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OPERATIONAL AMPLIFIERS EXPERIMENT 11: LINEAR OP-AMP CIRCUITS (revised 11/24/10) In this experiment we will examine the properties of operational amplifier circuits with various feedback networks. Circuits which perform four basic linear mathematical operations - addition, subtraction, integration, and differentiation - will be studied. We will use a model µA741, operational amplifier. This is a general purpose, integrated-circuit op-amp with detailed specifications listed in the appendix to this experiment. The op-amp requires a ±15 V power source. We will use a small power supply that provides these voltages plus a zero to ±5 V variable DC output. The op-amp will supply a maximum output current of about 25 mA and has typical offset currents of about 20 nA. This implies that resistors in the range 1 kΩ to 100 kΩ should be used. All of this information and more, including circuit suggestions, is shown on the component data sheet included at the end of the lab. Note that as with most integrated circuits, the first two characters “µA” identify the manufacturer, and “741” is the relevant portion of the part number. The LM741, OP741, or AD741 would be closely equivalent parts made by other companies. In most cases these can be freely substituted, but you should check the manufacturers’ data sheets to be sure for parameters critical to your application. Use a scope for all measurements. 1. (a) (b) Construct the operational feedback amplifier shown below with R1 = 1 kΩ and R2 = 20 kΩ with vin grounded, adjust the pot on the circuit board for zero output voltage. Using sine waves from the function generator for vin (with the amplitude set for 0.5 Volts peak-topeak), measure and tabulate the amplitude and phase of vout for 100 Hz ! f ! 1 MHz (take about 3 points/decade: 10,20,50,100,200,500, etc). Note that the VCC (+15V) and VEE (–15V) power supplies must be connected to the proper pins and their returns to circuit ground even though this is not conventionally shown on the schematic diagram. For a feedback amplifier the gain is given by: R2 A0 (" ) V A(" ) = out = VIN R1A0 (" ) + R1 + R2 where A0(ω) is the open loop gain and A(ω) is the closed loop gain. Use this formula and your measured values ! of A(ω) to find A0(ω) at 20 kHz and 200 kHz. Assuming that A0(ω) varies with frequency according to: A0 A0 (" ) = # "& %1+ j ( "C ' $ where ωC = 10π radians/s, find the DC open-loop gain, A0. Compare your result to the typical value given in the “Large Signal Differential Voltage Amplification” plot in the data ! sheet. Note that for frequencies >> ωC, all that matters is the product A0ωC. This is called the “gain-bandwidth product” of the op-amp, and will be equal to the closed loop gain × 3db closed loop corner frequency of your circuit. 1 OPERATIONAL AMPLIFIERS 2. 