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Applet Worksheet

[This worksheet may be suitable for Computer Lab Recitation or for Homework assignment for introductory-level microelectronics courses.  If you like, here is a MS Word file of this worksheet for three MOSFET applets.]

III. MOSFET Id vs. Vds CHARACTERISTICS
Applet:  http://jas.eng.buffalo.edu/education/mos/mosfet/v11/mos_2.html
Applet Introduction:  [This part of exercise is a repeat of the above exercise in II, with the bias Vgd replaced by Vds.]  This applet shows the Channel region versus the Gate-Source bias, Vgs, and the Drain-Source bias, Vds.  The I-V curves show the Id-Vds, the Drain current versus Drain-Source bias at all biasing conditions; and the Id-Vgs, the Drain current versus Gate-Source bias only when the MOSFET is in Saturation.  The red-dot indicates the current Biasing condition.
Goal of this exercise:  (a) Repeat the channel study (triode/saturation) using Vds instead of Vgd.  (b) Verify the equivalence of the conditions: (II) Vgd vs. Vt and (III) Vds vs. Vgs-Vt.

5. N-channel

xix) Applet Preparation: Select N-channel, Vt=1.5 V ==> Use Up/Down arrows to change Vgs and Vds.  Set Vds = 0V
xx) Change Vgs and find at what Vgs the channel forms ?
Vgs = (    ) volts
xxi) From the above, what is the relationship of Vgs vs. Vt for the N-channel to form ?
Vgs  vs. Vt:   (                                            )
xxii) Now, set Vgs = 3.5 V, and change Vds to find the Vds value at which the Channel is pinched off at the Drain-end and verify if it is equal to Vgs-Vt:
Vds = (          ) Volts.
xxiii) From the above, give a relationship for Vds vs. Vgs-Vt for the N-channel.
Continuous Channel (Triode) :   Vds vs. Vgs-Vt ==> (                           )
Channel is pinched off at Drain end (Saturation): Vds vs. Vgs-Vt ==> (                    )
Note the location of red-dot on the Id-Vds curve.  The red-dot is the current biasing condition Vgs and Vds of the MOSFET.
xxiv) Hand derivation and Applet verification of the conditions of MOSFET Operating mode in terms of Vgd and Vds:
(Hand derivation) Show that the conditions that you found are equivalent for the Triode mode whether in terms of  Vds vs. Vgs-Vt  or  in terms of  Vgd vs. Vt.  Show the same for the Saturation mode
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(Applet verification) Verify this equivalence using the applets (applets in exercise II and in III):  Triode/Saturation using Vds   <=>   Triode/Saturation using Vgd.
6. P-channel
xxv) Applet Preparation: Select P-channel, Vt=-1.5 V ==>  Use the Up/Down arrows to change Vgs and Vds.  Set Vds = 0V
xxvi) Change Vgs and find at what Vgs the channel forms ?
Vgs = (    ) volts
xxvii) From the above, what is the relationship of Vgs vs. Vt for the P-channel to form ?
Give the condition for Vgs  vs. Vt:   (                                            )
xxviii) Now, set Vgs = -3.5 V, and change Vds to find the Vds value at which the Channel is pinched off at the Drain-end and verify if it is equal to Vgs-Vt:
Vds = (          ) Volts.
xxix) From the above, give a relationship for Vds vs. Vgs-Vt for the P-channel.
Continuous Channel (Triode) :   Vds vs. Vgs-Vt ? (                           )
Channel is pinched off at Drain end (Saturation): Vds vs. Vgs-Vt ? (                    )
Note the location of red-dot on the Id-Vds curve.  The red-dot is the current biasing condition Vgs and Vds of the MOSFET.

xxx) Hand derivation and Applet verification of the equivalence of the Vgd and Vds conditions of MOSFET Operating mode:

(Hand derivation) Show that the conditions that you found are equivalent for the Triode mode whether in terms of  Vds vs. Vgs-Vt  or  in terms of  Vgd vs. Vt.  Show the same for the Saturation mode

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(Applet verification) Verify this equivalence using the applets (applets in exercise II and in III):  Triode/Saturation using Vds   <=>   Triode/Saturation using Vgd.

[Now, print this page out, and complete 3 questions  with the applet.]

1. Find the pinch-off voltage with the threshold voltages set as follows for the n-channel MOSFET. Make sure that at your Vgs and Vds, the channel is pinched off and the "red-dot" in the Id - Vds curve is located at the right place.

 Vt(V) 0.5 1.0 1.5 2.0 3.0 4.0 Vgs(V) . . . . . . Vds(V) . . . . . .
2. Set Vt = 1.5V, n-channel, Vgs =3.2V , and vary Vds from 0.5V to 2.2V. From the applet, is the device in the Saturation, Triode or Cutoff region ?

3. In  the same manner, Set Vt = -1.0V, p-channel, Vgs = -2.5V and change Vds from - 0.5V to - 2.5V. Is the device in the Saturation, Triode or Cutoff region ?