Active envelope detector bias point

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ranaiftikhar

Joined Nov 1, 2016
42
hi
Attached below is an active envelope detector. If the differential signal is applied at the inputs, output should cancel out all even order harmonics. For proper cancellation the transistor should be in saturation region where square law holds. can you guide me why it is being biased in class AB region?

The reference of image is:
J. Lee, Y. Chen and Y. Huang, "A Low-Power Low-Cost Fully-Integrated 60-GHz Transceiver System With OOK Modulation and On-Board Antenna Assembly," in IEEE Journal of Solid-State Circuits, vol. 45, no. 2, pp. 264-275, Feb. 2010.

Thanks

paperpic.PNG
 

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