passive phase shifter design?

Got an intersting problem:

inputs: sine wave, 50 to 500 Hz, 10 volts p-p, 50 ohms, and its 180 degree opposite.

Outputs: two sine waves, 90 degrees apart, within 2% in phase, 20% in amplitude. Working into a 100K ohm load, at least 2v p-p.

Catch: has to be done with just r's and c's, no active components.

I see lots of phase-shifters that use op-amps, or work at one frequency, or work from 300-3000 Hz, but nothing in the range I need.

Any hints appreciated.

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If you have one that you're satisfied with from 300-3000Hz, then just scale the capacitors up by 300/50 = 6. Or scale the resistors down by that factor, or do a combination of the two.

Sorry, that was more than a hint.

Another non-hint: look for designs of phasing-type SSB encoders/exciters/decoders/detectors. They must somehow accomplish the same sort of thing. Note that the phase of the output will NOT be constant relative to the input, just 90 degrees apart between the two.

Cheers, Tom

Reply to
Tom Bruhns

Thanks Tom, that is the hint I needed. The old ARRL handbooks show audio phase shift networks for the "communications" audio range. I just didnt know whether to scale the resistors, the capacitors, the impedances, or some combination of those.

Also found some "polyphase" networks that are supposedly less tolerance sensitive.



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(1) Broadband phase shifters are non-trivial. Surf old Bell Labs journals, Darlington... yep, the same guy of compound transistor fame.

(2) If you can adjust at a single frequency...

R/C between VIN (0°) and -VIN (180°) can be set to almost any phase angle at the tap between the R and C... amplitude is constant!

...Jim Thompson

|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Jim Thompson

Can inductance be used? Why Not Active Components? What about non-linear Components? (EG Diodes, transistors?)

Assuming the limitation is because it cant use separate power source, It would be quite simple to suck a bit of power from the sine input to drive some active components. (EG A digital quadrature divider... which is quite simple with a couple of 74series ICs.) How "sine" does it have to be? (is a sq wave ok?).

It may be possible with an analog feedback system of L, C & R & transistors, so that feedback biases so as to null a multiplied sample of the outputs. (multiplying 2 sines 90Deg apart produces A DC of 0V, and deviations in phase from 90Deg produce DC..)

David Merrett

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Simone Merrett

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