S8361_技术文档

S OLID

STATE ^{DIVIS IO N}

PSD

(

)

POSITION SENSITIVE DETECTOR

What is PSD?

Various methods are available for detecting the position of incident light. These

include methods using small discrete detector arrays or multi-element sensors such

as CCD sensors. In contrast to these sensors, PSDs (Position Sensitive Detectors)

are comprised of a monolithic detector with no discrete elements and provide

continuous position data by making use of the surface resistance of the photodiode.

PSDs offer advantages such as high position resolution, high-speed response and

reliability.

Features of PSD

· Excellent position resolution

· Wide spectral response range

· High-speed response

· Detects center-of-gravity position of spot light

· Simultaneously detects light intensity and center-of-gravity position of spot light

· High reliability

Applications of PSD

· Position and angle sensing

· Distortion and vibration measurements

· Lens reflection and refraction measurements

· Laser displacement sensing

· Optical remote control

· Optical range finders

· Optical switches

· Camera auto focusing

CONTENTS

Selection guide ················································································································· 1

Description of terms ········································································································· 4

Characteristic and use ······································································································ 5

1. Basic Principle ············································································································

2. One-dimensional PSD ·································································································

3. Two-dimensional PSD ·································································································

4. Position detection error ·······························································································

5. Position resolution ·······································································································

5

7

8

6. Response speed ········································································································· 10

7. Saturation photocurrent ································································································ 11

Selection guide

PSD (Position Sensitive Detector) is an optoelectronic position sensor utiliz-

ing photodiode surface resistance. Unlike discrete element detectors such as

CCD, PSD provides continuous position data (X or Y coordinate data) and

features high position resolution and high-speed response.

One-dimensional PSD

······························

1

2

7

3

4

5

11

14

Hamamatsu provides various types of one-dimensional PSDs designed

for high-precision distance measurement such as displacement meters,

camera auto focusing and optical switches. Our product line includes a

visible-cut type for near infrared detection, a red sensitivity enhanced type

for red light detection, a microscopic spot light (LD beam, etc.) detection

type, and a long, narrow type with an active area exceeding 30 mm.

15

12 13

6

8

9

10

Interelectrode

Spectral response

range

resistance

Vb=0.1 V

(kΩ)

Active area

Resistance length

Type No.

Package

(mm)

1 × 1

1 × 1.2

(mm)

1

1.2

(nm)

760 to 1100

320 to 1100

760 to 1060

320 to 1060

760 to 1060

760 to 1100

320 to 1100

760 to 1100

320 to 1100

760 to 1100

440 to 1100

400 to 1100

760 to 1100

320 to 1100

760 to 1100

320 to 1100

760 to 1100

320 to 1100

760 to 1100

320 to 1100

700 to 1100

S6407

S6515

200

140

1

2

3

S4580-04

S4580-06

S4581-04

S4581-06

S3271-05

S4582-04

S4582-06

S3272-05

S4583-04

S4583-06

S3273-05

S7879

S8361 *

S4584-04

S4584-06

S3274-05

S7105-04

S7105-06

S7105-05

S5629

0.8 × 1.5

1.5

140

2

140

400

140

400

140

400

110

3

1 × 2

2

4

2

3

1 × 2.5

1 × 3

2.5

3

4

2

3

Plastic

4

5

6

2

140

400

140

400

50

3

1 × 3.5

1 × 4.2

1 × 6

3.5

4.2

6

4

7

8

7

9

10

9

S5629-01

S5629-02

S3979

S3931

S3932

300

140

50

20

11

12

13

14

15

1 × 3

1 × 6

1 × 12

2.5 × 34

1 × 37

3

6

12

34

37

TO-5

Ceramic

S1352

S3270

15

* High sensitivity in the red region type

Works with microscopic spot light detection.

1

Selection guide

4

7

Two-dimensional PSD

······························

6

Two-dimensional PSDs are classified by structure into a tetra-lateral type and a

duo-lateral type. The tetra-lateral type features high-speed response and low

dark current. The duo-lateral type offers small position detection error and high

position resolution. A pin-cushion type, which is a tetra-lateral type with

improved active area and electrodes, has a position detection error as small as

the duo-lateral type while still having the advantages of the tetra-lateral type.

1

2

3

8

9

5

(Typ.)

Interelectrode

Resistance

length

Spectral response

range

Active area

resistance

Vb=0.1 V

(kΩ)

Type No.

