had bad luck with them.I couldn't get any with the production code 0191 to work.Here's a video of their output vs a good one I made to send the seller.https://youtu.be/42DIeGp0tXo

author: David Hess
author_rank: Super Contributor
timestamp: October 15, 2016, 09:59:18 pm
content: Quote from: vinicius.jlantunes on December 18, 2014, 01:09:34 amTake a look at some of the older well documented designs like the Tektronix FG50x series and various HP function generators for ideas. Except for frequency accuracy and stability, modern DDS implementations do not generally perform as well.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 15, 2016, 10:37:38 pm
content: Many of the old function generators used custom circuits to do the triangle to sine conversion. These are even more difficult to get than an XR2206. If you don't need super low THD, there are relatively simple circuits (log shaper) than could be used for this step. However amplitude stability / temperature dependence can be a problem. National Semi AN263 has some examples.For getting a low THD sine the DDS generator chips (e.g. AD9850) are quite good and easily outperform the XR2206. It is just the cheap Chinese generators based on an FPGA and poor quality DAC that are really bad.For the triangle wave the DDS versions are not good, at least at higher frequencies. Many chips don't even support it.Another difference is the user Interface: the analog way uses pot and switches (e.g. for decades), while the DDS uses a digital value and usually use a µC based user interface.

author: David Hess
author_rank: Super Contributor
timestamp: October 15, 2016, 11:09:36 pm
content: Quote from: Kleinstein on October 15, 2016, 10:37:38 pmThe Tektronix ones I mentioned use discrete piece-wise and log shapers for distortion down to 0.25% which is why I used them as examples to study.QuoteMany of them seem to have high output glitch energy causing problems with false triggering. I think Dave made a video showing this problem.Up to maybe 200 kHz, another way to do sine shaping is with a clock tunable switched capacitor filter and I have seen some simple analog function generator designs which did it this way.QuoteThis is not universally the case; the more complex analog designs support phase locking so an external or internal digital frequency reference can be used.Other features like sweep, voltage control, and especially input/output triggering are something I miss in almost all DDS function generator implementations. I can take one or two of my old analog function generators and combine them with an oscilloscope to make a quick and dirty real time network analyser. I have yet to find a DDS based function generator which will allow that.

author: dannyf
author_rank: Super Contributor
timestamp: October 15, 2016, 11:11:04 pm
content: Quotea lot can go wrong in a design so without more information it is tough to pin the blame on the chip.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: October 15, 2016, 11:20:54 pm
content: Quote from: dannyf on December 14, 2014, 11:13:08 pmSure, an engineer, technician or hobbyist can frequently make something work. But if the part is not conforming to it's datasheet you have not done decent engineering because you can't predict that your next implementation of the circuit will work, or that next years lot from the factory will work, or that someone else will have to do less work than you did to make it work.Finding one area of non-compliance with a data sheet for a new vendor is a red flag that would put me off from using that part and probably that vendor. There are few cases where it is worth doing the work to characterize and qualify a part inside or outside the vendors assertions.Making one off copies of something is mostly a hobby activity. Rarely done by professionals. There are exceptions. In research you might make one of something to make a specific type of measurement or test. And there are a few cases (often in support of someone else's hobby) where you can be paid to make a single working copy of a design.

author: ez24
author_rank: Super Contributor
timestamp: October 16, 2016, 05:23:36 am
content: Quote from: idpromnut on December 17, 2014, 04:27:46 pmYou would think after almost 2 years idpromnut would let us know if they worked !

author: Bud
author_rank: Super Contributor
timestamp: October 16, 2016, 05:28:53 am
content: That reminded me i have a genuine 2206 somewhere in one of the parts bins. Can anyone recommend a project with the PCB/Gerbers ?

author: ez24
author_rank: Super Contributor
timestamp: October 16, 2016, 05:46:54 am
content: Quote from: Bud on October 16, 2016, 05:28:53 amMake a board that would use it to compare a Chinese chip with. Then if the clone works you could say it tested good. So two circuits (on one board) and one with a ZIP socket for the clone chip. Then sell them here and on ebay. I think I would use a break before make power switch that would power up each circuit and use the same output for both circuits so you do not have to move probes.

