Basics of op amp
- 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!
- 6. ● 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-)
- 7. ➔ 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
- 13. 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)
- 14. 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
- 16. Single-Ended Input ● + terminal : Ground ● – terminal : Source ● 180o phase change ● + terminal : Source ● – terminal : Ground ● 0o phase change
- 17. 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
- 20. IC Product DIP-741 Dual op-amp 1458 device
- 21. 741
- 22. Applications •Non Inverting Amplifier •Inverting Amplifier •Adder (Summing amp) –(and Subtractor using an Inverter) •Differential Amplifier •Integrator •Differentiator
- 23. 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