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I need a 3phase (0-120-240deg) signal from one sine wave reference. I want control reference signal frequency in 5hz-50khz range with constant output phase shift in all frequency range. What would be the best way to implement such circuit? Simple RC shifter won't work because it's phase shift changes with frequency

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  • \$\begingroup\$ You could use an all-pass filter (Google it) or you could digitize and re-synthesize. Depends on your requirements for accuracy/distortion etc. \$\endgroup\$ – John D Mar 13 '17 at 2:04
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6 stage SIPO register with feedback from 3rd stage inverted to D input with outputs in Q2,Q4,Q6 and variable clock input x6

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  • \$\begingroup\$ Thanks. After googling I figured out that this is sort of hard task to implement analog circuit so started thinking similar way to generate digital squares and make sines from them and then you posted exact solution. Thank you \$\endgroup\$ – user1940679 Mar 13 '17 at 2:35
  • \$\begingroup\$ With binary weight R's you can also make 3 pseudo sine waves with 6 steps. \$\endgroup\$ – Tony Stewart EE75 Mar 13 '17 at 2:37
  • \$\begingroup\$ @user1940679 It is quite easy to get the required sine waves purely by analog means. Just use "phase-sequence network" ( see Horowitz and Hill 2nd ed. page 295 or google it ). But the digital solution is much simpler. \$\endgroup\$ – user117884 Mar 14 '17 at 19:14
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An RC shifter will work if your R-C sections are adjusted together in synchronized fashion, which is relatively easy with transconductance amplifiers. see figure 35 Just make the three sections of a phase-shift oscillator each have 60 degrees phase shift (the first stage output is 0, the third stage output is 120, and an inverting amplifier on the second stage output will give you 240 degrees).

Closing the feedback loop and keeping a stable oscillation amplitude is ... left as an exercise. The program current into the three sections adjusts the oscillation frequency, and that program current can be driven so as to phase-lock to a reference oscillator.

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One way to achieve a result is to use a sine-Digital/Analog or PWM lookup with just the required offsets into the table for each phase.
Microchip had a great app note on how.
This won't give you step less signals but will give good phase stability with frequency.

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