author: Bud
author_rank: Super Contributor
timestamp: October 16, 2016, 06:11:07 am
content: That would be intersting to compare but i do not have time for this . However from reading i infer it is easy to validate by cranking up the supply voltage. It seems Chinese clone gives up somewhere pass 12v mark.

author: ez24
author_rank: Super Contributor
timestamp: October 16, 2016, 06:15:34 am
content: Quote from: Bud on October 16, 2016, 06:11:07 amBummer

author: setq
author_rank: Frequent Contributor
timestamp: October 16, 2016, 07:01:11 am
content: Just a heads up with those Chinese XR2206s. Before I bought a proper one, I had an XR2206 based function generator that I built myself. The thing worked fine up to about 1MHz with no distortion other than what can be expected from a cheap diode clamp sine generator.However when changing the output transistors after a little accident, I manage to blow up the XR2206 by shorting the output with a probe tip.So off to eBay, bought another one and used direct substitution. Total shit. Distorted wave output above about 300KHz and there are switching transients at the peak and trough of the wave. Plus it got very hot and the integrator is impossible to control at the high end of the frequency ranges.So I thought screw this and bought a discrete 1980s Exact branded unit from eBay and won't touch an XR2206 again.I also won't buy any crap from China any more. RS for parts and eBay for branded test gear only.

author: David Hess
author_rank: Super Contributor
timestamp: October 16, 2016, 08:52:42 am
content: Quote from: Bud on October 16, 2016, 06:11:07 amThat makes sense. The Chinese copy is probably built on a modern low voltage analog process instead of the obsolete 36V NPN junction isolated process that the original likely used.

author: stj
author_rank: Super Contributor
timestamp: October 18, 2016, 08:52:46 am
content: wouldnt a modern MCU like an ARM4 or ARM7 with a fast dac be able to leave these things in the dust?i'v seen diy generators based on Nucleo/Discovery boards that have pre-calculated wave-tables streaming to the dac under dma that look very fast.

author: setq
author_rank: Frequent Contributor
timestamp: October 18, 2016, 09:20:15 am
content: This is pretty much how AFGs work although there is usually an ASIC with a LUT or something in it instead. Think the AD9850 works the same as well. They are much more expensive than cheap analog function generators as they have some difficult problems to solve with harmonic content, clock division, control, feedback etc. Plus once you've solved all of these you still have a driver amp on the end of it, a power supply on the front end. Literally 50% of the device is still analogue.Personally I find that full analogue generators have a nice manual control which fits better with some use cases than encoders or manual frequency programming. Sometimes you need to frequency sweep by hand. I have the RF equivalent of an AFG (Marconi 2019A, repaired yesterday whoohoo!) i.e. it does sine only and it's pretty much useless for sweeping frequencies. If you want a spot frequency and power level/amplitude you're fine. If you want to sweep by hand forget it. If you want to sweep automatically, AFGs have some nice features but you can do that with two analogue generators with the VCF in of the second one connected to the ramp out of the first one.I'd still like a nice HP 33120a, but it's not happening.

author: stj
author_rank: Super Contributor
timestamp: October 18, 2016, 09:32:33 am
content: that marconi sounds like it was designed for jamming radio signals!

author: setq
author_rank: Frequent Contributor
timestamp: October 18, 2016, 09:40:36 am
content: It probably could be set up to cause some trouble with much as anything RF related. The RF output power isn't particularly high though so you'd need a big PA and a noise source to modulate it against. By which time Ofcom and the fuzz would probably kick your door down and take it away so that sort of stuff is a self-deprecating game.I'm using it for testing IF amplifiers and keeping the living room warm at the moment which is something it can just about handle.

author: dannyf
author_rank: Super Contributor
timestamp: October 18, 2016, 10:13:20 am
content: Quotedepends on your set-up. I think 16-points per cycle is probably the minimum for most people. that means a 16Mhz F_CPU chip can output a waveform of 1Mhz waveform. Plus overhead and stuff like that, you are likely to be much slower.

