Download Experiment1_EE391_F13

ELE 391 Digital Circuits Laboratory
Fall Semester 2013 Experiment #1
Characterizing Transistors and Inverters
Implementation due Date:
Final Report due Date :
Sept 11, 2013
Sept 18, 2013
Comparing measured data to Multisim
Choose the 2N7000 n-type MOSFET. Set up the circuit required to measure the characteristic
curves of the 2N7000 transistor. Choose three evenly spaced gate voltages, such that the
maximum gate voltage produces a drain current of about 10-100mA. For each fixed value of
VGS, measure the drain current versus drain voltage when varying VDS from 0 to 15V. Choose
enough points to create a proper looking characteristic curve. Plot the characteristic curve using
excel or Matlab and tape the plot into your notebook. Have the instructor sign off on your plot.
Now measure the transfer curve data for the 2N7000 n-type MOSFET. For this experiment
choose three evenly spaced drain voltages; VDS=5V, 10V, 15V. Adjust VGS such that the drain
current covers the range from about 10μA to the maximum current measured in the previous
step. Measure the drain current versus gate voltage at enough points to create a proper transfer
curve. Make sure to adjust the gate voltage so the drain current is approximately evenly spaced
on a LOG scale. Plot the transfer curve using excel or Matlab and tape the plot into your
notebook. Have the instructor sign off on your plot.
Repeat this experiment using Multisim and the 2N7000 model. Generate the same characteristic
curve and transfer curve as you did experimentally. Export the data to Excel or Matlab. Plot the
Multisim data on the same graphs as your measured data. Use points for your measured data and
lines for the Multisim data. Tape your plot into your notebook and have the instructor sign off
on your plot.
Be sure to include a qualitative description of how well the Multisim model describes the actual
transistor you measured in your report.
Repeat the experiment for ZVP2106A p-type MOSFET.
Creating SPICE models from measured data
The equations that describe the drain current, ID as a function of drain to source voltage,VDS, and
gate to source voltage,VGS are in Chapter 4.2 and Chapter 4.3 of your book (There is a table
named mathematical model summary for NMOS and PMOS respectively.). Fit the data you
measured for the 2N7000 in the previous step to these equations by determining the parameters;
K(n or p), VTO, and λ. (Note; VTO=VTN=VTP for three terminal devices.) Re-plot the graphs from
the previous step, but this time include the lines determined by the equations from the book.
Be sure to include a qualitative description comparing how the multisim model and the
mathematical model predict the actual transistor you measured, for your report.
Repeat the experiment for ZVP2106A p-type MOSFET.
Creating a SPICE model for an unknown transistor
Repeat the same experiment as above for the n-type MOSFET in the CD4007 integrated circuit.
Plot the characteristic curve and transfer curve and have the instructor sign off on each plot.
Use the information the two previous figures to determine the SPICE model parameters k’ (KP),
VTO (VTO), and λ (LAMBDA). Use the published diagram to determine W and L.
Create a SPICE model for the CD4007 n-type MOSFET in Multisim. Use Multisim to generate
the characteristic curve and the transfer curve. Export the data to Excel or Matlab and create the
two new plots with measured data and Multisim data on the same graph. Have the instructor
sign off on each plot.
Repeat the experiment for the p-type MOSFET in the CD4007 integrated circuit. (Note; VTO is
a negative number for PMOS)
Inverter transfer curve
Design an NMOS inverter with resistive load (described in Chapter 6.5) using the n-type
MOSFET in the CD4007 package. Your experiment will test the inverter using a power supply
voltage of 5V, 10V, and 15V. The resistor value used in your inverter will not change, so choose
an appropriate resistance for that range of power supply voltages. Use one of the variable power
supplies to power the inverter and the other as the input. Use the DC voltmeter to measure the
output voltage. Vary the input voltage from 0V to the supply voltage. Make smaller changes in
the input voltage if the output is changing rapidly and make larger changes in the input voltage if
the output is not changing much. Plot Vout versus Vin for all three power supply voltages and
indicate VIL, VIH, VOL, and VOH on the graph as shown in Figure 6.15 of your book. Have the
instructor sign off on the plot(s). Calculate the theoretical values of VIL, VIH, VOL, VOH, NML,
and NMH as shown in Chapters 6.5.6-6.5.8 in your book. Compare the values determined from
the graph to the theoretical values determined from the equations.
Use Multisim to make the same graph of Vout versus Vin. Export the data to Matlab or Excel and
superimpose the measured data points and the modeled curve on the same graph. Have the
instructor sign off on the plot.
