Added description

applications/lofar2/libraries/sdp/src/vhdl/node_sdp_filterbank.vhd

@@ -21,9 +21,16 @@
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 --
 -- Author: R. van der Walle
--- Purpose: .
+-- Purpose: 
+-- . Implements the functionality of the subband filterbank (Fsub) in the 
+--   LOFAR2 SDPFW design.
 -- Description:
--- .  
+-- . The subband filterbank seperates the incoming timestamped ADC samples into
+--   512 frequency bands called subbands. 
+-- . It implements a critically sampled poly-phase filterbank (PFB). The PFB consists of a 
+--   poly-phase finite impulse response (PFIR) filter per real input and a 
+--   complex fast fourier transform (FFT) per 2 real inputs. 
+-- . The number of points of the FFT is 1024.
 -- Remark:
 -- .
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