Unformatted text preview: Name _______________________ ECE Box # _____________ Problem Score Points 1 2 3 4 ______ ______ ______ ______ 30 30 20 20 EE4902 C2002 Analog IC Design Exam 2
• This is a closed book test! • Show all your work. Partial credit may be given. If you think you need something that you can't remember, write down what you need and what you'd do if you remembered it. • Look for the simple, straightforward way to solve the problem for the level of accuracy required. Don't get entangled in unnecessary algebra. • You may assume all opamps to be ideal, except as otherwise noted. • As in real life, some problems may give you more information than you need. Don't assume that all information must be used! It's your job to decide what's relevant to the solution. • You have until 12 noon to complete this exam. four problems on a total of 13 pages. There are 1 2 MOSFET LARGE SIGNAL CHARACTERISTICS N CHANNEL P CHANNEL CIRCUIT SYMBOL D G ID
B  D VGD G+ + VGS  S ID
+ VDS G S B + S VSG G+ VGD  D + VSD  S D ID ID ACTIVE I D = µnCox W (VGS  Vtn) 2 [1 + ln (VDS  Veff )] I D = µpCox W (VSG + Vtp )2 [1 + lp (VSD  Veff)]
2 L Veff 2 L Veff VDS > Veff
ACTIVE ID VDS < Veff ID VSD < Veff
TRIODE VSD > Veff
ACTIVE IDVDS CHARACTERISTIC TRIODE INCREASING VGS INCREASING VSG VDS VGS < Vtn
OFF VDS VSG < Vtp
OFF ID ID
Vtn Vtn IDVGS CHARACTERISTIC (ACTIVE REGION) VGS VGS < Vtn
OFF VGS VSG < Vtp
OFF VGS > Vtn
ACTIVE VSG > Vtp
ACTIVE TRIODE REGION I D = µnCox W [ (VGS  Vtn)VDS  VDS ]
L 2 2 I D= µpCox W [ (VSG + Vtp)VSD  VSD ]
L 2 2 3 1. This problem involves design of a common source amplifier circuit with active load. The circuit is shown in Figure 1a. You may assume that the substrate (body) terminal is tied to the source terminal. Use the following MOSFET parameters for this 2µm process: Parameter Nchannel +1.10 5.2E5 0.03 Pchannel 1.20 1.5E5 0.02 V A/V2 V1 [4] Units Vt µCox l a) Choose RB for a current of IB=200µA in the current mirror. RB = _______ b) Choose the input bias voltage VBIAS to achieve an output voltage in the linear range (both M1 and M2 in the active region). [4] VBIAS = _______ Determine the magnitude of the lowfrequency smallsignal gain from vin to vout. v av = out = vin c) [8] d) Determine the maximum and minimum output voltages for both M1 and M2 to be in the active region. [4] VOUT(MAX) = _______ VOUT(MIN) = _______ 4 VDD M3 80 2 M2 80 2 IB
RB
Vin
+ ID
M1 16 2 Vout VBIAS
 Figure 1a. *** MORE ON THE NEXT PAGE !!! *** 5 A load impedance of 150kΩ  20pF is added to the output as shown in Figure 1b. e) Will the lowfrequency small signal gain magnitude av  decrease, remain the same, or increase? [1]
DECREASE SAME INCREASE EXPLAIN! [4] f) Determine the DC gain and 3dB bandwidth frequency (f3dB) for the circuit with the load impedance of 150kΩ  20pF added to the output. [5] DC gain = _______ f3dB = _______ 6 VDD M3 80 2 M2 80 2
Vout RB
Vin
+ M1 16 2 RL 150kΩ CL 20pF VBIAS
 Figure 1b. 7 8 9 This problem concerns the design of the differential amplifier shown in Fig. 2. You may assume that the substrate (body) terminal is tied to the source terminal. You may also ignore channel length modulation (assume l=0) Use the following MOSFET parameters for this 2µm process: Parameter Vt µCox a) Nchannel +1.10 5.2E5 Pchannel 1.20 1.5E5 V A/V2 [4] Units Choose IBIAS for an output DC bias level of VO1(DC) = VO2(DC) = +3.0V. IBIAS = _______ b) Determine the magnitude of the lowfrequency smallsignal differential mode gain av(dm) from input v+v to output vo 1vo 2. [8] vout(dm) v v av(dm ) = = o1 o2 = vin(dm) v+  v c) Determine the magnitude of the lowfrequency smallsignal common mode gain av(cm) from input vcm to output vo 1 or vo 2. [8] av(cm) = 10 Your design from the previous problem is modified by splitting the bias current source and inserting resistor RS between the sources of M1 and M2, as shown in Figure 3b. a) Will the magnitude of common mode gain av(cm) decrease, remain the same, or increase?
DECREASE REMAIN THE SAME INCREASE [1] EXPLAIN! [6] b) Will the magnitude of the differential mode gain av(dm) decrease, remain the same, or increase? [1]
DECREASE REMAIN THE SAME INCREASE EXPLAIN! [6] c) Determine the magnitude of the differential mode gain av(dm). [6] 11 VDD = +5V RD1 5kΩ RD1 5kΩ VO1
+ M1 80 2 RS 5kΩ VSS = 5V M2 80 2 VO2
+ V+ IBIAS
2 VIBIAS
2 Figure 3b. 12 4. The Common Gate Amplifier, or “Trust the smallsignal model, Luke” The input impedance of the common source amplifier is (ideally) infinite, since the input voltage “sees” only the MOSFET gate terminal, which draws essentially no gate current due to the gate oxide. This high input impedance is usually an advantage, but in some highfrequency applications it is desired to have a relatively low input impedance. For example, in some RF circuit design applications, the amplifier input impedance can be used to match the characteristic impedance of a transmission line. Figure 4 shows the common gate amplifier, which is often used in this type of application. You may assume that the substrate (body) terminal is tied to the source terminal. You may also assume channel length modulation to be negligible (l=0). Use the following MOSFET parameters for this process: Parameter Nchannel +1.10 5.2E5 Pchannel 1.20 1.5E5 V A/V2 Units . Vt µCox a) Using the space on the following page, draw the lowfrequency smallsignal model for this amplifier circuit. [8] Determine av , the magnitude of the lowfrequency smallsignal gain from vin to vout. v av = out = _______ vin • [6] c) Determine rin, the smallsignal input resistance looking into the input at the source terminal of the MOSFET. [6] rin = _______ 13 vDD = +5V
5kΩ vout
340µm 1.6µm vin
+ VBIAS +1.4V vin
 rin Figure 4. Small signal model for part (a): 14 ...
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This note was uploaded on 10/13/2009 for the course ECE 4902 taught by Professor Mcneill during the Spring '01 term at WPI.
 Spring '01
 MCNEILL
 Integrated Circuit

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