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Basics of op amp


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Opamp basics...

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Basics of op amp

  1. 1. OPAMP... OPerational AMPlifier
  2. 2. Intro... ● Op-amps are among the most widely used electronic devices today. ● One of the basic building blocks of Analogue Electronic Circuits. ● A DC-coupled high-gain electronic voltage amplifier. ● Has a differential input and, usually, a single-ended output. ● High open loop gain, typically it is ~ 10^4-10^5. ● By using negative feedback, we throw most of that away!
  3. 3. ● An ideal Operational Amplifier is basically a three-terminal device which consists of two high impedance inputs. ● One called the Inverting Input, marked with a negative or "minus" sign, ( - ) and the other one called the Non-inverting Input, marked with a positive or "plus" sign ( + ). ● The output signal is the amplification factor, known as the amplifiers gain ( A ) multiplied by the value of the input signal. Vo=A(V+ - V-)
  4. 4. ➔ A generalized form of a differential amplifier: ● V1,V2: Inputs ● The two identical transistors TR1 and TR2 are both biased at the same operating point with their emitters connected together and returned to the common rail, -Vee by way of resistor Re. ● The circuit operates from a dual supply+Vcc and -Vee which ensures a constant supply. ● Vout=V1-V2 Equivalent Circuit for Ideal Operational Amplifiers: - ● V1 : Inverting input ● V2: Inverting input ● A: Gain ● Vdiff: V1-V2 ● +Vsupply: +ve power supply ● -Vsupply: -ve power supply
  5. 5. Properties of ideal op amp... ● Infinite open-loop gain ● Infinite voltage range available at the output ● Infinite bandwidth with zero phase shift and infinite slew rate ● Infinite input impedance. So zero input current and zero input offset voltage ● Zero output impedance ● Zero noise ● Infinite Common-mode rejection ratio (CMRR)
  6. 6. Common-Mode Operation ● Same voltage source is applied at both terminals ● Ideally, two input are equally amplified ● Output voltage is ideally zero due to differential voltage is zero ● Practically, a small output signal can still be measured ● Note for differential circuits: ○ Opposite inputs : highly amplified ○ Common inputs : slightly amplified Common-Mode Rejection
  7. 7. Single-Ended Input ● + terminal : Ground ● – terminal : Source ● 180o phase change ● + terminal : Source ● – terminal : Ground ● 0o phase change
  8. 8. Ideal Practical Open Loop gain A µ 10 5 Bandwidth BW µ 0-100Hz Input Impedance Z in µ >1MW Output Impedance Z out 0 W 10-100 W Output Voltage Vout Depends only on V d = (V + -V - ) Differential mode signal Depends slightly on average input V c = (V + +V - )/2 Common- Mode signal CMRR µ 10-100dB IDEAL v/s PRAC TICAL
  9. 9. IC Product DIP-741 Dual op-amp 1458 device
  10. 10. 741
  11. 11. Applications •Non Inverting Amplifier •Inverting Amplifier •Adder (Summing amp) –(and Subtractor using an Inverter) •Differential Amplifier •Integrator •Differentiator
  12. 12. Noninverting amplifier Inverting amplifier Voltage follower Less than unity gain Vo=Vi Vo = 1+(Rf/Ra)Vi Vo = 1+(Rf/Ra)(R1/(R1+R2)Vi
  13. 13. Differential amplifier