Hi,
I want to use the multi-cycle averaging mode for TDC7200 in mode2. Can you please provide the example to calculate the TOF for multicycle averaging?
I have the TDC1000_TDC7200EVM and I am working on water flow meter application. I have implemented the equation for "Multi-Cycle Averaging" mentioned in "TDC7200 Time-to-Digital Converter for Time-of-Flight Applications in LIDAR, Magnetostrictive and Flow Meters" document.
TOFn = normLSB[TIME1 - TIME(n+1)] + [CLOCK_COUNTn >> log 2 (AVG_CYCLES)] x [CLOCKperiod]
I have used the example source for "demo4_tdc1000_tdc7200_usb" available after installing GUI.
The piece of code is:
/*********************************************************************************************************************************
#define AVG_CYCLES_BITS 0x38
uint8_t cnfg2;
uint8_t avg_count;
uint8_t buffer[50] = {0};
cnfg2 = TI_TDC7200_SPIByteReadReg(TI_TDC7200_CONFIG2_REG);
avg_count = (cnfg2 & AVG_CYCLES_BITS) >> 0x03;
//mreg[0] = Time1, mreg[1] = Clk_count1, mreg[2] = Time2
//mreg[3] = Clk_count2, mreg[4] = Time3, mreg[5] = Clk_count3
//mreg[6] = Time4, mreg[7] = Clk_count4, mreg[8] = Time5
//mreg[9] = Clk_count5, mreg[10] = Time6, mreg[11] = Calibration1
//mreg[12] = Calibration2
if (avg_count)
{
for(n=0; n < MAX_STOPS; n++)
{
start2stop[n] = norm_lsb * (meas_result_regrs[0] - meas_result_regrs[2*(n+1)]) +
tdc_clk_period * (( meas_result_regrs[2*(n+1)-1]) >> (int16_t)log2(avg_count) );
}
} else {
for(n=0; n < MAX_STOPS; n++)
{
start2stop[n] = norm_lsb * (meas_result_regrs[0] - meas_result_regrs[2*(n+1)]) +
tdc_clk_period * meas_result_regrs[2*(n+1)-1];
}
}
tof = start2stop[0];
/*********************************************************************************************************************************
but I get different values of TOF(in ns) for different measurement cycles as below for no flow.
Averaging cycle : 1 TOF : 37604.136719 ns
Averaging cycle : 2 TOF : 75176.921875 ns
Averaging cycle : 4 TOF : 75172.750000 ns
Averaging cycle : 8 TOF : 150298.187500 ns
Averaging cycle : 16 TOF : 150298.578125 ns
Averaging cycle : 32 TOF : 300548.906250 ns
Averaging cycle : 64 TOF : 601049.187500 ns
Averaging cycle : 128 TOF : 1202049.250000 ns
For no flow, these all values must be equal for different measurement cycles. But I am getting different values for different averaging cycles.
As per datasheet, AVG_CYCLES is
000: 1 Measurement Cycle only (no Multi-Cycle Averaging Mode)
001: 2 Measurement Cycles
010: 4 Measurement Cycles
011: 8 Measurement Cycles
100: 16 Measurement Cycles
101: 32 Measurement Cycles
110: 64 Measurement Cycles
111: 128 Measurement Cycles
If I select 8 Measurement Cycles, Should I have to pass AVG_CYCLES as 3 as per datasheet or 8 in the below equation TOF?
TOFn = normLSB[TIME1 - TIME(n+1)] + [CLOCK_COUNTn >> log 2 (AVG_CYCLES)] x [CLOCKperiod]
Thanks,
Khushbu
