TDC7200_15 Datasheet, PDF (16/50 Pages) Texas Instruments – TDC7200 Time-to-Digital Converter for Time-of-Flight Applications in LIDAR,Magnetostrictive and Flow Meters

TDC7200
SNAS647C – FEBRUARY 2015 – REVISED AUGUST 2015
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Device Functional Modes (continued)
8.4.2.1.1 Calculating Time-of-Flight (Measurement Mode 1)
For measurement mode 1, the time-of-flight (TOF) between the START to the n^th STOP can be calculated using
Equation 1:
where
•
•
•
TOF_n [sec] = time-of-flight measurement from the START to the n^th STOP
TIME_n = n^th TIME measurement given by the TIME1 to TIME6 registers
normLSB [sec] = normalized LSB value from calibration
• CLOCKperiod [sec] = external CLOCK period
• CALIBRATION1 [count] = TDC count for first calibration cycle
• CALIBRATION2 [count] = TDC count for second calibration cycle
• CALIBRATION2_PERIODS = setting for the second calibration cycle; located in register CONFIG2
(1)
For example, assume the time-of-flight between the START to the 1^st STOP is desired, and the following
readouts were obtained:
• CALIBRATION2 = 21121 (decimal)
• CALIBRATION1 = 2110 (decimal)
• CALIBRATION2_PERIODS = 10
• CLOCK = 8MHz
• TIME1 = 4175 (decimal)
Therefore, the calculation for time-of-flight is:
• calCount = (21121 – 2110) / (10 – 1) = 2112.33
• normLSB = (1/8MHz) / (2112.33) = 5.917 x 10^-11
• TOF1 = (4175)(5.917 x 10^-11) = 247.061 ns
8.4.2.2 Measurement Mode 2
In measurement mode 2, the internal ring oscillator of the TDC7200 is used only to count fractional parts of the
total measured time. As shown in Figure 18, the internal ring oscillator starts counting from when it receives the
START signal until the first rising edge of the CLOCK. Then, the internal ring oscillator switches off, and the
Clock counter starts counting the clock cycles of the external CLOCK input until a STOP pulse is received. The
internal ring oscillator again starts counting from the STOP signal until the next rising edge of the CLOCK.
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