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
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.
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.