Use c_switch_dat_w = g_fft.in_dat_w + 1 to fit negate of most negative input value.

libraries/dsp/fft/src/vhdl/fft_r2_pipe.vhd

@@ -63,8 +63,7 @@ entity fft_r2_pipe is
     g_pipeline           : t_fft_pipeline := c_fft_pipeline; -- generics for pipelining in each stage, defined in rTwoSDF_lib.rTwoSDFPkg
     g_dont_flip_channels : boolean := false;       -- generic to prevent re-ordering of the channels
     g_r2_mul_extra_w     : natural := 0;           -- extra bits at rTwoWMul output in rTwoSDFStage to improve rTwoSDFStage output requantization
-    g_sepa_extra_w       : natural := 0;           -- extra LSbits in output of last rTwoSDFStage to improve two real separate requantization
-    g_sepa_switch_en     : boolean := false        -- when true apply switch/unswitch to two real inputs to mitigate quantization crosstalk
+    g_sepa_extra_w       : natural := 0            -- extra LSbits in output of last rTwoSDFStage to improve two real separate requantization
   );
   port (
     clk      : in  std_logic;
@@ -82,22 +81,28 @@ architecture str of fft_r2_pipe is
 
   constant c_pipeline_remove_lsb : natural := 0;
   
+  constant c_switch_en          : boolean := g_fft.use_separate;  -- default do apply switch/unswitch per real input to mitigate quantization crosstalk
+  constant c_switch_sz_w        : natural := ceil_log2(g_fft.nof_points) + g_fft.nof_chan;
+  constant c_switch_dat_w       : natural := g_fft.in_dat_w + 1;  -- add 1 extra bit to fit negation of most negative value per real input switch function
+  constant c_unswitch_dat_w     : natural := g_fft.out_dat_w;  -- no need for extra bit, because most negative value cannot occur in output
   constant c_nof_stages         : natural := ceil_log2(g_fft.nof_points);
   constant c_stage_offset       : natural := true_log2(g_fft.wb_factor);                         -- Stage offset is required for twiddle generation in wideband fft
   constant c_in_scale_w         : natural := g_fft.stage_dat_w - g_fft.in_dat_w - sel_a_b(g_fft.guard_enable, g_fft.guard_w, 0);              
   constant c_out_scale_w        : integer := g_fft.stage_dat_w - g_fft.out_dat_w - g_fft.out_gain_w;  -- Estimate number of LSBs to throw throw away when > 0 or insert when < 0
   constant c_raw_dat_extra_w    : natural := sel_a_b(g_fft.use_separate, g_sepa_extra_w, 0);
   constant c_raw_dat_w          : natural := g_fft.stage_dat_w + c_raw_dat_extra_w;
-  constant c_sepa_mitigate      : std_logic := sel_a_b(g_fft.use_separate, '1', '0');  -- apply switch/unswitch to two real inputs to mitigate quantization crosstalk
-  constant c_switch_en          : std_logic := sel_a_b(g_sepa_switch_en, c_sepa_mitigate, '0');
 
   -- number the stage instances from c_nof_stages:1
   -- . the data input for the first stage has index c_nof_stages
   -- . the data output of the last stage has index 0
   type t_data_arr is array(c_nof_stages downto 0) of std_logic_vector(g_fft.stage_dat_w-1 downto 0);
 
-  signal switch_re    : std_logic_vector(g_fft.in_dat_w-1 downto 0);
-  signal switch_im    : std_logic_vector(g_fft.in_dat_w-1 downto 0);
+  signal in_dat_re    : std_logic_vector(c_switch_dat_w-1 downto 0);
+  signal in_dat_im    : std_logic_vector(c_switch_dat_w-1 downto 0);
+  signal in_dat_val   : std_logic;
+
+  signal switch_re    : std_logic_vector(c_switch_dat_w-1 downto 0);
+  signal switch_im    : std_logic_vector(c_switch_dat_w-1 downto 0);
   signal switch_val   : std_logic;
 
   signal data_re      : t_data_arr;
@@ -123,16 +128,21 @@ begin
   -- the inputs per lock in a random pattern, when g_fft.use_separate = TRUE.
   ------------------------------------------------------------------------------
 
+  -- Inputs
+  in_dat_re  <= RESIZE_SVEC(in_re, c_switch_dat_w);
+  in_dat_im  <= RESIZE_SVEC(in_im, c_switch_dat_w);
+  in_dat_val <= in_val;
+
   u_switch : ENTITY work.fft_switch
   GENERIC MAP (
-    g_fft_sz_w  => ceil_log2(g_fft.nof_points),
-    g_dat_w     => g_fft.in_dat_w
+    g_switch_en => c_switch_en,
+    g_fft_sz_w  => c_switch_sz_w,
+    g_dat_w     => c_switch_dat_w
   )
   PORT MAP (
-    in_re      => in_re,
-    in_im      => in_im,
-    in_val     => in_val,
-    switch_en  => c_switch_en,
+    in_re      => in_dat_re,
+    in_im      => in_dat_im,
+    in_val     => in_dat_val,
     out_re     => switch_re,
     out_im     => switch_im,
     out_val    => switch_val,
@@ -140,7 +150,6 @@ begin
     rst        => rst
   );
 
-  -- Inputs
   data_re( c_nof_stages) <= scale_and_resize_svec(switch_re, c_in_scale_w, g_fft.stage_dat_w);
   data_im( c_nof_stages) <= scale_and_resize_svec(switch_im, c_in_scale_w, g_fft.stage_dat_w);
   data_val(c_nof_stages) <= switch_val;
@@ -188,12 +197,11 @@ begin
     in_re     => data_re(1),
     in_im     => data_im(1),
     in_val    => data_val(1),
-    out_re    => last_re,
-    out_im    => last_im,
+    out_re    => last_re,  -- = data_re(0), but may instead have c_raw_dat_w bits
+    out_im    => last_im,  -- = data_im(0), but may instead have c_raw_dat_w bits
     out_val   => data_val(0)
   );
 
-
   ------------------------------------------------------------------------------
   -- Optional output reorder and separation
   ------------------------------------------------------------------------------
@@ -287,14 +295,14 @@ begin
   -- Undo input random negation of u_switch at output when g_fft.use_separate = TRUE
   u_unswitch : ENTITY work.fft_unswitch
   GENERIC MAP (
-    g_fft_sz_w  => ceil_log2(g_fft.nof_points),
-    g_dat_w     => g_fft.out_dat_w
+    g_switch_en => c_switch_en,
+    g_fft_sz_w  => c_switch_sz_w,
+    g_dat_w     => c_unswitch_dat_w
   )
   PORT MAP (
     in_re      => quant_re,
     in_im      => quant_im,
     in_val     => quant_val,
-    switch_en  => c_switch_en,
     out_re     => out_re,
     out_im     => out_im,
     out_val    => out_val,