Structure

Package

Ceramic

(mm)

(nm)

S1200

1

2

3

4

Tetra-lateral type

Duo-lateral type

320 to 1060

320 to 1100

13 × 13

10

S1300

S1880

S1881

12 × 12

22 × 22

14 × 14

26 × 26

10

Pin-cushion type

(improved tetra-lateral type)

320 to 1060

320 to 1100

Ceramic

Metal

Pin-cushion type

(improved tetra-lateral type)

5

S2044

4.7 × 4.7

5.7 × 5.7

10

6

7

8

9

S5990-01

S5991-01

S7848

4 × 4

9 × 9

4.5 × 4.5

10 × 10

7

Ceramic

chip carrier

Pin-cushion type

(improved tetra-lateral type)

760 to 1100

320 to 1100

2 × 2

100

Plastic

Tetra-lateral type

S7848-01

Works with microscopic spot light detection

Examples of position detectability (Ta=25 ˚C, λ=890 nm, spot light size: φ200 µm)

S1200

S1300

S1880

LINE INTERVAL: 1 mm

KPSDC0017EA

KPSDC0015EA

KPSDC0020EA

S5991-01

S7848

LINE INTERVAL: 1 mm

LINE INTERVAL: 0.2 mm

KPSDC0065EA

KPSDC0084EA

128-element PSD array

S5681 is a 128-element PSD linear array. By scanning a slit-form light beam right and left based

···························································

on the slit light projection method, S5681 allows measuring a 3-D shape of the object.

(Typ.)

Interelectrode resistance Spectral response

Resistance length

(mm)

Active area

(mm)

Vb=0.1 V

range

(nm)

Type No.

S5681

Package

(kΩ)

0.025 × 6.375/

128 elements

Ceramic

6.375

100

320 to 1100

2

Selection guide

PSD signal processing circuit

Features

No complicated adjustments required

Position measurements can be made by just connecting to a PSD and power supply (±15 V).

The position (mm) of a spot light from the PSD center is obtained as an output voltage (V).

(except C3683-01)

Stable position detection

Accurate position data can be detected independent of incident light intensity.

Compact size

Head amplifiers, signal addition/subtraction circuits, and analog divider are mounted on a

compact PC board.

···············································

DC signal processing circuit

Designed specifically for DC light detection.

Dimensional outline

(mm)

PSD type

1-D PSD

Type No.

C3683-01

66 × 56 × 15

90 × 65 × 15

92 × 70 × 15

90 × 65 × 15

C4674

C4757

C4758

Pin-cushion type 2-D PSD

Duo-lateral type 2-D PSD

Tetra-lateral type 2-D PSD

AC signal processing circuit ···············································

Designed specifically for pulse (AC) signal detection.

Has a synchronous circuit, S/H (sample & hold) circuit and LED driver circuit.

Use of a pulse-driven LED ensures reliable operation even under background light.

LED repetition frequency *

Dimensional outline

(mm)

PSD type

Type No.

(kHz)

C5923

C7563

1-D PSD

3.3

110 × 75 × 15

Pin-cushion type 2-D PSD

0.33

* Can not be modulated.

3

Description of terms

1. Spectral response

7. Interelectrode resistance: Rie

The photocurrent produced by a given level of incident

light varies with the wavelength. This relation between

the photoelectric sensitivity and wavelength is referred to

as the spectral response characteristic and is expressed

in terms of photo sensitivity, quantum efficiency, etc.

This is the resistance between opposing electrodes in a

dark state. The interelectrode resistance is an important

factor that determines the response speed, position res-

olution and saturation photocurrent.

The interelectrode resistance is measured with 0.1 V ap-

plied across the opposing electrodes and the common

electrode left open. When measuring the interelectrode re-

sistance of two-dimensional PSDs, the output electrodes

other than the opposing electrodes under measurement

are left open.

2. Photo sensitivity: S

This measure of sensitivity is the ratio of radiant energy

expressed in watts (W) incident on the device, to the re-

sulting photocurrent expressed in amperes (A). It may be

represented as either an absolute sensitivity (A/W) or as

a relative sensitivity normalized for the sensitivity at the

peak wavelength, usually expressed in percent (%) with

respect to the peak value. For the purpose of our PSD

data sheets (separately available), the photo sensitivity

is represented as the absolute sensitivity, and the spec-

tral response range is defined as the region in which the

relative sensitivity is higher than 5 % of the peak value.

8. Dark current: I

D

When a reverse voltage is applied to a PSD, a slight cur-

rent flows even in a dark state. This is termed the dark

current and is a source of noise. The dark current listed in

our PSD data sheets (separately available) are the total

dark current values measured from all output electrodes.

