[Laser] Re: MORE XE2AT PART 2 (Art)

[Art]

At 10:23 AM 2/11/04, you wrote:
>Would there be any advantage to transformer coupling the photodetector
>to the rest of the system?  While doing some experimentation on my own
>design, I frequently had problems with ambient illumination causing
>saturation effects while using a fixed load resistor for the photodetector.

I don't think this would offer an advantage in the case of a 
phototransistor. Saturation in the phototransistor is determined by the 
series resistor between the collector and Vcc. The phototransistor is much 
more sensitive at 50/60 Hz than at 18 Khz. So, the method of interstage 
coupling doesn't make much difference because the saturation is at the 
input stage (front end, the phototransistor itself).

The photodiode has a tremendous dynamic range and about the same 
sensitivity at 50/60 Hz as it has at 18 Khz. So a photodiode can see 
massive amounts of 50/60 Hz energy and still respond to the 18 Khz laser 
signal even though it is much smaller.

Smile..

Art