We implement directly equation (5) by the structure described in figure 1. This implementation is modular since the LIF of order N is deduced from the LIF of order N-1 just by connecting a new module to it. Each module involves basically two multiplications and two additions. The complete structure for a LIF of order N has N modules. In a delay varying environment, updating the delay costs one additional addition and multiplication for each module. Notice that in time-varying application, this structure implies fewer arithmetic operations than any other known structure. For instance, the modified Farrow structure ([Farrow, 1988]) of a LIF of order 3 involves 11 additions and 9 multiplications whereas our modular structure involves only only 8 additions and 5 multiplications.
: Modular LIF structure with 
