ADPD103BCPZ datasheet(19/53 Pages) AD

19 / 53 page

ADPD103

Data Sheet

Rev. B | Page 18 of 52

AFE OPERATION

The timing within each pulse burst is important for optimizing

the operation of theADPD103. Figure 17 shows the timing wave-

forms for a single time slot as an LED pulse response propagates

through the analog block of the AFE. The first graph, shown in

green, shows the ideal LED pulsed output. The filtered LED

response, shown in blue, shows the output of the analog integrator.

The third graph, shown in orange, illustrates an optimally placed

integration window. When programmed to the optimized value,

the full signal of the filtered LED response can be integrated. The

AFE integration window is then applied to the output of the band-

pass filter (BPF) and the result is sent to the ADC and summed

for N pulses. If theAFE window is not correctly sized or located, all

of the receive signal is not properly reported and system perfor-

mance is not optimal; therefore, it is important to verify proper

AFE position for every new hardware design or the LED width.

AFE INTEGRATION OFFSET ADJUSTMENT

TheAFE integration width must be equal or larger than the LED

width. As AFE width increases, the output noise increases and

the ability to suppress high frequency content from the environ-

ment decreases. It is therefore desirable to keep theAFE integration

width small. However, if the AFE width is too small, the LED

signal is attenuated. With most hardware selections, the AFE

width produces the optimal SNR at 1 μs more than the LED

width. After setting LED width, LED offset, and AFE width, the

ADC offset can then be optimized. The AFE offset must be

manually set such that the falling edge of the first segment of the

integration window matches the zero crossing of the filtered LED

response.

Figure 17. AFE Operation Diagram

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