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