Question

Your team’s task for this project is to simulate an NMOS transistor, compute the DC operating point and then design a bias network to properly operate the transistor in saturation. The transistor you will use is described by the spice model below:

ltSPICE:

.model NMOS0P5               NMOS(Level=1 VTO=0.7 GAMMA=0.5 PHI=0.8

+                              LD=0.08E-06 WD=0 UO=460 LAMBDA=0.001 TOX=9.5E-9 PB=0.9 CJ=0.57E-3

+                              CJSW=120E-12 MJ=0.5 MJSW=0.4 CGDO=0.4E-9 JS=10E-9 CGBO=0.38E-9

+                              CGSO=0.4E-9)

MultiSim:

.SUBCKT NMOS0P5 1 2 3 4

M 1 2 3 4 NMOS0P5 W=5u L=0.5u

.model NMOS0P5               NMOS(Level=1 VTO=0.7 GAMMA=0.5 PHI=0.8

+                              LD=0.08E-06 WD=0 UO=460 LAMBDA=0.001 TOX=9.5E-9 PB=0.9 CJ=0.57E-3

+                              CJSW=120E-12 MJ=0.5 MJSW=0.4 CGDO=0.4E-9 JS=10E-9 CGBO=0.38E-9

+                              CGSO=0.4E-9)

.ENDS NMOS0P5

In ltSPICE use the NMOS4 schematic component and a SPICE directive to properly load your model. In multisim use the component wizard and the MOS_N_4T schematic component. (see Figure 1 for proper multisim component creation). If you are using multisim.com online simulator, simply use a ‘NMOS’ device and input the Vt, Kn’ (shown as Kp) and W/L in the right side menu.

Figure 1. Custom component model

NOTE: for NMOS4 and MOS_N_4T you must connect the base to your source terminal as seen in Figure 3.

Figure 2. NMOS4 component

For the first part, you are to use the saturation equation for an NMOS with a Vt = 0.7V, K_n’ of 2.469 x10^-4 and a W/L of 10 (use 0.5u for L 5u for W in your simulation) to get a I_D of 4 mA. Once you find you V_OV value solve for your V_GS. Once your have your V_GS simulate the I/V curve you are familiar with using DC sweep on V_DS (start at 0V finish at 5V with 0.5V steps) and a fixed V_gs that you found using your equation. If you are using multisim.com you can simply show a transient line graph of 4mA Id.

For the second part, you are to find resistor values in the configuration shown in figure 3 to achieve the V_GS you solved for analytically in part 1 (use resistors in the 100k-1000 kOhm range for R_G1-2) as well as a V_D of 3V so that the transistor is operating in saturation. (use the DC operating point simulation to find these values, use V_DD = 5V).

Lastly, if we are to operate this transistor in deep triode, what is the resistor value r_ds?

Figure 3. Classical bias NMOS configuration

In summary:

Find V_GS analytically

Graph the I/V curve at this V_GS using DC Sweep

Find R_G1 R_G2 and R_D for a V_D of 3V

Show the DC Operating Point in saturation

Find r_ds analytically

Answer 1

TSPICE simulation)

b)I/V curve

c)Operating ponit

  

--- Operating Point ---

V(n003): 2.05295 voltage

V(n002): 2.5 voltage

V(n001): 5 voltage

Id(M1): 0.0058941 device_current

Ig(M1): 0 device_current

Ib(M1): -2.06295e-012 device_current

Is(M1): -0.0058941 device_current

I(R3): 2.27273e-005 device_current

I(R2): 2.27273e-005 device_current

I(R1): 0.0058941 device_current

I(V1): -0.00591683 device_current