Other Parts Discussed in Thread: TDC7200
I set Vthld to -35 mV and use the combination of TDC1000 and TDC7200 to sense ultrasonic waves.
My understanding is that when the COMPIN signal passes through VCOM and Vthld, STOP pulses should be generated.
Here is my question: When operating with the settings of Standard TOF Measurement,
T1 = 1 MHz, T0 = 8 MHz, and AUTOZERO_PERIOD = 0, the time from TRIG to ECHO_LISTEN should be 27 µs,
but STOP pulses are not generated until after 30 µs.
※ READY = 3 µs (3 × T0), TRANSMIT = 0 µs (since TX is input externally), COMMON-MODE = 16 µs (128 × T0), AUTOZERO = 8 µs (2^0 × 64 × T0)
Even though the COMPIN signal is clearly going below Vthld, STOP pulses are not generated until after 30 µs from TRIG.
The minimum time from TRIG to ECHO_LISTEN is theoretically expected to be 27 µs, so why are STOP pulses not generated until after 30 µs?
CH2 = TRIG
CH3 = COMPIN signal
CH4 = STOP pulse
TDC1000 Figure 8-24. Standard TOF Measurement
Measurement result
