Lab 1 - Revisited Display signals on scope Measure the time, frequency, voltage visually and with the scope Voltage measurement* Build simple circuits on a protoboard.* Oscilloscope demo 6.091 IAP Lecture 2 1
RMS Voltage 0-5v square wave (50%) duty cycle has a rms value of 5 / 2 = 3.54v 5v peak-peak square wave (-2.5v to +2.5v 50% duty cycle) has a rms value of 2.5v 6.091 IAP Lecture 2 2
General Conventions Wire coding red: positive or signal source black: ground or common reference point Circuit flow, signal flow left to right Higher voltage on top, ground negative voltage on bottom 6.091 IAP Lecture 2 3
Lab Hints & Cautions Current measure must be taken in series not parallel. There are tools for most situations: wire strippers, de-soldering tool, etc.. Power ratings of components must not be exceeded Polarity of electrolytic capacitors must be observed. 6.091 IAP Lecture 2 4
Lab 1 Circuits R c + V o - R + V o - 6.091 IAP Lecture 2 5
Field Effect Transistors (FET) MOSFET: Metal Oxide Semiconductor FET JFET: Junction FET FETs are voltage controlled device with very high input impedance (little current) N channel JFET P channel JFET 6.091 IAP Lecture 2 6
Simple Model of MOSFET G D i ds + v ds D + v gs - S - G MOSFET made VSLI (microprocessors and memories) possible. Very high input resistance S OFF ON Voltage controlled device V gs < V t V gs V t ~25 V max operating 6.091 IAP Lecture 2 7
Bipolar Junction Transistors NPN collector base i b emitter PNP + V ce - i c = β i b β ~50-300 i e = β i b +i b BJT can operate in a linear mode (amplifier) or can operate as a digital switch. Current controlled device Two families: npn and pnp. BJT s are current controlled devices NPN 2N2222 PNP 2N2907 V CE ~30V, 500 mw power 6.091 IAP Lecture 2 8
BJT Switching Models +15V 1K +15V 1K 100k 100k Off On 6.091 IAP Lecture 2 9
Light Emitting Diode LED s are pn junction devices which emit light. The frequency of the light is determined by a combination of gallium, arsenic and phosphorus. Red, yellow and green LED s are in the lab Diodes have polarity Typical forward current 10-20ma 6.091 IAP Lecture 2 10
Lab Exercise 100k +15V 1K Wire up protoboard. Turn on function generator and using a ramp signal try to get a pulsing light 2N2222 6.091 IAP Lecture 2 11
Optical Isolators Pin Configurations (Top View) 1: Anode 2: Cathode 3: NC 4: Emitter 5: Collector 6: Base 1: Anode 2: Cathode 3: NC 4: Emitter 5: Collector 6: Base TLP731 1 2 3 TLP732 1 2 3 6 5 4 6 5 4 Optical Isolators are used to transmit information optically without physical contact. Single package with LED and photosensor (BJT, thyristor, etc.) Isolation up to 4000 Vrms Figure by MIT OpenCourseWare. 6.091 IAP Lecture 2 12
Proto-Board +5v, +15v, -15v available Pins within row or column connected Use bypass capacitors liberally 6.091 IAP Lecture 2 13
Op-Amps Active device: V 0 = A(V + -V - ); note that it is the difference of the input voltage! V+ V- V o A=open loop gain ~ 10 5 10 6 Most applications use negative feedback. Comparator: no feedback Active device requires power. No shown for simplicity. Classics op-amps: 741, 357 ~ $0.20 6.091 IAP Lecture 2 14
741 Circuit 22 transistors, 11 resistors, 1 capacitor, 1 diode Reprinted with permission of National Semiconductor Corporation. 6.091 IAP Lecture 2 15
356 JFET Input Op-amp Reprinted with permission of National Semiconductor Corporation. 6.091 IAP Lecture 2 16
741 Op Amp Max Ratings Reprinted with permission of National Semiconductor Corporation. 6.091 IAP Lecture 2 17
741 Electrical Characteristics Reprinted with permission of National Semiconductor Corporation. 6.091 IAP Lecture 2 18
