![Difference Amplifier
The difference amplifier and subtractor circuits are used to obtain the subtraction of
two input voltages.
Fig. shows the difference amplifier.
Assume V2 = 0, then circuit become non-inverting amplifier with output voltage VO1 and
it is given by,
VO1 = AV x VA
VO1 = [1 + (Rf / R1)] x [Rf / (Rf + R1)] V1
= [(R1 + Rf) / R1] x [Rf /(Rf + R1)] V1
∴ VO1 = (Rf / R1) V1
The output voltage of the difference amplifier is given as,
VO = (Rf / R1) x (V1 – V2)
(Rf / R1) is called as the “gain of the difference amplifier”.](https://image.slidesharecdn.com/unit-3opamp-231030084011-1a747de8/85/UNIT-3-OPAMP-pptx-38-320.jpg)
UNIT-3 OPAMP.pptx
- 1. Unit : III Linear Integrated Circuits OP-AMP (Operational Amplifier)
- 3. Blocks of operational amplifier
- 4. Burr Brown- BB Fairchild- µA,µAF National Semiconductor-LM, LH, LF, TBA Motorola- MC, MR Texas instruments- SN Signetics- N/S, NE/SE, SU LM 741
- 14. ● S t a ges of an op-amp INPUT STAGE OUTPUT STAGE GAIN STAGE 14
- 15. Ideal Op-Amp ● Infinite input impedance ● Zero output impedance ● Infinite open-loop gain ● Infinite bandwidth ● Zero noise contribution ● Zero DC output offset 15 Practical Op-Amp ■ Input impedance 500k-2M ■ Output impedance 20-100 ■ Open-loop gain (20k to 200k) ■ Bandwidth limited (a few kHz) ■ Has noise contribution ■ Non-zero DC output offset Properties
- 16. ■ Zero Noise Contribution 16 ■ In an ideal op amp, all noise voltages produced are external to the op amp. Thus any noise in the output signal must have been in the input signal as well. ■ The ideal op amp contributes nothing extra to the output noise. ■ In real op-amp, there is noise due to the internal circuitry of the op-amp that contributes to the output noise.
- 17. Op-Amp Parameters 17 ● COMMON-MODE REJECTION (CMRR) ● COMMON-MODE INPUT VOLTAGE ● INPUT OFFSET VOLTAGE ● INPUT BIAS CURRENT ● INPUT IMPEDANCE ● INPUT OFFSET CURRENT ● OUTPUT IMPEDANCE ● SLEW RATE
- 18. ●Common-Mode Rejection Ratio (CMRR) ● The ability of amplifier to reject the common-mode signals (unwanted signals) while amplifying the differential signal (desired signal). ● ● Ratio of open-loop gain, Aol to common-mode gain, Acm A o l C M R R = A c m C M RR = 20 log A ol Ac m 18 ( ) ■ The higher the CMRR, the better, in which the open-loop gain is high and common-mode gain is low. ■ CMRR is usually expressed in dB & decreases with frequency.
- 19. ■ Input Offset Voltage ■ Ideally, output of an op-amp is 0 Volt if the input is 0 Volt. ■ Realistically, a small dc voltage will appear at the output when no input voltage is applied. ■ Thus, differential dc voltage is required between the inputs to force the output to zero volts. ■ This is called the Input Offset Voltage, Vos. Range between 2 mV or less. 19
- 20. ●Input Bias Current ● Ideally should be zero. ● The dc current required by the inputs of the amplifier to properly operate the first stage. ● Is the average of both input currents. 20
- 21. ● Input Impedance ● Is the total resistance between the inverting and non-inverting inputs. ● Differential input impedance : total resistance between the inverting and non-inverting inputs. ● Common-mode input impedance: total resistance between each input and ground. 21
- 22. ● Input Offset Current ● It is the difference of input bias currents. 12 Offset voltage Vos=I1 Rin−I2 Rin=(I1−I2)Rin Vos=Ios Rin Input offset current Ios= ∣I1−I2 ∣ Thus, error Vout(error)=Av IosRin
- 23. ● Slew Rate ● It is the maximum rate of change of the output voltage in response to a step input voltage. ΔVout SlewRate= Δt 13 where ΔVout =+Vmax max −(−V )
- 24. ●Slew Rate ● It’s a measure of how fast the output can “follow” the input signal. 24
- 25. ● Example Determine the slew rate: ΔVout SlewRate= Δt 25 1μs SlewRate= + 9V−(−9V) =18V/μs
- 38. Difference Amplifier The difference amplifier and subtractor circuits are used to obtain the subtraction of two input voltages. Fig. shows the difference amplifier. Assume V2 = 0, then circuit become non-inverting amplifier with output voltage VO1 and it is given by, VO1 = AV x VA VO1 = [1 + (Rf / R1)] x [Rf / (Rf + R1)] V1 = [(R1 + Rf) / R1] x [Rf /(Rf + R1)] V1 ∴ VO1 = (Rf / R1) V1 The output voltage of the difference amplifier is given as, VO = (Rf / R1) x (V1 – V2) (Rf / R1) is called as the “gain of the difference amplifier”.
