Rev. 14/02/2018 subject to change without notice www.first-sensor.com contact@first-sensor.com Page 1/2
First Sensor Evaluation Boards Data Sheet
Quad Sum and Difference Amplifier
Part Description QP50-6-18u SD2
US Order # 10-027
International Order # 5000022
V-
GND
V+
V(SUM)
V(L-R)
V(B-T)
PD BIAS
3.2
19.05
25.4
PD L
C31.75
38.1
17.8
14.4
2X Ø2.54
TOOLING HOLE
3.3 1.57
6.3
2.54
CHIP SURFACE
NO CONNECTION
Q2
Q4
Q3
COMMON
CATHODE
Q1 12.7
6.0
3.2
5.9
PD L
C
CENTERS
TOP VIEW
ALL DIMENSIONS IN MILLIMETERS
Q1Q2 Q4Q3
17
2
(7.80 mm DIA w/ 18 µm GAPS)
ACTIVE AREA: 4 X 11.78 mm
PINS ON 2.54
Description
Applications
RoHS
The QP50-6-18u SD2 is a quad photodiode array with current-to-voltage amplifiers that provide bottom minus
top and left minus right difference signals. Additionally the QP50-6-18u SD2 provides a signal that is the sum
of all four quadrant diode signals. The difference signals are voltage analogs of the light intensity difference
sensed by the pairs of photodiode elements in the array. The board has a 7 pin connector attached for easy
hook up.
NIR & visible pulsed light positioning
and tracking
Laser beam centering
2011/65/EU
Options
Can be purchased without connector, use order # 10-007.
For alternate gap size, see data sheet QP50-6-42u SD2 for 42 µm gap version.
Also available with quad detector active area sizes ranging from 1mm2 to 20 mm2.
Absolute maximum ratings
Spectral response @ 22C
Symbol
Parameter
Min
Max
Units
TSTG
Storage Temp
-15
+100
C
TOP
Operating Temp
0
+70
C
VS
Power Supply Voltage
Recommended ±15V
±4.5
±18
V
VR
Applied Bias Voltage*
0
15
V
Electro-optical characteristics @ 22 C
Symbol
Characteristic
Test conditions
Min
Typ
Max
Units
VO
Output Voltage (all outputs)
---
+Vs -3
---
V
---
-Vs +3
---
IO
Output Current Limit
Vs = ± 15 V; VR = 0 V
---
---
25
mA
Slew Rate
Vs = ± 15 V; VR = 0 V
---
---
10
V/s
Theoretical noise
Vs = ± 15 V; VR = 0 V
---
15
---
nV/√Hz
-3dB
Bandwidth**
Vs = ± 15 V; VR = 5 V; = 880 nm
---
250
---
kHz
* actual bias voltage to photodiode: pad 1 voltage times 0.91. Do not apply negative voltages to pad 1.
** dependant on bias voltage
11001000900
800700600
500
400
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
WAVELENGTH (nm)
RESPONSIVITY (A/W)
V-
GND
V+
V(SUM)
V(L-R)
V(B-T)
PD BIAS
17
Connections
Rev. 14/02/2018 subject to change without notice www.first-sensor.com contact@first-sensor.com Page 2/2
The QP50-6-18u SD2 outputs are labeled as B-T for bottom minus top, L-R for left
minus right. The output voltages are obtained by routing the diode element currents
into current-to-voltage amplifiers with a gain of 104:
VB-T = [(I3,4) - (I1,2)] (104) on Pad 2.
VL-R = [(I2,3) - (I1,4)] (104) on Pad 3.
VSUM = [(I1,2,3,4) (104) on Pad 4.
I X,Y is the sum of the currents generated by photodiode elements
x and y. Looking down through the window of the photodiode, the quadrants are
identified in drawing on page one.
X1
SUM AND
DIFFERENCE
AMPLIFIERS
QP50-6-18u-TO8
i4 V4 = i4 X 104
i1 V1 = i1 X 104
i3 V3 = i3 X 104
i2 V2 = i2 X 104
X0.91 PHOTODIODE BIAS
PAD 1
(V3 +V4) - (V1 + V2)
PAD 2
(V2 +V3) - (V1 + V4)
PAD 3
-
+
V1 + V2 + V3 + V4
PAD 4
+15V +15V PAD 5
GROUND PAD 6
-15V -15V PAD 7
BLOCK DIAGRAM
APPLICATION NOTES
Beam Size
The light spot applied to the QP50-6-18u SD2 must be smaller than the diameter of the quadrant photodiode array. The detector active area has a diameter of 7.8 millimeters. If
the light spot is too large, it may be reduced to fit the photodiode array by use of a lens. A decrease in output signal strength is observed as the light spot crosses the separation
boundary of the quadrants, usually referred to as the “gap”. This effect is more pronounced as the diameter of the light spot decreases, as a larger percentage of the light spot’s
power falls within the non-active gap. For this reason, the minimum light beam diameter should be a least one millimeter. A lens may be used to increase the beam diameter.
Photodiode Bias Operation
The QP50-6-18u SD2 array may be operated either in the zero bias or the reverse bias mode. Pin 1 is connected, via a resistor divider, to the non-inverting input of a voltage
follower operational amplifier. This line may be left unterminated, grounded or connected to a voltage source of zero volts to operate in the zero bias mode. If the photodiode bias
line is connected to a positive voltage source (but less than Vcc), then the photodiode elements in the array will be biased at 0.91 x VBias. Do not connect Pin 1 to negative
voltages, as this will forward bias the photodiode array, making it inoperable and possibly damaging the circuit.
Use of Sum and Difference Signals for Alignment
The sum output signal may be used to help preliminary alignment of the QP50-6-18u SD2 to the source light beam. First, the beam or the QP50-6-18u SD2 is adjusted for
maximum sum output signal. Second, the beam or QP50-6-18u SD2 is adjusted until the L-R and B-T signals are at minimum. This procedure results in the beam being centered on
the quad photodiode array.
Signal Null Detector for Servo Applications
A common application for the QP50-6-18u SD2 is a signal null detector as part of a servo system that maintains the position of a light beam. Errors in beam position are reported
by the QP50-6-18u SD2 and may be used to adjust a positioning device that restores the beam or the beam’s source to a null position.
Speed of Response
Increasing the photodiode bias voltage will increase the speed of the QP50-6-18u SD2. Operating with zero reverse bias is sufficient for many applications (-3dB is around 150 kHz
at 880 nm). As noted above, Pin 1 is provided for applying positive bias voltage to the quad for higher frequency response. Care should be taken not to exceed the circuit common
mode values and the breakdown voltage of the quad photodiode. See Absolute Maximum Ratings on page one for maximum values.
Temperature Considerations
The operation temperature must be between 0 and 70 C. For best resolution the temperature should be kept at or below 25 C. Thermal gradients across the detector will cause
position errors and should be avoided.
Offsets
Precision components are used in the circuitry but as much as 10 millivolts of dark offset may still be present in the outputs. If this causes a problem the offsets should be removed
externally.
