Well, they're a fair amount faster, which means that the edge artifacts aren't as serious, and their output resistance is less, which means that the total resistance in each tap is more predictable.
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
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Yeah, a switched cap filter on the back side might be cool. Then the thing wouldn't be limited on the low frequency end. I've got some from another project.
It'd be trivial to make an N-path filter following a square wave, then a simple-minded smoothing R/C. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Hi James, Yeah I was loading down the output of the 4017. I measured an output impedance of ~180 ohms. I put this number in and recalcualted values, and then selected them to ~0.1% with a DMM. The result.... I've got all the harmonics below the 9th down by ~70dB! I don't know how repeatable the the output imedance is? I put in a few different 4017's and say no difference, but these were all from the same order, so...
Here's a plot from the SRS770.
formatting link
Now I've got to get it off the white proto-board and crank up the frequency.
Beautiful, and well worth the resistors, right? Compared to the cost and complexity of extra hardware, it's a bargain.
For each half-wave, I'd analyze this as the sum of three impulses, one inside the other, added together. The phasing and amplitude of those impulses is critical to canceling harmonics.
.---. .--' '--. | | .-' '-. ___| |___ | | -' '-
My gut wants to say--but I'm too lazy to prove right now--that having the same voltages repeated symmetrically on either side of each peak is critical to harmonic rejection.
Where the voltage is unequal on either side, you introduce a new impulse with a magnitude equal to the difference in voltages. It's easy to *introduce* a 2nd harmonic component that way. For example, taking the middle impulse:
My original thinking was to have an up/down counter, a single homemade DAC, cycle up and down through the same (sine-weighted) values, then invert (externally) for the negative swing. That gets you 4x as many steps and automatic symmetry, but it's not nearly as cute as Phil's
I posted several links (last month?) and a paper by Franks and Sandberg. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Cool! 4017s rule--they're dead useful and just complicated enough that the anti-555 fascists don't notice. :)
I use them for things like getting guaranteed break-before-make from
74HC4016-style analogue switches. Of course, I've also used PALs as analogue components, so I have no shame whatever.
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
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Yeah, I was hoping for 60dB. When I crank up the frequency capacitance is going to start to byte me, but now I've got dB's to spare.
Hmm you're suggesting that matching between equal value resistors is more important than hitting some exact number. I think, that might be true.... or does matching effect the odd harmonics and absolute value the even?
I'm suggesting the possibility, but that's only a suspicion--I showed one example below. OTOH, I also just installed a virtual caterpillar grommet backwards in another thread. :-)
As a practical matter, Phil's 'HC4017 with precision resistors seems best.
FWIW, here's what I'd imagined, where v0-v7 encode a half-wave:
Ha, following your bipolar idea, I was wondering if I could program the 4017 for 1/2 a sine wave and use the carry output to flip a +/-1 opamp down stream. I guess that means another chip.
Oh don't do any math on my account. And thanks for the ideas! Doubling the number of steps doubles the clock frequency, which seems to suggest that capacitance will get you at some lower output frequency. I'm assuming that rounding off the nice sharp steps will screw things up.
Here we were thinking what a talented woman she must be, jumping straight in on topic like that. ;)
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
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
(Just back from visiting my daughter, who has an apartment a block from Bourbon Street. The difference seems to be that in the French Quarter the dives cater mostly to tourists, whereas in Key West they're for the locals!)
--
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
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
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