[Solved] Limitations of op-amp phase shifter design

simonov Asks: Limitations of op-amp phase shifter design
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:

  1. 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.
  2. 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.
  3. 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?

Ten-tools.com may not be responsible for the answers or solutions given to any question asked by the users. All Answers or responses are user generated answers and we do not have proof of its validity or correctness. Please vote for the answer that helped you in order to help others find out which is the most helpful answer. Questions labeled as solved may be solved or may not be solved depending on the type of question and the date posted for some posts may be scheduled to be deleted periodically. Do not hesitate to share your response here to help other visitors like you. Thank you, Ten-tools.