Decibel (db) db = V 20log V o i db = 10log P P o i log 10 (2)=.301 3 db point =? 6.091 IAP Lecture 2 19
741 Open Loop Frequency Gain 6.091 IAP Lecture 2 20
741 vs 356 Comparison 741 356 Input device BJT JFET Input bias current 0.5uA 0.0001uA Input resistance 0.3 MΩ 10 6 MΩ Slew rate* 0.5 v/us 7.5 v/us Gain Bandwidth product 1 Mhz 5 Mhz Output short circuit duration Continuous continuous Identical pin out * comparators have >50 v/us slew rate 6.091 IAP Lecture 2 21
Comparator Operation Supply voltage = +15v, -15V V- = +5 V For V in = +4, V o =? For V in = +5.1, V o =? Comparators are design for fast response time and high slew rate. V in +5 V+ V- V o 6.091 IAP Lecture 2 22
Lab Exercise - Comparator Wire up a comparator on the proto-board using 741 op-amp. Be sure to supply power and ground. 1k +5 2 V- +15 7 6 Turn on function generator using a ramp. Display both the input and the output on an oscilloscope. Describe what is happening. Vin 3 V+ 4 V o What is the maximum output voltage (the plus rail)? What is the minimum output voltage (negative rail)? 6.091 IAP Lecture 2 23
Lab Exercise - Oscillator Wire up a comparator on the proto-board using 741 op-amp. Be sure to supply power and ground. R1=10k, R2=4.7k, R3=10K, C=.33uf Display V- and V out on the scope. Describe what is happening. Set R3=4.7k. Predict what happens to the frequency. 6.091 IAP Lecture 2 24
Lab Exercise Inverting amplifier Wire up a comparator on the proto-board using 741 op-amp. Be sure to supply power and ground. Find the pin # 1k V- 10k Turn on function generator using a ramp. Display both the input and the output on an oscilloscope. How is the output related to the input? Vin V+ V o What is the peak output voltage? What is the minimum output voltage? What at frequency does the gain start to drop below ten? 6.091 IAP Lecture 2 25
Negative Feedback 1k V- 10k Take product with 100,000 gain and reduce it to 10? Vin V+ V o 6.091 IAP Lecture 2 26
Lab Exercise Integrator R1 C Op-amps are frequently used as integrators. Wire up an integrator on the proto-board using a 741 op-amp. Be sure to supply power and ground. R1=47K, C=0.1uf Vin V- V+ V o Input a square wave to the integrator. What is the minimum frequency for for which the integrates? Display both the input and the output on an oscilloscope. Notice that for a square wave, the output voltage is proportional to the on time. 6.091 IAP Lecture 2 27
Lab Exercise - Schmitt Trigger Vin V- V o Schmitt trigger have different triggers points for rising edge and falling edge. V+ R2 R1 Can be used to reduce false triggering This is NOT a negative feedback circuit. 6.091 IAP Lecture 2 28
Current Source +15V Household application: battery charger (car, laptop, mp3 players) Differential amplifier current source Ramp waveform generator High Speed DA converter using capacitors Simple circuit: 2N5459 Nchannel JFET 5 Common Drain-Source TYP V GS(OFF) = -1.8V T A = 25 o C 2N5459 i D I DSS = current with V GS =0 V P = pinchoff voltage i D I v 1 GS V = DSS P 2 IO - Drain Current (ma) 4 3 2 1 0 0 1 2 3 4 5 V DS - Drain-Source Voltage V GS = 0V V GS = -0.25V V GS = -0.5V V GS = -0.75V V GS = -1V V GS = -1.25V 6.091 IAP Lecture 2 29 Figure by MIT OpenCourseWare.
Voltage Control Current Source * Feedback forces V + =V -. +15 R E =100 +15 R E =100, β F =100, Vin=5 R3 i E i E ~i C Vin R2 R1 V- V+ +15-15 V o i c R1=10k, R2=4.7k, R3=10K, C=.33uf R1, R2 can be replaced with a pot. R L * Fall 2006 6.101 lab exercise 6.091 IAP Lecture 2 30
Lecture 2 Summary BJT, MOSFET Op Amp circuits Comparator Oscillator Schmitt trigger Current Source 6.091 IAP Lecture 2 31