How should I analyse this circuit? I did it assuming PNP MOSFET on and NPN off and then change the assumption. It became too complex. Can I solve it simply be looking at options available?
NPN and PNP refers to the polarity of BJTs. MOSFETs are defined as N-channel or P-channel. The circuit is in the linear region when both MOSFETs are conducting at the same time. So under what input voltage conditions is that true? Do you know what Vtp and Vtn means?
How would you defined the linear region? And without any calculation I would pick answer B. http://forum.allaboutcircuits.com/threads/pmos-souce-drain-voltage.47763/#post-314871
Yes, I know what Vtp/Vtn means. It specifies the minimum |Vgs| needed to turn the mosfet on. This is required to create the channel. Which region should I choose ? Linear or sturation?
Thank you for the video. It was helpful. Option C and D are ruled out. Because for PMOS to turn on Vin<4V. Why did you prefer B to A?
Good question. But forget about that, I wrongly understood the question. They ask only about M1 transistor. And ask about the linear region (triode region). So in this case I choose A as a right answer.
Jony, I understand that A is correct answer among these. But what does the value of 1.875V signifies here? Why it is a boundary? Or is it to be solved by just looking at options?
Well for Vin>1.875 the M1 transistor leaves the linear region and enters the saturation region. So, M1 is in linear region and M2 is in saturation. ID1 = ID2 Id1 = Kp*(Vgs - Vtp)*Vds - Vds^2/2 Id1 = 0.5*Kn*(Vgs - Vtn)^2 Then (Vin - Vdd - Vtp)*(Vout-Vdd) - (Vout - Vdd)^2/2 = 0.5*(Vin - Vtn)^2 And M1 leaves the linear region when Vds = (Vgs - Vtp) hence Vout - Vdd = Vin - Vdd - Vtp then Vout = Vin - Vt And after we solve this for Vin I get 1.8333V http://www.wolframalpha.com/input/?i=(X+-+5+-+(-1))+*+(X+-+1+-+5)+-+(X+-+1+-+5)^2/2+=+(X+-+1)^2/2 But I made a error so this solution is not true. http://oldeee.see.ed.ac.uk/private/ee3/med/rc/week5MOSFET.pdf http://www.prenhall.com/howe3/microelectronics/pdf_folder/lectures/tth/lecture11.fm5.pdf http://nptel.ac.in/courses/117101058/downloads/Lec-15.pdf
Thanks a lot Jony!! You have helped me a lot here. I guess in case of PMOS the Vgs,Vds should be Vsg and Vsd respectively.