Sine generator IC solution?

Don't they make single chip modems for this very purpose? My Baycom has a TCM3105, whatever that is... mike

I read in sci.electronics.design that mike wrote (in ) about 'Sine generator IC solution?', on Sun, 30 Jan 2005:

No, much more. 12.8% - I just measured it.

I think that this presupposes a certain knowledge on the part of the questioner. For instance I was looking for a colpitts oscillator on the internet. I found a number of examples, but I couldn't easily find any that discussed how it operated, or how one should decide on the ratio of the values of the capacitors in the circuit, or which of a comparator, opamp, Cmos inverter, Fet, or MosFet etc would be best.

I read in sci.electronics.design that Spehro Pefhany wrote (in ) about 'Sine generator IC solution?', on Sun, 30 Jan 2005:

WIEN - Vienna, not WEIN - wine.

Sure. If he has the ability to write and burn in a simple microcontroller program, and to deal with 0.5~0.65mm pitch SMT parts, that could be a very good (and simple) solution.

Best regards, Spehro Pefhany

Yeah, I've seen a couple since I first posted this question. Most of the ones I've seen so far don't fit too well in my application. The best I've seen is the XR2206 and NTE864 (replacement for the ICL8038), but both appear to operate at 10V+, and I haven't been able to find low-temp versions (-40C). The MAX038 is 5V and has a low temp version, but it's hard to find a distributor for that version (and it's a little pricey). The AD9833 with SPI interface is an option, although I'd really only be working with 2 output frequencies, so I was hoping to be able to configure the IC/circuit to modulate between those 2 frequencies with a high or low input.

Thanks again all for all the good options, although I'm still open to others.

Dave

mike wrote:

AMTOR-FEC

PIC

issue.

and

and

Interesting how significant additional requirements keep popping up.

-40C?? Assum> Yeah, I've seen a couple since I first posted this question. Most of

Invest in a good Metcal soldering iron and tips, and a Mantis magnifier. That might make it fun again.

And include a lot of pth test points in your layouts.

John

I'm sinking into that same pit of dispair. I need to upgrade my picstart+. I have the chip, I have the code that goes into it. I made the board layout. I just can't fabricate the board with 0.5mil pitch traces. That $30 upgrade kit is starting to look better all the time. mike

You're not going to do much in the way of a 10:1 tuning range in Wien bridge- fussy little high Q and amplitude unstable thing that it is. These days the most practical and high performance approach, at these frequencies, would be to generate a variable frequency square wave at fundamental and 100x fundamental which are then processed by cheap switching tracking filter.

Some of it surely depends on what he wants the thing for. That 10:1 tuning range may be the reason for calling for an IC, or it may just be that he's unfamiliar with the alternatives.

One neat thing about those IC function generators is their wide continuous range. But of course, they go do those non-traditional schemes in order to be able to get 10:1 or wider range in one segment. If one needs the range, one often doesn't need the purity of the sinewave. If one needs the purity of the sinewave, they may not need continuous tuning, or at least can live with discrete steps.

Michael

questioner.

a number of examples, but I couldn't easily find

the values of the capacitors in the circuit, or

No, that would seem to presuppose that people are unfamiliary with that traditional source of information, the book. They are still indeed useful sources.

And people limit themselves if they see a solution before properly looking at what's available. People don't have to know how traditional sine wave oscillators work, or even draw them out, but they ought to be aware of such things so their automatic response to a problem is "what kind of IC...". When the problem arises, they should have enough of a grounding to think, "wait, I remember seeing something about that, I better find that book".

New generations come in, and since they've not bothered with looking at historical books on electronics, they don't know how things used to be, and then they can't decide whether an old solution is valid or not.

The old puts the new in context.

Michael

I read in sci.electronics.design that dave.harper wrote (in ) about 'Sine generator IC solution?', on Sun, 30 Jan

I wasn't criticizing you; I was having a go at the people who advised you to use complex solutions instead of a simple one.

But you don't need a 10:1 tuning range. The frequency shift should be much less. Amateur Teletype originally used 850Hz shift, specifically 2125Hz and 2975Hz for the two frequencies. When narrow shift came in, the differential between the frequencies was 170Hz, using 2125 and 2295Hz as the specific tones.

If this was done at audio frequencies, there'd be an LC oscillator, and then a capacitor would be switched in for the lower frequency.

Of course, one could get shift by moving the actual frequency of the transmitter, and this too was done by adding in a capacitor when the lower frequency was being sent. Of course, doing frequency shift rather than shifting an audio signal, you had to either use an SSB receiver to shift the signal down to audio where an audio demodulator worked, or have an FM receiver so you could use the output of the discriminator.

With narrow shift, the solution becomes far easier. You can use just about anything, triangle or even square wave, and feed it into a low pass filter. Given those traditional frequencies (and they were chosen to fit into an audio passband but so harmonics would not be in that passband), the low pass filter can be fixed, and will not really distort the waveform as the frequency shifts.

People did use square wave tone generators, but of course they were fed to existing transmitters that would have a response to limit the audio passband.

Michael

Spehro Pefhany wrote in news: snipped-for-privacy@4ax.com:

You dont even need to know how to program a micro (though these days not being aquainted with these matters rather limits your options).You can program some of them with a dip switch (parallel load). The godawful small packages are a bittovabitch however, and it's only going to get worse (leadless packages, BGA etc).The shrinking of the lead pitches almost exactly matches my progressive loss of visual acuity. M

Nowadays my heart sinks every time I've completed a design, knowing that in

Didn't the original HP oscillator do just exactly that?

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I should remember that- I just shipped something to there. But mostly I was struggling with "Heiligenstädterstrasse" on the customs form.

Best regards, Spehro Pefhany

An 8038-variety is still the easiest approach if not much better than 1% THD is ok.

Your approach is nifty and could be very handy if (say) something like a 2-phase sine/cosine was required.

Note that there is a 3-step square-wave approximation of a sine which has zero third harmonic content, very useful if going into a low pass filter.