Page 32 ams Datasheet
Document Feedback [v1-06] 2015-Apr-09
TMG3993 − Detailed Description
During operation, the Gesture engine is entered when Gesture
Enable, GEN, and Gesture Mode bit, GMODE, are both set.
GMODE can be set/reset manually, via I2C, or becomes set when
proximity results, in PDATA, are greater or equal to the gesture
proximity entry threshold, GPENTH. If the Gesture Enter Always,
GENAL, bit is set, then any PDATA result will cause an entry into
the gesture engine. Exit of the gesture engine will not occur
until GMODE is reset to zero. During normal operation, GMODE
is reset when all 4-bytes of a gesture dataset fall below the exit
threshold, GEXTH, for GEXPERS times. This exit condition is also
influenced by the gesture exit mask, GEXMSK, which includes
all non-masked datum (i.e. singular 1-byte N, S, W, E points). To
prevent premature exit, a persistence filter is also included; exit
will only occur if a consecutive number of below-threshold
results is greater or equal to the persistence value, GEXPERS.
Each dataset result that is above-threshold will reset the
persistence count. False or incomplete gestures (engine entry
and exit without GVALID transitioning high) will not generate
a gesture interrupt, GINT, and FIFO data will automatically be
purged.
During North-South-West-East Gesture operation, the IR
reception signal path begins with IR detection at the
photodiodes and ends with the four, 8-bit gesture results
loading into the FIFO. Each 8-bit result corresponds to the
amount of IR energy measured by each photodiode sensor.
Signal from the four photodiodes is amplified, and offset
adjusted to optimize performance.
Photodiodes are paired to form two signal paths: North/South
and West/East. Photodiode pairs can be masked to exclude its
results from the gesture FIFO data. For example, if only
North-South motions detection is required then the gesture
dimension control bits, GDIMS, may be set to 0x01. FIFO data
will be zero for East/West results and accumulation/ADC
integration time will be approximately halved. Gain is
adjustable from 1x to 8x using the GGAIN control bits. Offset
correction is accomplished by individual adjustment to
GOFFSET_N, GOFFSET_S, GOFFSET_W, GOFFSET_E registers
which improves cross-talk performance. The analog circuitry of
the device applies offset values as a subtraction to the signal
accumulation; therefore a positive offset value has the effect of
decreasing the results.
Optically, the IR emission appears as a pulse train. The number
of pulses is set by the GPULSE bits and the period of each pulse
is adjustable using the GPLEN bits. Pulse train repetition (I.e. the
circular flow of operation inside the gesture state machine) can
be delayed by setting a non-zero value in the gesture wait time
bits, GWTIME. The inclusion of a wait state reduces both the
power consumption and the data rate.
The intensity of the IR emission is selectable using the GLDRIVE
control bits. These bits correspond to four factory calibrated
current levels. If a higher intensity is required (E.g. longer