Op amp


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introduction to operational amplifiers
this slides helps u to know...what is op-amp...how it works...what are its uses...etc

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  • 8- nc (not connected)
  • Virtual ground means what ever be the voltage at non inverting will appear at inverting
  • Op amp

    1. 1. Op-Amp
    2. 2. Contents  Introduction  Schematic And Realistic View  Equivalent circuit of an op-amp  Op-amp characteristics  Ideal Op-Amp V/s Real Op-Amp  Open loop Op-Amp  Close loop Op-Amp  Closed loop Inverting amplifier  Closed loop non-Inverting amplifier  Distortion  Few applications of op-amp
    3. 3.  Full form of Op-Amp is “Operational amplifier”  Op-Amp is called so, as previously they were used for mathematical operations in analog computers.  It is “Direct coupled high gain voltage amplifier”  It uses differential amplifier which amplifies difference between inputs
    4. 4. Op-Amp is….  Solid state device capable of sensing and amplifying the dc and ac input signals.  Inexpensive, take up less space and consume less power.  Used in the field of communication, computers, power and signal sources, displays and measuring system.
    5. 5.  It Was introduced in 1940s.  The most popular op-amp is 741 IC.  IC version of op-amp make use of transistors, with result in simple circuit designing.  Modern op-amp works on lower voltage.  Op Amps ideally increase the signal amplitude without affecting its other properties
    6. 6. SCHEMATIC AND REALISTIC VIEW » Pins (1,5) are control pin used to eliminate the effects of internal component voltages on the output of the device
    7. 7. Equivalent circuit of an op-amp From figure.. • Vin = (V+ - V-) • G= Gain (Vout /Vin) • Vout = G. Vin • Rout must be low • Rin must be high
    8. 8. Op-amp characteristics Input offset voltage – Voltage which if applied to input terminals, would reduce op-amp output voltage to zero. Slew rate – Maximum rate at which output of op-amp can change. It should be high.(volts/microseconds) Open loop gain – Gain without feedback CMRR(Common mode rejection ratio)-Ratio of differential gain to common mode gain. i.e., CMRR= Aid/ Acm
    9. 9. Ideal Op-Amp V/s Real Op-Amp Ideal op-amps  Infinite open-loop gain  Infinite bandwidth  Infinite slew rate  Infinite input impedance and so zero input current  Zero input offset voltage  Zero output impedance  Zero noise  Infinite Common-mode rejection ratio (CMRR) Real op-amps  Finite open-loop gain  Finite bandwidth  Finite slew rate  Finite input impedance and so a little input current  Small input offset voltage  Small output impedance  Small noise  Finite Common-mode rejection ratio (CMRR)
    10. 10. Open loop Op-Amp (Op-amp without negative feedback) +  Vo ~ Vi +  Vo ~ Vi • + terminal : Source • – terminal : Ground • 0o phase change • + terminal : Ground • – terminal : Source • 180o phase change Non-Inverting amplifier Inverting amplifier Gain is very high so unstable
    11. 11. Closed loop Op-Amp (Op-amp with negative feedback) Negative feedback weaken the input signal. It reduces gain thus stability increases. Reduction in nonlinear distortion. Reduces effect of input offset voltage Increase bandwidth
    12. 12. 0n f s o s f s f o s s i i i v v R R R v v R        0 i i i s f n v v n p v si s R s v oi f R f       “Virtual” ground This is closed loop gain(Af) and negative sign shows the inverted o/p w.r.t i/p Mag. Of o/p can be controlled by Rf and RS
    13. 13. “Virtual” ground Closed loop gain(Af) and no phase shift and gain is always >1 Mag. Of o/p can be controlled by Rf and RS 1               p g s n p g o s f s f o g s f o g s v v R v v v v R R R R v v R R v v R
    14. 14. Vd +  Vo +Vcc=+5V Vcc=5V 0 +5V 5V The output voltage never excess the DC voltage supply of the Op-Amp When the output voltage is equal to or greater than the supply voltage are referred to as saturation of the amplifier which results in distortion due to non-linear behavior.
    15. 15. Few applications of op-amp Uses: Add multiple sensors inputs
    16. 16. COMPARATORS Compares two Voltage and switches its output to indicate which is larger. Op-Amp operating in open-loop configuration (without negative feedback) may be used as comparator. Where Vs+ and Vs- are nominally the positive and negative supply voltages
    17. 17. OP-AMP INTEGRATOR Performs the mathematical operation of integration with respect to time; that is, its output voltage is proportional to the input voltage over time