DATA SHEET
DL100-7PCBA3
DUAL AXIS PSD SUM AND DIFFERENCE AMPLIFIER SPECIFICATION
APPLICATION NOTES
Ambient Light Considerations
Ambient light can cause errors and reduced resolution. If the ambient light is of homogeneous power density over the
entire diode surface it will appear as a current source at the diode center. Since this apparent current source adds to
the signal current the overall current is increased. The differencing circuits will eliminate this current from the X, Y
outputs but it will still be included in the sum circuit outputs.
If the beam to be tracked is monochromatic, or nearly so, a bandpass filter can be placed in front of the diode to
eliminate most of the ambient light. If the ambient light contains shadows that fall on the diode surface, the apparent
current source will be off center and will contribute to an offset in the position outputs as well as contributing to the
sum outputs. Again, an optical filter can eliminate or reduce most of these undesirable effects.
If the ambient light contains shadows that are changing with time then the position outputs and the sum circuit outputs
will also show a time varying signal that is related to the shifting ambient light.
Resolution
Best resolution is obtained with the maximum allowable light intensity and optimum wavelength. The temperature
should be held within specification. Resolution obtainable under specified conditions is 0.5µm or less.
Speed of Response
Increasing the PSD bias voltage will increase the speed of the DL100-7PCBA3. The internally created reverse bias of
14.3V is sufficient for most applications. As noted above, Pins 1 and 2 are provided to reduce or increase the 14.3V
reverse bias, but biasing above 14.3V provides only a small increase in speed. Care should be taken not to exceed the
circuit common mode values and the breakdown voltage of the diode. See the DL100-7PCBA3 data sheet for
maximum values.
2
The rise and fall time of the DL100-7PCBA3 module with the 1cm DL100-7-CER diode is better than 5µs.
Linearity
Linearity improves with increased reverse bias. The 14.3V bias provided by the DL100-7PCBA3 module gives a linearity
of ±1 percent of full scale or better.
Temperature Considerations
The operating temperature must be between 0 to 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 100 millivolts of offset may still be present in the
outputs. If this causes a problem the offsets should be removed externally.
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