* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download word
Audio crossover wikipedia , lookup
Signal Corps (United States Army) wikipedia , lookup
Audio power wikipedia , lookup
Superheterodyne receiver wikipedia , lookup
Oscilloscope wikipedia , lookup
Flip-flop (electronics) wikipedia , lookup
Analog television wikipedia , lookup
Oscilloscope types wikipedia , lookup
Cellular repeater wikipedia , lookup
Wilson current mirror wikipedia , lookup
Integrating ADC wikipedia , lookup
Voltage regulator wikipedia , lookup
Phase-locked loop wikipedia , lookup
Index of electronics articles wikipedia , lookup
Transistor–transistor logic wikipedia , lookup
Dynamic range compression wikipedia , lookup
Current mirror wikipedia , lookup
Power electronics wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Analog-to-digital converter wikipedia , lookup
Oscilloscope history wikipedia , lookup
Negative feedback wikipedia , lookup
Regenerative circuit wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Schmitt trigger wikipedia , lookup
Radio transmitter design wikipedia , lookup
Operational amplifier wikipedia , lookup
Valve RF amplifier wikipedia , lookup
Rectiverter wikipedia , lookup
PHY3802L: INTERMEDIATE LAB Iel.1 Summing (inverting) amplifier 1. Purpose: Learn about operational amplifiers. 2. Apparatus: power supply (+/- 15V) function generator oscilloscope breadboard electronic components (resistors, op.amp. chip, ..) DMM 3. Background information: 3.1 About operational amplifiers: An operational amplifier is a differential amplifier with very high gain ("open-loop gain" A0), very high input impedance (Zin), and very low output impedance (Z out). V+ v+ v- 8 1 + _ vout V- Fig. 1 2 _ 7 3 + 6 5 4 Fig.2 In normal operation, it needs to be supplied by symmetric voltages V+ and V- (V- = -V+ ). Its behavior is described by vout = A0 (v+ - v- ). In amplifier applications it is usually used with "negative feedback", i.e. part of the output signal is fed back to the negative input (i.e. effectively subtracted from the input signal). The behavior of such circuits can be calculated using the "golden opamp rules": 1. the input currents are 0: i+ = i- = 0 2. the input voltage difference is 0: v+ - v- = 0 (These rules are strictly speaking only valid for a circuit with an ideal opamp, but are a reasonable approximation also for circuits with real opamps). The opamp chip that we are using in this lab is the 741A opamp. It comes in an 8-pin dualinline package (DIP) (see fig. 2). The connections for the pins are as follows: pins 2 and 3 are for input signals v- and v+ , pin 4 is for negative supply voltage, pin 7 for positive supply voltage, and pin 6 is for the output. 3.2 Negative feedback In amplifiers, opamps are used in circuits with "negative feedback", i.e. a circuit in which a fraction of the output voltage is subtracted from the input. The effective input voltage v' is therefore v' = vin - B ∙ vout , where B = "feedback factor" (feedback fraction) is determined by details of the feedback circuit. The amplification with feedback, Af (called "closed-loop gain"), is defined as vout vin From the property of the opamp, it follows that and therefore A0 Af 1 A0 B Af vout = A0 v' = A0 (vin - B vout ), Note: The “closed loop gain” is smaller than the open loop gain: Af < A0 If A0 B >> 1, then Af ≈ 1/B , i.e. the gain of the amplifier depends only on the feedback fraction B, not on the open-loop gain A0 of the opamp; so, variation of A0 does not matter! 4. Procedure: Fig. 3: Summing amplifier (1) Construct the summing amplifier shown in fig. 3, using resistor values Rf 10k, R1 2k and R2 1k. (Measure the resistances of the resistors that you actually use in the circuit, record them and use these values in calculating the expected gain). Use ±12 V as supply voltage, unless instructed otherwise. (2) Apply a 1kHz sinusoidal signal of about 200mV amplitude (from the function generator) to each input separately with the other grounded and measure the sign and magnitude of the amplification factor. (3) Then connect the same signal to both inputs (i.e. make va = vb = vin) and measure the output magnitude. Compare with predicted values (do they agree within errors? Estimate how precisely you measure the voltages and thus the gain, and how precisely you measure resistances