I want to implement a phase shifter using an op-amp, also known as active all-pass filter, according to this schematic.
Formula for the phase shift is: π-2*arctan(2πfRC).
I think there are some limitations of this circuit:
- Argument of the arctan will be allways positive, that means resulting phase shift can be theoretically between π-0 = π and π-2*π/2 = 0. Negative phase shift or greater than π cannot be achieved.
- Function arctan can only approach (asymptotically) π/2, so resulting phase shift will never be really zero. You can choose very large R (or C) to be very close, but with R as variable resistor this would have a negative side-effect of low resolution in the lower range of resitance.
- You also cannot set R to zero to achieve π phase shift, as this would short the input of the op-amp to ground.
Are my assumptions about this circuit correct? Are there some workarounds, or other examples of active all-pass filters, which would allow to overcome this limitations?
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