Op-Amp Fundamental
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  • 1. OPERATIONAL AMPLIFIER
    • An operational amplifier or OP AMP is a very high gain differential amplifier with high input impedance and low output impedance .
  • 2. A basic OP AMP has 2 input and 1 output - + V O , OUTPUT 2 3 6 + V CC 4 7 - V CC INPUT 1 5
  • 3. LM 741 OP AMP IC PIN ASSIGNMENT OP-AMP LM741 IC Pin Assignment NULL OFFSET 1 INVERTING INPUT NONINVERTING INPUT - V cc NULL OFFSET 2 Output +V cc COMP 1 2 3 4 8 7 6 5
  • 4. Single ended Input operation results when the input signal is connected to one input and with the other input is connected to the ground . SINGLE ENDED INPUT  
  • 5. - + V O 2 3 6 + V CC 4 7 - V CC Grounded SINGLE ENDED INPUT  
  • 6. A double-ended input can be designed using a single input or using double inputs DOUBLE ENDED INPUT  
  • 7. DOUBLE ENDED INPUT WITH SINGLE INPUT - + V O 2 3 6 + V CC 4 7 - V CC V d Single input
  • 8. DOUBLE ENDED INPUT WITH DOUBLE INPUT - + V O 2 3 6 + V CC 4 7 - V CC V 2 V 1 TWO INPUTS
  • 9. For the double input circuit the supplied voltage is equal to the difference between the two input signals. DOUBLE ENDED INPUT  
  • 10. DIFFERENTIAL INPUT When separate inputs are applied to the op-amp, the resulting difference signal is the difference between the two inputs.
  • 11. COMMON INPUT When both input signals are the same, a common signal element due to the two inputs can be defined as the average of the sum of the two signals.
  • 12. OUTPUT VOLTAGE The resulting output voltage of any op-amp can be defined as, Where, A d = Differential gain of the amplifier A c = Common-mode gain of the amplifier
  • 13. OPPOSITE POLARITY INPUTS If an ideal opposite polarity inputs, V 1 = Vs and V 2 = –Vs are applied to an op-amp, The resulting differential voltage, V d is defined as
  • 14. OPPOSITE POLARITY INPUTS The resulting common voltage, V c is defined as So, the resulting output voltage, V o is,
  • 15. SAME POLARITY INPUTS If an ideal same polarity inputs are applied to an op-amp V 1 = V 2 = V S The resulting differential voltage, V d is defined as
  • 16. SAME POLARITY INPUTS The resulting common voltage, V c is defined as So, the resulting output voltage, V o is,
  • 17. COMMON MODE REJECTION RATIO Having obtained A d and A c , we can now calculate a value for the common-mode rejection ratio (CMRR), which is defined by the following equation, or
  • 18. TYPICAL VALUE FOR LM741 Open loop voltage gain A VOL 2 X 10 5 Slew Rate SR 0.5 V/  s Full Power Bandwidth f PL  6 kHz Gain Bandwidth Product GBP 1 MHz Saturation Voltage V sat  14V Input Offset Voltage V io 5 mV max Input Offset Current I io 20 nA Input Bias Current (average) I B 80 nA Common Mode Rejection Ratio CMRR 90 dB Power supply Rejection Ratio PSRR 30  V/V