Data Sheet

ADPD2140

Rev. 0 | Page 7 of 12

THEORY OF OPERATION

ANGULAR RESPONSE

The ADPD2140 consists of arrays of silicon p-type, intrinsic,

n-type (PIN) photodiodes that provide a linear measurement of

incident infrared light angle. There are four separate channels on

the ADPD2140, each corresponding to one photodiode.

The ADPD2140 enables a 2-axis light angle measurement, in

both the x and y direction. To calculate angles in the x and y

direction with respect to the sensor use the four photodiode

(1)

(2)

The resulting quantities (x and y) are ratios related to angles

through a constant term, M. Calculate angles in the horizontal and

vertical direction by dividing x and y by the constant term, M

(see Table 1). Angles measured by the ADPD2140 are linear to ±5°

within an angular field of view of ±35° and zero crossing offset at

±5°, as seen in Figure 9. The directionality when using Equation 1

and Equation 2 is shown in Figure 10, which indicates positive

angles in the x and y directions.

ADPD2140

x

y

Figure 10. Directionality Response

The ADPD2140 is typically used in conjunction with a LED or

laser emitter operating at a near infrared wavelength. The

ADPD2140 provides light angle measurement without the need

for an external lens. An external lens is neither required nor

recommended for operation.

An integrated visible light blocking optical filter on the ADPD2140

provides built in rejection of unwanted visible ambient light

signals, such as sunlight and indoor lighting. Figure 7 shows the

combined responsivity of the ADPD2140 with the integrated

optical filter.

The low junction capacitance and low dark current of the

ADPD2140 allows optimal integration with the ADPD1080

photometric front end. This complete solution offers additional

ambient light rejection, low power operation, and analog-to-digital

conversion of the ADPD2140 analog signals.

TYPICAL CONNECTION DIAGRAM

Figure 11 shows the ADPD2140 connections with the ADPD1080

photometric front end. With up to eight photodiode input

channels, the ADPD1080 is a preferred choice for the analog

front end for interfacing with the ADPD2140. In this configuration,

the ADPD2140 and ADPD1080 solution can operate using

synchronous LED pulses to detect the angle of light reflected from

objects or used in ambient measurement mode to provide a

measure of the incident angle of an ambient or other unsyn-

chronized light source. For reference, the optimal choice of

reverse bias for typical operation with the ADPD2140 is 0.2 V.

GPIO0

GPIO1

DVDD

AGND

VREF

AVDD

PD1

YT YB XL

PDC

XR

ADPD2140

PD8

NIC

NIC

NIC

NIC

NIC

NIC

1

7

21

15

28

22

8

14

ADPD1080

TOP VIEW

(Not to Scale)

4.7µF

TO/FROM

HOST PROCESSOR

POWER-DOWN

CONTROL

0.1µF

0.1µF

0.1µF

1.8V

Figure 11. Typical Connection Diagram for the ADPD2140 and the

ADPD1080