# +- 90 phase shifter

Discussion in 'Electronic Design' started by greysky, Jun 18, 2013.

1. ### greyskyGuest

Anyone know how to make a phase shifter that will shift a sine wave +- 90
degrees without distorting it in the process?
Thanks.

2. ### JoergGuest

Unless you do it digitally that will only work over a limited frequency
range. Check our Hilbert transform circuitry. Usually consist of lots of
precision R's and C's. There are also tricks how to do those with
switched capacitor filters. Mostly used in ultrasound, Radar and

¨
Audio ?

Microwave ?

4. ### tmGuest

The right length of coax? For just one frequency.

5. ### JamieGuest

Sure, one be long piece of wire, or what ever the freq you are working
with. calculate the wave length in free space and then apply the
velocity factor to shorten that figure up a bit. Of course it depends
on what you're using as a conductor, you''ll also need to worry about
matching the line to avoid reflection distortion.

THen again, you could always use a delay line

Jamie

6. ### Lawrence StattonGuest

No, but yes, kinda.

Any circuit, even as simple as a single conductor distorts its input
increases in complexity, it will have distortions in amplitude, and
delay that vary based on the incoming signal.

Engineering is all about defining the parameters of that distortion
that are acceptable to your application, described in one of several
domains, and developing a circuit that meets those parametrs.

The circuit I think you're looking for is often called an "all passs"
filter in the analog domain, or a Hilbert Transform.

For a signal of a single frequency, it is nothing more than a fixed
delay. If your signal can take one of many frequencies, you need a
delay that is variable based on frequency, such that the delay is
always the time that represents 90-degrees at each frequency.

The implementation I'm thinking of has one input and two outputs, that are
each delayed from the input, but one is delayed 90 degrees more than
the other over some range of frequencies.

Putting it in the concrete -- if I want to create a single-sideband
signal to carry Voice Modulation, I can use a phase splitter that
gives me 0 and 90-degree shifts over a limited band from roughly 300
to 3000 hertz.

7. ### Phil AllisonGuest

** Completely ambiguous question.

Why don't people just SAY what it is they are trying to do.

.... Phil

8. ### JoergGuest

Well, if it was just one frequency all you need is one inductor and one
capacitor, not a whole PLL

9. ### Bill SlomanGuest

M.J. Gingell “Single Sideband Modulation using Sequence Asymmetric Polyphase Networks” Electrical Communication 48 21-25 (1973). See also http://traktoria.org/files/electronics/networks/polyphase_networks.pdf

describes an approach that provides a close approximation to a 90 degree phase shift over an appreciable range of frequencies. It's in the second edition of "The Art of Electronics" by Horowitz and Hill (ISBN 0-521-37095-7) in section 5.17 as a "phase sequence filter".

10. ### George HeroldGuest

Hey, could you stick a divider before the mixer, lock to 1/2 the freq. and get
the full 180? (I guess you'd need a divider after the VCO too.)

George H.
So would integrator or

11. ### George HeroldGuest

Yeah, a long piece of wire with a tap... how can you make the velocity really low?
For microwave frequecies, we had this trombone like thing at the FEL.
(not cheap!!!)

George H.

12. ### misoGuest

Are you generating this sine wave? If so, just generate it in quadrature.

IIRC a biquad implementation of a bandpass filter has a 90 phase
difference between the op amps. But that is a narrow band solution.

I recall a project where I needed a wide band 90 degree phase shift and
ended up using a paper out of the IRE journal. (RE as in Radio
Engineers). It was a SSB phase splitter filter.

13. ### Robert BaerGuest

Act ignorant and use a L-C network..

14. ### Robert BaerGuest

Too simple for management..

15. ### Spehro PefhanyGuest

As well as the other suggestions, analog configurations with all-pass
filters can give you 90 degree phase shift over a range of
frequencies, practical up to maybe the entire audio range (lots of
op-amps and resistors and capacitors).

Or, assuming audio, maybe consider a DSP with a Hilbert filter
algorithm.

16. ### JamieGuest

Freq of interest would help immensely. We use coax phase matching.
Just roll up some turns according to what you need and there you are..

Just remember what one famous person said.

"No matter where you go, there you are"

Jamie

17. ### Guest

If its analog audio, you can do it with two parallel paths of allpass filters that approximate a 90 degree phase difference over some frequency range.The closer you want to get to DC , the more filter sections you will need.To design this you may need to use an optimizer of some sort. Same approach can be used in digital, but with another restriction that you can't get 90 degrees at Fs/2, and the harder you try the more filter sections you willburn.
Bob

Bob

18. ### whit3rdGuest

Howzabout... make a 20F oscillator, use flip/flops to divide it down
to a 5F quadrature pair/quartet of signals, and upmix your X with one of those
then downmix the 5F + X with a different phase?

If the X signal is narrowband, and you filter the result well, it is a sine wave
at X with phase according to the chosen downmix signal.