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FPGA changes ISO14443B:

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* slightly increase reader field strength
* increase sensitivity when reading, allowing increased reading distance
This commit is contained in:
pwpiwi 2017-09-07 09:33:32 +02:00
commit d372569b45
3 changed files with 26 additions and 21 deletions
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31
fpga/hi_read_rx_xcorr.v
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@ -34,13 +34,13 @@ always @(negedge ck_1356megb)
(* clock_signal = "yes" *) reg adc_clk; // sample frequency, always 16 * fc
always @(ck_1356megb, xcorr_is_848, xcorr_quarter_freq, fc_div)
if (xcorr_is_848 & ~xcorr_quarter_freq) // fc = 847.5 kHz
if (xcorr_is_848 & ~xcorr_quarter_freq) // fc = 847.5 kHz, standard ISO14443B
adc_clk <= ck_1356megb;
else if (~xcorr_is_848 & ~xcorr_quarter_freq) // fc = 424.25 kHz
else if (~xcorr_is_848 & ~xcorr_quarter_freq) // fc = 423.75 kHz
adc_clk <= fc_div[0];
else if (xcorr_is_848 & xcorr_quarter_freq) // fc = 212.125 kHz
else if (xcorr_is_848 & xcorr_quarter_freq) // fc = 211.875 kHz
adc_clk <= fc_div[1];
else // fc = 106.0625 kHz
else // fc = 105.9375 kHz
adc_clk <= fc_div[2];
// When we're a reader, we just need to do the BPSK demod; but when we're an
@ -69,13 +69,16 @@ begin
end
end
// Let us report a correlation every 4 subcarrier cycles, or 4*16 samples,
// Let us report a correlation every 4 subcarrier cycles, or 4*16=64 samples,
// so we need a 6-bit counter.
reg [5:0] corr_i_cnt;
// And a couple of registers in which to accumulate the correlations.
// we would add/sub at most 32 times adc_d, the signed result can be held in 14 bits.
reg signed [13:0] corr_i_accum;
reg signed [13:0] corr_q_accum;
// We would add at most 32 times the difference between unmodulated and modulated signal. It should
// be safe to assume that a tag will not be able to modulate the carrier signal by more than 25%.
// 32 * 255 * 0,25 = 2040, which can be held in 11 bits. Add 1 bit for sign.
reg signed [11:0] corr_i_accum;
reg signed [11:0] corr_q_accum;
// we will report maximum 8 significant bits
reg signed [7:0] corr_i_out;
reg signed [7:0] corr_q_out;
// clock and frame signal for communication to ARM
@ -99,16 +102,16 @@ begin
begin
if(snoop)
begin
// Send only 7 most significant bits of tag signal (signed), LSB is reader signal:
corr_i_out <= {corr_i_accum[13:7], after_hysteresis_prev_prev};
corr_q_out <= {corr_q_accum[13:7], after_hysteresis_prev};
// Send 7 most significant bits of tag signal (signed), plus 1 bit reader signal
corr_i_out <= {corr_i_accum[11:5], after_hysteresis_prev_prev};
corr_q_out <= {corr_q_accum[11:5], after_hysteresis_prev};
after_hysteresis_prev_prev <= after_hysteresis;
end
else
begin
// 8 most significant bits of tag signal
corr_i_out <= corr_i_accum[13:6];
corr_q_out <= corr_q_accum[13:6];
// 8 bits of tag signal
corr_i_out <= corr_i_accum[11:4];
corr_q_out <= corr_q_accum[11:4];
end
corr_i_accum <= adc_d;