9. Terminal capacitance: Ct

3. Quantum efficiency: QE

A capacitor is formed at the PN junction of a PSD and its

capacitance is called the junction capacitance. The ter-

minal capacitance is the sum of the junction capacitance

plus the package stray capacitance, and is a factor in

determining the response speed. The terminal capaci-

tance listed in our PSD data sheets are the total capaci-

tance values measured from all output electrodes.

The quantum efficiency is the number of electrons or

holes that can be detected as a photocurrent divided by

the number of the incident photons. This is commonly

expressed in percent (%). The quantum efficiency and

photo sensitivity S have the following relationship at a

given wavelength (nm):

S × 1240

QE =

× 100 [%]

10. Rise time: tr

λ

The rise time is defined as the time required for the PSD

output to rise from 10 to 90 % of the steady output level,

when a step function light is input to the PSD. The rise

time depends on the incident light wavelength, load

resistance, light incident position and reverse voltage,

and is measured under the following conditions.

λ: Wavelength (nm)

S: Photo sensitivity at wavelength λ (A/W)

4. Resistance length: L

This is the distance between electrodes on a PSD and is

used to calculate the position from the PSD outputs. The

resistance length is equivalent to the active area size,

except for the pin-cushion type (improved tetra-lateral

type) whose resistance length is expressed by the

distance actually used to calculate the position.

· Light source

· Incident spot light

: λ=890 nm

: φ1 mm

· Incident light position: Center point of PSD

· Load resistance : 1 kΩ

(connected to all output electrodes)

5. Position detection error

If a light beam strikes the electrical center of a PSD, the sig-

nal currents extracted from the output electrodes are equal.

When this electrical center is viewed as the origin, the posi-

tion detection error is defined as the difference between the

position at which the light is actually incident on the PSD

and the position calculated from the PSD outputs. Measure-

ment conditions for position detection error are as follows:

11. Saturation photocurrent: Ist

This is the maximum photocurrent value obtained from a

PSD as long as it still functions as a position sensor.

This value depends on the reverse voltage and interelec-

trode resistance, and is defined as the total photocurrent

when the entire active area is illuminated.

Light source

Incident spot light: φ200 µm

Photocurrent : 10 µA

: λ=890 nm

12. Maximum reverse voltage: VR Max.

Increasing the reverse voltage applied to a PSD can

cause it to breakdown at a certain level and result in se-

vere deterioration of PSD performance. To avoid this,

the maximum reverse voltage is specified as the abso-

lute maximum rating (this value must not be exceeded

even momentarily) at a reverse voltage somewhat lower

than the breakdown voltage.

6. Position resolution: ∆R

This is the minimum detectable displacement of a spot light

incident on a PSD, and is expressed as a distance on the

PSD surface. Resolution is mainly determined by the S/N

and given by “resistance length × noise / signal”. The

resolution values listed in our PSD data sheets (separately

available) are calculated based on the RMS values for

noise measured under the following conditions.

· Interelectrode resistance: Typical value

(listed in the data sheets)

· Photocurrent

: 1 µA

· Frequency bandwidth : 1 kHz

· Equivalent noise input voltage to circuit: 1 µV

4

Characteristic and use

By finding the difference or ratio of Ix1 to Ix2, the light input

1. Basic principle

position can be obtained by the formulas (1-3), (1-4), (1-7)

and (1-8) irrespective of the incident light intensity level

and its changes. The light input position obtained here cor-

responds to the center-of-gravity of the light beam.

A PSD basically consists of a uniform resistive layer

formed on one or both surfaces of a high-resistivity semi-

conductor substrate, and a pair of electrodes formed on

both ends of the resistive layer for extracting position

signals. The active area, which is also a resistive layer,

has a PN junction that generates photocurrent by means

of the photovoltaic effect.

2. One-dimensional PSD

Figure 2-1 Structure chart, equivalent circuit (one-dimensional PSD)

Figure 1-1 PSD sectional view

Rp

ANODE (X1)

X

B

X

A

OUTPUT IX1

OUTPUT IX2

P

D

C

j

Rsh

INCIDENT

LIGHT

ANODE (X

CATHODE

(COMMON)

2)

ELECTRODE X

2

PHOTOCURRENT

ELECTRODE X

1

P LAYER

I LAYER

P

D

C

: CURRENT GENERATOR

: IDEAL DIODE

: JUNCTION CAPACITANCE

N LAYER

j

Rsh: SHUNT RESISTANCE

Rp : POSITIONING RESISTANCE

COMMON

ELECTRODE

KPSDC0006EA

RESISTANCE LENGTH L

X

Figure 2-2 Active area chart (one-dimensional PSD)

