EXPERIMENT:-3 AIM: To study and perform summing amplifier



To study and perform summing amplifier.


Trainer board, DC power supplies, Oscilloscope


It is very common in circuit design to combine several signals into a single common signal. one good example of this is in the broadcast & recording industries. The typical modern music recording will require the use of perhaps dozen of microphones, yet the final product consists of only two stereo o/p signals. if signal are joined haphazardly, excessive interference, noise & distortion may result. the ideal summing amplifier would present each i/p with an isolated load not affected by other channels. The most common form of summing amplifier is really nothing more than an extension of the inverting voltage amplifier. Since the i/p to the op-amp is at virtual ground, it makes an ideal current-summing node. Instead of placing a single i/p resister at this point, several i/p resisters may be used. Each i/p source drives its own resister & there is very little effect from neighboring i/ps. The virtual ground is the key. The i/p impedance for the first channel is Ri1,&its voltage gain is –Rf/Ri1 ,in general for channel N, we have ZinN=RiN AvN=-Rf/RiN The o/p sigal is the sum of the all i/ps multiplied by their associated gains:

Vout =Vin1Av1+ Vin12Av2+…….. VinNAvN Which is written more conveniently as Vout= ∑ ViniAvi A summing applifier may have equal gain for each i/p channel.This is reffered to as an equal weighted configuration.