Dirty sine wave generator

Not really. Until you get the weights right it will be more like a triangle wave. The wide pulse coming from the FF has to be three times the amplitude of the pulse coming from the clock. It looks like in your circuit the ratio isn't even 2:1.

BTW, something is wrong with the timing, but maybe that's because this is a simulation with unrealistic numbers. The glitch should be much smaller than you are showing.

Why can't you use an 8 bit shift register? It can't be that much more than the dual FF. What parts are you using?

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  Rick C. 

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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.

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

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The sim is 74HC but 74LVC likely for the actual device as needs to go down to 1.8 volts on the supply hence the CMOS low-voltage type op amps. I already need at least 1 XOR elsewhere. also a square wave that's 90 degrees advanced from the "sine."

A counter could work, too. If I could use up the extra XORs in something like this:

using up the extra gates in a quad 74LVC86 would be nice. D flip flops let you easily make the phase-shifted square.

a 4 "step" sine will probably be fine. Don't really want to use more op-amp sections 1.8 volt CMOS amps with the bandwidth I need aren't that cheap relatively speaking. this is to go in a semi-disposable product I got a budget!!

Thank you looks good. How to get a quadrature signal then becomes a question. All-pass phase-shifter, maybe.

Add a second set of resistors/capacitor to the Q outputs, same values but slipped along by 2 outputs.

But, your 8-way flipflop thing only requires a second chip (reset on an edge of bit 4) to a second summing junction. Why would you want a phase-shifted square?

A second 74HC273 is not going to break the bank on cost... Heck, with two of 'em you could lengthen the period to ten steps from eight, and have a D-flop to spare. (fifteen steps is 1.5 periods, use the first ten for I, last ten for Q).

Great! I'll use an extra XOR section for inverter A9 and Bob's yer Dad's uncle (is that the saying)

But, Rick C's 8-way flipflop thing only requires a few extra sections tacked on the end (and a second summing junction).

Why would you also want a phase-shifted square?

A second 74HC273 is not going to break the bank on cost... Heck, with two of 'em you could lengthen the half-period to ten steps from eight, and have a section to spare. (fifteen steps is 1.5 half-periods, resistors to sum from the first ten for I, last ten for Q).

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.

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An XOR is an inverter. A two input AND or OR gate will give you any phasing of square wave you want on the Johnson ring counter.

For an MCU that is the silliest circuit I've ever seen. The MCU can count any sequence needed without the XORs, not that you are talking about using an MCU.

Maybe you need to read a little about ring counters. They have a lot of nice features.

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  Rick C. 

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Why would you need *more* op amps? Every amplifier is also a filter... or can be.

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  Rick C. 

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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!

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.

o n d

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.

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The faster you try to clock it the worse things will get with

I am inclined to agree. I thought he was pushing hard up against the actual speed capabilities of the parts not down at a few hundred kHz.

A two step approximation to a sine wave is always going to look pretty dreadful - that is why is suggested piecewise linear approximation which would otherwise work fairly well for a spot frequency - even more so with a bit of diode shaping to lop the top off.

The important thing that the 2 FF ring does provide is a locked phase quadrature output which was one of his other unsatisfied requirements.

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This 4 flip-flopper with the outputs taken from Q and "delayed" not Q for two phases the should be good enuff

300kHz FS square wave out of an op amp with a barely 7 V/uS slew rate (because it's a micro-power part) - sucks!