Post by thread:[OT] Wavefrom generator IC

I'm working on an application where I need to generate a sine wave and sweep its frequency. I want to use a pic to control the process of the frequency sweep (most of the chips I've seen take an analog control voltage to adjust the frequency). The range of frequencies I'm interested in is from 1 to about 35 kHz. I want a low distortion wave (no more than .5%, esp in the lower part of the range) Two of the best contenders I've come up with are the exar 2206 and max 038 that can be found at http://www.exar.com/products/xr2206.html http://dbserv.maxim-ic.com/quick_view2.cfm?pdf_num=1257 Anyway, I was just getting a feel for if anyone has used these guys in a similar application, or knew of a better option. Whats easiest to interface with a PIC? Ben Langhals

This isn't really a reply, but I am interested in using DDS chips for this purpose rather than analog waveform generator IC's such as Ben has mentioned. The ones from Harris and Analog Devices seem to be intended more for RF signals rather than audio. Plus they are rather expensive. Someone (Micrel?) makes an audio-frequency DDS chip, but its distortion spec is pretty awful. If anyone can recommend a better IC for audio-frequency use, I'd like to hear about it either on the list or by email if you prefer. Brian Aase {Quote hidden}> I'm working on an application where I need to generate a sine wave and > sweep its frequency. I want to use a pic to control the process of > the frequency sweep (most of the chips I've seen take an analog > control voltage to adjust the frequency). The range of frequencies > I'm interested in is from 1 to about 35 kHz. I want a low distortion > wave (no more than .5%, esp in the lower part of the range) Two of the > best contenders I've come up with are the exar 2206 and max 038 that > can be found at > > > http://www.exar.com/products/xr2206.html > > http://dbserv.maxim-ic.com/quick_view2.cfm?pdf_num=1257 > > Anyway, I was just getting a feel for if anyone has used these guys in > a similar application, or knew of a better option. Whats easiest to > interface with a PIC? > > Ben Langhals >

I too am looking for a similar IC so please count me in on any offlist emails. Looking for audible range (20Hz-20kHz odd) sine, square (w\ PWM), saw (up\down), triangle. Looking at 0.01-0.001 Hz accuracy across the whole range ideally. I had also considered deigning my own with a Scenix. The sine wold be a bit of a trick to get smooth. A 50ms cycle (20Hz) is pretty long. But with a nice sine table it'd be possible. As part of this I'm looking for a cheap, high accuracy, multichannel (looking at up to 32 oscilators) DAC system. Best I've seen so far is the Analog Devices Octal Mux'ed SHAs. Except there nonlinearity only allows 10-12bit and I ideally want 16. AD also have a 16bit rated SHA but it's a single package. Havn't even looked at pricing yet. Tom. {Original Message removed}

Ben Langhals wrote: > >I'm working on an application where I need to generate a sine wave and >sweep its frequency. I want to use a pic to control the process of the >frequency sweep (most of the chips I've seen take an analog control voltage >to adjust the frequency). The range of frequencies I'm interested in is >from 1 to about 35 kHz. I want a low distortion wave (no more than .5%, >esp in the lower part of the range) Two of the best contenders I've come up >with are the exar 2206 and max 038 that can be found at > I looked at both, and ended up using the 2206. Seemed to me to be easier to interface to control circuitry than the 8038. Distortion is rated as 0.5% nominal. And also lots cheaper than digital synthesis chips. [plus it's analog - so it's certainly more difficult to get it to work right]. You can control the frequency using a PIC's PWM output feeding into an NPN inverter, with 40K to base to 3.3K to gnd, in parallel with a cap for filtering. 390 ohm emitter to gnd. Collector to pin 7 of 2206, and 5-10M from collector to gnd. You can actually get up to 500:1 frequency sweep with this kind of ckt. You have to tradeoff the size of the cap across the 3.3K base resistor. Too small, the frequency wobbles, too big, the sweep is slow. 3.3K and 10uF gives 33 msec time constant, and the total sweep time would be somewhat less than that. BTW, power to the 2206 was +/-6v, and the NPN inverter ckt was referenced to -6v. If you use 0-10v, say, on the 2206, you would have to fiddle with the values I gave. Now for the fun part. Take the squarewave out of the 2206, measure its frequency with the PIC, and close the loop back to the PWM to stabilize the frequency. [the problem, and funnest part, with analog is drift]. For frequency-setting, use a good cap, like COG, 30 PPM. Tie a small cap, .003 uf or so, directly on the chip output (600 ohms Rout) to filter out the little nibs on the top/bottom of the sinewave. Total price, $3 and change. best regards, - Dan Michaels Oricom Technologies http://www.sni.net/~oricom ==========================

