13-04-2013, 04:33 PM
OP AMP Applications – Adder, Subtractor, Comparator Circuits
AIM:
To design adder, subtractor and comparator for the given signals by using operational amplifier.
THEORY:
Adder:
A two input summing amplifier may be constructed using the inverting mode. The adder can be obtained by using either non-inverting mode or differential amplifier. Here the inverting mode is used. So the inputs are applied through resistors to the inverting terminal and non-inverting terminal is grounded. This is called “virtual ground”, i.e. the voltage at that terminal is zero. The gain of this summing amplifier is 1, any scale factor can be used for the inputs by selecting proper external resistors.
Subtractor:
A basic differential amplifier can be used as a subtractor as shown in the circuit diagram. In this circuit, input signals can be scaled to the desired values by selecting appropriate values for the resistors. When this is done, the circuit is referred to as scaling amplifier. However in this circuit all external resistors are equal in value. So the gain of amplifier is equal to one. The output voltage Vo is equal to the voltage applied to the non-inverting terminal minus the voltage applied to the inverting terminal; hence the circuit is called a subtractor.
Comparator:
The circuit diagram shows an op-amp used as a comparator. A fixed reference voltage Vref is applied to the (-) input, and the other time – varying signal voltage Vin is applied to the (+) input; Because of this arrangement, the circuit is called the non-inverting comparator. Depending upon the levels of Vin and Vref, the circuit produces output. In short, the comparator is a type of analog-to-digital converter. At any given time the output waveform shows whether Vin is greater or less than Vref. The comparator is sometimes also called a voltage-level detector because, for a desired value of Vref, the voltage level of the input Vin can be detected.
PROCEDURES:
Adder:
1. Connect the circuit as per the diagram shown in Fig.8.1.
2. Apply the supply voltages of +15V to pin7 and pin4 of IC741 respectively.
3. Apply the inputs V1 and V2 as shown in Fig. 8.1.
4. Apply two different signals (DC/AC ) to the inputs
5. Vary the input voltages and note down the corresponding output at pin 6 of the IC 741 adder circuit.
6. Notice that the output is equal to the sum of the two inputs.
B) Subtractor:
1. Connect the circuit as per the diagram shown in Fig.8.2.
2. Apply the supply voltages of +15V to pin7 and pin4 of IC741 respectively.
3 Apply the inputs V1 and V2 as shown in Fig.8.2.
4. Apply two different signals (DC/AC ) to the inputs
5. Vary the input voltages and note down the corresponding output at pin 6 of the IC 741 subtractor circuit.
6. Notice that the output is equal to the difference of the two inputs.