An adding unit adds {HEAD ~ the reference signal} to {TAIL ~ the filtered signal} to generate an output signal 
An adding unit adds { HEAD ~ the reference signal } to { TAIL ~ the filtered signal } to generate an output signal
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH