Problem set #4 Clarifications

Last updated: 10/21/Tue midnight

General

• Other than Problem 2, please use the level 1 models (the parameters given in Table 2.1.).
• Please assume that all L's are Ldrawn for all the remaining problem sets and the project.
  Please IGNORE the book saying "all device dimensions are effective values".
  (I.e. you have to calculate Leff youeself for Problem 3~6.)

Problem 1.

• Ignore the channel length modulation and the body effect.

Problem 2.

• As for the differential-mode transconductance, you will need to look at the derivative of the differential output current to the differential input voltage.
  To get a hint on how you would measure the differential-mode transconductance using HSPICE, imagine how you would do to measure gm for a single device: since gm is d(Id)/d(Vgs) for a fixed Vds (at a given bias), you will run a DC simulation for sweeping over Vgs (e.g. from 0 to Vdd) to get Id versus Vgs plot, and then calculate the derivative of Id over Vgs.
  What you will need to do in this problem is quite similar to this, but now you are twisting the "differential" input voltage.
• It is traditional to use the terms "wide" or "narrow" when they describe the width of a MOS transistor. As for the length of a MOS, we use "long" or "short".
• Vdd = 3V.
• HSPICE hints for Problem 1.
  • As for the input voltage set up, you may use the same one as that shown in the HSPICE review session, with the Vin1 and Vin2 changed into a DC voltage source. You don't need to run an AC simulations at all, since you are measuring the operating point parameters evaluated at different biases.
  • To find out what the Vth is for the transistor (to find out the overdrive voltage), you may include the following line in your HSPICE input file:
    .print dc LV9(Mname)
    then you will find it on mwaves' result browser. You may use it together with other output voltages' in the expression builder (from mwaves) to get the overdrive voltage defined as (Vgs - Vth).
  • To measure the drain current of a transistor, M1, then you have to include the following line in your input file:
    .print i(M1)
• You may use LTspice for this problem.
• You may use any schematic editor available.
• Please turn in your SPICE input file (or if you are using schematics in LTspice, submit a copy of the schematics.)

Problem 3. P4.2

• Rd = 2kOhm.
• Ignore channel length modulation and the body effect.

Problem 4. P4.15

• You may ignore the body effect.

Problem 5. P5.1

• In part (c), find both the cases when the Vth is increased and decreased.