For the differential amplifier shown below, assume IQ to be a current source with output resistance Rout = 100 kohms. Ignoring mismatches, what is the common-mode gain of the circuit if the output is taken differentially (i. e. , vo = vc1 - vc2)? Assume Rc = 20 kohms. Acm = 0 Acm = 0.008 Acm = 0.02
![(a) Figure Q2(a) shows a differential amplifier with a current source at the bottom. It is given that VDD = VSS = 15 V, ISS = 300 μA, Early effect can be ignored (λ = 0), Kn = 400 μA/V2 and VTN = 1 V. You may assume MOSFET in saturation region. (i) For single ended outputs, draw the half-circuits and derive the algebraic equations for the differential mode and common-mode gains as well as CMRR. [6 Marks] (ii) For the above case of single ended output, what should be the value of Rss to get CMRR = 100? [4 Marks] Figure Q2(a) (b) Figure Q2(b) shows a MOSFET based current mirror. Draw the AC small signal model and derive an equation for output resistance Rout as shown in the figure. You can keep your answer in terms of gm, ro etc but denote the subscript 1,2,3 etc to indicate which transistor. In other words, denote transconductance of M2 by writing gm2 and so on. [6 marks] (c) Draw the diagram of a BJT based Class B push-pull power amplifier and derive the maximum possible power efficiency of this circuit. You may ignore crossover distortion and assume |VCE(sat)| = 0 V. [9 marks]](https://www.doubtrix.com/uploads/editor/1710360410ITbaKcVzzE.jpg)
