User Manual

11
Figure 8. Detailed Proximity Diagram
Proximity results are aected by three fundamental
factors: IR LED emission, IR reception, and environmental
factors, including target distance and surface reectivity.
The IR reception signal path begins with IR detection from
four [directional gesture] photodiodes and ends with the
8-bit proximity result in PDATA register. Signal from the
photodiodes is combined, amplied, and oset adjusted
to optimize performance. The same four photodiodes are
used for gesture operation as well as proximity operation.
Diodes are paired to form two signal paths: UP/RIGHT and
DOWN/LEFT. Regardless of pairing, any of the photodiodes
can be masked to exclude its contribution to the proxim-
ity result. Masking one of the paired diodes eectively
reduces the signal by half and causes the full-scale result
to be reduced from 255 to 127. To correct this reduction
in full-scale, the proximity gain compensation bit, PCMP,
can be set, returning F.S. to 255. Gain is adjustable from
1x to 8x using the PGAIN control bits. Oset correction or
cross-talk compensation is accomplished by adjustment
to the POFFSET_UR and POFSET_DL registers.The analog
circuitry of the device applies the oset value as a subtrac-
tion to the signal accumulation; therefore a positive oset
value has the eect of decreasing the results.
Optically, the IR emission appears as a pulse train. The
number of pulses is set by the PPULSE bits and the period
of each pulse is adjustable using the PPLEN bits. The in-
tensity of the IR emission is selectable using the LDRIVE
control bits; corresponding to four, factory calibrated,
current levels. If a higher intensity is required (E.g. longer
detection distance or device placement beneath dark
glass) then the LEDBOOST bit can be used to boost current
up to an additional 300%.
LED duty cycle and subsequent power consumption of
the integrated IR LED can be calculated using the follow-
ing table shown in Table 2, and equations. If proximity
events are separated by a wait time, as set by AWAIT and
WLONG, then the total LED o time must be increased by
the wait time.
Table 2. Approximate Proximity Timing
PPLEN
tINIT
(μs)
tLED ON
(μs)
tACC
(μs)
tCNVT
(μs)
4 μs 40.8 5.4 28.6 796.6
8 μs 44.9 9.5 36.73 796.6
16 μs 53.0 17.7 53.1 796.6
32 μs 69.4 34.0 85.7 796.6
t
PROX RESULT
= t
INIT
+ t
CNVT
+ PPULSE x t
ACC
t
TOTAL LED ON
= PPULSE x t
LED ON
t
TOTAL LED OFF
= t
PROX RESULT
– t
TOTAL LED ON
COLLECT
PROX
DATA
DATA TO
PDATA
PVALID = 1
PEN = 1
ENTER
PROX
PERSISTANCE++
PILT <=
PDATA
<= PIHT
N
Y
RESET
PERSISTANCE
PERSISTANCE
>=
PPERS
N
PINT = 1
Y
ASSERT INT PIN
PIEN ==1
?
Y
N
EXIT
PROXIMITY ENGINE
PVALID is automatically reset
whenever PDATA is read.
PINT must be manually reset
by a write-access to PICLEAR
or AICLEAR.