6

l Position conversion formula (See Figure 3-2.)

The tetra-lateral type has four electrodes on the upper

surface, formed along each of the four edges. Photocur-

rent is divided into 4 parts through the same resistive

layer and extracted as position signals from the four

electrodes. Compared to the duo-lateral type, interaction

between the electrodes tends to occur near the corners

of the active area, making position distortion larger. But

the tetra-lateral type features an easy-to-apply reverse

bias voltage, small dark current and high-speed re-

sponse. The light input position for the tetra-lateral type

shown in Figure 3-4 is given by conversion formulas (3-

3) and (3-4), which are the same as for the duo-lateral

type.

3-2 Tetra-lateral type PSD

Figure 3-1 Structure chart, equivalent circuit (duo-lateral type PSD)

Figure 3-2 Active area chart (duo-lateral type PSD)

KPSDC0007EA

KPSDC0011EA

This is a variant of the tetra-lateral type PSD with an im-

proved active area and reduced interaction between elec-

trodes. In addition to the advantages of small dark current,

high-speed response and easy application of reverse bias

that the tetra-lateral type offers, the circumference distor-

tion has been greatly reduced. The light input position of

the pin-cushion type shown in Figure 3-6 is calculated from

conversion formulas (3-5) and (3-6), which are different

from those for the duo-lateral and tetra-lateral types.

l Position conversion formula (See Figure 3-4.)

l Position conversion formula (See Figure 3-6.)

3-3 Pin-cushion type (improved tetra-lateral type) PSD

Figure 3-3 Structure chart, equivalent circuit (tetra-lateral type PSD)

KPSDC0008EA

Figure 3-4 Active area chart (tetra-lateral type PSD)

KPSDC0011EA

=

........ (3-1)

=

........ (3-2)

Figure 3-5 Structure chart, equivalent circuit (pin-cushion type PSD)

Figure 3-6 Active area chart (pin-cushion type PSD)

KPSDC0012EA

KPSDC0009EA

=

........ (3-3)

=

........ (3-4)

=

........ (3-5)

=

........ (3-6)

Characteristic and use

x

y

ACTIVE AREA

x

y

ACTIVE AREA

x

y

ACTIVE AREA *

* Active area is specified at the inscribed square.

ANODE (

CATHODE (

Rp

PD Cj Rsh

P

D

Cj

Rsh

Rp

Rp

: CURRENT GENERATOR

: IDEAL DIODE

: JUNCTION CAPACITANCE

: SHUNT RESISTANCE

: POSITIONING RESISTANCE

CATHODE

PD

Cj

Rsh

P

D

Cj

Rsh

Rp

Rp

: CURRENT GENERATOR

: IDEAL DIODE

: JUNCTION CAPACITANCE

: SHUNT RESISTANCE

: POSITIONING RESISTANCE

Rp

P

D

Cj

Rsh

P

D

Cj

Rsh

Rp

ANODE (

ANODE (

ANODE (

ANODE (

CATHODE

: CURRENT GENERATOR

: IDEAL DIODE

: JUNCTION CAPACITANCE

: SHUNT RESISTANCE

: POSITIONING RESISTANCE