On-Trak - Position Sensing Detectors

On-Trak - Detector Amplifiers

Dec. 23, 2002: The information on this page is no longer accurate. Please refer to www.on-trak.com for updated information or call them in Lake Forest, CA at 949-587-0769. - JW
On-Trak Photonics Inc.
22471 Aspan St.
Lake Forest, CA 92630
TEL: (714) 587-0769
FAX: (714) 587-9524

POSITION SENSING DETECTORS

For Non-Contact Measurement Of

ON-TRAK PHOTONICS PSD'S FEATURE:

Description:

Position Sensing Detectors "PSD" are silicon photodiodes that provide an analog output directly proportional to the position of a light spot on the detector active area. The PSD allows you to simultaneously monitor position and light intensity. The PSD is a continuous analog position sensor and compared to discrete element devices the PSD offers outstanding position linearity, high analog resolution, fast response time and simple operating circuits.

Theory of Operation:

The Position Sensing Detector consists of n-type silicon substrate with two resistive layers separated by a p-n junction. The front side has an ion implanted p-type resistive layer with two contacts at opposite ends. The back side as an ion implanted n-type resistive layer with two contacts at opposite ends placed orthogonally to the contacts on the front side. On a single axis PSD the electrodes are placed at opposite ends of the p-type resistive layer. A light spot within the spectral range of silicon will generate a photocurrent which flows from the incident point through the resistive layers to the electrodes. The resistivity of the ion implanted layer is extremely uniform so the photogenerated current at each electrode is inversely proportional to the distance between the incident spot of light and electrodes. The PSD outputs track the motion of the "centroid of power density" to an extremely high resolution and ultra high linearity. The ON-TRAK Position Sensing Amplifiers takes the photocurrent from each electrode and processes the signals to give X, Y outputs independent of light intensity.

STRUCTURE

Position Resolution:

The position resolution of a PSD is the minimum detectable displacement of a spot of light on the detector surface. The position resolution of ON-TRAK PSD's have been proven better than one part in ten million!

Resolution is dependent on:

Position Linearity:

The position non-linearity is defined as the geometric position error divided by the detector length and is measured within 80% of the detector length. Position non-linearity is typically better than 0.05% for the single axis PSD and better than 0.3% for the duolateral. The ON-TRAK vs competitor two dimensional linearity plot shows the ultra linear characteristic of these PSD's!

SPECTRAL RESPONSE

PSD Type     Spectral Range          Responsivity
-----------------------------------------------------------
Standard        400 - 1100 nm           0.70 A/W @ 940 nm

UV              200 - 1100 nm           0.14 A/W @ 254 nm
                                        0.19 A/W @ 340 nm

YAG             400 - 1150 nm           0.52 A/W @ 1064 nm
                                        0.76 A/W @ 1000 nm

Nuclear         < 500 Angst             FWHM < 20 KEV
                Dead Layer              (5.5 MEV Alpha)
-----------------------------------------------------------

Duolateral PSD Linearity

        Active  Responsivity    Dark     Noise      Thermal Drift   Capacitance  Interlectrode   Rise Time    Position +/- %
Model    Area     @ 940 nm     Current  Current     Over 23-70deg      (pf)       Resistance     (10-90%)     Non Linearity
        (mm^2)     (A/W)        (nA)   (pA/Hz^.5)   PPM/Deg C Max                   (Ohm)        (microsec)   Typ  /  Max
-----------------------------------------------------------------------------------------------------------------------------
One Dimensional PSD Series
1L2.5SP 2.5x0.6     .7           40       0.6            40             1.6          50K           0.03       0.05    0.15
1L55P     5x1       .7           50       0.6            40               5          50K           0.05       0.05    0.15
1LlOSP   lOx2       .7          100       0.6            40              15          50K           0.20       0.05    0.15
lL30     30x4       .7          300       0.7            40              90          50K           1.00       0.05    0.15

Circular PSD Series
lLC281   28x1       .7           20       0.5            40             300         150K            10        0.05    0.15

Two Dimensional PSD Series
2L2SP     2x2      .7            50       1.3            40               7          10K           0.02       0.3     0.8
2L4SP     4x4      .7           100       1.3            40              20          l0K           0.04       0.3     0.8
2Ll0SP   10xlO     .7           200       1.3            40              90          l0K           0.20       0.3     0 8
2L20SP   20x20     .7           400       1.5            40             360          10K           0.80       0.3     0 8
-----------------------------------------------------------------------------------------------------------------------------
NOTE: Bias 15V except lLC281 (lOV) Temperature 23 DegC. max operating temp 70 DegC. max storage temp 100 DegC  
      Position Non-linearity and thermal drift measured within 80% of detector length

One-Dimensional PSD:

The one-dimensional PSD is able to detect a light spot moving over its surface in one dimension. The photoelectric current generated by the incident light flows through the device and can be seen as an input bias current divided into two output currents. The distribution of the output currents show the light position on the detector.

