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Does anyone know of any old-school function generator ICs (similar to the ICL8038 or XR2206) that are still on the market? (i.e. not obsolete / NFFD - I'm not interested in scouring the globe for old inventory)

I'm aware of digitally-programmable parts that use I2C / SPI, but am looking for something that won't involve adding a micro to a legacy design.

I'm looking primarily for an IC that will output a triangular waveform at low frequency (640Hz). The XR2206 was the original part in the application which is now obsolete. The frequency can be adjusted a small amount from an external input (+/- 50Hz or so).

Exar has obsoleted most (all?) of their function generator parts:

enter image description here

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What features do you need? Sine/Square/PWM/Saw/Triangle, frequency, etc. – Kevin Vermeer Apr 1 '11 at 19:38
Updated the question. – Madmanguruman Apr 1 '11 at 20:03
What properties do you want from this triangle wave that can't be provided by something simple like a 555/556 IC? Frequency stability or wave shape is critical? Consistent amplitude at different frequencies? – endolith Apr 4 '11 at 16:37
The legacy design has an XR2206. The behaviour of the triangle wave should be 'compatible' with the XR2206 - fixed amplitude and clean egdes. The engineer working on this activity isn't comfortable going with a discrete design. – Madmanguruman Apr 4 '11 at 20:43

3 Answers

up vote 6 down vote

This would seem to be similar to the XR2206 :)

The XR2209 is a monolithic voltage-controlled oscillator (VCO) integrated circuit featuring excellent frequency stability and a wide tuning range. The circuit provides simultaneous triangle and squarewave outputs over a frequency range of 0.01Hz to 1MHz. It is ideally suited for FM, FSK and sweep or tone generation, as well as for phase-locked loop applications.

Applications

  • Waveform Generation Triangle, Sawtooth, Pulse, Squarewave
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That's what I get for listening to my colleague whine, "We've scoured the globe and can't find anything equivalent!" Well done sir. – Madmanguruman Apr 2 '11 at 15:15
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Sorry, I had to toggle this answer off - my colleague contacted Exar and was told that this part was also discontinued, as per PDN 07-003-01 (which obsoleted the XR2209, coincidentally). – Madmanguruman Apr 4 '11 at 14:48
Weird. It doesn't mention that anywhere on the website? It's still listed in parametric searches and is still for sale. – endolith Apr 4 '11 at 15:34
Agreed. I updated the question with the PCN they sent us. – Madmanguruman Apr 4 '11 at 16:20
up vote 2 down vote

If you can't find a proper part in your area, then you might end up with a micro and software based DDS like this. Small AVR and resistor ladder is all it takes.

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How does the cost and accuracy of a resistor ladder compare with that of a DAC? – supercat Dec 13 '11 at 19:56
@supercat, wow, didn't know that until you made me aware. Thanks. – abdullah kahraman Jul 8 '12 at 20:30
@abdullahkahraman: I should have been a bit less brief in my comment. I've built and used R/2R DACs in the past, back in the days when the only EEPROM-based Microchip part was the 16C84. They are certainly cheap in mass-production (sixteen 1% resistors would cost less than $0.02 as discrete components, or $0.06 as four arrays of four), but the accuracy isn't great. Further, for hand-built projects, soldering a DIP8 may be a lot more convenient than soldering sixteen resistors (and of course, using a processor with built-in DAC may be more convenient yet). – supercat Jul 9 '12 at 15:34
@supercat this R2R ladder is $0.46/2k pcs. [This] IC from Microchip is $0.54/100 pcs. Well, cheaper, smaller and more accurate. Am I doing the comparison wrong? – abdullah kahraman Jul 9 '12 at 16:21
That's a better price for those R/2R packages than I remember the last time I looked at them. On the other hand, the accuracy of an R/2R DAC will be limited by the cleanliness of VDD and the ability of the processor's pins to pull cleanly to that level, while using a monolithic DAC will generally allow one to use a filtered supply as a source. – supercat Jul 9 '12 at 18:20
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up vote 0 down vote

I encounted this issue about one year ago trying to source an analogue function generator and noticed that they are generally obsolete or not for new design.

I also had a restriction that prevented the use of a microcontroller for the design. In the end I settled on 555 timer with supporting components and was able to obtain a reasonably precise sawtooth generator. It worked well, and took a few attempts to get my calculations correct, in the end the result was ideal.

With a 555 timer you can use it to generate various waveforms and it does not require any digital components.

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