Engineering tools and Principles 2 - ENGE1002 (Electronics) Lab 2 - Operational Amplifiers Time allocated: 2 hours Objective: 1. To understand the operation of inverting and non-inverting operational amplifiers. 2.

To understand the concept of voltage gain in an OpAmp. Equipment: DC power supply 0-20V 0-5A Opamp IC 741 Oscilloscope, probes Resistors – 100ΚΩ, 10ΚΩ, 25ΚΩ, 2.2ΚΩ Insulated wire leads, connector clips, bread board Background: The main function of an opamp is to amplify small AC voltage signals. OpAmp ICs are designed either using Bipolar Junction Transistors BJTs or Junction Field Effect Transistors JFETs. In this experiment we shall use the 741 OpAmp IC. This IC has 8 pins (Figure 1) with pins 2(-) and 3(+) as the inverting and non-inverting inputs respectively and pin 6 where the output signal is drawn. The supply voltage for this IC is a dual-rail supply with a maximum of +18V at pins 7(+) and 4(-). Offset null 1 Inverting input 2 Non-inverting input 3 ENGE1002 Electronics - Lab 2 -V 4 + UA741 co 8 7 5 6 Output Figure 1: Pin out diagram of 741 opamp NC Dr. Vijay Pakka/ Dr. Prakash Pandey +V Offset null Page 1 of 4 Inverting OpAmp The two basic forms of OpAmps are the inverting and non-inverting amplifiers. When used as an inverting amplifier as shown in Figure 2, the input signal is given to Pin 2(-), while Pin 3(+) is grounded. The output in this configuration is the amplified but inverted signal of the input. The signal is amplified in proportion to the Gain of the configuration in Figure 2. -Rf. The gain for the inverting OpAmp is given as; R = Therefore Peak-Peak value of output voltage for inverting amplifier will be Vo Vin Rin 10ΚΩ Ov Rf= 100k A Figure 2: An inverting OpAmp Vout - (R£) v. Procedure for inverting amplifier: 1. Connect the IC in the configuration given in Figure 2. 2. Please make sure the dual rail supply is properly connected to get two DC voltage sources of +15V and -15V respectively to pins 7 and 4. 3. The input signal given to Pin 2(-) via the input resistor of 10kOhms is a sinusoidal waveform of 1kHz and 1V Peak-Peak. Measure the amplitude on the Oscilloscope to verify the peak- peak value. 4. Observe the input signal and the output (taken at pin 6) on the oscilloscope and measure the Output Peak-Peak voltage value. ENGE1002 Electronics - Lab 2 Dr. Vijay Pakka/ Dr. Prakash Pandey 5. Calculate the theoretical value of the Gain and compare this with the ratio of the output v/s input voltage peak-peak values. Also observe the change in the phase of the output signal. Take screenshots and append to your logbook. Page 2 of 4 ROHDE & SCHWARZ HM01002 Series 1 GSa/s/1 MB Oscilloscope TB: 200μs T:Os Vp+: 508.00mv U Vp--516.00mV CH1: 200mME RMS: 357.04 mV AUX OUT TB: 200 μs T: Os ENGE1002 Electronics - Lab 2 CHI: -4mV/DC tr: 309.76 us MENY Vpp: 1.02 V T: 998.20μs f: 1.00 kHz ROHDE & SCHWARZ LOGIC CHANNEL POD VAmp: 1.01 V tл: 498.80μs Dty+: 50.00% wwwww USE RECOMMENDED PROBE ONLY CHI 2.5MSB 4 mv SDC Mean: -4.53mV HMO1002 Series 1 GSa//1 MB Oscilloscope th 290.96μs- Refresh Cnt J: 3 tu: 498.80μs Dty-: 49.92% PATTERN GENERATOR PROBE COMP SO S1 S2 S3 ILA 480 to 236.0ops - - 2 20cm a Corton BWL-NY UI-8 OZO Mean: 47187mv PASS Refresh V 492 40μs ON/OFF Dr. Vijay Pakka/ Dr. Prakash Pandey IVEN OFF COARSE FINE CURSOR/MENU SCROLL BAR POSITION UTIL VERTICAL MENU VOLTS/DIV EXT TRIG IN 1MQ 16pF max. 100 Vpk SELECT KEYPAD TEST DATE teen CH1 CH2 POD MATH REF BUS INTENS PERSIST CURSOR MEASURE AUTO NORM TRIG M TYPE SOURCE CHI ANALYZE TRIGGER LEVEL 6. Change the values of resistors so that the Gain > 30 and observe the change in the output signal and comment on the results. Take screenshots and append to your logbook. AUTO MEASURE SINGLE SLOPE SLOPE FILTER FFT QUICK VIEW ZOOM 200 Vp ▶ RUN STOP D SET CLR 1 CH2 Page 3 of 4 Non-Inverting OpAmp For the non-inverting amplifier given in Figure 3, the input is given to Pin 3 (+) while the resistor at Pin 2 is grounded. The negative feedback is however still given to Pin 2 (-). The gain for the non-inverting OpAmp is given as 1 + Rf R₂ (30%) Therefore Peak-Peak value of output voltage for a non-inverting amplifier will be given by Vo = (1+1) V Notice that the output voltage in the non-inverting amplifier has the same sign (is in phase) as that of the input voltage. ENGE1002 Electronics - Lab 2 Dr. Vijay Pakka/ Dr. Prakash Pandey Page 4 of 4 Vin Iin V₁ MHI R₂ A m RE Iout Figure 3: A non-inverting OpAmp Ov Vout Procedure for non-inverting amplifier: 1. Connect the IC in the configuration given in Figure 3. 2. Please make sure the dual rail supply is properly connected to get two DC voltage sources of +15V and -15V respectively to pins 7 and 4. 3. The input signal given to Pin 3(+) is a sinusoidal waveform of 1kHz and 1V Peak-Peak. Measure the amplitude on the Oscilloscope to verify the peak-peak value. 4. Observe the input signal and the output (taken at pin 6) on the oscilloscope and measure the Output Peak-Peak voltage value. 5. ENGE1002 Electronics - Lab 2 Dr. Vijay Pakka/ Dr. Prakash Pandey Calculate the theoretical value of the Gain and compare this with the ratio of the output v/s input voltage peak-peak values. Take screenshots and append to your logbook. Page 5 of 4