and thus how precisely you can predict the gain). (4) Apply a 1kHz sinusoidal signal to both inputs (i.e. make va = vb = vin); vary the amplitude vin of the input signal from 100mV to 1.2V (in 100mV steps) and measure the output voltage amplitude vout and determine the gain (i.e. vout / vin , the ratio of amplitude of the output signal and amplitude of input signal). Plot the output amplitude as a function of the nominal output signal amplitude (i.e. the output signal amplitude expected from the formula given in fig.3). Estimate uncertainties on measured and expected signal size and gain. Describe your observations, and try to explain what you observe. (5) Change the supply voltage to ±10V, and repeat the measurements of (4) for the same set of input signal amplitudes (from 100mV to 1.2V). (6) Restore the supply voltage to ±12V. For a fixed input amplitude (abut 0.5V), measure the gain (vout / vin) as a function of frequency of the sinusoidal input signal, from about 100Hz to the maximum frequency available on the function generator ( 2MHz). Take data for 3 frequency values per decade (e.g. 100, 200, 500, 1000, 2000,…). Discuss the frequency dependence of the gain, and establish a relation between it and the observations of steps (7) and (8) (Consult appropriate sources – textbooks, websites,..to learn about this). (7) Instead of a sinusoidal signal, use a triangular wave and a square wave as input, and observe the output waveforms for three frequencies (lowest, highest, and a value in the middle of your range). Draw the waveforms and comment on your observations. (8) Set the frequency of the function generator to about 1kHz, keeping the amplitude at 0.5V. Measure the rise time of the square wave signal (both input to and output from the amplifier). Determine the slew rate from your measurement. Compare the slew rate determined from the observed rise times to the typical value expected for this chip (see data sheet). Relate your measurement of the slew rate of the opamp to the frequency dependence of the gain. Given the slew rate, can you estimate at what frequency you would expect the gain to start decreasing? (Consult appropriate sources – textbooks, websites,..to learn about this). 5. Notes: Things to note: determine measurement uncertainty of input/output signal amplitude, as well as uncertainty of measured and expected gain (understand your measuring instruments to estimate uncertainties on voltages and resistances); compare measurement with expectation -- agreement within measurement uncertainties? about gain vs. input amplitude: - think about the fact that the output signal size saturates at some value -- no matter what the input is, the output does not exceed a certain value; - the saturation value is lower for supply voltage of 10 V than for 12 V supply voltage -- any explanation for this? - what is the difference between supply voltage and saturation value of the output? -- Do you see a pattern there? - do you think it would be possible to build an opamp chip which does not have this limitation? add a graph of output amplitude (or gain) vs. frequency (plot frequency on log scale -- i.e. plot gain or amplitude vs. log of frequency) From the measured rise time and size of the square wave output you can determine the slew rate of the opamp. Slew rate = dVout/dt = speed at which opamp output voltage can follow an input voltage step (input with zero rise time); observed rise time of output signal has two contributions: one from input rise time and one from slew rate. Note that “rise time” is the time it takes for signal to rise from fraction 0.1 to 0.9 of its maximal (peak-to-peak) size. 6. Bibliography: There are many books on electronics; examples of more useful ones are: (1) Robert E. Simpson: Introductory Electronics for Scientists and Engineers, Allyn and Bacon, Newton, Mass. 1987 (2) William L. Faissler: An Introduction to Modern Electronics John Wiley & Sons, New York 1991 (3) Paul Horowitz and Winfield Hill: The Art of Electronics, Cambridge University Press, Cambridge 1989 (4) D.V. Bugg: Electronics Circuits, Amplifiers and Gates, Institute of Physics Publishing, Bristol 1991 (5) Mark N. Horenstein: Microelectronic Circuits and Devices, 2nd ed., Prentice Hall, 1995 (6) A. de Sa: Electronics for Scientists, Prentice Hall, 1997