- 40. A B
- 41. Subtractor The output voltage of difference amplifier is given by, VO = (Rf / R1) x (V1 – V2) If we substitute Rf = R1 = R in above equation, then we get, VO = V1 – V2 And difference amplifier gets transformed into a subtractor.
- 43. The ideal integrator circuit is obtained by replacing the feedback resistor Rf in the inverting amplifier configuration by “C”. The output voltage of integrator is: .
- 44. Practical Integrator: Applications of an integrator: In the triangular wave or ramp generator In the analog to digital converter In analog computers to solve differential equations. As a low pass filter.
- 46. The differentiator can be constructed from the basic inverting amplifier by interchanging resistance Rf and C1. The expression for the output voltage of differentiator is given by,
- 48. Applications of differentiator: 1. In the P-I-D controller. 2. As a high pass filter 3. In the wave shaping circuits to generate narrow pulses corresponding to any sharp change in the input signal.
- 49. Comparators Op-AMP used in open loop mode of operation, operates as a comparator. A comparator will produce either a high output voltage equal to + Vsat or a low output voltage equal to – Vsat only, hence it can not be used as an amplifier. There are two types of comparators: 1. Non inverting comparator 2. Inverting comparator
- 50. Non Inverting Comparator In non-inverting comparator, ac signal is connected to non inverting terminal while positive dc reference voltage is applied to the inverting terminal. As the current through resistors R is almost zero, the voltage drop across them will be equal to zero. Hence V1 = Vin and V2 = Vref. Hence Vd = V1 – V2 = Vin - Vref
- 51. The operation of this circuit is given in following table. Input voltage Difference Voltage Vd Output voltage VO Vin > Vref Vd positive VO = + Vsat Vin < Vref Vd negative VO = - Vsat sat sat
- 52. Inverting Comparator In inverting comparator, ac input voltage is applied to inverting terminal while dc reference voltage Vref is applied to non inverting terminal. Here, differential input voltage Vd is given by, Vd = V1 – V2 = Vref - Vin
- 53. The operation of this circuit is given in following table. Input voltage Difference Voltage Vd Output voltage VO Vin < Vref Vd positive VO = + Vsat Vin > Vref Vd negative VO = - Vsat
- 54. TIMERS
- 55. IC 555 Timer The timing and counting circuits find their applications in many of the mechanical and electronic process control systems. one of the most popular timer integrated circuit is IC 555. Features of IC NE 555: 1. Supply voltage range: 5 to 18 Volt. 2. Current sinking and sourcing capacity : 200 mA 3. High temperature stability. 4. Timing can be adjusted from microseconds to hours. 5. Duty cycle of the output is adjustable. 6. Output is compatible with CMOS and TTL. 7. Good timing stability against supply voltage variations. 8. Low cost. 9. Versatile in operation.
- 56. Functional block diagram of IC NE 555
- 57. Pin Diagram of IC 555
- 58. Pin configuration of Timer IC NE 555: 1. Ground: It is connected to ground terminal of the dc voltage source used to supply power to the timer IC. 2. Trigger input: When voltage at this pin goes below (1/3)VCC, the lower comparator output goes high which switches the timer output high and it turns off the discharge transistor T1. 3. Output: This is the output of the timer and load is connected to this pin. The status of this pin is decided by the two comparators. 4. Reset: For normal operation of the timer, this pin should be connected to + VCC. If reset pin is connected to a low voltage then transistor T2 is turn on which in turn switches on the discharge transistor T1 to bring voltage at pin no.7 to zero. 5. Control: The dc voltage at this pin is (2/3)VCC.
- 59. 6. Threshold: As soon as voltage at this pin goes above (2/3)VCC, the output of upper comparator become high and this will bring output voltage of timer to low level. 7. Discharge: This pin is the collector of the transistor T1.as soon as the output of upper comparator goes high, this will turn on the transistor T1. 8. VCC: A positive regulated power supply is connected to this pin. Resistive voltage divider: The three resistances of value 5 KΩ each form the resistive voltage divider. It generates two reference voltages, (1/3)VCC for lower comparator and (2/3)VCC for upper comparator.
- 60. Multivibrators Multivibrator is an electronic circuits which can have no, one or two stable stages of operation. Depending on the number of stable states we can classify the multivibrators as: Multivibrators Astable Multivibrators (AMV) Monostable Multivibrators (MMV) Bistable Multivibrators (BMV)
- 61. IC 555 as an Astable Multivibrator (AMV)
- 63. Operation of the circuit: When the voltage at trigger pin i.e pin no. 2 is less than (1/3) VCC, output is high and capacitor starts charging through R1 and R2. After some time “Ton”, voltage on C reaches a level of (2/3) VCC. As soon as VC = (2/3) VCC, the upper comparator output will reset the flip flop and output switches to low state. The internal transistor “T1” is turned on and the capacitor discharges exponentially through R2 and T1. After some time “Toff”, voltage on C reaches a level of (1/3) VCC, the output is switches to a high state.
- 64. Applications of astable multivibrator: 1. Square wave oscillator 2. Ramp generator 3. Voltage controlled oscillator 4. In the flasher circuit