TMG3992 datasheet(33/96 Pages) OSRAM

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[v1-06] 2018-Feb-27

TMG3992 − Detailed Description

Gesture results are affected by three fundamental factors: IR

LED emission, IR reception, and environmental factors,

including motion.

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.

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