Cascode amplifier circuit

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Construct the full circuit (including the DC biasing circuitry,coupling capacitors) in MultiSim.Important things to note in constructing the circuit.

a. Add biasing DC sources/resistive networks to ensure the both transistors arebiased in the satuation mode.

b. Place an AC sinusoidal source of 1V pk-pk (Peak to Peak) with 1kHz frequency.This source will represent the input signal to the circuit that needs to be amplified.

c. Place capacitors at the input and the output of the circuit. The capacitor at theinput will couple the AC input source to the circuit while isolating the DC biassource to the circuit. The capacitor at the output is intended to filter the AC signalwhile blocking the DC from the output node.

d. Choose the values of the capacitances to guarantee that the capacitor will notinterfere with the desired function of the circuit: amplifying a signal at 1kHzfrequency.

1 Note that this circuit is the same circuit that was used in the previous assignment.1.07352 mA/V21.2 mA

e. Place Oscilloscopes (see Figure 3) in the circuit schematic to measure the inputand output voltage and compare them on a single display. Connect the B probesof the oscilloscope to the output signal and the channel A probe to the inputsource. The purpose of this step is to enable you to visualize the two signal on thesame display.

f. Adjust the parameters of the MOSFETs in the circuit to match exactly thespecifications indicated above on Figure 1.

Sample Solution

Component Selection and Placement

  1. MOSFETs: Place two n-channel MOSFETs (e.g., 2N7000) on the breadboard.
  2. DC Sources: Use two DC voltage sources to bias the MOSFETs. The gate voltage should be set to a value slightly higher than the threshold voltage of the MOSFETs to ensure they are in saturation.
  3. Resistors: Place resistors in the source and drain circuits to set the operating point of the MOSFETs.
  4. AC Source: Place an AC voltage source with a peak-to-peak amplitude of 1V and a frequency of 1kHz.
  5. Capacitors: Place capacitors at the input and output of the circuit. The values should be chosen to ensure that the capacitors have a negligible reactance at the desired frequency of 1kHz.

Circuit Diagram

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circuit diagram showing two MOSFETs, DC sources, resistors, an AC source, and capacitors

Biasing and Coupling

  • Biasing: Adjust the DC voltage sources and resistors to ensure that the MOSFETs are biased in the saturation region. This can be verified by measuring the gate-source voltage (Vgs) and drain-source voltage (Vds).
  • Coupling: The capacitors at the input and output will couple the AC signal to and from the circuit while blocking the DC bias. The values of the capacitors should be chosen to have a negligible reactance at 1kHz.

Oscilloscope Setup

  • Connect probes: Connect the channel A probe of the oscilloscope to the input source and the channel B probe to the output of the circuit.
  • Adjust settings: Adjust the oscilloscope settings to display both signals on the same screen. You may need to adjust the amplitude, timebase, and triggering settings to obtain a clear view of the input and output waveforms.

MOSFET Parameter Adjustment

  • Refer to the datasheet: Consult the datasheet for the 2N7000 MOSFETs to determine the exact specifications.
  • Adjust parameters: In MultiSim, you can adjust the parameters of the MOSFETs, such as the threshold voltage (Vth) and transconductance (gm), to match the datasheet values.

By following these steps and carefully adjusting the components and parameters, you should be able to construct a functional amplifier circuit in MultiSim. You can then use the oscilloscope to visualize the input and output signals and analyze the circuit’s performance.

 

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