Integrated Circuits Operational Amplifier

Operational amplifier or commonly referred to as op-amp is a high gain, integrated circuit, direct coupled amplifier capable of performing a large number of linear and non-linear amplification and signal processing functions. Because of its inherent simplicity and myriad applications, the op-amp is probably one of the most famous IC ever existed in the world of electronics

Originally, op-amps were implemented with vacuum tubes. With the advent of transistors, these circuits were then implemented into a single chip, the μA702, designed by Bob Wildar of Fairchild Semiconductors. Although partly unstable, this device was best in its days. Through several years op-amps were developed into an IC (integrated circuits) which is the μA741 which will be used in the experiment because all op-amps IC are based on this said device

Ideal Op-Amp (will have the following assumptions)

a) High Input Impedance- the op-amp will have infinite input impedance that will cancel any loading effect in the input side (internal resistance) of the op-amp and no current can pass in and out of the op-amp.

b) Low Output Impedance- the op-amp will have infinite output impedance that will also cancel any loading effect on the output side (load resistance) of the op-amp.

c) Open Loop Gain (AOL) – the op-amp will have very large or infinite gain without external feedback probably 10K to 20K.


Op-Amp Symbol and Circuit Model

Shown above are the schematic symbol (left) and the µA741 pin configuration (middle). The –V will be the inverting input +V will be the non-inverting input, have nothing to do with the polarities at the terminal input, but if an input will be placed in the inverting input its polarities will be varied depending on what polarities the non-inverting have and how the op-amp circuit will be configured. On the pin configuration, pin #4 and #7 is the positive and negative DC supply power respectively, and pin #1 and #5 are the offset null which move the reference level of the output signal( DC input level) and pin #6 will be the output of the op-amp. At the ideal circuit model of an op-amp (right) we can see there is an dependent source which is in parallel with the output this is equal to the which is the differential voltage (Vin/Vd) multiply with the open loop gain (G/Aol) therefore Vout = Aol(Vd)= Aol(V+-V-). The Rin and Rout are the input and output impedance.


Slew Rate

- It is the op-amp characteristic that determines the operating rate of the device or the

finite rate at which the op-amp can operate, also called as the slew rate limitation, unit is in (V/µs). For slew rate limitation to be easily to internalize it is the limitation of an op-amp of how fast it can compensate with the input signal with the output, for example if an of amp is rated at 2MHz and an input signal of 0.5Ghz (an exaggerated example) the output of the op-amp will be unreliable because of the mismatch of the operating frequencies. Slew rate limitation may not be applicable to constant input signal (DC signal).


Voltage Saturation

- Op-amp have an assumption having an infinite or very large open loop gain and op-amp

IC construction is based on transistor, reviewing what we learn on electronics 1 that transistor will saturate or will have its maximum output when the collector current (Ic) is zero and the output will become Vce=Vout=Vcc (for BJT) therefore it explain the maximum output voltage (Vce) will only be dependent on your input voltage (Vcc). To be easily to internalize, your output voltage cannot exceed to your supply voltage, no matter what is the input voltage and the gain. For example if you have supplied your op-amp with 5 volts, your gain is 10 and your input voltage is 2 volt, using the above equation your voltage output will be 20 voltspp but your supply is only +5 and -5 volts or equal to 10 volts, therefore the op-amp will saturate and will only have a saturation output voltage (Vsat) of 10 voltspp and the other ten volts will be clipped off or in short the output can never go up to to +5 V or go down to -5 V.


Voltage Follower

­- is one of the basic op-amp configurations, which the output is equal to the input Vout=Vin and will have a gain equal to one or called the unity gain.

Inverting Amplifier

- It is an op-amp configuration which the input is connected to the inverting input that the output is equal to the inverse of the input (-V-) multiplied with the gain and according to the derived equation we can vary the gain with the feedback resistor (Rf) over the input resistor (Ri), therefore overall equation is Vout= (Rf /Ri)(-V-)

Non-Inverting Amplifier

- It is the configuration where the input is connected to the non-inverting input and that

the output is equal to the input (V+) multiplied with the gain and same with the inverting amplifier the gain can be vary by the ratio of resistor connected plus 1’ for the for the non-inverting amplifier, therefore the overall equation is Vout= [1+(Rf /Ri)](V+)


Therefore, op-amp has three assumptions (high gain variation, infinite input and output impedance) used for analysis and to derived useful equation for a certain configuration and some limitations (slew rate and voltage saturation) for future analysis and op-amp designing purposes.

Also op-amp have three useful basic configuration (voltage follower, inverting and non-inverting amplifier) that is important foundation for the application of op-amps nowadays.