The resistance Rs in the circuit of Fig. P8.21 can be implemented by using a MOS

Question

The resistance Rs in the circuit of Fig. P8.21 can be implemented by using a MOSFET operated in the triode region, as shown in Fig. P8.22. Here Q3 implements Rs with the value of Rs determined by the voltage Vc at the gate of Q3.

(a) With vg1 = vg2 = 0V, and assuming that Q1 and Q2 are operating in saturation, waht dc voltages appear at the sources of Q1 and Q2. Express these in terms of the overdrive voltage of Oov at which each of Q1 and Q2 operates, and Vt.

(b) For the situation in (a), what current flows in Q3? What overdrive voltage of Vov3 is Q3 operating at, in terms of Vc, Vov, and Vt?

(c) Now consider the case Vg1 = Vid/2 and Vg2 = -Vid/2, where Vid is a small signal. Convince yourself that Q3 now conducts current and operates n the triode region with a small Vds. What resistance Rds does it have, expressed in terms of the overdrive voltage Vov3 at which it is operating. THis is the resistance Rs. Now if all three transistors have the same W/L, express Rs in terms of Vov, Vov3, and gm1,2.

(d) Find Vov3 and hence Vc that result in i) Rs - 1/gm1,2; ii) Rs = 0.5/gm1,2

Explanation / Answer

http://prof.usb.ve/mirodriguez/electronico/0495667722MicroelecCircuits.pdf

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.