Quadrant Detector Amplifiers

QD7-0-SD or QD50-0-SD are quadrant photodiode arrays with associated circuitry to provide two difference signals and a sum signal. The two difference signals are voltage analogs of the relative intensity difference of the light sensed by opposing pairs of the photodiode quadrant elements. In addition, the amplified sum of all 4 quadrant elements is provided as the sum signal. This makes the QD7-0-SD or QD50-0-SD ideal for both light beam nulling and position applications. Very precise light beam alignments are possible, and the circuit can also be used for target acquisition and alignment.
Please note that the QD50-0 and QD7-0 model numbers refer to the stand alone quadrant photodiodes. In order to complete Sum and Difference modules please use the following models number: QD50-0-SD and QD7-0-SD for the 50mm2 and 7mm2 version respectively.

The Output is defined as follows,
Where ix is the current from quadrant x
VT-B = -{(i1+i2) - (i3+i4)} x (104)
VL-R = -{(i2+i3) - (i1+ i4)} x (104)
VSUM = -{(i1+i2 + i3 + i4)} x (104)

Image Datasheet Model Number Power supply Photoiode Bias Output Voltage (max.) Frequency Response at -3dB Slew Rate (max.) Output Current Limit Theoretical noise View
PDF QDXX-0-SD* ±4.5 to ±18 V 0.91 x VPDBIAS -3 to +3 V 250 kHz 10 V/µs 25 mA 15 nV/Hz½ View

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