Added g_sepa_switch_en to support mitigation of quantization noise crosstalk...

Added g_sepa_switch_en to support mitigation of quantization noise crosstalk between two real inputs.

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

@@ -63,7 +63,8 @@ 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_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
   );
   port (
     clk      : in  std_logic;
@@ -87,12 +88,18 @@ architecture str of fft_r2_pipe is
   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 switch_val   : std_logic;
+
   signal data_re      : t_data_arr;
   signal data_im      : t_data_arr;
   signal last_re      : std_logic_vector(c_raw_dat_w-1 downto 0);
@@ -105,13 +112,39 @@ architecture str of fft_r2_pipe is
   signal raw_out_im   : std_logic_vector(c_raw_dat_w-1 downto 0);
   signal raw_out_val  : std_logic;
 
+  signal quant_re     : std_logic_vector(g_fft.out_dat_w-1 downto 0);
+  signal quant_im     : std_logic_vector(g_fft.out_dat_w-1 downto 0);
+  signal quant_val    : std_logic;
+
 begin
  
+  ------------------------------------------------------------------------------
+  -- Mitigate quantization noise crosstalk between two real inputs by negating
+  -- the inputs per lock in a random pattern, when g_fft.use_separate = TRUE.
+  ------------------------------------------------------------------------------
+
+  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
+  )
+  PORT MAP (
+    in_re      => in_re,
+    in_im      => in_im,
+    in_val     => in_val,
+    switch_en  => c_switch_en,
+    out_re     => switch_re,
+    out_im     => switch_im,
+    out_val    => switch_val,
+    clk        => clk,
+    rst        => rst
+  );
+
   -- Inputs
-  data_re( c_nof_stages) <= scale_and_resize_svec(in_re, c_in_scale_w, g_fft.stage_dat_w);
-  data_im( c_nof_stages) <= scale_and_resize_svec(in_im, c_in_scale_w, g_fft.stage_dat_w);
-  data_val(c_nof_stages) <= in_val;
-  
+  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;
+
   ------------------------------------------------------------------------------
   -- pipelined FFT stages
   ------------------------------------------------------------------------------
@@ -190,7 +223,7 @@ begin
    
   end generate;
   
-  no_reorder_no_generate : if(g_fft.use_separate=false and g_fft.use_reorder=false) generate 
+  no_reorder_no_seperate : if(g_fft.use_separate=false and g_fft.use_reorder=false) generate
     raw_out_re  <= last_re;
     raw_out_im  <= last_im;
     raw_out_val <= data_val(0);
@@ -215,7 +248,7 @@ begin
   port map (
     clk        => clk,
     in_dat     => raw_out_re,
-    out_dat    => out_re, 
+    out_dat    => quant_re,
     out_ovr    => open
   );       
 
@@ -235,7 +268,7 @@ begin
   port map (
     clk        => clk,
     in_dat     => raw_out_im,
-    out_dat    => out_im, 
+    out_dat    => quant_im,
     out_ovr    => open
   );
   
@@ -248,8 +281,26 @@ begin
     rst     => rst,
     clk     => clk,
     in_dat  => raw_out_val,
-    out_dat => out_val
+    out_dat => quant_val
   );
   
+  -- 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
+  )
+  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,
+    clk        => clk,
+    rst        => rst
+  );
+
 end str;