3. Change R2 to 10 kΩ and set f = 1 kHz. Increase the amplitude of vin until vout exhibits saturation at both positive and negative voltages. Sketch and determine the saturation voltages. (a) The slew rate of the amplifier is defined as the maximum rate of change of the output voltage. Switch the input to square waves and set f = 10 kHz. Adjust the amplitude to obtain a peakto-peak output voltage of 10 Volts. Measure the slew rate by observing dvout/dt and compare your result to the typical value listed in the appendix. (b) Suppose you want to use the amplifier to produce a sine wave output with an amplitude of 10 Volts peak-to-peak. What is the maximum frequency you can use before the output wave begins to be distorted by the finite slew rate of the amplifier? Switch the input to sine waves and observe what happens when you exceed that frequency. Sketch the input and output waveforms. 4. Set up the summing amp circuit shown below with Ri = Rf = 10 kΩ. Use the Lambda DC power supply for V1, and the ±5 V supply for V2. Measure Vout for three or four different values of V1 and V2 (using both positive and negative values of V2) and verify that Vout = (− Rf /Ri)(V1 + V2). 5. Set up the circuit shown below for amplifying the difference of two voltages. As in the previous step, use Ri = Rf = 10 kΩ. Measure Vout for three or four different values of V1 and V2, and verify that Vout = (Rf/Ri) (V2 − V1). If we define VOUT = AD (V2–V1) + AC ((V2+V1)/2), what should the common mode gain AC of this circuit be? Can you measure it? adder or summing amp differential or “instrumentation” amplifier 2 OPERATIONAL AMPLIFIERS 6. 7. (a) Set up the differentiator circuit shown below with C = 100 nF and R = 2 kΩ. For the input use a 2 Volt peak-to-peak, f = 1 kHz triangle wave. Sketch the input and output waves and measure the magnitude of vout. Compare your measured value with the expected result, vout = − RC x dvin/dt. Also, measure and tabulate the values of vout (no sketches required) for f = 2 kHz with C = 100 nF, and for f =2 kHz with C= 50 nF. (b) Switch the input waveform to square wave and sketch vin and vout. Explain why vout looks the way it does. (Consider the square wave as a Fourier series sum of sine waves.) (a) Set up the integrator circuit shown below, with C = 100 nF, RF = 200 kΩ, and R = 10 kΩ. Use a 2 Volt peak-to-peak, f = 1 kHz square wave for vin. Sketch the input and output wave forms and determine the magnitude of vout. Compare your measurement with the expected result v out = !(1/ RC) " # vin dt . (b) Observe what happens to the output voltage as you make RF larger and smaller. What happens when RF is removed (=∞)? Explain why we need to have a feedback resistor in any integrating circuit. (c) Switch the input waveform to triangle wave and sketch the resulting input and output waveforms. In this case vout looks quite similar to a sine wave. See if you can understand this result by writing down the integral of a triangle wave. differentiator integrator 3 LM741 Operational Amplifier General Description The LM741 series are general purpose operational amplifiers which feature improved performance over industry standards like the LM709. They are direct, plug-in replacements for the 709C, LM201, MC1439 and 748 in most applications. The amplifiers offer many features which make their application nearly foolproof: overload protection on the input and output, no latch-up when the common mode range is exceeded, as well as freedom from oscillations. The LM741C/LM741E are identical to the LM741/LM741A except that the LM741C/LM741E have their performance guaranteed over a 0˚C to +70˚C temperature range, instead of −55˚C to +125˚C. Schematic Diagram DS009341-1 