Phase shifter question

• posted

The phase shifter described in H&H has a phase that starts at 0 at DC and then goes to negative 180 at high freq. (excuse me if I got the definition of phase backwards) Is there a phase shifter that shifts phase the other direction with respect to freq, i.e. start at -180 at low freq and increases to 0?

• posted

The phase shifter that exists shifts the phase later with higher frequencies. Later in phase is minus values of degrees. The phase goes from 0 to -180 as frequency increases.

The phase shifter you want poses a bit of a problem. It requires that the phase go earlier with higher frequencies. Over a limited band this can be done but not without also having a variation in gain. This is because, in real life, only information from the past can be used in creation of the output.

• posted

Then how about those time machines?

```--
SCNR, Joerg

http://www.analogconsultants.com/```
• posted

Just invert the output.

John

• posted

-180° is _always_ lagging.

...Jim Thompson

```--
|  James E.Thompson, P.E.                           |    mens     |
• posted

Technically that will yield a phase shifter that goes from -180 degrees to -360 -- the endpoints will be right, but if the OP needs a positive slope then he needs to find the contact information for Non-Causal Systems, Inc. to get the parts. (their number is in next year's phone book).

```--
Tim Wescott
Wescott Design Services```
• posted

If the OP is referring to H&H figure 2.29, just reverse inputs phi1 and phi2.

Or as I would designate them (as shown in H&H)...

phi1 => +ein

phi2 => -ein

180° phase difference between inputs +ein and -ein.

...Jim Thompson

```--
|  James E.Thompson, P.E.                           |    mens     |
• posted

Or he could use those dilithium capacitors that JL figured the guy in the other thread uses.

Ed

• posted

Oh, come oh, the digital guys use non-casual filters all the time.

You just to overlook the input-output latency involved and designs can be as non-casual as you'd like. :-)

• posted

You'd be lagging at -180=B0 too.=20

--=20 Keith

• posted

Yes and no. Let's say you have a differential signal.

in out

• ----C-----+

- ----C----- +

+----L------ -

- ----L ---- +

So feed the low frequency with crossed inductors and feed the high frequency is non-crossed capacitors.

Assuming source and load resistors, this should end up as an all-pass network with phase shift.

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