Adding DC Offset in AC Signal
Category: Operational Amplifier
Designer: RANA MUHAMMAD ADNAN KHALIL
Notes
This circuit is designed and simulated in Proteus 7.10. In this circuit you will learn how operational amplifier (op-amp) is used to add DC voltage offset in AC input signal. 1. The op-amp used in this circuit is LM837, and it is in inverting summing amplifier configuration. 2. Before understanding this circuit, it is recommened to understand previous circuit "Op-Amp as Summing Amplifier" in Operational Amplifier category. 3. The positive input of op-amp is grounded via 10k ohm resistor (R1). 4. The two input signals are given via 10k ohm resistors R2, and R3. 5. The feedback resistor R4 of 10k ohm is used to maintain unity gain of each signal which is R4/R2 and R4/R3. 6. The output voltage is the sum of all the input signals present at inverting input of op-amp as shown in animation. 7. The output voltage signal is Vo = -(R4/R2 + R4/R3), the negative sign is because it is in inverting amplifier configuration. 8. When switch S1 is open then input signal at R2 is zero and only 3Vac signal is present at input resistor R3, the output is -3Vac. 9. When switch is closed, then dc input voltage of 3V will add, and output voltage become -(3Vdc+3Vac). That is the addition of 3Vdc offset in the ac signal. Which can be seen in animation. Application: 1. This circuit can be used to add dc voltage offset in ac signals. 2. This circuit is used to understand the concept of summing amplifier.