Offset Nulling Circuit DS009341-7 © 1999 National Semiconductor Corporation DS009341 www.national.com LM741 Operational Amplifier May 1998 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. (Note 6) LM741A LM741E LM741 LM741C ± 22V ± 22V ± 22V ± 18V Supply Voltage Power Dissipation (Note 2) 500 mW 500 mW 500 mW 500 mW ± 30V ± 30V ± 30V ± 30V Differential Input Voltage ± 15V ± 15V ± 15V ± 15V Input Voltage (Note 3) Output Short Circuit Duration Continuous Continuous Continuous Continuous Operating Temperature Range −55˚C to +125˚C 0˚C to +70˚C −55˚C to +125˚C 0˚C to +70˚C Storage Temperature Range −65˚C to +150˚C −65˚C to +150˚C −65˚C to +150˚C −65˚C to +150˚C Junction Temperature 150˚C 100˚C 150˚C 100˚C Soldering Information N-Package (10 seconds) 260˚C 260˚C 260˚C 260˚C J- or H-Package (10 seconds) 300˚C 300˚C 300˚C 300˚C M-Package Vapor Phase (60 seconds) 215˚C 215˚C 215˚C 215˚C Infrared (15 seconds) 215˚C 215˚C 215˚C 215˚C See AN-450 “Surface Mounting Methods and Their Effect on Product Reliability” for other methods of soldering surface mount devices. ESD Tolerance (Note 7) 400V 400V 400V 400V Electrical Characteristics (Note 4) Parameter Conditions LM741A/LM741E Min Input Offset Voltage Typ Max 0.8 3.0 LM741 Min LM741C Typ Max 1.0 5.0 Min Units Typ Max 2.0 6.0 TA = 25˚C RS ≤ 10 kΩ RS ≤ 50Ω mV mV TAMIN ≤ TA ≤ TAMAX RS ≤ 50Ω 4.0 mV RS ≤ 10 kΩ 6.0 Average Input Offset 7.5 15 mV µV/˚C Voltage Drift Input Offset Voltage TA = 25˚C, VS = ± 20V ± 10 ± 15 ± 15 mV Adjustment Range Input Offset Current TA = 25˚C 3.0 TAMIN ≤ TA ≤ TAMAX Average Input Offset 30 20 200 70 85 500 20 200 nA 300 nA 0.5 nA/˚C Current Drift Input Bias Current TA = 25˚C Input Resistance TAMIN ≤ TA ≤ TAMAX TA = 25˚C, VS = ± 20V TAMIN ≤ TA ≤ TAMAX, VS = ± 20V Input Voltage Range 30 1.0 80 6.0 500 80 1.5 0.3 2.0 0.3 2.0 0.5 500 nA 0.8 µA MΩ MΩ ± 12 TA = 25˚C TAMIN ≤ TA ≤ TAMAX www.national.com 80 0.210 ± 12 2 ± 13 ± 13 V V Electrical Characteristics (Note 4) Parameter (Continued) Conditions LM741A/LM741E Min Large Signal Voltage Gain TA = 25˚C, RL ≥ 2 kΩ VS = ± 20V, VO = ± 15V VS = ± 15V, VO = ± 10V Typ Max LM741 Min Typ 50 200 LM741C Max Min Typ 20 200 Units Max 50 V/mV V/mV TAMIN ≤ TA ≤ TAMAX, RL ≥ 2 kΩ, VS = ± 20V, VO = ± 15V VS = ± 15V, VO = ± 10V VS = ± 5V, VO = ± 2V Output Voltage Swing 32 V/mV 25 RL ≥ 10 kΩ 10 V/mV ± 16 ± 15 V V RL ≥ 10 kΩ ± 12 ± 10 RL ≥ 2 kΩ TA = 25˚C 10 Current TAMIN ≤ TA ≤ TAMAX 10 Common-Mode TAMIN ≤ TA ≤ TAMAX RS ≤ 10 kΩ, VCM = ± 12V Rejection Ratio RS ≤ 50Ω, VCM = ± 12V Supply Voltage Rejection Ratio 25 35 ± 14 ± 13 ± 12 ± 10 25 ± 14 ± 13 V 25 mA 40 mA 70 80 95 86 96 90 70 90 dB RS ≤ 10 kΩ TA = 25˚C, Unity Gain 77 96 77 96 dB µs 0.25 0.8 0.3 0.3 Overshoot 6.0 20 5 5 Slew Rate Supply Current Power Consumption LM741A dB dB Rise Time Bandwidth (Note 5) V TAMIN ≤ TA ≤ TAMAX, VS = ± 20V to VS = ± 5V RS ≤ 50Ω Transient Response V/mV VS = ± 20V RL ≥ 2 kΩ VS = ± 15V Output Short Circuit 15 TA = 25˚C TA = 25˚C, Unity Gain TA = 25˚C 0.437 1.5 0.3 0.7 TA = 25˚C VS = ± 20V VS = ± 15V 80 VS = ± 20V TA = TAMIN % MHz 0.5 0.5 V/µs 1.7 2.8 1.7 2.8 50 85 50 85 150 mA mW mW 165 mW 135 mW LM741E TA = TAMAX VS = ± 20V TA = TAMIN 150 mW 150 mW LM741 TA = TAMAX VS = ± 15V TA = TAMIN TA = TAMAX 60 100 mW 45 75 mW Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. 