KPSDC0005EA

LX

Figure 1-1 shows a sectional view of a PSD using a simple

illustration to explain the operating principle. The PSD has

a P-type resistive layer formed on an N-type high-resistive

silicon substrate. This P-layer serves as an active area for

photoelectric conversion and a pair of output electrodes

are formed on the both ends of the P-layer. On the

backside of the silicon substrate is an N-layer to which a

common electrode is connected. Basically, this is the

same structure as that of PIN photodiodes except for the

P-type resistive layer on the surface.

X

1

X2

x

ACTIVE AREA

KPSDC0010EA

Position conversion formula (See Figure 2-2.)

2x

I

X2 - IX1

=

........ (2-1)

When a spot light strikes the PSD, an electric charge

proportional to the light intensity is generated at the

incident position. This electric charge is driven through the

X1 + IX2

LX

In the above formula, IX1 and IX2 are the output currents

obtained from the electrodes shown in Figure 2-2.

resistive layer and collected by the output electrodes X

1

and X as photocurrents, while being divided in inverse

2

proportion to the distance between the incident position

and each electrode.

The relation between the incident light position and the

3. Two-dimensional PSD

Two-dimensional PSDs are grouped by structure into duo-

lateral and tetra-lateral types. Among the tetra-lateral type

PSDs, a pin-cushion type with an improved active area

and electrodes is also provided. (See “3-3”.) The position

conversion formulas slightly differ according to the PSD

structure. Two-dimensional PSDs have two pairs of output

photocurrents from the output electrodes X

the following formulas.

1, X2 is given by

When the center point of PSD is set at the origin:

L

2

X

LX

2

L

- X

A

+ XA

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

...... (1-2)

× Io

IX1

=

× Io

IX2

=

electrodes, X1, X2 and Y1, Y2.

L

X

I

X2 - IX1

2X

A

I

X1

LX - 2X

^A.............. (1-4)

3-1 Duo-lateral type PSD

=

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

=

I

X1 + IX2

LX

IX2

LX

+ 2X

When the end of PSD is set at the origin:

- X

A

On the duo-lateral type, the N-layer shown in the sectional

view of Figure 1-1 is processed to form a resistive layer,

and two pair of electrodes are formed on both surfaces as

X and Y electrodes arranged at right angles. (See Figure

3-1.) The X position signals are extracted from the X elec-

trodes on the upper surface, while the Y position signals

are extracted from the Y electrodes on the bottom surface.

As shown in Figure 3-1, a photocurrent with a polarity op-

posite that of the other surface is on each surface, to pro-

duce signal currents twice as large as the tetra-lateral type

and achieve a higher position resolution. In addition, when

compared to the tetra-lateral type, the duo-lateral type of-

fers excellent position detection characteristics because

the electrodes are not in close proximity. The light input

position can be calculated from conversion formulas (3-1)

and (3-2).

L

X

B

XB

.

Io ................. (1-6)

IX1

=

Io ............. (1-5)

IX2

=

L

X

LX

IX2 - IX1

2XB

I

X1

L

X

- X

^B................ (1-8)

=

^X...... (1-7)

- L

=

IX1 + IX2

L

X

X2

XB

Io : Total photocurrent (IX1 + IX2

)

IX1: Output current from electrode X

1

IX2: Output current from electrode X

2

LX: Resistance length (length of the active area)

XA: Distance from the electrical center of PSD to the light input position

XB: Distance from the electrode X1 to the light input position

5

Characteristic and use

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

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

LX

CATHODE (Y2)

Rp

ANODE (X1)

Y2

P

D

C Rsh

j

ANODE (X2)

y

Rp

X1

X2

CATHODE (Y1)

x

P

D

C

: CURRENT GENERATOR

: IDEAL DIODE

: JUNCTION CAPACITANCE

j

Rsh: SHUNT RESISTANCE

Rp : POSITIONING RESISTANCE

ACTIVE AREA

Y1

KPSDC0007EA

KPSDC0011EA

Position conversion formula (See Figure 3-4.)

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

L

X

IX2 - IX1

2x

=

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

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

I

X1 + IX2

Y2 - IY1

Y1 + IY2

LX

Y

2

I

2y

LY

y

X

1

X2

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

x

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.

ACTIVE AREA

Y

1

KPSDC0011EA

Position conversion formula (See Figure 3-2.)

