Unveiling the input a neuron receives and distinguishing between excitation and inhibition provides information on local connectivity and brain operating conditions. However, experimental techniques do not allow direct recordings of synaptic inputs, and thus inverse methods are sought to retrieve synaptic currents/conductances from cell voltage. We propose a new method to estimate synaptic currents in neuron models using control theory (equivalent control and robust exact differentiation) and disentangle excitatory from inhibitory synaptic conductances.