Download - Catalyst

Lab 4 – EE332
Procedure 2 CE-CB cascode with EF buffer
Modify the circuit of Fig. E4.1 to that of Fig. E4.2 by inserting another
BJT, shown as Q4, to produce the cascode. R6 will also need to be
added to adjust the biasing.
Measurement-2
Adjust the circuit and signal generator to produce clean 1.0 kHz
sinewaves on the input and output. Measure and record the amplitude
of both input and output, and then take the ratio to determine the
voltage gain.
Increase the frequency of the signal generator until the voltage gain
falls to 70 percent of its value at 1.0 kHz. Measure and record this -3
dB bandwidth of the amplifier.
Restore the frequency to 1.0 kHz, and increase the amplitude of the
signal generator until the output signal is clipped at both the positive
and negative peaks. Measure and record the output voltage levels at
which clipping occurs.
The gain of the circuit was found to be 2.83/1 = 2.83.
The 70% drop off point of the circuit due to increased frequency was 11.961MHz.
Clipping of the circuit occurred @ 3.55vpp input with an output clipping level of 7.63vpp.
Regular gain of circuit
70% cutoff (-3dB) due to increased frequency
Clipping voltage of circuit
Question-2
a) Using your measured data, calculate the voltage gain of the amplifier in decibells (dB).
b) Explain what determines the bias current level of Q4.
c) Explain what advantage the addition of Q4 provides over the amplifier of procedure 1.
Repsponses-2
a) The conversion to decibels would be 20Log(Vout/Vin) = 20Log(2.83/1) = 9.036dB
b) Vth is applied to the base and Rth is the effective resistance at this point. Vth/Rth will
determine how much current available to the base. In this case, Rth = R2||R6. Vth is
determined by Vcc*(R6/(R6+R2)) = Vth.
c) It will increase the bandwidth ,voltage, and current gain.
Conclusion:
The circuits built in this lab demonstrate how different configurations of transistors can be
connected to construct an effective amplifier. By adding more transistors to an existing topology,
we can improve the amplifier’s performance once we identify the part of the circuit that could
use the improvement.