# design of a 120 degree phase shifter

Discussion in 'Electronic Design' started by rony, Oct 10, 2007.

1. ### ronyGuest

can anyone tell me how to implement a 120degree phase shifter for
using in a high power circuit and possibly a opamp model that can be
used for the same pls also let me know anyalternate methhods for
implementing the same with some other components instead of op amps

F range??
D from BC

3. ### HardySpicerGuest

You need an RLC circuit. An RC would attenuate the signal too
much.Take the output at the cap and put all three in series. The phase
shift is easy to calculate.Take the Laplace Transform and find the
transfer function - then work out the phase using arctan(imag/Real).
The solution is not unique of course. Watch the ratings of the
cap,inductor and resistor and stand well back when switching on!

Hardy

4. ### neon

1,325
0
Oct 21, 2006
take an op-amp amplify if need be add an rc network to get what you want. and amplify again use AND gates cross couple to generate square wave OR USE COMPARATORS

5. ### Tom BruhnsGuest

What's the signal source? What frequency range? Do you need a 3-
phase output (0--120--240 degrees) or only a 120 degree shift? Do you
need the output to be 120 degrees from the input, or can you use a
circuit that takes an input and provides two outputs separated by 120
degrees? (Or three outputs, 0--120--240 from each other?) What will
the load be on the output(s)?

If you're operating on a fixed frequency, it's relatively easy to use
a fixed LC circuit to get the phase shift you want, but if you need it
to operate over a range of frequencies, it likely will be easier if
you can use a set of three outputs that maintain a particular
relationship to each other, but a variable phase relative to the
input. This assumes you want the amplitudes to be held close to each
other.

A more complete description in the question is likely going to get you

Cheers,
Tom

The

6. ### Jim ThompsonGuest

Easiest way to make an adjustable phase shifter without amplitude
variation is push-pull drive....

+E
o
|
\
/ Variable R
\
|
o----> Output
|
|
|
--- C
---
|
|
|
o
-E

( -E is 180° out-of-phase from +E )

...Jim Thompson

7. ### Ken S. TuckerGuest

A bit OT, but around 1980 I built a sound card to
go off a TRS-80 Output, using this,
http://en.wikipedia.org/wiki/Phase-shift_oscillator

(I used a transistor instead of an Op-Amp).

Using the output I programmed the resistor
values, (IIRC it was 8 bit O/P, maybe 16),
using CMOS switches, latched.
Anyway the tone was nearly perfect sinsodial
and sounded great pumped through a big old
Hi-Fi. (I don't like square wave audio).

Phase-shift oscillators are great for Audio.
Ken

8. ### John FieldsGuest

---
View in Courier:

..[CLOCK]--+--[COUNTER]--+--[LUT 0°]--[DAC]--[LPF]--> 0° OUT
.. | | |
.. +-----------------------------------+
.. | |
.. | +--[LUT 120°]--[DAC]--[LPF]-> 120° OUT
.. | |
.. +-------------------------------------+

9. ### Tom BruhnsGuest

Yes, indeed--but the phase shift of that circuit depends on frequency,
so we need to know if the OP wants the circuit to operate over a range
of frequencies or only at one frequency. It will help to know what

Cheers,
Tom

10. ### JamieGuest

if you were talking about a steady CW, I would say a
PLL OSC so that it's 120 degree's offset.
But, I don't think we're talking about the same thing here
are we?