To configure op-amp in inverting and non-inverting amplifier mode and measure their gain.

Transcription

1 AIM: SUBJECT: ANALOG ELECTRONICS (2392) EXPERIMENT NO. 5 DATE : TITLE: TO CONFIGURE OP-AMP IN INVERTING AND NON- INVERTING AMPLIFIER MODE AND MEASURE THEIR GAIN. DOC. CODE : DIET/EE/3 rd SEM REV. NO. :./JUNE-25 To configure op-amp in inverting and non-inverting amplifier mode and measure their gain. APPARATUS: IC74 CONNECTING CORDS POWER SUPPLY FUNCTION GENERATOR C.R.O. THEORY: An ideal op-amp by itself is not a very useful device, since any finite non-zero input signal would result in infinite output. (For a real op-amp, the range of the output signal is limited by the positive and negative power-supply voltages.) However, by connecting external components to the ideal opamp, we can construct useful amplifier circuits. Figure shows basic op-amp circuit, the non-inverting amplifier. The triangular block symbol is used to represent an ideal op-amp. The input terminal marked with a + (corresponding to Vp) is called the non-inverting input; the input terminal marked with a (corresponding to Vn) is called the inverting input. Figure. Basic op-amp circuit Darshan Institute of Engineering And Technologies, Rajkot Page 4

2 Non-Inverting Amplifier An op-amp connected in a closed-loop configuration as a noninverting amplifier with a controlled amount of voltage gain is shown in Figure 2. The input signal is applied to the noninverting (+) input. The output is applied back to the inverting input through the feedback circuit (closed loop) formed by the input resistor Ri and the feedback resistor Rf. This creates negative feedback. Resistors Ri and Rf form a voltage-divider circuit, which reduces Vout and connects the reduced voltage Vf (Vn)to the inverting input. The feedback voltage is expressed as Figure.2: Noninverting amplifier To understand how the non-inverting amplifier circuit works, we need to derive a relationship between the input voltage Vin and the output voltage Vout. For an ideal op-amp, there is no loading effect at the input, as well input impedance is infinite. Therefore current entering into both the input terminals of OPAMP will have zero value. DESIGN EQUATION: - Applying Kirchhof s current law at the inverting terminal (at node B), But because of the infinite input impedance of the op-amp =. Therefore Darshan Institute of Engineering And Technologies, Rajkot Page 5

3 Inverting Amplifier An op-amp connected as an inverting amplifier with a controlled amount of voltage gain is shown in Figure 3. The input signal is applied through a series input resistor Ri to the inverting input. Also, the output is fed back through Rf to the same input. The noninverting (+) input is grounded. Figure.3: Inverting amplifier At this point, the ideal op-amp parameters mentioned earlier are useful in simplifying the analysis of this circuit. In particular, the concept of infinite input impedance is of great value. An infinite input impedance implies zero current at the inverting input. If there is zero current through the input impedance, then there must be no voltage drop between the inverting and noninverting inputs. This means that the voltage at the inverting input is zero because the noninverting (+) input is grounded. This zero voltage at the inverting input terminal is referred to as virtual ground. Darshan Institute of Engineering And Technologies, Rajkot Page 6

4 DESIGN EQUATION: - Since there is no current at the inverting input, the current through Ri and the current through Rf are equal, The voltage across Ri equals Vin because the resistor is connected to virtual ground at the inverting input of the op-amp. Therefore, Also, the voltage across Rf equals to Vout because of virtual ground, and therefore So using above equation, ( ) PROCEDURE:. Connect the circuit as shown in figure 2 (Non-inverting Mode) and provide necessary supply of +Vcc and Vcc. 2. Select the appropriate values of necessary resisters (Rf, Ri) and note it in observation table. 3. Using function generator, provide a supply Vin and note that it in observation table. 4. Now calculate Vout for respective circuits using CRO, and note in observation table. 5. Repeat the same process for different values of resisters. 6. Now compute Theoretical Vout and compare the same with practical Vout. 7. Calculate practical gain and Theoretical gain and mention it in observation table. 8. Repeat the same process for Figure 3. (inverting mode)) Darshan Institute of Engineering And Technologies, Rajkot Page 7

5 OBSEVATION TABLE SR. NO. MODE Vi R Rf Vout Gain Theoretical Practical Theoretical Practical. Inv. 2. Inv. 3. Non-Inv. 4. Non-Inv. CALCULATION: CONCLUSION: LAB-INCHARGE H.O.D Darshan Institute of Engineering And Technologies, Rajkot Page 8