The following step$-$by$-$step assignments are designed to enhance your understanding of BJT amplifiers. A new PSPICE schematic is required for parts $3\mathrm{.}3,3\mathrm{.}5,3\mathrm{.}6,3\mathrm{.}7,3\mathrm{.}8,3\mathrm{.}9,$ and $3\mathrm{.}10.$

$3\mathrm{.}1.$For the BJT circuit in Figure $3,$ calculate the DC values for $V_C,V_B,V_E,I_C,I_B,$ and $I_E.$ Check and confirm the active mode operation for Q$1$ in Figure $3.$

$3\mathrm{.}2.$ Next, compute the AC small signal parameters $g_m,r_{},r_e,$ and $r_o.$ Assume the transistor $=150,V_{BE}=0\mathrm{.}7V,V_A=74V$ and $V_T=25mV.$ Calculate $R_{in}.$ Calculate the gain $|)/(r_e$

$3\mathrm{.}3.$ Start your simulations by setting up the amplifier's circuit in Figure $3.$ Simulate the amplifier in Bias Point. Turn on annotation for the DC voltages and currents. A new PSPICE schematic is required.

$3\mathrm{.}4.$ Measure $V_{BE}$ and $$ and record these values from the PSPICE schematics.

$3\mathrm{.}5.$ How would you modify the circuit to have a collector current of exactly $1\mathrm{.}4$ mA $?[$Hint: The most convenient component to change, if we want to modify the DC current, is $[$:$R_E\}.$ A new PSPICE schematic is required.

$3\mathrm{.}6.$ What should you do if we want to change $I_C$ to $0\mathrm{.}55$ mA $?$ Demonstrate by simulating how this tweaking is done. A new PSPICE schematic is required.

$3\mathrm{.}7.$Simulate the amplifier in Transient. Watch the voltages V $($in$)$ and V $($out$)$ and compute the small$-$signal gain using ratio of peak$-$to$-$peak amplitudes. Compare the measured value to the theoretical value from part $3\mathrm{.}2$ above. How do you explain any noticeable gain difference? A new PSPICE schematic is required.

$3\mathrm{.}8.$Increase the load resistance Rload to $1$MEG, simulate in transient and observe the influence on the gain. A new PSPICE schematic is required.

$3\mathrm{.}9.$ Keeping Rload at $1$MEG, change the collector resistor R$5$ to $4$ k $,$ simulate in transient and comment on the influence on the gain. A new PSPICE schematic is required.

$3\mathrm{.}10.$ Go back to the initial Rc and Rload values from $3\mathrm{.}3$ above. Change the emitter resistor Re to $3$ k and simulate in transient and comment on its influence on the DC emitter current, and on the voltage gain. The formulas $r_e=\frac{V_T}{I_E}$ and $|)/(r_e$ may help you understand what's going on$.$ A new PSPICE schematic is required.

Hint: One more source of error has to do with the computation of $r_e.$ Typically, "room temperature" in electronics is $20C$ and that yields a thermal voltage of $V_T$~~$25mV.$ In PSPICE however the default temperature is $300K,$ and for that $V_T$~~$26mV.$