ADPD107 datasheet(25/66 Pages) AD

25 / 66 page

Data Sheet

ADPD105/ADPD106/ADPD107

Rev. A | Page 25 of 66

AFE OPERATION

The timing within each pulse burst is important for optimizing

the operation of the ADPD105/ADPD106/ADPD107. Figure 27

shows the timing waveforms 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 the AFE window is not

correctly sized or located, all of the receive signal is not properly

reported and system performance 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

The AFE 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 the AFE 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.

FOR N PULSES

ADC

CONVERSION

LED PULSE

FILTERED LED

RESPONSE

AFE INTEGRATION

WINDOW

TIME (µs)

CONTROLLED BY:

TIA SETTINGS

AFE SETTINGS

LED OFFSET

LED WIDTH

LED PERIOD

9µs + AFE OFFSET

N LED PULSES

LED DRIVE STRENGTH

ADC

CONVERSION

AFE

WIDTH

AFE

WIDTH

Figure 27. AFE Operation Diagram

ADPD107 датащи(PDF) 25 Page - Analog Devices

ADPD107 датащи(HTML) 25 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66

датащи скачать

ссылки URL