TDC1011_15 Datasheet, PDF (26/49 Pages) Texas Instruments – TDC1011 Single Channel Ultrasonic Sensing Analog Front End (AFE) for Level Sensing,Concentration Sensing Applications

TDC1011
SNAS662 – JULY 2015
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Device Function Description (continued)
The length of the window when the comparators are able to qualify and generate STOP pulses is configured by
the TOF_TIMEOUT_CTRL field. A timeout will occur if the number of expected pulses is not received during the
allocated time and an error condition is reported to the ERROR_FLAGS register and the ERRB pin. It is possible
to disable the echo timeout (see TOF Measurement Interval). The TOF_TIMEOUT_CTRL field is located in the
TIMEOUT register.
See the Timing Control and Frequency Scaling (CLKIN) section for the definition of the time periods T0 and T1.
8.4.6.2 Standard TOF Measurement
TRIG
Analog OFF
Analog ON
Echo listen period
TX
(see Note A)
START
(see Note B)
RX
(see Note C)
STOP
READY
TRANSMIT
NUM_TX x T1
COMMON-MODE
128 x T0
AUTOZERO
2^{AUTOZERO_PERIOD} x 64 x T0
WAIT / ECHO LISTEN
(TIMING_REG ± 30) x 8 x T0
ECHO LISTEN
END READY
2^{TOF_TIMEOUT_CTRL} x 128 x T0 1 x T1
A. Clock alignment.
B. If NUM_TX < 3, the width of the START pulse is equal to NUM_TX × T1. If NUM_TX ≥ 3, the width of the START
pulse is equal to 3 × T1.
C. Common-mode settling time.
Figure 38. Standard TOF Measurement
In a standard time of flight measurement, the RX path is activated after the TX burst is completed, as shown in
Figure 38.
The standard TOF measurement sequence is enabled if the value of the TIMING_REG field is greater than or
equal to 30, and only if the FORCE_SHORT_TOF bit is set to 0. The TIMING_REG is a 10-bit wide field, with its
2 most significant bits located in the TOF_1 register, and the 8 least significant bits located in the TOF_0 register.
The FORCE_SHORT_TOF bit is located in the TIMEOUT register.
The comparator's input offset is stored in an internal capacitor during the auto-zero period. The length of the
auto-zero period is controlled by the AUTOZERO_PERIOD field in the CLOCK_RATE register.
The length of the window when the comparators are able to qualify and generate STOP pulses is configured by a
combination of the TIMING_REG field and the TOF_TIMEOUT_CTRL field. With the addition of the
TIMING_REG in the calculation, the standard TOF measurement allows for a longer wait time and listening
window. A timeout will occur if the number of expected pulses is not received during the allocated time and an
error condition is reported to the ERROR_FLAGS register and the ERRB pin. It is possible to disable the echo
timeout (see TOF Measurement Interval). The TOF_TIMEOUT_CTRL field is located in the TIMEOUT register.
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