I

X2 - IX1

2x

LX

=

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

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

I

X1 + IX2

Y2 - IY1

Y1 + IY2

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

I

2y

LY

ANODE (Y2)

ANODE (X1)

I

Rp

ANODE (X2)

3-2 Tetra-lateral type PSD

ANODE (Y1)

Rsh

D

P

CATHODE

C

j

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.

P

D

C

Rsh

Rp

: CURRENT GENERATOR

: IDEAL DIODE

: JUNCTION CAPACITANCE

: SHUNT RESISTANCE

: POSITIONING RESISTANCE

j

KPSDC0009EA

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

L

X

Y

2

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

y

X1

X2

x

Rp

ANODE (Y2)

ANODE (X

1)

ACTIVE AREA *

Y1

P

D

Rsh

C

j

ANODE (X

2)

ANODE (Y

1)

* Active area is specified at the inscribed square.

CATHODE

KPSDC0012EA

Position conversion formula (See Figure 3-6.)

P

D

C

: CURRENT GENERATOR

: IDEAL DIODE

: JUNCTION CAPACITANCE

(IX2 + IY1) - (IX1 + IY2

)

2x

=

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

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

j

I

X1 + IX2 + IY1 + IY2

(IX2 + IY2) - (IX1 + IY1

X1 + IX2 + IY1 + IY2

LX

Rsh: SHUNT RESISTANCE

Rp : POSITIONING RESISTANCE

)

2y

LY

KPSDC0008EA

I

6

Characteristic and use

Figure 4-2 shows the photocurrent output example from

electrodes of a one-dimensional PSD with a resistance

length of 3 mm (S4583-04, etc.), measured when a light

beam is scanned over the active surface. The position de-

tection error estimated from the obtained data is also

shown in the lower graph.

4. Position detection error

Position detection capability is the most important charac-

teristic of a PSD. The position of a spot light incident on the

PSD surface can be measured by making calculations

based on the photocurrent extracted from each electrode.

The position obtained here with the PSD is the center-of-

gravity of the spot light, and is independent of the spot light

size, shape and intensity.

However, the calculated position usually varies slightly in

each PSD from the actual position of the incident light. This

difference is referred to as the “position detection error” and

is explained below.

If a light beam strikes the electrical center of a PSD, the

signal currents extracted from the output electrodes are

equal. When this electrical center is viewed as the origin,

the position detection error is defined as the difference be-

tween the position at which the light is actually incident on

the PSD and the position calculated from the PSD outputs.

Figure 4-2 Photocurrent output example of one-

dimensional PSD (S4583-04, etc.)

I

X1

IX2

1.0

0.5

0

Figure 4-1 Cross section of PSD

SPOT

LIGHT

X

1

X2

RESISTANCE LENGTH L

X

-1.5

0

+1.5

Xi

Xm

ELECTRICAL

CENTER B

POSITION ON PSD (mm)

Position detection error example of one-

dimensional PSD (S4583-04, etc)

P-TYPE

RESISTIVE LAYER

+50

I LAYER

N LAYER

ACTUAL POSITION Xi

CALCULATED POSITION Xm

COMMON ELECTRODE

KPSDC0071EA

0

In Figure 4-1 above, if the actual position of incident light

is Xi and the position calculated by the photocurrents

(IX1 and IX2) from electrodes X1 and X2 is Xm, then the

difference in distance between Xi and Xm is defined as

the position detection error as calculated below.

Position detection error E = Xi - Xm [µm] ........ (4-1)

Xi : Actual position of incident light (µm)

-50

-1.5

-1.0 -0.5

0

+0.5 +1.0 +1.5

Xm: Calculated position of incident light (µm)

POSITION ON PSD (mm)

KPSDB0005EA

I

X2 - IX1

LX

2

.

........ (4-2)

Specific area for position detection error

Xm =

IX1 + IX2

The light beam position can be detected over the entire ac-

tive area of PSD. However, if part of the light beam strikes

outside the active area, a positional shift in the center-of-

gravity occurs between the entire light beam and the light

spot falling within the active area, making the position

measurement unreliable. It is therefore necessary to select

a PSD whose active area matches the incident spot light.

The position detection error is measured under the follow-

ing conditions.

