(a) In the BiMOS Darlington circuit of Fig. P4.25 replace each transistor with its small-signal model and use the test-signal method to obtain an expression for the ac resistance seen looking into...

(a) In the BiMOS Darlington circuit of Fig. P4.25 replace each transistor with its small-signal model and use the test-signal method to obtain an expression for the ac resistance seen looking into each terminal of the composite device if the other two terminals are at ac ground. (b) Calculate the above resistances if gm1 5 0.5 mA/V, gm2 5 50 mA/V, ro1 5 ro2 5 50 kV, and r2 5 2.0 kV.