Data Sheet

ADPD2140W

Rev. 0 | Page 7 of 10

THEORY OF OPERATION

ANGULAR RESPONSE

The ADPD2140W 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 ADPD2140W, each corresponding to one photodiode.

The ADPD2140W 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. These quantities can be seen as a function

of incident light angle in Figure 4. The directionality when using

Equation 1 and Equation 2 is shown in Figure 10, which indicates

positive angles in the x and y directions.

ADPD2140W

+x

PIN 1

+y

Figure 10. Directionality Response As Viewed from Top

The ADPD2140W is typically used in conjunction with an LED

or laser emitter operating at a near infrared wavelength. The

ADPD2140W 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

ADPD2140W provides built in rejection of unwanted visible

ambient light signals, such as sunlight and indoor lighting.

Figure 7 shows the responsivity of the ADPD2140W with its

integrated optical filter.

The low diode capacitance and low dark current of the

ADPD2140W 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 ADPD2140W analog signals.

TYPICAL CONNECTION DIAGRAM

Figure 11 shows the ADPD2140W 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 ADPD2140W. In this

configuration, the ADPD2140W and ADPD1080 solution can

operate using synchronous LED pulses to detect the angle of light

reflected from objects or be used in ambient measurement mode

to provide a measure of the incident angle of an ambient or

other unsynchronized light source.

or XR) and the cathode (PDC) is denoted as positive from an

positive from the cathode to an anode. For reference, the optimal

choice of reverse bias for typical operation with the ADPD2140W

GPIO0

GPIO1

DVDD

AGND

VREF

AVDD

PD1

YT YB XL

PDC

XR

ADPD2140W

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

1µF

1.8V

Figure 11. Typical Connection Diagram for the ADPD2140W and the

ADPD1080