Sheffield Hallam University Dep of Eng&Maths AnlElecEng 55-400226 Analogue Electronic Engineering 55-400226 Practical introduction to operational amplifiers (Op-Amps) (wks 34&35) Student's name: Lecturer: Date of starting labwork: Date of completing labwork: Aim to finish parts 1-4 in the first lab session. Prepare for & then work through this lab work. Record your results on this sheet and demonstrate your work during your lab sessions. Connect +VS = ±15V dc power supply rails, with +15V to pin 7, and -15V to pin 4. Connect 0.1µF (100nF) bypass capacitors between supply pins 7 & 4 and OV ground. Place each capacitor as close as possible to the chip, as recommended in uA741 data sheets. Check through device specifications, advice, circuit hints and other information from manufacturers, including www.ti.com, search for uA741. Texas Instruments Incorporated's datasheet (available via Blackboard), section 10, pages 14 & 15, shows how 100nF capacitors can be used to bypass noise from rough DC power supplies. Reminders: for ac signals, maximum, peak value = amplitude, Vp (or Vm or Ŷ ) root mean square, rms value = Vp÷√2 1 I vertical, Vp-p top to bottom, use AY = Y2-Y₁ on scope, peak to trough, +peak to -peak. When a signal has OV offset, Vp-p = 2 × Vp- horizontal time, peak to next peak, AX on scope = time period, T ; frequency, f = 1/T AnlElecEng-S2-OpAmp 1 of 7 Sheffield Hallam University Dep of Eng&Maths AnlElecEng 55-400226 1 Op-amp level detector, simple non-inverting switching comparator. To predict typical results using PSpice circuit simulations use library: eval.olb or opamp.olb. Search for uA741 part and add it into the schematic. Connect the circuit as shown in each figure. Please look at the PSPICE lab sheets to review how to create this circuit in ORCAD. Use VCC_BAR for positive and negative power supply rails. For these timetabled lab sessions you will be building and testing practical circuits. Beware: op-amp +Vs DC power supply rails are always required, but are frequently left out of circuit diagrams, as it is assumed that anyone using an op-amp already knows that they do need to first connect the power supply rails. You are also advised to add 100nF capacitors from DC + supply pin 7 to 0V and from DC – supply pin 4 to 0V. These are not shown on the circuit diagrams. 1 8 top view 23 2 7 of uA741 3 6 op-amp 4 5 +15V, red lead +Vs 2 7 10kQ, R1 6 3 reference input, V₁1 10kQ, R2 + output, Vo V2, variable input -15V,blue lead, -Vs OV Figure 1: simple comparator Note: voltage arrow head → red/positive/higher potential connection, other end of voltage arrow to black, OV, common ground or reference connection. Monitor output, Vo, on scope and on DMM Leave pins 1 and 5 open. (a) Use a variable dc power supply for dc inputs V₁ and V2. Set V₁ =1V, observe the behaviour of Vo whilst V2 is varied from OV to 15V. = Note the upper and lower Vo values: Voн = and VOL = (b) Repeat for V₁ = 10V. VOH = and VOL = Summarize the relationship between inputs V₁ and V2 and output, V。: AnlElecEng-S2-OpAmp 2 of 7 Dep of Eng&Maths Sheffield Hallam University 2 Non-inverting amplifier Connect the circuit as shown in figure 2. OV 100kQ, RF 10kQ, R 9.1KQ, RB + Vin AnlElecEng 55-400226 Figure 2: non-inverting amplifier (a) Set Vin to 600mV peak to peak, p-p, (amplitude 0.3V, rms value 0.21V) at f = 1kHz Observe both input, Vin, and output, vo, ac signal waveforms. Display both signals and show two complete waves (2×T) across the screen. Two different voltage scales can be used if desired. volts, V↑ 0 time, ms→ Record output peak to peak value Vo p-p = (use scope cursor) and rms value V。 = V 0 Calculate the amplifier's gain: numerical gain Av = = Vin Compare your practical results with the theoretical gain. either use rms values for both input and output or use p-p values (for A, calculation) AnlElecEng-S2-OpAmp 3 of 7 Sheffield Hallam University 3 Inverting amplifier Dep of Eng&Maths AnlElecEng 55-400226 Connect the circuit as shown in figure 3 (simply swap the Vin and OV input connections compared to figure 2). 100kQ, RF 10kQ, Rin Vin 9.1KQ, RB + ον Figure 3: inverting amplifier Repeat the measurements, sketches and calculations of section 2 as below: (a) Set Vin to 600mV peak to peak, (amplitude 0.3V, rms value 0.21V) at f = 1kHz. Record vo peak to peak value Vo p-p = (from scope) and rms value v。 = V Calculate the amplifier's gain: numerical gain Av 0 = = in Compare your practical results with the theoretical gain. volts, V↑ 0 AnlElecEng-S2-OpAmp time, ms→ 4 of 7 Sheffield Hallam University 4 Clipping (a form of distortion) Dep of Eng&Maths AnlElecEng 55-400226 Use the inverting amplifier of figure 3 to investigate the effect of increasing the amplitude of Vin .Keep the frequency steady at 1kHz. Sketch both Vin and v。 on the same axes for Vin = 4V p-p volts, V↑ 0 time, ms→ AnlElecEng-S2-OpAmp 5 of 7