– So far we have seen isolated transistor and diode circuits.
– No we will see how some ICs that use all the devices discussed so far are used for specific applications.
– Thus, we will deal with the external of the circuit, rather than the internal workings of it.
– We will talk, more specifically, about operational amplifiers, op-amps.
– These devices are the most widely used of all linear ICs.
– Early applications of amplifiers were to perform mathematical operations (addition, subtraction, integration, etc).
– Hence its denomination: operational.
– They were previously constructed, as were most electronic devices, with vacuum tubes and worked with high voltages.
– Currently they use low voltages and are packaged in ICs.
– It has two inputs: the inverting (-) and the noninverting (+) inputs.
– It has one output terminal.
– Typically two dc voltage supplies (one positive and one negative) drive an op-amp.
– Since they are always used, it is common to leave them out of the schematic.
– The symbol is shown below.
– Although such a device does not exist, it is easier to understand and analyze the ideal case.
– It has several characteristics:
i) Infinite voltage gain.
ii) Infinite bandwidth.
iii) Infinite input impedance (open circuit) so that id does not load the driving source.
iv) Zero output impedance.
– Vin appears between the two input terminals and the output voltage is Vout=AvVin.
– The practical op-amp has several limitations, such as limiting the peak-to-peak output to less than twice the supply voltage.
– Current is restricted by power dissipation, etc.
– However, the characteristics are still there: high voltage gain and input impedance, very low, output impedance, and wide bandwidth.
For Further Information:
- Op-amp Input Modes
- Negative Feedback
- Op-amps With Negative Feedback
- Effects of Negative Feedback
- Bias Current and Offset Voltage
- Open Loop Response
- Closed Loop Response