· Light source

· Spot light size

: λ=890 nm

: φ200 µm

· Total photocurrent: 10 µA

Reverse voltage : Specified value (listed in data sheets)

·

Figure 4-3 Center-of-gravity of incident spot light

ACTIVE

AREA

SPOT

LIGHT

OUTPUT

ELECTRODE X

CENTER-OF-GRAVITY

OF SPOT LIGHT FALLING

WITHIN ACTIVE AREA

1

CENTER-OF-GRAVITY

OF ENTIRE SPOT LIGHT

OUTPUT

ELECTRODE X

2

KPSDC0073EA

7

Characteristic and use

The position detection error is usually measured with a

light beam of φ200 µm, so the specified areas shown in

Figures 4-4 to 4-6 are used for position detection error.

5. Position resolution

Position resolution is the minimum detectable displace-

ment of a spot light incident on PSD, expressed as a dis-

tance on the PSD surface. Resolution is determined by the

PSD resistance length and the S/N. Using formula (1-6) as

an example, the following equation can be established.

Figure 4-4 Specific area for one-dimensional PSD position

detection error (resistance length ≤ 12 mm)

OUTPUT

ELECTRODE X

1

ELECTRODE X2

ACTIVE AREA

XB + ∆x

.

Io ......... (5-1)

IX2 + ∆I =

LX

∆x: Small displacement

∆I: Change in output current

SPECIFIED RANGE

× 0.75

L

X

RESISTANCE LENGTH L

X

Then, ∆x can be expressed by the following equation.

KPSDC0074EA

∆I

Io

.

Figure 4-5 Specific area for one-dimensional PSD position

detection error (resistance length > 12 mm)

∆x = L

X

........................... (5-2)

OUTPUT

In cases where the positional displacement is infinitely

small, the noise component contained in the output current

ELECTRODE X

1

ELECTRODE X2

ACTIVE AREA

I

X2 clearly determines the position resolution. Generally, if

the PSD noise current is In, then the position resolution ∆R

is given as follows:

In

Io

.

∆R = L

X

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

SPECIFIED RANGE

× 0.90

L

X

RESISTANCE LENGTH L

X

Figure 5-1 shows the basic connection example when us-

ing a PSD in conjunction with current-to-voltage amplifiers.

The noise model for this circuit is shown in Figure 5-2.

KPSDC0075EA

Figure 4-6 Specific area for two-dimensional PSD

position detection error

Figure 5-1 Basic connection example of one-dimensional

PSD and current-to-voltage conversion type

operational amplifier

ZONE A

ZONE B

Rf

Cf

Rf

Cf

PSD

ACTIVE AREA

-

A

KPSDC0063EA

+

Position detection error for two-dimensional PSDs is sep-

arately measured in two areas: Zone A and Zone B. Two

zones are used because position detection error in the

circumference is larger than that in the center of the ac-

tive area,

V

R

KPSDC0076EA

· Zone A: Within a circle with a diameter equal to 40 % of

one side length of the active area.

· Zone B: Within a circle with a diameter equal to 80 % of

one side length of the active area.

Figure 5-2 Noise model

Rf

Cf

PSD

-

in

en

~

I

O

I

D

Rie

Cj

Vo

A

+

KPSDC0077EA

Io : Photocurrent

: Dark current

ID

Rie: Interelectrode resistance

Cj : Junction capacitance

Rf : Feedback resistance

Cf : Feedback capacitance

en : Equivalent noise input voltage of operational amplifier

in : Equivalent noise input current of operational amplifier

Vo : Output voltage

8

Characteristic and use

Figure 5-3 shows the shot noise current plotted along the

signal photocurrent value when Rf >>Rie. Figure 5-4

shows the thermal noise current and the noise current by

the equivalent noise input voltage of the operational

amplifier, plotted along the interelectrode resistance value.

When using a PSD with an interelectrode resistance of

about 10 k , the operational amplifier becomes a crucial

factor in determining the noise current, so a low-noise-

current operational amplifier must be used. When using a

PSD with an interelectrode resistance exceeding 100 k ,

the thermal noise generated from the interelectrode

resistance of the PSD itself will be predominant.

As explained above, PSD position resolution is determined

by interelectrode resistance and light intensity. This is the

point in which the PSD greatly differs from discrete type

position detectors.

Noise currents are calculated below, assuming that the

feedback resistance Rf of the current-to-voltage conversion

circuit is sufficiently greater than the PSD interelectrode

resistance Rie. In this case, 1/Rf can be ignored since it is

sufficiently small compared to 1/Rie. Position resolution as

listed in our PSD data sheets is calculated by this method.

1) Shot noise current Is originating from photocurrent and

dark current

. .

2q (Io + ID) B [A] ............ (5-4)

Is =

q : Electron charge (1.60 × 10^-19C)

Io: Signal photocurrent (A)

ID: Dark current (A)

B : Bandwidth (Hz)

The following methods are effective for increasing the PSD

position resolution.