Tom Wrote > I too am looking for a similar IC so please count me in on any offlist > emails. Looking for audible range (20Hz-20kHz odd) sine, square (w\ PWM), > saw (up\down), triangle. Looking at 0.01-0.001 Hz accuracy across the whole > range ideally. > > I had also considered deigning my own with a Scenix. The sine wold be a bit > of a trick to get smooth. A 50ms cycle (20Hz) is pretty long. But with a > nice sine table it'd be possible. > I have used a number of DDS applications where very low distortion wasnt as critical as frequency accuracy and agility. However, I am probably going to have a go in the the near future at seeing how low I can get the distortion using a tracking lowpass filter after a DDS generator, since I have had some very pleasing results using tracking filters and sampled waves before. Should work well at the lower frequencies. Anyone done this? _____________________________ Lance Allen Technical Officer Uni of Auckland Psych Dept New Zealand http://www.psych.auckland.ac.nz _____________________________

I put together a couple of versions of DDS using the Scenix. For details on this see: http://www.rhoent.com/examples.htm There is enough information there to build it yourself to play with :-) -- Rich "Brandon, Tom" wrote: {Quote hidden}> > I too am looking for a similar IC so please count me in on any offlist > emails. Looking for audible range (20Hz-20kHz odd) sine, square (w\ PWM), > saw (up\down), triangle. Looking at 0.01-0.001 Hz accuracy across the whole > range ideally. > > I had also considered deigning my own with a Scenix. The sine wold be a bit > of a trick to get smooth. A 50ms cycle (20Hz) is pretty long. But with a > nice sine table it'd be possible. > > As part of this I'm looking for a cheap, high accuracy, multichannel > (looking at up to 32 oscilators) DAC system. Best I've seen so far is the > Analog Devices Octal Mux'ed SHAs. Except there nonlinearity only allows > 10-12bit and I ideally want 16. AD also have a 16bit rated SHA but it's a > single package. Havn't even looked at pricing yet. > > Tom. > {Original Message removed}

I have played with several of the signal generator chips: ICL8038, XR-2206 and the MAX038. I think all of them are going to be marginal generating less than 0.5% distortion even with some tweaking. For instance the XR-2206 is specified as having 0.4% distortion TYPICAL with adjustment and 1.5% maximum when adjusted! The ICL8038 is even worse 0.8% typical when adjusted. (There is no maximum spec.) The MAX038 is also only specified for typical distortion. Its spec. is 0.75% adjusted. I think that the MAX038 is the easiest to work with although I think it is also much more expensive than the other two. Ben Langhals wrote: {Quote hidden}> > I'm working on an application where I need to generate a sine wave and > sweep its frequency. I want to use a pic to control the process of the > frequency sweep (most of the chips I've seen take an analog control voltage > to adjust the frequency). The range of frequencies I'm interested in is > from 1 to about 35 kHz. I want a low distortion wave (no more than .5%, > esp in the lower part of the range) Two of the best contenders I've come up > with are the exar 2206 and max 038 that can be found at > > http://www.exar.com/products/xr2206.html > > http://dbserv.maxim-ic.com/quick_view2.cfm?pdf_num=1257 > > Anyway, I was just getting a feel for if anyone has used these guys in a > similar application, or knew of a better option. Whats easiest to > interface with a PIC? > > Ben Langhals

Ben, take a look at Micro Linear's ML2036 Programmable Sinewave Generator. I've been looking into this as part of my PIC-based DAQ system. I'm currently testing the ML2036, MAX038, and looking at Analog Devices' DDS family. For your application, the ML2036 seems ideal. All you need is a crystal (literally, no capacitors). It requires +/- 5V and has a 3-wire SPI-style interface. You clock-in 16 Bits, LSB first, and set a Latch Enable line to set the frequency from 1 to 50KHz (I tested it to 65,535KHz). By using a 8.388608MHz crystal (Digi-Key PN: SE3415 / Epson CA-301 family), you get a direct one-to-one program data to frequency setting with a 1Hz resolution. The chip provides Osc/2 and Osc/8 outputs which may be of use if you want to clock a PIC at 4.194304MHz. There is a voltage reference input. Tying this to +5V gives a maximum output swing of +/- 2.5Vp-p. You can reduce this via an external reference. Harmonic distortion is -45db max. The device comes in a 14-pin DIP or 16-pin SOIC package. For more info: http://www.microlinear.com/ - Tom At 06:19 PM 3/29/00 -0500, Ben Langhals wrote: {Quote hidden}>I'm working on an application where I need to generate a sine wave and >sweep its frequency. I want to use a pic to control the process of the >frequency sweep (most of the chips I've seen take an analog control voltage >to adjust the frequency). The range of frequencies I'm interested in is >from 1 to about 35 kHz. I want a low distortion wave (no more than .5%, >esp in the lower part of the range) Two of the best contenders I've come up >with are the exar 2206 and max 038 that can be found at > > >http://www.exar.com/products/xr2206.html > >http://dbserv.maxim-ic.com/quick_view2.cfm?pdf_num=1257 > >Anyway, I was just getting a feel for if anyone has used these guys in a >similar application, or knew of a better option. Whats easiest to >interface with a PIC? > >Ben Langhals ------------------------------------------------------------------------ Tom Handley New Age Communications Since '75 before "New Age" and no one around here is waiting for UFOs ;-)