Ip = Photocurrent generated by incident light
D = Ideal diode. PN junction of PSD
C = Junction capacitance
Rsh = Shunt resistance
Rpos = Position resistance

Duo-Lateral Two-Dimensional PSD:

The duo-lateral two-dimensional PSD is able to detect an incident light spot position on its rectangular surface. It has four terminals. The photoelectric current generated by the incident light flows through the device and can be seen as two input currents and two output currents. The distribution of the output currents show the light position of one (Y) dimension. and the distribution of the input currents show the light position of the second (X) dimension.

Ip = Photoelectric current generated by the incident light
D = Ideal diode
C = Junction capacitance
Rsh = Shunt resistance
Rposx = Position resistance x-axis
Rposy = Position resistance y-axis

Packages

(All dimensions in mm)

One-Dimensional PSD's

1L2.5-SP, 1L5-SP

1L10-SP

1L30

1LC281

Two-Dimensional PSD's

2L2-SP

Position Sensing Amplifiers

OT-300:

The ON-TRAK OT-300 is designed to provide an X-Y position output and sum output from duolateral, tetralateral, Quadrant and Bi-cell position sensing detectors. The OT-300 has four transimpedance amplifiers and signal processing electronics to provide a normalized position and sum output. The OT-300 has five gain settings to accommodate input current ranges from lnA to 2mA with a frequency response to 15KHz. Also featured is a zero offset and Cal adjust to allow calibration to absolute position.

OT-300L Amplifier for Duolateral PSD:

The OT300L is a printed circuit board amplifier designed for direct integration into users instrumentation. It is optimized for duolateral Position Sensing Detectors (PSD's) with adjustable bias voltages and three switch selectable gain ranges. The PSD is used to accurately measure the position of a small beam of light incident on the detector's surface.

The OT300L contains all the circuit elements to add. subtract and divide detector signals very accurately. Precision op-amps and precision resistor networks provide the addition and subtraction operations and optimized analog dividers provide the final ratio.

ACCESSORIES:

ON-TRAK PHOTONICS can supply Custom Systems. Instruments and Components for your special PSD applications. Whether your specific requirement is analog design. digital design. opto-mechanical housings or systems requirements. ON-TRAK can provide your PSD solution.

Capabilities:

BASIC OPERATING CIRCUITS:

Basic Operating Circuit: The position of a light spot on a PSD is determined by the difference in signals at opposite electrodes divided by the sum of the signals, as shown in the circuit at right.

The PSD yields a photocurrent output, which is converted to voltage and amplified by the op-amp/feedback circuit. The voltage signals are further processed to yield the sum and difference signals, which are divided using an analog divider circuit. The resulting signal yields position information independent of fluxuations in the intensity of the light spot.

PM-Kit Position Measuring Kit

PM Kit Processing Boards:

The PM Kit (Position Measurement Kit) is a set of general-purpose preamp and signal processing boards, designed to allow the user to quickly become familiar with the operating principles and feasibility of PSD systems. 

PM Kit Boards
-----------------------------------------------------
1D Analog       Provides detector bias and converts signal
Preamp          current to voltage. Adjustable gain.

2D Analog       Two-channel preamp board for 2L Series
Preamp          PSD's.

PM Processing   Amplifies and rectifies signals from analog
Board           preamp board, yields sum and difference
                signals. performs analog division and fast
                11-bit A/D conversion. Optional analog
                output. (2L systems require two PM
                Processing Boards.)

PM Preamp       Connects 1D or 2D Preamp Board to PM
Cable           Processing Board.

PM LED Driver   Modulates LED signal source. provides
                synchronization signal to PM Processing
                Board if desired.


RS 232 C        Converts PM Processing Board output
Interface       signals from parallel digital to serial digital.
                Adjustable baud rates.
-----------------------------------------------------
PM Kit Features:
Joe Wagner