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Re: Dirty sine wave generator
On Sunday, September 22, 2019 at 4:58:25 AM UTC-4, Martin Brown wrote:
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Don't know what your point is.  The Johnson ring counter gives you a number
 of phases with adjustable edges both leading and trailing.  You can have h
alf of the 50/50 duty cycle waveforms with no gates, the other half with a  
simple inverter.  Quadrature square wave are no gate signals.  Best of all,
 all these signals, 50/50 duty cycle or not, are glitch free!  You would ne
ed to be pretty ignorant of the circuit to want to use anything else or hav
e some very odd and special needs.  Both circuits use a 14 pin 7400 type de
vice and an extra gate, XOR in one case and an inverter in the other (which
 can be an XOR with a pin pulled high).  The Johnson ring counter has more  
bits of resolution, so it requires more resistors.  That's the only differe
nce.  

--  

  Rick C.

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Re: Dirty sine wave generator
On Wednesday, September 18, 2019 at 10:35:33 PM UTC-7, bitrex wrote:
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Well, you can go for small improvements with the 'magic sine waves' approach,
and get a factor of two or four, or the more-parts solution of switched capacitor
filtering (clock at a hundred times the sinewave frequency, there's an MF-10
application note on this somewhere).

The issues, though, are that you only push the harmonic distortions higher in
frequency, they don't go away unless you ALSO have a filter - and that will
limit any adjustment range for the sinewave frequency.

For direct synthesis, any of the lossless audio schemes can put a high quality
sinewave onto your iPod, or boxes with buttons on front can synthesize
the waveforms offered in the menus; usually sine, triangle, square and
sometimes others.

Re: Dirty sine wave generator

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That violates all the usual "rules" of logic design. The clock to the
first flop is gated, and the pair of flops is a ripple counter. Expect
worse glitches if more flops are added in this style.


Re: Dirty sine wave generator
On 9/19/19 11:31 AM, snipped-for-privacy@highlandsniptechnology.com wrote:
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 From the age of the drawing and the site it's on looks like it was  
designed by communists!!! they probably never ran it fast with their  
commmunist-logic so it was okay.

The glitch comes from this issue right here with the XOR, with the  
output in red and the other two colors inputs:

<https://imgur.com/a/54VO6jP

Without it, it does produce a quite nice modified sine with a minimum of  
parts. I think it might be possible to lock out the glitch by  
synchronizing the XOR input with a third flop, maybe.



Re: Dirty sine wave generator
On 9/19/19 12:17 PM, bitrex wrote:
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If we are to build a successful gay space communist future in space, for  
everyone, then we must correct the failures of the past!

Re: Dirty sine wave generator
On Thursday, September 19, 2019 at 1:35:33 AM UTC-4, bitrex wrote:
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Two chips, 10 passives.  The register does need a reset pulse which can be provided with a cap and resistor on power up if you don't already have one.  

https://www.dropbox.com/s/4oiddnggiygir9v/SimpleSineSchematic.png?dl=0

https://www.dropbox.com/s/6npfc9xdkq64fl5/SimpleSineStep.png?dl=0

https://www.dropbox.com/s/cc2861e5n85ki7b/SimpleSineSmooth.png?dl=0

Can't do any better with anything remotely as simple or few chips.  

--  

  Rick C.

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Re: Dirty sine wave generator
On 9/21/19 1:28 AM, Rick C wrote:
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Thank you looks good. How to get a quadrature signal then becomes a  
question. All-pass phase-shifter, maybe.

Re: Dirty sine wave generator
On 21/09/19 06:52, bitrex wrote:
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Add a second set of resistors/capacitor to the Q outputs,
same values but slipped along by 2 outputs.

Re: Dirty sine wave generator
On 9/21/19 2:27 AM, Tom Gardner wrote:
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Great! I'll use an extra XOR section for inverter A9 and Bob's yer Dad's  
uncle (is that the saying)

Re: Dirty sine wave generator
On 21.9.19 08:52, bitrex wrote:
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Are you intending to use the outputs as oscillator signals to
an I/Q (image reject) mixer?

If yes, you do not need to create a sine wave, as practically all
analog (non-DSP) mixers work by switching the incoming signal
with the oscillator signal sign bit. I balanced mixers the input
is inverted according to the sign of the oscillator signal, and
in single-ended mixers the input is just switched on and off in
sync with the oscillator signal sign bit.

In this case a two-flip-flop twisted ring counter will produce
two square waves in perfect quadrature.

--  

-TV


Re: Dirty sine wave generator
On 9/21/19 7:39 AM, Tauno Voipio wrote:
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One of the phases has to be put thru an inductive transducer first, V ->  
I, then Kelvin-sense V across the transducer. If I had a high supply  
voltage to work with I'd just use some fast op amps, square waves and no  
prob as you say. I don't I'm really constrained on the supply voltage in  
this app.

They can support sines or modified-sines at the freq I need to go at and  
in my tests with bench signal gen the phase shift detector works great.  
Drive the analog portion with a square and run into the slew rate limit  
of the op amps and blech!

Re: Dirty sine wave generator
On 9/21/19 12:10 PM, bitrex wrote:

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Mind you another requirement is it has to run from a clock I can't just  
DDS some sines of the appropriate phase relationships from a uP as I'd  
do in my own project or something.


Re: Dirty sine wave generator
On Saturday, September 21, 2019 at 12:11:57 PM UTC-4, bitrex wrote:
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I don't get what that means.  Why is an MCU not an option because of the cl
ock???  The MCU can run on an internal RC clock and sync to the supplied cl
ock using an interrupt or polling.  Finish the calculation or table lookup  
and stop the CPU to wait for the clock edge.  

--  

  Rick C.

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