2) Thermal noise current (Johnson noise current) Ij generated

from interelectrode resistance (This can be ignored as Rsh

>> Rie.)

· Increase the signal photocurrent Io.

· Increase the interelectrode resistance Rie.

· Shorten the resistance length L.

· Use a low noise operational amplifier.

4 kTB

Rie

Ij =

[A] ............ (5-5)

The position resolution listed in our PSD data sheets is

measured under the following conditions.

· Photocurrent: 1 µA

k : Boltzmann constant (1.38 × 10^-23J/K)

T : Absolute temperature (K)

· Circuit input noise: 1 µV (31.6 nV/Hz^1/2)

· Frequency bandwidth: 1 kHz

Rie: Interelectrode resistance ( )

3) Noise current Ien by equivalent noise input voltage of

operational amplifier

Figure 5-3 Shot noise vs. signal photocurrent

en

(Typ. Ta=25 ˚C)

Ien =

B [A] ............ (5-6)

10

Rie

en: Equivalent noise input voltage of operational amplifier

(V/Hz^1/2

)

1

By taking the sum of equations (5-4), (5-5) and (5-6), the

PSD noise current can be expressed as an RMS value

as follows:

0.1

In =

Is²+ Ij²+ Ien²[A] ............ (5-7)

If Rf cannot be ignored versus Rie (as a guide, Rie/Rf >

0.1), then the equivalent noise output voltage must be

taken into account. In this case, equations (5-4), (5-5)

and (5-6) are converted into output voltages as follows:

0.01

0.1

1

10

SIGNAL PHOTOCURRENT (µA)

KPSDB0083EA

.

D

Vs = Rf

Vj = Rf

2q (Io + I

) B [V] ............ (5-8)

Figure 5-4 Noise current vs. interelectrode resistance

4 kTB

Rie

(Typ. Ta=25 ˚C)

.

[V] .............................. (5-9)

10

Thermal noise current Ij generated from

interelectrode resistance

Noise current (en=10 nV) by equivalent

Rf

Rie

noise input voltage of operational amplifier

.

Ven

= 1 +

en

B [V] .............. (5-10)

Noise current (en=30 nV) by equivalent

noise input voltage of operational amplifier

1

The thermal noise from the feedback resistance and the

equivalent noise input current of the operational amplifier

are also added as follows:

0.1

4 kTB

Rf

.

VRf

= Rf

[V] ............................ (5-11)

.

Vin

= Rf in

B [V] ............................ (5-12)

0.01

10

100

1000

The equivalent noise input voltage of the operational am-

plifier is then expressed as an RMS value by the following

equation.

INTERELECTRODE RESISTANCE (kΩ)

KPSDB0084EA

2

Vn =

Vs²+ Vj²+ Ve

n

²+ V

Rf

²+ Vi

n

[V] ............ (5-13)

9

Characteristic and use

Figure 6-2 shows the relation between the rise time and re-

verse voltage measured at different wavelengths. The rise

time can be reduced by increasing the reverse voltage and

using a light beam of shorter wavelengths. Selecting a PSD

with a small Rie is also effective in improving the rise time.

6. Response speed

As with photodiodes, the response speed of PSD is the

time required for the generated carriers to be extracted as

current by an external circuit. This is generally expressed

as the rise time tr and is an important parameter when de-

tecting a spot light traveling over the active surface at high

speeds or using pulse-modulated light for subtracting the

background light. The rise time is defined as the time need-

ed for the output signal to rise from 10 to 90 % of its peak

value and is chiefly determined by the following two factors.

Figure 6-2 Rise time vs. reverse voltage (S4583-06)

(Typ. Ta=25 ˚C)

10

8

6

1) Time constant t1 determined by the interelectrode resist-

=890 nm

ance, load resistance and terminal capacitance

The interelectrode resistance Rie of PSD basically acts as

load resistance RL, so the time constant t1 is given by the

interelectrode resistance Rie and terminal capacitance Ct,

as follows:

4

2

=650 nm

. .

t1 = 2.2 Ct (Rie + RL) ......... (6-1)

0

0.1

1

10

100

The rise time listed in our PSD datasheets is measured

with a spot light striking the center of the active area with

the interelectrode resistance Rie distributed between the

REVERSE VOLTAGE (V)

KPSDB0110EA

electrodes. So the time constant t

1

is as follows:

A method for integrating position signals can be used when

detecting pulsed light having a pulse width shorter than the

PSD rise time.

