Name ______

ES 330 Electronics IIHomework #8

(Fall 2017 – Due Wednesday, November13, 2017)

Problem 1(16 points)

You are given a common-emitter BJT and a common-source MOSFET (n-channel). Fill in the table below. Assume the BJT to be in the forward active mode and the n-channel MOSFET to be in the saturation region of operation. [The purpose of this exercise is to compare BJT and MOSFET parameters. Remember that A0 is the voltage gain without a separate load resistance RL.]

NPN BJT Cell
 = 100,VA = 100 V and
VTH = kT/q = 25 millivolt / N-channel MOSFET Cell
nCOX = 200 A/V2, (W/L) = 40
and VA = 10 V
Bias Current is / IC = 0.1 mA / IC = 1 mA / ID = 0.1 mA / ID = 1 mA
gm (mA/V)
r0 (k)
A0 (V/V)
RIN (k)

Problem 2 (20 points)

You are given the circuit drawn below. It is fabricated in a CMOS process for which nCOX = 2pCOX = 200 A/V2, V’An = |V’Ap| = 20 V/m, Vtn = -Vtp = 0.5 volt and VDD = 2.5 volts. The two transitor types have L = 0.5 m and are to be operated atID = 0.1 mA and|VOV| = 0.3 volt. Find the required gate node voltage VG applied to Q2 and the (W/L) ratios for both the n-channel and p-channel MOSFETs to meet the stated conditions. [The subscripts “n” and “p” denote n-channel and p-channel, respectfully.]

Problem 3 (14 points)

The schematic below shows a “cascoded” n-channel MOSFET pair used to achieve higher output resistance ROUT. We want to achieve ROUT = 200 k using this cascode pair operating at a drain current ID = 0.5 mA. Assuming identical geometrical device layouts, so that (W/L)1 = (W/L)2 = (W/L), nCOX= 0.1 mA/volt2,andVA = 10 volts; what is the required gate width-to-length ratio (W/L) for this circuit?

Problem 4 (10 points)

In a MOSFET cascode amplifier we want the transistor performing the cascoding function to increase the output resistance by a factor of 50. Reference: See Figure 8.30 on page 548.

(a) If the cascoding transistor is operated at VOV = 0.2 volt, what must the value of the Early voltageVA be to accomplish this?

(b) If the process technology specifies V’A as 5 V/m, what channel length L must the transistor have?

Problem 5 (20 points)

Given the cascoded current source as shown in the figure:

(a) Show that if the two transistors are identical, the current I supplied by the current source, and the output resistance R0 are related bythe expression, IR0 = 2|VA|2/|VOV|.

(b) Next, consider the case of transistors having |VA| = 4 volts and operated at |VOV| = 0.2 volt. Also, let nCOX = 100 A/V2. Find the W/L ratios required and the output resistance realized for different two currents: (1)I = 0.1 mA and (2)I = 0.5 mA. Assume that VSD for both devices is the minimum voltage required, that is, VSD = |VOV|.

Problem 6 (20 points)

Consider the cascoded amplifier shown schematically below. It is operated at a current I = 0.2 mA with all devices operating at |VOV| = 0.20 volt. All four devices have |VA| = 4 volts. Find gm1, the output resistance of the amplifier Ro,n, the output resistance of the current source Ro,pand the voltage gain AV.