Repeat the experiment for the p-type MOSFET in the CD4007 integrated circuit. (Chapter 6.12)
Repeat the experiment for a CMOS inverter in the CD4007 integrated circuit. (Chapter 7.2)
Transistor Switching Speed
Use the NMOS inverter you tested in the previous section and again perform the experiment at
5V, 10V, and 15V. Connect a 1nF capacitor to the output of the inverter to act as a load
capacitance. Use the function generator set to a square wave going from 0V to the supply
voltage. Place an oscilloscope probe at the input and output of the inverter. Capture the input
and output oscilloscope curve as well as the data points using the Ultrascope software. This will
allow you to export the data to Excel or Matlab. Determine the rise time and fall time for the
output signal as well as the high-to-low, low-to-high, and average propagation delays. (tr, tf, tpHL,
tpLH, and tp) Printout the oscilloscope data and have the instructor sign off on the plot.
Determine the values of tr, tf, tpHL, tpLH, and tp predicted by the theory outlined in the book.
(Chapter 6.11.2, see example 6.10.) Compare your measured values to the predicted values.
Repeat the experiment above using Multisim. Be sure to include the capacitor connected to the
inverter. Export the Multisim data to Excel or Matlab and plot the input and output signals
versus time. Have the instructor sign off on the plot.
Repeat the experiment for the p-type MOSFET in the CD4007 integrated circuit.
Repeat the experiment for a CMOS inverter in the CD4007 integrated circuit. (Chapter 7.3)
Power-delay product
Connect the DC current meter in series with the power supply, so you can measure the current
used by the inverter. Leave the 1nF capacitor connected to the output of the inverter. Drive the
inverter with a square wave at different frequencies and record the amount of current used by the
inverter. Power is current time voltage. Vary the frequency over three orders of magnitude. For
the highest frequency, make sure the output voltage has enough time to make it up to the supply
voltage VDD and back down to near ground potential. Perform the experiment with VDD set to
2
5V, 10V, and 15V. Compare your results to the equation 𝑃 = 𝐶 𝑉𝐷𝐷
𝑓, (Chapter 6.10.2). Do
this by making a graph of log(P) versus log(f). Plot all your data on the same graph. Show the
measured values as dots and the equation as lines. (The equation is different straight lines for
different values of VDD on log-log paper.)
Perform this experiment on the NMOS, PMOS, and CMOS inverters. Have the instructor sign
off on the plot.
Input Capacitance and Oxide thickness
In a normal circuit, a 1nF capacitor is NOT connected to the output of inverters. In a logic
system, the output signal drives the next gate. For example, an OR gate may be connected to a
NAND gate. It’s the input capacitance of the NAND gate that is connected to the output of the
OR gate. The input capacitance is the gate capacitance of the transistor. If we connect the
output of one inverter to the input of a second inverter and measure how fast the first inverter
switches, we should be able to determine the capacitance that is connected to that inverter. It’s
as if we replaced the 1nF capacitor in the previous experiments with an inverter. Measure any
(or all) of the rise, fall, propagation time, or even power delay values for the two cascaded
inverters. From your measurements calculate the input capacitance.
Unfortunately, this capacitance value includes the amount contributed by the oscilloscope probe.
(Which is nothing more than a transistor amplifier having its own input capacitance!) We can
determine how big this is by making the first inverter drive two inverters. (This is called a fanout of 2.) Add one more inverter connected to the first inverter and re-measure the switching
speed. Calculate the new capacitance when driving two inverters and it should be bigger than
the previous capacitance by one inverter’s input capacitance.
Measure the input capacitance for the NMOS, PMOS inverters.
Once you know the transistor’s input capacitance, assume it is all due the gate oxide layer, COX.
Because you know W and L you can calculate TOX from 𝐶𝑜𝑥 =
𝜀𝑆𝑖𝑂2 𝑊 𝐿
𝑇𝑂𝑋
. Notice that TOX is the
sixth SPICE parameter (KP, VTO, LAMBDA, W, L, and TOX) required to make a complete
dynamic model of a transistor. Modify the TOX parameter in the multisim model. Repeat the
measurements of the switching speed characteristics you made above, using multisim. Compare
the simulated results to the measured results.
Notice from the Transistor equations, once you know COX, you can determine the mobility of the
electrons and holes in silicon. For silicon MOSFETs, μn ≈ 450 cm2/V-s and μp ≈ 200 cm2/V-s.
Determine the mobility for each of the carriers and compare it to the theoretical values.