Operational amplifier circuits lab report

Lab

Operational Amplifiers

This lab involves a study of the properties of operational amplifiers connected in the inverting and non-inverting configurations, as well as the application of op-amps, such as integrating and differentiating amplifiers.

2.1 Inverting Amplifier

Calculate the closed loop voltage gain of the circuit, as shown in Fig. 2.1.
Simulate the circuit in LTSpice using Operational Amplifier OP27 with RF=10kΩ and RS=1kΩ.
Do a Transient Analysiswith sinusoidal input of 0.5Vpp and 1kHz; for setup see LTSpice Guide, Transient Analysis. Ensure to plot bothVSand Vout and calculate the Gain.
Do an AC Sweep and obtain the Frequency Response for the Transfer Function (Vout/Vin) in dBs, or, 20×log10 (abs(Vout/Vs)).
From the frequency response, locate the f3dB point, or the amplifier’s Bandwidth.
From the frequency response, determine ft. ft is the unity gain frequency at which the gain = 0dB.
Take a look at the the OP27 datasheet available online. (Just Google it.)

Fig. 2.1 Inverting Amplifier

Calculate – use your handheld calculator to get results

Simulate – use LTSpice Software to get results

2.2 Non-Inverting Amplifier

1. Calculate the closed loop voltage gain of the circuit, shown in Fig. 2.3.

2. Simulate the circuit in LTSpice using Operational Amplifier OP27with RF=10kΩ and RS=1kΩ.

a. Do a Transient Analysis with sinusoidal input of 0.5Vpp and 1kHz; for set up see LTSpice Guide, Transient Analysis. Ensure to plot bothVSand Vout and calculate the Gain

b. Do an AC Sweep and obtain the Frequency Response for the Transfer Function (Vout/Vin) in dB, or, 20×log10 (abs(Vout/Vs)

3. From the frequency response, locate the f3dB point, or the amplifier’s Bandwidth.

4. From the frequency response, determine ft. ft is the unity gain frequency at which the gain = 0dB.

Fig. 2.3 Non-inverting Amplifier

2.3 Integrating Amplifier

Calculate the Gain of the Amplifier circuit shown in Fig. 2.4.
Simulate the circuit in LTspice using a VSIN of 0.4 Vpp (0.2V amplitude) at 1 kHz with CF=.01uf and RS=10kΩ.
Do a Transient Analysis of Vout and Vs.
Determine the relationship between Vs and Vout.
Hint: Notice the name of the amplifier

Determine the Gain of the Amplifier, (RMS_Vout/RMS_Vs)
(Is the gain what you expected to be?)

Hint : To see rms or average value of a waveform in LTSpice, hold CTRL and click on the voltage or current label on top of the waveform pane.

NOTE :LTSpice calculates rms value including the full DC offset in the waveform if any. The result therefore may at times not be consistent with what you expect. ADK oscilloscope on the other hand excludes offsets (if any) while measuring rms values.

Fig. 2.4 Integrating Amplifier

2.4 Differentiating Amplifier

Calculate the Gain of the Amplifier circuit shown in Fig. 2.5.
Simulate the circuit in LTSpiceusinga VSIN of 0.4 Vpp (0.2V amplitude) at 1 kHz with CS=.01uf and RF=10kΩ.(NOTE: Use a series resistance of 100Ω placed between the input voltage source and the capacitor. This essentially emulates a real life voltage source which has some series output impedance.)
Do a Transient Analysis of Vout and Vs.
NOTE: Also, try doing the transient simulation without having the 100Ω series resistance in the circuit. What do you observe?

Determine the relationship between Vs and Vout.
Hint: Notice the name of the amplifier.

Determine the Gain of the Amplifier, (RMS_Vout/RMS_Vs).

Fig. 2.5 Differentiating Amplifier

Post-lab questions: (Use your calculator and LTSpice to answer these questions)

Determine the new values of Rf, without changing Rs in the circuits, to achieve a theoretical Gain of 7.5 for the following two cases:
Inverting amplifier
Non-inverting amplifier
Use LTSpice to implement and discuss the outcomes of the followings:
Applying a sinusoidal input signal of 2Vpp and 4kHz in the inverting op-amp shown in Fig. 2.1, as a substitute of 0.4Vpp and 1kHz.
Modifying the capacitor CF to be .001uf for the integrating op-amp circuit with sine wave, VS, instead of .01uf.
Discuss the purpose of connecting the op-amp as shown in the circuit of Fig. 2.6? Explain the function of the circuit.

Fig. 2.6

Hint: Simulate the circuit using LTSpice and notice the relationship between the input and output waveform.