Because they're a convenience store. Why does milk from 7-11 cost more than milk from Safeway?
-- Tim Wescott Control systems, embedded software and circuit design I'm looking for work! See my website if you're interested http://www.wescottdesign.com
** So you refuse to point to it ?
Wot a colossal prick.
Output amplitude is linear on input, so it's not a PLL with logic. It seems to be the moral equivalent of an all-pass phase shifter.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
In an IQ modulator, the phase shift is applied to the oscillator injection signal, but the linearity requirement applies to the I and Q inputs. From linearity standpoint, it is a good thing if the oscillator signal amplitude variations do not pass through to the output.
In theory, a balanced modulator multiplies the analog sine signals from the oscillator and signal inputs, but in practice, the oscillator input will be overdriven so that the mixing happens as multiplication with the sign of the oscillator input only.
-- -TV
do not confuse the IQ baseband inputs with the LO input
m
Do not suggest that I am so stupid as to do that.
The output is clearly the sum of the outputs of two 4-quadrant linear mixers.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
They do, up to saturation.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Yes, I see no reason not to believe the datasheet - they say it uses a broadband poly-phase network. I imagine something like what radio hams used to call Gingell networks.
The datasheet does not explicitly say how far it deviates from the ideal
90degrees but study of the image rejection vs LO frequency plots on pages 5,6,7 should help deduce the number of stages and their corner points. The accuracy varies with temp and Vcc which implies varactor like effects in the networks?piglet
Might be something like a phase sequence filter implemented with OTAs.
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
** On page 10 under "LO Section" heading.
** But table 1 on the last page of the App Notes does.
It's within 1.2 degrees from 20MHz up to 1600MHz.
So over an 80:1 range.
.... Phil
Thanks Phil, well spotted!
piglet
That is why the best mixers are well overdriven diode rings or Gilbert multiplier cells, or also just CMOS bus switches (Google for 'Tayloe mixer').
-- -TV
Just curious as I am not familiar with the terminology. Is what you call a phase sequence filter something like these:
US Patent US3559042
Thanks
piglet
I plan to measure absolute in-to-out phase shifts vs frequency vs I and Q inputs. The classic SSB-type all-pass network has two outputs that are 90 degrees apart, but the "0 degree" output is not generally in phase with the input.
Gotta Dremel another test board.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Maybe, but maybe not. If you don't overdrive the Gilbert cell, you can ignore the odd harmonics of the LO. That's sometimes important.
My application, simulating an aircraft sensor, works best if the modulator is linear. I'm happy to find that it is.
So the phase shifter remains impressive.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Why? A digital phase shifter can generate digital signals to drive a switch ing demodulator.
The output from the demodulator can be a linear function of the RF input le vel at any particular constant phase.
If the demodulator was a merely an exclusive OR, the output wouldn't be a l inear function of the input RF amplitude but a Gilbert Cell multiplier or t he old Carter and Faulkner current steering phase detector can give a linea r relation between the RF input amplitude and the demodulated output.
CARTER, S.F., and FAULKNER, E.A. (1977): "New phase-sensitive rectifier cir cuit", Electron. Lett., 13, pp. 339-340, and 381-382.
This can happen, but it doesn't have to be a problem.
-- Bill Sloman, Sydney
Googling Gingell network and phase shift.. I get some IEEE pay doors, and this for free.
Is that what you mean? (Phase sequence filter?)
George H.
Yeah, See AoE (I don't know if it made it into the 3rd ed.) I've used these at audio frequencies...
George H.
This sure makes pretty pictures:
It's even prettier in real life, without the moire' junk.
I asked LTC if the output amplitude depends on RF input amplitude, and they said no. I measured it, and I say yes.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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