I have a 10Hz sine wave and would like to introduce a repetitive _random_ phase shift of between 1 and 10 degrees.
IOW to have the sine wave's phase change randomly each cycle, and for this to occur continuously over time and with a smooth (not stepped) transition.
What would be the simplest method of achieving this using analog circuitry?
Robert Miller
Sounds like a homebrew I/Q modulator would work. With your small phase shift, just one multiplier might be all you need, namely modulate one phase and sum with the other. The multiplier might be a real analog multiplier, an MDAC, or a DPOT.
You will need some sort of modulation source noise generator. Random shift register thing maybe.
If you can *generate* the sine wave, not have it already, you could FM the generator. Some benchtop fungens have FM/VCF inputs.
What's the application?
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Well, using
sin(w*T + F) = sin(w*T) cos(F) + sin(F) cos(w*T) and considering that for small F (phase difference) that "cos(F)" is nearly one, you just need to generate the 90-degree-out-of-phase cosine of your frequency of interest, and multiply it by that sin(F) which is just a low-pass of a random number generator. It might as well be a pseudorandom sequence with a low pass filter that generates the 'F' signal.
The error introduced in amplitude of the result, is under | 1-cos(10 degrees) |, about
1.5%, which can show up as AM modulation. The error in sin(F) = F, for that same 10 degrees (but converted to radians, for that equation) is small, about a tenth percent.
You can replace the bottom resistor in the diagram with some kind of voltage-controlled resistance, a JFET with feedback will work, to get a voltage-controlled phase shift. Then you just need a filtered noise source of appropriate amplitude
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** How about an LDR modulated by an LED ?The OP wanted the "simplest method".
.... Phil
Sound card.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
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** The OP asked for "analog circuitry" - f*****ad..... Phil
Sure why not, it's just that if it's something that's going to be made in any quantity as a product to sell CdS cells aren't RoHS-compliant.
That does seem pretty simple. For such low frequencies it'll need big R's and C's. I'm not sure the resistance of a jfet will be high enough.
George H.
+1 on the I/Q idea. The amplitude error caused by making a 10 degree shift by adding a small Q component is only
sin(10 degrees)**2 = 3%.
At +- 1-10 degrees and 10 Hz, I'd probably use an LM13700 as the multiplier. Put the 90-degree phase shifted wave (with a suitable DC offset) into the I_ABC input and apply the phase shift voltage to the
+/- inputs. Sum the output with the unshifted waveform, and use an RC highpass to get rid of the DC.LM13700s are on sale at Newark for $0.77 in onesies.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
The LM13700 is a really handy chip; I wish they made something similar with a little higher bandwidth though
And perhaps optimized for lower supply voltages. Single parts in smt packages. Modern, up-to-date.
--
Thanks,
- Win
AD633 is impressive. Inputs are +-10, product output is +-10.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
AD633 is 1 MHz. AD835 is 250. Both are real multipliers.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Hmm never used it. Do you know of any good app notes? (nothing on TI's site but the data sheet.. which I'll read.)
What kind of stuff do you use it for? VCO's? (Well CCO's)
George H.
Spendy though, also can have a fair amount of DC offset.
George H.
Den torsdag den 26. oktober 2017 kl. 02.45.51 UTC+2 skrev Robert Miller:
make an oscillator with a crappy frequency stability?
continuously changing the phase is the same as running at a slightly different frequency
The AD633 is like 10 bux
There are hamburgers around here that are $16.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Larkin provided the basic I-Q solution, then Hobbs suggested the simple way to do it.
All the rest of the posts are garbage. Time to killfile the thread and go build it. ...Jim Thompson
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