design of a 120 degree phase shifter

F range?? D from BC

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

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 a better answer...

Cheers, Tom

The

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

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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A bit OT, but around 1980 I built a sound card to go off a TRS-80 Output, using this,

(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

--- View in Courier:

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

-- JF

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 the load is, too, and if the load is stable.

Cheers, Tom

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?

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