Hi I have a doubt in CN0276.
In Fig. 12, the phase shift between EXC and SIN is about 40 degree, however, the filter design for EXC amplifier has about 180 degree phase shift, is there something that I miss? thanks.
I suggest to move or ask this question to Reference Circuits community. Someone here may be able to assist you.
Figure 12 is the phase shift between the AD2S1210 EXC and SIN pins which shows how the noise from EXC pins of AD2S1210 was improved. This is because of the amplifiers which acts as an active filter found at the resolver excitation(which uses AD8692) and at the resolver sin/cos receiver(which uses AD8694).
Both amplifiers acts as an active filters configured as a multiple feedback (MFB) third order Butterworth lowpass filter. The active filter has a gain of -1 which results to a 180° phase shift. Since the resolver excitation and the resolver sin/cos receiver both have these active filter, the phase of the signal that pass-through ends up shifting back to 0°.
Let me know if that answered your question.
Thanks for answering my question. I do know that the EXC filter has -1 gain, however, for SIN and COS filter, the circuit is not exactly the same and it has zero phase shift at low frequencies and start to roll off as frequency goes higher. I have simulated both circuits and confirm this. Could it be the connection to the resolver EXC and EXC(bar) is reversed to obtain Figure 12?
Upon checking the schematic both for SIN and COS filter found in CN0276, I found no difference at all. Can you share with me the simulation results you got so far for me to further understand the issue?
kindly see the attached figures (EXC followed by SIN/COS). I modified the gain from the original values. Thanks.