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Unformatted text preview: 1 EE4902 C2009 Lab 3 Qualitative MOSFET V-I Characteristic SPICE Parameter Extraction using MOSFET Current Mirror The purpose of this lab is for you to make both qualitative observations and quantitative measurements of MOSFET behavior in different operating regions. Upon completion of this lab you should be able to: Recognize the V DS-I D characteristic of an N-channel MOSFET Recognize the triode and saturation regions of operation in the V DS-I D characteristic Have an idea of how small the "small V DS " requirement is for resistive behavior of the drain- source channel Compare drain-source channel resistance calculated from the V DS-I D plot to resistance measurements made using the DVM in Lab 2 Recognize the compliance voltage, the smallest V DS for which the drain-source channel looks like a current source in the saturation region Recognize the finite output resistance in the saturation region that makes the drain-source channel look like a nonideal current source Distinguish between the "true" resistance R on of the drain-source channel in the resistive part of the triode region, and the small-signal drain output resistance r o in the saturation region Extract SPICE parameters VTO (threshold voltage) and UO (mobility) for both P-channel and N-channel MOSFETs in the saturation region of operation. Recognize the current mirror configuration, and the voltage range over which the current mirror behavior applies. Determine the channel length modulation parameter and relate to the substrate doping NSUB. Lab Exercise In lecture, we showed how the MOSFET channel behaves differently as the channel (drain-source voltage V DS increases: Small V DS linear V DS-I D relationship (model as resistance R on ) Medium V DS < V GS- V TH nonlinear triode relationship Large V DS > V GS- V TH approximately constant current determined (mostly) by V GS In the first part of this lab exercise, you will build a circuit that provides a plot of drain current I D vs drain-source voltage V DS on the oscilloscope. By sweeping V DS over a range of 0V to +5V, you will see the output characteristic in the triode and saturation regions. In the second part of the lab exercise, you will build up the same plot from measured data points to determine SPICE parameters for N-channel and P-channel MOSFETs. 2 Qualitative MOSFET V-I Characteristic 8 7 6 CD4007 VGS +- 1k ! RS =100 ! I S =I D VDS +- I D VDS t +5V SCOPE CH 1 (X) SCOPE CH 2 (Y) NOTE: VGS FLOATING WITH RESPECT TO GROUND! Fig. L3-1. L3-1. Build the circuit in Fig. L3-1. The MOSFET gate-source voltage will be maintained at a constant value while the drain voltage is swept from 0V to 5V. From Ohm's law at the MOSFET source, the oscilloscope CH2 voltage will be V S = 100 ....
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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
- Integrated Circuit