author: bktemp
author_rank: Super Contributor
timestamp: October 18, 2016, 11:28:34 am
content: Quote from: stj on October 18, 2016, 08:52:46 amIt depends on the waveform and how much "postprocessing" is done in the analogue domain: For a sinewave with a good (brick wall) filter, you need 2 samples per cycle and still get a good looking sinewave (the amplitude will drop a bit due to sinc rolloff). For any other waveform you need a much higher samplerate, because of the harmonic contents (Nyquist-Shannon).A FPGA is probably much better suited than a microcontroller for DDS because DMA can't do variable steps between the waveform table. The only solution I can think of is calculating the waveform in software and using DMA only for transferring the samples from a FIFO to the output ports at a fixed rate.Even a cheap FPGA can easily do >100MS/s for at least 20MHz sinewave and 1-10MHz squarewave, triangle or arbitrary waveform (depending on you signal quality requirements).I wouldn't use a microcontroller for anything above 100kHz.

author: stj
author_rank: Super Contributor
timestamp: October 18, 2016, 01:03:35 pm
content: the ARM thing i saw was a lot faster than that, it was playing a loop sample from ram via dma with no cpu overhead, the dac can exceed 80MHz afaik.cpu was clocking at either 120 or 180 MHz.

author: dannyf
author_rank: Super Contributor
timestamp: October 18, 2016, 01:07:19 pm
content: Try to load up a table to the DAC, and allow a user selected fine tuned output frequency and then you may appreciate the challenges.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 18, 2016, 02:25:28 pm
content: DDS sine generation uses constant output rate, so DMA for buffering and software to calculate the values is ok. An FPGA is just faster than most µCs (single cycle compared to maybe 5 to 15 with an µC).One can do DDS in software in an µC. There are some AVR based solutions that go up to around 2 MHz output sampling and thus a maybe useful maximum output frequency of up to 500 kHz (depends on the filter). However this is only 8 Bit data and one still needs the DAC. Also the µC is busy with output, so any change in frequency will cause glitches.So it should be possible to use one of the ARM µCs with integrated DAC to make a reasonable low cost sine generator up to maybe 2 or 10 MHz, depending on the DAC. You still need the filter, attenuator and amplifier, just like with an fully analog FGen. The filter part sounds complicated, but is can be just a passive LC filter combination, if the clock is not too slow.

author: bktemp
author_rank: Super Contributor
timestamp: October 18, 2016, 05:32:31 pm
content: Quote from: stj on October 18, 2016, 01:03:35 pmIf the samplerate is fixed, the available output frequencies are limited to samplerate/n where n is an integer from 2 (for sinewave with brick wall filter) to number of sample that fit into available memory. You can increase the resolution for higher frequencies by putting multiple cycles into the loop buffer, but the resolution is still limited to samplerate*m/n. And you need to recalcutate the sample memory whenever the frequency is changed. So you can't change the frequency without interrupting the waveform.The big advantage of DDS is the almost infinite frequency resolution: You have a frequency resolution of samplerate/DDC accumulator width from 0Hz up to samplerate/2. For the common accumulator width of 32bits, the frequency resolution is better than 0.1Hz even for 400MHz samplerate.

author: CJay
author_rank: Super Contributor
timestamp: October 18, 2016, 05:45:26 pm
content: Quote from: stj on October 18, 2016, 09:32:33 amIt was quite instructive to take a wander with a handheld to see just how far the sig gen in my spectrum analyser was audible for.I'm a lot more careful with where I set it now.

author: TechieTX
author_rank: Contributor
timestamp: April 25, 2018, 01:23:31 am
content: How to spot the cheap-@ss Chinese clone chips:If your chip looks more like the lower image, you gottaken. Don't rely on the datecode, as that changes when they want to. The logo and font used on the real chip don't match the clone by a noticeable degree, and the clone is so far off-center that the logo is nearly off of the chip.