OP-AMP Application

OPAMP applications:

1. Amplification

The amplified output signal from the OpAmp is the difference between the two input signals.

The diagram shown above is the Op-Amp simple connection. If both the inputs are supplied with the same voltage, the OpAmp will then takes the difference between the two voltages and it will be zero. The Op Amp will multiply this difference with its gain 1,000,000 so the output voltage is again zero. Suppose 2 volts is given to one input and 1 volt in the other, then the OpAmp will take a difference between these two inputs and multiply with the gain. That is 1 volt x 1,000,000. But this gain is very high so to reduce the gain, feedback from the output to the input is usually connected through a resistor.

Inverting Amplifier:

The circuit shown above is an inverting amplifier with the Non-inverting input connected to the ground. Two resistors R1 and R2 are connected in the circuit in such a manner that R1 feeds the input signal and R2 returns the output to the Inverting input.  When the input signal is connected to a positive voltage the output will be negative and vice versa. The voltage change at the output relative to the input and also it depends on the ratio of the resistors R1 and R2. R1 is selected as 1KΩ and R2 as 10KΩ. If the input receives 1 volt, then there will be 1 mA current through R1 and the output will have to become – 10 volts in order to supply 1 mA current through R2 and to maintain zero voltage at the Inverting input. Here the voltage gain is R2/R1. That is 10KΩ/1KΩ = 10kΩ

Non-inverting Amplifier:

The circuit shown above is a connection of Noninverting amplifier. Here the Non-inverting input receives the positive or negative signal while the Inverting input is connected between R2 and R1. When the input signal moves either positive or negative, the output will be in phase and keeps the voltage at the inverting input same as that of Non inverting input. The voltage gain, in this case, will be always higher than 1 so (1+R2/R1).

2. Voltage Follower

The circuit above is a voltage follower. Here it provides high input impedance, low output impedance. When the input voltage changes, the output, and the inverting input will change equally.

3. Comparator

Operational amplifier work as a comparator when it compares the voltage applied at one input to the voltage applied at the other input. Any difference between the voltages ever either it is small or large it drives the op-amp into saturation. When the voltages supplied to both the inputs are of the same magnitude with the same polarity, then the op-amp output is 0Volts.

4.      Phase Shifter

Op-Amp is used for direct coupling procedure applications and as a result, DC voltage level at the emitter terminal increases from phase to phase. This rapidly increasing DC level is caused to shift the operating point of the further stages. This is to move down the increasing voltage swing and changes, this phase shifter is applied. The phase shifter performs by adding a DC voltage level to the output of fall stage to pass the output to a ground level.

5.      Scale Changer

Op-Amp working as a scale changer through small signals when we apply constant-gain in both inverting and non-inverting amplifiers.

Non-inverting terminal is grounded whereas R₁ connected the input signal v₁ to the inverting input. A feedback resistor R_f is here in this circuit connected from output to the inverting input. The closed loop gain of the inverting amplifier works based on the ratio of the two external resistors R₁ and R_f and in this situation Op-Amp acts as a negative scalar where it multiplies the input by a negative constant factor. For positive scalar, circuit is achieved by applying negative feedback.

6.       Adder or Summing Amplifier

Op-amp can be used in applications where it sums the input voltage of two or more sources into a single output voltage. As shown in the circuit diagram op-amp as an adder or summing amplifier. The many input voltages are applied to the inverting terminal of the op-amp. Here inverting terminal is grounded. The output voltage produced is proportional to the sum of the input voltages.

7.      Differentiator

Op-amp can be used as a differentiator application where the output is the first derivative of the input signal. The following equation gives the relation between the input signal and the output signal.

As you can observe that the output voltage is a first derivative of the input voltage.

8.      Integrator

Op-amp is used as an integrator application also. The integrator op-amp produces an output that is proportional to the amplitude of the input signal as well as the duration of the input signal so it works as an integrator. In place of a resistor in the feedback loop, we connected capacitor. It is able to perform the mathematical operation of integration as the output varies with the input and duration of the signal.

9.       Voltage to Current Converter

An op-amp in voltage to current converter a negative feedback is generally as shown in below circuit diagram. Here voltage is applied to the non-inverting terminal and the output is feedback to the inverting terminal as shown. It is also grounded using a resistor.

10. Current to Voltage Converter

Op-amp can be used as a current to voltage converter by using a very simple circuit as shown below. In this circuit feedback resistance connected to the output of the op-amp. The current source is connected to the inverting terminal and the non-inverting terminal is connected to ground. Here we obtained the output voltage proportional to the input current. As an ideal op-amp has infinite resistance or impedance, the current cannot flow through the op-amp. So the current flows through the feedback resistance and the voltage across it totally depends on the current source.

11. Logarithmic Amplifier

The logarithmic amplifier using op-amp is made by connecting a diode in place of a resistance in the feedback loop. The non-inverting terminal is connected to ground and the input voltage is connected to the inverting terminal. Here the output voltage is proportional to the logarithm of the input voltage and so it can be used as a logarithmic amplifier.

12.  Half Wave Rectifier

The circuit diagram is shown in above figure use op-amp as a half wave rectifier. During the positive cycle of voltage, diode D₂ is reversed biased and do not conduct as a result the positive signal is inverted by the op-amp. So there will be no output generated. However, during the negative cycle of the input voltage, the diode D₂ becomes forward biased and conducts.

13.  Peak Detector

The circuit above shows op-amp working as a peak detector. The circuit uses a diode and a capacitor as shown. When V_out is more as compare to V_in, the output is positive and the diode starts conducting. Whereas when V_out is less as compare to V_in, the diode is reversed biased and does not conduct and the capacitor charges to the most positive value.