.

t

1

= 0.5 Ct (Rie + R

L

) ......... (6-2)

2) Diffusion time t2 of carriers generated outside the deple-

tion layer

Carriers are also generated outside the depletion layer

when light is absorbed in the PSD chip surrounding areas

outside the active area or at locations deeper than the de-

pletion layer in the substrate. These carriers diffuse through

the substrate and are extracted as an output. The time t

2

required for these carriers to diffuse may be more than sev-

eral microseconds.

The equation below gives the approximate rise time tr of a

PSD. Figure 6-1 shows typical output waveforms in re-

sponse to stepped light input.

2

tr

t1

²+ t

2

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

Figure 6-1 Response wavelength example of PSD

LIGHT INPUT

OUTPUT WAVEFORM

(t1>>t2)

OUTPUT WAVEFORM

(t >>t

2

1)

KPSDC0078EB

10

Characteristic and use

Figure 7-3 Saturation photocurrent vs. interelectrode resistance

(entire active area fully illuminated)

7. Saturation photocurrent

(Typ. Ta=25 ˚C)

Photocurrent saturation must be taken into account when a

PSD is used outdoors, in locations where the background

light level is high, or the signal light amount is extremely

large. Figure 7-1 shows typical photocurrent output of a

PSD in a non-saturated state. This PSD is operating nor-

mally with good output linearity over the entire active area.

If the background light level is excessively high or the sig-

nal light amount is extremely large, the PSD photocurrent

will saturate. A typical output from a saturated PSD is

shown in Figure 7-2. The output linearity of the PSD is im-

paired so the correct position cannot be detected in this

case.

10

VR=5 V

V

R=2 V

1

0.1

VR=1 V

Photocurrent saturation of a PSD depends on the interelec-

trode resistance and reverse voltage, as shown in Figure 7-

3. The saturated photocurrent is measured as the total

photocurrent of a PSD when the entire active area is illumi-

nated. If a small spot light is focused on the active area, the

photocurrent that is generated is concentrated only on a lo-

calized portion, so saturation occurs at a lower level.

V

R

=0 V

0.01

10

100

1000

INTERELECTRODE RESISTANCE (kΩ)

KPSDB0085EA

To avoid the saturation effect, use the following methods.

·

Reduce the background light level by using an optical filter.

· Use a PSD with a small active area.

· Increase the reverse voltage.

· Decrease the interelectrode resistance.

·

Avoid concentrating the light beam on a small area.

Figure 7-1 Photocurrent output example of PSD in

normal operation (S5629)

(Ta=25 ˚C)

120

I

X1 + IX2

100

80

60

40

20

0

I

X1

IX2

CENTER OF

ELECTRICITY

-4

-3

-2

-1

0

1

2

3

4

INCIDENT POSITION (mm)

KPSDB0087EA

Figure 7-2 Photocurrent output example of saturated

PSD (S5629)

(Ta=25 ˚C)

120

I

X2

100

80

60

40

20

0

I

X1

I

X2

I

X1 + IX2

CENTER OF

ELECTRICITY

-4

-3

-2

-1

0

1

2

3

4

INCIDENT POSITION (mm)

KPSDB0086EA

11

Notice

· The information contained in this catalog does not represent or create any warranty, express or implied, including

any warranty of merchantability or fitness for any particular purpose.

The terms and conditions of sale contain complete warranty information and is available upon request from your

local HAMAMATSU representative.

· The products described in this catalog should be used by persons who are accustomed to the properties of

photoelectronics devices, and have expertise in handling and operating them.

They should not be used by persons who are not experienced or trained in the necessary precations surrounding their

use.

· The information in this catalog is subject to change without prior notice.

· Information furnished by HAMAMATSU is believed to be reliable. However, no responsibility is assumed for

possible inaccuracies or ommission.

· No patent rights are granted to any of the circuits described herein.

HAMAMATSU PHOTONICS K.K., Solid State Division

1126-1, Ichino-cho, Hamamatsu City, 435-8558, Japan

Telephone: (81)53-434-3311, Fax: (81)53-434-5184

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possible inaccuracies or omission.

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change without notice. No patent

rights are granted to any of the

circuits described herein.

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Cat. No. KPSD0001E01

Jan. 2002 DN

Printed in Japan (7,000)

Quality, technology, and service are part of every product.


型号：	S8361
厂家：	ETC
描述：	POSITION SENSITIVE DETECTOR 位置敏感
文件：	总16页 (文件大小：1288K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

S8361 [ETC]

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