The Operational Amplifier Lab Report

1 Table of Contents

  • Objectives

  • Preparation

  • Experiments
      - Open-Loop Response
      - Inverting Amplifier Circuit
      - Differential, Variable-Gain Amplifier with Maximum CMRR

  • Lab Wrap Up

  • Lab Report

2 Objectives

  • In this lab, you will:
      - Characterize an operational amplifier (opamp) in an open-loop configuration.
      - Design, build, and characterize a differential amplifier circuit.

  • You will jump directly into implementing and testing circuits.
      - Requires understanding from Prelab 3, which includes an instrumentation amplifier.

  • Submission Requirement: A couple of pictures of the final circuit for neatness points (subjective).

3 Preparation

  • Ensure understanding of the analysis of the circuits to be built, as studied in Prelab 3.

  • Review lecture notes on operational amplifiers and differential amplifiers in preparation for the lab.

4 Experiments

4.1 Open-Loop Response

  • Purpose: Measure the open-loop response of the opamp to estimate the open-loop gain.

4.1.1 Build Your Circuit

  • Components Required:
      - Breadboard
      - 3 x UA741 opamps
        - Note: Datasheet for the UA741 is available on Canvas in the Lab 3 module.
      - 8-10 short jumper wires
      - Chip-removing tweezers (be careful to avoid bending pins)

  • Construct the open-loop circuit:
      - Familiarize yourself with the pinout of the UA741 as shown in Figure 1. Pin numbering begins from the upper-left with the notch upwards.
      - Insert the UA741 into the breadboard, straddling the central channel, allowing accessibility to all 8 pins.
      - Connect the SMUs as depicted in Figure 2.
      - Power the opamp using the dual DC power supply:
        - Without connecting to the breadboard, power-on the supply, set +/-20V to display +6V and -6V readings using the tracking ratio knob set to fixed.
      - Confirm the output voltages with a Digital Multimeter (DMM).
      - Connect the DC power supply to the breadboard.

4.1.2 Test Your Circuit

  • Program the Source Measurement Units (SMUs):
      - Utilize the Keithley program for controlling SMUs (LabTracer).
        - One sweep of the SMU will measure:
          1. Estimate the gain of the UA741.
          2. Input impedance of the UA741.
          3. Input offset voltage of the UA741.
          4. Input bias current for the UA741.

  • Energize and Validate the Circuit:
      - Turn on the DC power supply, ensuring the current is minimal (under a few mA).
      - Conduct the following:
        a. Program SMU1 to sweep voltage from -10mV to +10mV in 501 steps with a compliance of 1mA.
        b. Select voltage meter for SMU2 and set compliance to 10V.
        c. Execute LabTracer and analyze data to plot Vout versus Vin, observing trends and confirm if results make sense.
        d. Zoom in the region around Vin=0V (sweep from -5mV to +5mV) considering filtering measurements to reduce noise.
        e. Measure transfer function and approximate slope of the graph to deduce gain, saving data for report.
        f. Turn off the DC supply and disconnect outputs of the SMUs.

4.2 Inverting Amplifier Circuit
4.2.1 Build Your Circuit

  • Construct an inverting amplifier using UA741 with:
      - Input resistance R1 = 1kΩ.
      - Gain = -20.

  • Obtain resistors R1 and Rf and confirm with a DMM (Digital Multimeter).

  • Assemble the circuit on the breadboard (reference Figure 4) and set up a signal generator to produce a sine wave, 1kHz with a peak-to-peak amplitude of 0.1Vpp.

  • Ensure proper grounding connections between the generator and circuit.

4.2.2 Test Your Circuit

  • Attach oscilloscope probes (CH1 to Vin and CH2 to Vout):
      - Confirm the DC power supply remains at 6V.
      - Observe waveforms on the oscilloscope and adjust settings for clarity.
        - CH1 Scale about 20.0mV/div and CH2 Scale about 200mV/div.
        - Set horizontal scale to view multiple oscillations (400μs/div suggested).
      - Trigger source should be CH1 for stability in display. Set averaging to 16 to smooth trace visibility.

  • Use oscilloscope features to measure values for CH1 and CH2. Save observations and calculations for report.

4.3 Differential, Variable-Gain Amplifier with Maximum CMRR

  • Goal: Build an amplifier that boosts certain differential signals while suppressing common-mode signals.

4.3.1 Design the Amplifier

  • Requirements:
      - High input impedance: Zin >> 100kΩ.
      - High gain to achieve Vout > 1Vpp from |Vin| of a few mV (Goals: At least differential gain of 200).
      - Low common-mode gain, ideally <20% of the differential output.

  • Utilize two-stage amplifier configuration:
      - Analyze compensatory circuit properties and document design features, noting resistor values needed to achieve desired gain.

4.3.2 Build Your Amplifier Circuits

  • Construct two stage amplifiers as per specifications ensuring not to initially connect output stages together, testing each individually first.

4.3.3 Test Your Circuits

4.3.3.1 Input Stage by Itself

  • Common Mode Gains:
      - Set frequency to 1 kHz, 1Vpp. Short-circuit inputs.
      - Connect signal generator and observe output on oscilloscope checking for trace quality.

  • Differential Mode Gains:
      - Set 1kHz frequency, 500mVpp, connect respective grounds and inputs, observing outputs and downloading traces for reporting.

4.3.3.2 Full Circuit Testing

  • Combining circuit stages:

  • Repeat the above procedures for Common Mode Gain and Differential Boost measuring and validating results.

5 Lab Wrap Up

  • Turn off instruments, dismantle and organize workspace ensuring equipment is neat.

  • Save all data and graphical content to compile into the lab report. Engage TA for verification of workspace cleanliness and collected work.

6 Lab Report

  • Work Distribution: Document each member’s contribution.

6.1 Open Loop Op Amp Response

  • Plot characteristics and estimate open-loop gain, comparing with datasheet values and evaluating measurement methodology reliability.

6.2 Inverting Amplifier Transfer Characteristics

  • Document resistor values, and calculate gain comparison from oscilloscope data.

6.3 Input Stage by Itself

  • Sketch schematic, compare common and differential mode gains against theoretical expectations.

6.4 Full Circuit Results

  • Provide oscilloscope data for both modes of the full circuit and analyze accordingly.

  • Include photographs of the breadboard setup for record-keeping.