It can be obtained by applying more than one input to the basic integrator circuit. The circuit is shown in the Fig. 2.43.
The node B is ground hence node A is at virtual ground i.e. VA = 0. Hence we can write for various currents,
Integrating both sides,
Applying KCL at node A,
Substituting in (5),
The expression shows that the output is the integration of the sum of the input voltages. Hence the circuit is called as summing integrators.