Operational Amplifier Introduction

Basic Features Operational Amplifier (Op-Amp)

• Operational Amplifier is a Voltage Control Voltage Source (VCVS)
•  Input Resistance (Ri) of Op-Amp is very very High (About 1MΩ) then Source Resistance (i.e. Ri>>Rs)  so that all the input applied Voltage or signal appear Across input resistance(i.e. Vs=Vi) . Ideally Input Resistance of Op-amp is said to have infinite.
• Output Resistance (Ro) of Op-Amp is very very low (10-100Ω) then Load Resistance (i.e. Ro<<Rl) so that all the Output gained Voltage or signal appear across Load resistance and no loss of power occur in the op-amp (i.e. Vo= Av Vi=Vl). Ideally output Resistance of Op-amp is said to have zero.
• The Gain of Ideal op-amp is infinite but which is practically not possible at all since input Power is limited. To have very very high gain of Op-amp generally multi-staging of amplifier is done.
• Bandwidth of any ideal op-amp is said to have infinite but Practically it is not that high i.e. BW of Practical op-amp is about 1MegaHz. (BW is the range of Frequencies of input signal that can be processed by the op-amp and give rated Amplification to the signal. And produce Output. Lower and Upper Cut-off Frequency is decided by 3db  point below the maximum rated  amplification of the Op-amp )
•  Ideally the gain BW product of any op-amp is said to have Infinite But Practically it is finite and for any signal the gain BW product is Constant i.e. Gain x BW=Constant. Practically G*BW= 10^6 Hz and Gain=1
•   In general Op-amp is Multi-stage Amplifier and due to this B.W. cannot be infinite due to the presence of, Transient Capacitance and Depletion Capacitance respectively.
• Common Mod rejection Ratio (CMRR) of any ideal Op-amp is said to have Infinite But Practically it is 10^6 or 100dB. 
•   Slew Rate of any Ideal op-amp is infinite but practically it is 80V/usec.
•  A negative Feedback is provided to the Op-amp to decrease the Gain of the System and to increase the BW and hence to increase the Stability of the system.
•  Operational Amplifier is a Monolithic IC or Semiconductor VLSI Chip, fabricated using Epitaxial Method. Here Entire IC is fabricated on single crystal of Silicon.
• IC-741 is the basically and frequently used op-amp. It works on +15 and -15 power supply.
•  Op-amps are generally operated under closed Loop condition i.e. a ( –ve) Feedback is applied to the system.
•  Op-amp is low power device have various other features like versatile, predictable, and economic. It also can act as system building block due to its small size.