(Op-Amp) s Prof. Dr. M. Zahurul Haq zahurul@me.buet.ac.bd http://teacher.buet.ac.bd/zahurul/ Department of Mechanical Engineering Bangladesh University of Engineering & Technology ME 475: Mechatronics The OP-Amp is a low-cost and versatile I (Integrated ircuit) consisting of many internal transistors, resistors, and capacitors. These are basic building blocks for: Amplifiers Integrators and Differentiators Summers omparators A/D and D/A converters Active filters Sample and Hold circuits...etc. Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 / 3 Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 2 / 3 OP-Amp: omponents Internal Design of LM74 The OP-Amp has Single Output and Two Inputs: Noninverting input []: output is in phase with input. 2 Inverting input [-]: output is 80 o out of phase with input. e560.eps e039.eps Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 3 / 3 Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 4 / 3
OP-Amp: Equivalent ircuit OP-Amp: haracteristics ule. Infinite input impedance, Z in = ½ =µ I = I = 0; ule 2. Infinite gain, =µ E = E ; ule 3. Zero output impedance, Z out = 0 =µ = f (I o ). ½ ½ haracteristics Ideal Value Typical real-world value Open-loop gain 0 5 V V Offset voltage 0 mv Bias currents 0 0 6 0 4 A Input impedance 0 5 0 Ω Output impedance 0 0Ω Ideal op-amps rejects inputs common to both inputs (common mode rejection). Actual ommon Mode ejection atio, M = Eo E cm 0 6 the larger the M, the better the amplifier. e427.eps Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 5 / 3 Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 6 / 3 OP-Amp: Examples OP-Amp: Voltage omparator e76.eps E ref E o 5 V e77.eps 0.0002 V V V 2 5 V V out 2 V 2 V x007.eps In comparator circuit, there is no negative feedback, hence the circuit exhibits infinite gain and the op-amps will saturate, i.e. the output remains at the most positive or most negative output value. Hence, Esat E = i E ref E sat E ref Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 7 / 3 Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 8 / 3
omparator ircuit: Application Window omparator ircuit e040.eps hatter is a practical problem, output voltage oscillates back-and-forth when input voltage is near to the threshold. Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 9 / 3 e04.eps Window omparator is with inbuilt hysteresis; hysteresis means that switch-on voltage is greater than switch-off voltage. Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 0 / 3 OP-Amp: Inverting Amplifier OP-Amp: Noninverting Amplifier F F X I i I F I 00 i X I F x008.eps At X, I i I F = 0 (KL & ule ), & E X = 0 (ule 2); I E i E X i = I F Eo E X F =µ gain G = Eo = F x009.eps At X, I i I F = 0 (KL & ule ), & E X = (ule 2); I E X i = I F Eo E X F =µ G = F Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 / 3 Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 2 / 3
OP-Amp: Follower/Buffer Op-Amp: Voltage Follower Application In a noninverting amplifier with = ½ & F = 0, gain, G is unity and there is no voltage amplification. This circuit is known as a buffer or follower. It has a high input impedance and low output impedance. The high input impedance effectively isolates the source from the rest of the circuit. 5 Sensor V in = 0.45 V ontroller 5 V V in = 0.45 V (a) Signal experiences voltage drop (b) Equivalent circuit 5 5 V V in = 5 V Sensor ontroller x00.eps Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 3 / 3 (c) No signal voltage drop Prof. e78.eps Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 4 / 3 Op-Amp: Summing Amplifier Summing Amplifier: Application e79.eps E V 2 V 4 V V 7 V 2 V? 4 V F 4 V Example: Interface circuit for an air conditioning system when the sum of the voltages of temperature and humidity sensors goes above.0 V, & a threshold circuit in air conditioner require 5.0 V. x0.eps E 2 E 3 00 E o = E F E2 2 E3 3 Temperature e042.eps Humidity V t V h 5 kω (V t V h ) 5 Inverter V out = (V t V h ) 5 If = 2 = 3 is a weighted sum of input voltages. Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 5 / 3 Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 6 / 3
OP-Amp: Differential Amplifier Instrument Amplifier E E 2 I e E 00 e o 2 E 00 I A 2 c 2 a D 3 b I 2 4 E 2 B 2 c 2 x02.eps e = e =µ E = E 2 2 2 4 2 3 4 = (E 2 E ) 2 E o 2 = E 4 2 3 4 E 2 = c(e 2 E ) if 2 = 4 3 = c Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 7 / 3 x03.eps I = Ec E D = E E2 = E A E B a b ; & = c(e A E B ) G = Eo E 2 E = c( a b) Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 8 / 3 OP-Amp: Integrator Output of an Integrator ircuit ( = ) 00 X I00 i I F x04.eps I i = I F = c deo dt & I i I F = 0(KL) Ê = Ei ()d Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 9 / 3 e043.eps Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 20 / 3
OP-Amp: Differentiator Output of a Differentiator kt. ( = ) d 00 X 00 I i I F V in (Volts) c a b 0 2 3 Time (sec) Time (sec) 0 2 3 x05.eps V out * 2 I i = d dt I F = c Eo & I i I F = 0(KL) = d dt e044.eps 3 Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 2 / 3 Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 22 / 3 OP-Amp: Differentiator & Integrator OP-Amp: Proportional ontroller 5 V B Bias Sensor (05 V) Set point 5 V (3 V) U Error Differential amp 20 kω U 2 Proportional gain amp U 3 Inverter To valve (05 V) e80.eps e428.eps Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 23 / 3 Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 24 / 3
OP-Amp: PID ontroller OP-Amp: Sample and Hold ircuit Process variable (feedback) Set point U Error 2 U 2 Proportional U Output PID 5 Summer and Multiplier Analog Input ontrol Switch D e8.eps U 3 Integral 3 U 4 Derivative Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 25 / 3 x06.eps S/H amplifier holds an analog value, until an A/D converter is ready to convert it to digital. The basis circuit consists of an electronic switch to the sample, with a capacitor for the hold and an op-amp voltage follower. Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 26 / 3 OP-Amps: urrent Source Low-Pass Filter ircuit f 2 i 2 load 3 I I = E 2 i 3 if 2 > > load. V in f c = 2π V out x07.eps e0.eps Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 27 / 3 Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 28 / 3
High-Pass Filter ircuit Band-Pass/Band-eject Filter ircuits i f Band-Pass Filter - A band-pass filter can be built by cascading a low-pass filter and a high-pass filter together. The cut-off frequency of the low-pass filter must be higher than the cut-off frequency of the high-pass filter. Band-eject Filter - V in f c = 2π V out V in 2 f n = 2π V out 2 e02.eps e03.eps Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 29 / 3 Prof. Dr. M. Zahurul Haq (BUET) OP-Amp ME 475 30 / 3