(Solved): B.JT Transistors Problem 1: BJT DC Circuits. Let the NI'N B.J Q_(N) have the following properties: { ...
B.JT Transistors Problem 1: BJT DC Circuits. Let the NI'N B.J
Q_(N)have the following properties:
{(V_(DEN)=0.7(V)):}when BE junction is
ON,\beta =100 and
V_(CENsat )=0.1V_(j). Let
R_(BIN)=R_(B2N)and each has resistance value in the range of tens of
K\Omega . Let
R_(C)and
R_(FN)have resistance values in the range of a few
K\Omega . 1.a Choose all the resistors so that
I_(CA)=1mAand
V_(CEN)=3V. For your convenience, assume that
R_(BIN)and
R_(R2N)create an "almost-voltage-divider". Then you can easily determine
V_(R)and
V_(F)and choose
R_(IN)to set the desired
I_(CN)spee and then set
R_(CN)to meet the VCen spec. Of course, don't forget to justify the Active Mode assumption and the "almost-voltage-divider" assumption. 1.b Now, change one of the
R_(BN)resistors (to another finite and nonzero value) to drive the BJT into Saturation Mode. Once you violate the Active Mode assumption, while still keeping the BI: junction forward biased, solve the circuit that now operates in Saturation Mode. 1.c In your design of 1.a offer a change of one of the
R_(BV)resistors (to another finite and nonzero value) in order to drive the BJT into Cutoff Mode. Solve the circuit in the Cutoff Mode. Problem 2: B.JT small-signal amplifier. Let the PNP BJT QP properties be
{(V_(EBP)=0.7(V)):}if the EB junction is
ON,\beta =100and Early vollage
{:V_(A)=100(V)}. The internal resistance of the input signal source
v_(sig )(l)is
R_(sig )=200\Omega . The load resistance is
R_(L)=10K\Omega . You cannot change the source resistance nor the load. Let
R_(B1P)=R_(B2P)=
40K\Omega . Let
R_(EP)=3.9K\Omega and let
R_(CP)=3K\Omega . 2.a Find the DC voltages and currents of the amplifier, the BJT's small-signal parameters, and draw the small-signal diagram of the amplifier. Is the Active Mode assumption true? 2.b Find the amplifier's small-signal input resistance
R_(In )and the small-signal voltage gain. 2.d Modify one of the resistors in order to increase the voltage gain by 20%. Hint: It would be the simplest to tweak the only resistor that has nothing to do with setting the IC current
I_(CP).
