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Added pre-emphasis to PWMDAC - works but not impressed

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This commit is contained in:
Niels Moseley 2017-10-26 21:29:34 +02:00
parent 42ad37a956
commit 1c293f13e8
2 changed files with 29 additions and 6 deletions
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33
verilog/pwmdac/pwmdac.v
View File

@ -30,11 +30,33 @@ module PWMDAC (
input signed [7:0] din;
output reg din_ack; // is high for 1 clock cycle after reading the din signal
// internal counter and data registers
reg signed [7:0] counter;
reg signed [7:0] data;
// pre-emphasis filter
reg signed [7:0] last_data;
reg signed [10:0] sum1r_d;
reg signed [10:0] sum1r;
wire signed [10:0] sum1;
wire signed [13:0] sum2;
reg signed [7:0] quantdata;
assign sum1 = $signed({data[7] ,{data, 2'b00}}) + data - $signed({last_data, 2'b00});
assign sum2 = $signed({sum1r[10],{sum1r, 2'b00}}) + sum1r - $signed({sum1r_d, 2'b00});
// output saturation
always @(*)
begin
if (sum2[13] ^ sum2[12] != 0)
begin
// saturation needed
quantdata = sum2[13] ? 8'h80 : 8'h7F;
end
else
quantdata = sum2[12:5];
end
always @(posedge clk, negedge rst_an)
begin
if (rst_an == 0)
@ -52,7 +74,7 @@ module PWMDAC (
// compare counter with data
// and set output accordingly.
if (data > counter)
if (quantdata > counter)
dacout <= 1;
else
dacout <= 0;
@ -61,13 +83,14 @@ module PWMDAC (
// counter is 127
if (counter == 8'h7F)
begin
sum1r <= sum1;
sum1r_d <= sum1r;
last_data <= data;
data <= din;
din_ack <= 1;
end
else
din_ack <= 0;
din_ack <= 0;
end
end
endmodule

2
verilog/source/source.v
View File

@ -71,7 +71,7 @@ module SOURCE (
// lfsr polynomial is X^17 + X^3 + 1
lfsr = {lfsr[15:0], lfsr[16] ^ lfsr[2]};
source_out <= lfsr[0] ? {2'b00, amplitude[14:1]} : {2'b11, (~amplitude[14:1])};
source_out <= lfsr[0] ? {1'b0, amplitude} : {1'b1, ~amplitude};
end
else
begin