HW9 Due Tuesday April 25, 2017

In a p+np bipolar transistor circuit, grounded base circuit, α=0.99. The input circuit has a battery voltage of 1 V. Assume the input diode turns on at 0.6V(i.e. no IE until 0.6V, after that the diode current increases vertically without resistance) .The series resistance in the input circuit is 100 ohm. The output circuit has a battery voltage of 40 V, and a load resistance in the output is 1k ohm.

Draw the dc Q conditions for both input and output. What is the DC Q point current and             voltage  in the output collector-base circuit? Draw a load line curve for the input and         output. Show the intersection points for both.

In the above transistor, if Wb=1 micrometer, and the doping in the base is 2E17/cm3, and base and collector are equally doped, at what battery voltage in the CB circuit will the device break down? The Avalanche field  is 5E5 V/cm.
In the transistor of #2, if I reduce the base and collector doping to 1E16/cm3, at what battery voltage in the CB circuit will the transistor break down?
In problem 1, now I overdrive the transistor by reducing series resistance in the input circuit. [That drives more current in the input and therefore in the output circuit]. Assume that saturation occurs when Vcb flips sign and become +0 .4V.  What must the new series resistance in the input circuit be to achieve this? Assume that until then, α=0.99.
MOSFET amplifier. n channel. VT=1V. VGS=3 V. Z/L=40. Mobility=500 cm2/V-s. Cox=3.45E-7 F/cm2. Battery voltage in the output circuit= 40 V. RG (in the gate circuit)=100 ohm. RL in the output circuit =2k. A small ac voltage is in the input circuit.
Draw the dc and ac equivalent circuits
Draw the I-V curve on the output. Show the value of the saturation knee- point. Show the load line and intersection(Q) point. Calculate the Q point values for current(IDS) and voltage(VDS)

Calculate trans-conductance gm.

Calculate the amplification factor.


Now I use the MOSFET of #5 as a logic gate – inverter. Assume that the I-V curve only has two regions-linear from 0V to knee point for saturation, and then saturation I value (two straight lines). Using this approximation, draw IDS VDS curves (to scale) for values of VGS increasing by 1 V from 0V. A family of curves will result- 5 in all. Label each one with the VGS value. What is the value of the output voltage when the MOSFET is used as an inverter with VGS= 4V? What is the current?


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