{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

4902_C2009_Lab2

4902_C2009_Lab2 - ECE4902 Studio Lab 2 C2009 Carrier...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 4
Background image of page 5
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ECE4902 Studio Lab 2 C2009 Carrier Mobility, Channel “on” Resistance Ron MOSFET Threshold Voltage VTHH, VTHp SPICE Parameter Extraction PURPOSE: The purpose of this lab is to measure the resistive nature of the MOSFET drain—source channel. Upon completion of this lab you should be able to: ° Recognize that the channel of a MOSFET looks (mostly) resistive for small currents iD and small values of drain—source voltage vDS. ' Recognize that increasing the gate drive beyond the threshold voltage reduces the channel H H ' on reSIStance Ron, ' Determine the carrier mobility and threshold voltage for the N— and P—channel MOSFETS in the MC14007 ' Compare the measured data to predicted values based on extracted parameters Prelab P2—1. In the circuit of Fig. P2-1, a DVM is used to measure the drain~source resistance Ron as a function of applied gate—source voltage Vos- The following data is obtained: VGS Ron 1.5 V 00 2.0 3180 $2 2.5 710 $2 3.2. 330 $2 4.5 180 S2 Estimate the threshold voltage VTH and unC0x% for this MOSFET (see Writeup section for procedure) Figure P2—1. Lab Exercise: REDUCING ON RESISTANCE Ron BY INCREASING GATE DRIVE VGS 1.2—]. Use the circuit of Fig. L2—2 (using the DVM in ohmmeter mode) to measure the on resistance Ron directly. As you vary VGS, you will see variation in the on resistance. Resistor RG is solely for protection of the MOSFET gate; the voltage drop across RG is zero under normal conditions since the DC current into the MOSFET gate is zero. NOTE: Use the AFG3021 function generator in DC output mode (access through the button sequence More > More Waveform Menu > DC). Be sure to set the numerical amplitude display to the "High Z" load condition so the displayed DC level is correct. As an additional check, use the scope to look at the gate voltage so you can see vGS go up and down as you adjust the DC level. ADDITIONAL NOTE: It‘s important to observe the DVM lead polarity shown in Fig. 12-2. If the DVM connection is reversed, the DVM current iDVM will forward bias the substrate-to— drain diode when VGS < VTH. ANOTHER ADDITIONAL NOTE: For this part, it’s very important to leave the DVM on the 20V/20kQ range throughout. Changing the resistance range changes the current the DVM uses to measure resistance, which affects the resistance measured in the triode region. The problem: in the 2k§2 range, the DVM injects a larger test current than in the ZOkQ range. This causes a larger value of VDS, violating the “small VDs” condition for the resistive portion of the triode region. So, even though normal practice would be to use the 2kS2 range when measuring Ron less than 2kg (for better measurement resolution), in this case, we’ll live with lower resolution so as not to violate the “small vDS” condition. L2—2. Set the AFG3021 voltage VDC to provide VGS of approximately +5V. Measure Ron and VGS. The resistance R0n should be in the range of approximately 2009 to le (which will read : 0.2kQ to : 1k§2 with the DVM on the ZOkQ range). Reduce VGS until Ron has increased by about a factor of two. Measure Ron and vGS again. As sz decreases, you should see R0n increase. Continue decreasing the power supply voltage to decrease vGS in increments that approximately double the measured value of Ron. Measure Ron and v05 at each step and make a table of measurements in your lab notebook. As sz gets closer to the threshold voltage VTH, Ron will start increasing rapidly. As Ron increases, take a few data points with Ron values of about 2kg, 5kg, and 10kg. You should end up with a total of about 5 to 10 data points. In your lab notebook, plot Ron as a function of VGS . Note that increasing gate drive vGS reduces the value of on-resistance. Also, plot 1/ Ron as a function of VGS. You should see an approximately linear relationship between 1/ Ron and VGS; a line through the measured data points should intersect the vGS axis at the threshold voltage. iDVM AFCS 3OZ| R6 §M1 g1/6 CD4007/ M04007 DVM Figure L2—2. L2—3. Repeat the above procedure for a P—channel MOSFET as shown in Figure 12-3 below. Double-check your connections with the AFG3021 and the DVM since you will now be measuring VSG while applying a negative voltage to the gate. The range of resistances Ron should be similar to the previous part; follow the same procedure for gathering data, In your lab notebook, plot Ron as a function of VSG . Also, plot 1 / Ron as a function of v50. Note that, since your horizontal axis is vSG rather than v65, some care is needed in interpreting the plots. For the P—channe] MOSFET making the gate drive voltage vGS more negative reduces the value of on-resistance. On the 1/ Ron plot, you should also see an approximately linear relationship between 1/ Ron and VSG; however in this case a line through the measured data points should intersect the vSG axis at the negative of the threshold voltage. So, for example, if the vSG-intercept is at 2V, then the threshold voltage is V m : ~2V. Figure L2—3. WRITEUP RELATIONSHIP BETWEEN ON RESISTANCE rum") AND GATE DRIVE VQS N-Channel MOSFET W2-l , Plot Ron as a function of sz. W W2—2. Plot 1/ Ron as a function of v05. Using this plot, extract the slope unCox—L— , and the x—intercept (threshold voltage VTH ) for the triode region "on" resistance expression: 1 Run = _T“_ (2-1) Kurt OXT(VGS _VTH) W . . W2—3. From the slope unCox—L—, determine the value of mobility [4". Use your value of Cox from Lab 1 and the W/L = 350/10 for the MC14007. W24. Using your parameters from W2—2, plot the prediction of the MOSFET Ron model on the same axes with your measured data from part L2—2. How well does the model predict the measured data? P-Channel MOSFET W2—5. Plot Ron as a function of v30. W W2-6. Plot 1/ Ron as a function of v50. Using this plot, extract the slope MPC , and the 0x — L x—intercept (which will be —VTH , the negative of the p—channel threshold voltage) for the triode region "on" resistance expression: Ron = +_ (2-1) Hp 0x $050 " (—VTH )) W2—7. From the slope M pCox Kg, determine the value of mobility up. Use your value of Cox from Lab 1 and the W/L = 900/10 for the MC14007. W2—8. Using your parameters from W2—6, plot the prediction of the MOSFET Ron model on the same axes with your measured data from part L2-3. How well does the model predict the measured data? NOTE: The above procedure can be considerably simplified by using the MATLAB file rdsplot .m, available from the course website. Look at the source code to see where to put in your measurements. Your plots will look something like Figure L2—4 below. ...
View Full Document

{[ snackBarMessage ]}