BEAM POSITION DETECTOR BPD-8L OUTPUT SIGNALS DESCRIPTION APPLICATIONS • Sum of all four quadrants. • Difference between lower and upper halves. • Difference between left and right halves. The BPD-8L is designed for precise light beam position detection. The BPD-8L provides accurate measurement of small changes in the position of a light beam. Its large quad cell design accommodates both high resolution and larger area light detection. • Military • Industrial • Instrumentation SPECTRAL SENSITIVITY ABSOLUTE MAXIMUM RATING (TA)= 23°C UNLESS OTHERWISE NOTED 7 MIN TYP MAX UNITS ± 15 ± 18 V Vs Voltage Supplies ±5 TSTG Storage Temperature -25 +100 °C TA Operating Temperature 0 +70 °C Sensitivity (104V/W) SYMBOL PARAMETER 6 5 4 3 °C 2 1 1200 1150 1100 1050 950 1000 900 850 800 750 700 650 600 550 500 450 400 350 300 250 200 0 Wavelength (nm) ELECTRO-OPTICAL CHARACTERISTICS RATING SYMBOL f3db Gs Glr Gtb IT IN Iout CHARACTERISTIC Cutoff Frequency Output 1 = (I1+I2+I3+I4) × Gs Output 2 = ((I1+I2)-(I3+I4)) × Glr Output 3 = ((I1+I4)-(I2+I3)) × Gtb Cross Talk Input Voltage Noise Output Current Limit (TA)= 23°C, VS = ± 12V UNLESS OTHERWISE NOTED TEST CONDITIONS Vs = ± 15 V Vs = ± 15 V Vs = ± 15 V Vs = ± 15 V Vs = ± 15 V Vs = ± 15 V Vs = ± 15 V MIN .98×104 .98×104 .98×104 TYP 220 104 104 104 20 25 MAX 1.02×104 1.02×104 1.02×104 1 UNITS KHz % nV/Hz½ mA Information in this technical datasheet is believed to be correct and reliable. However, no responsibility is assumed for possible inaccuracies or omission. Specifications are subject to change without notice. Advanced Photonix Inc. 1240 Avenida Acaso, Camarillo CA 93012 • Phone (805) 987-0146 • Fax (805) 484-9935 • www.advancedphotonix.com BEAM POSITION DETECTOR BPD-8L Using the BPD for Position Sensing: Quadrant photodetectors can be used for highresolution position sensing of light beams. They provide very accurate position measurement using simple circuitry. When a light beam of a proper size illuminates a quad photodiode, it generates a photocurrent in each quadrant. By comparing those photocurrents, a change of a position in two axes can be detected. Figure 1 shows a typical quad-cell with a beam illuminating its surface. 4 1 3 2 Figure 2 Beam size too small Figure 3 Beam size too large y x Figure 1 The X and Y axis displacements of the beam relative to center of the quad cell can be calculated using the following formulas: X= (i1 +i2) −(i3 +i4) i1 +i2 +i3 +i4 Y= (i1 +i4) −(i2 +i3) i1 +i2 +i3 +i4 The accuracy of measurement depends on the beam size and the gap between the segments. To optimize the BPD’s performance, the following design rules should be observed: • The beam diameter must be bigger than the gap between the segments, such that when the beam is positioned in the center of the quad photodiode, it will still illuminate part of the active area. See Figure 2. • The beam area cannot exceed the total active area of the detector in order for the displacement of the beam to produce a change in photocurrents. See Figure 3. • The light beam spot size is proportional to the detection range, and inversely proportional to the detection resolution. Figure 4 shows the positional signal vs. beam position for three different beam sizes. As the beam size becomes smaller, the slope of the positional signal becomes steeper, which leads to a higher position detection accuracy. • Linearity of the sensor output is proportional to the uniformity of the light beam. 2 BEAM POSITION DETECTOR BPD-8L PAD 1 PAD 9 C B D A CHIP DETAIL 3