3 www.national.com Electrical Characteristics (Note 4) (Continued) Note 2: For operation at elevated temperatures, these devices must be derated based on thermal resistance, and Tj max. (listed under “Absolute Maximum Ratings”). Tj = TA + (θjA PD). Thermal Resistance θjA (Junction to Ambient) θjC (Junction to Case) Cerdip (J) DIP (N) HO8 (H) SO-8 (M) 100˚C/W 100˚C/W 170˚C/W 195˚C/W N/A N/A 25˚C/W N/A Note 3: For supply voltages less than ± 15V, the absolute maximum input voltage is equal to the supply voltage. Note 4: Unless otherwise specified, these specifications apply for VS = ± 15V, −55˚C ≤ TA ≤ +125˚C (LM741/LM741A). For the LM741C/LM741E, these specifications are limited to 0˚C ≤ TA ≤ +70˚C. Note 5: Calculated value from: BW (MHz) = 0.35/Rise Time(µs). Note 6: For military specifications see RETS741X for LM741 and RETS741AX for LM741A. Note 7: Human body model, 1.5 kΩ in series with 100 pF. Connection Diagram Metal Can Package Ceramic Dual-In-Line Package DS009341-2 Note 8: LM741H is available per JM38510/10101 DS009341-5 Order Number LM741H, LM741H/883 (Note 8), LM741AH/883 or LM741CH See NS Package Number H08C Note 9: also available per JM38510/10101 Note 10: also available per JM38510/10102 Order Number LM741J-14/883 (Note 9), LM741AJ-14/883 (Note 10) See NS Package Number J14A Dual-In-Line or S.O. Package Ceramic Flatpak DS009341-6 DS009341-3 Order Number LM741W/883 See NS Package Number W10A Order Number LM741J, LM741J/883, LM741CM, LM741CN or LM741EN See NS Package Number J08A, M08A or N08E www.national.com 4 µA741, µA741Y GENERAL-PURPOSE OPERATIONAL AMPLIFIERS SLOS094B – NOVEMBER 1970 – REVISED SEPTEMBER 2000 TYPICAL CHARACTERISTICS OPEN-LOOP SIGNAL DIFFERENTIAL VOLTAGE AMPLIFICATION vs SUPPLY VOLTAGE MAXIMUM PEAK OUTPUT VOLTAGE vs FREQUENCY ± 16 AVD – Open-Loop Signal Differential Voltage Amplification – V/mV ± 18 400 VCC+ = 15 V VCC – = –15 V RL = 10 kΩ TA = 25°C ± 14 ± 12 ± 10 ±8 ±6 ±4 VO = ±10 V RL = 2 kΩ TA = 25°C 200 100 40 20 ±2 0 100 10 1k 10k 100k 1M 0 2 4 6 8 10 12 14 16 18 20 VCC ± – Supply Voltage – V f – Frequency – Hz Figure 6 Figure 7 OPEN-LOOP LARGE-SIGNAL DIFFERENTIAL VOLTAGE AMPLIFICATION vs FREQUENCY 110 VCC+ = 15 V VCC – = –15 V VO = ±10 V RL = 2 kΩ TA = 25°C 100 AVD – Open-Loop Signal Differential Voltage Amplification – dB VOM – Maximum Peak Output Voltage – V ± 20 90 80 70 60 50 40 30 20 10 0 –10 1 10 100 1k 10k 100k 1M 10M f – Frequency – Hz POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 9 µA741, µA741Y GENERAL-PURPOSE OPERATIONAL AMPLIFIERS SLOS094B – NOVEMBER 1970 – REVISED SEPTEMBER 2000 TYPICAL CHARACTERISTICS COMMON-MODE REJECTION RATIO vs FREQUENCY OUTPUT VOLTAGE vs ELAPSED TIME 28 VCC+ = 15 V VCC– = –15 V BS = 10 kΩ TA = 25°C 90 80 24 VO – Output Voltage – mV CMRR – Common-Mode Rejection Ratio – dB 100 70 60 50 40 30 20 ÏÏ 20 90% 16 12 8 10% 0 10 tr 0 –4 1 100 10k 1M 100M 0 0.5 Figure 9 Figure 8 VOLTAGE-FOLLOWER LARGE-SIGNAL PULSE RESPONSE 8 VCC+ = 15 V VCC– = –15 V RL = 2 kΩ CL = 100 pF TA = 25°C 6 Input and Output Voltage – V 1 t – Time − µs f – Frequency – Hz 4 VO 2 0 VI –2 –4 –6 –8 0 10 20 30 40 50 60 70 t – Time – µs Figure 10 10 VCC+ = 15 V VCC– = –15 V RL = 2 kΩ CL = 100 pF TA = 25°C 4 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 80 90 1.5 2 2.5