"ROBERT SAYRE" wrote to "GREG MAYMAN" (29 Dec 02  18:14:00)
 --- on the topic of "DIGITAL CLOCKS"

 RS> My understanding is that the transistors take a
 RS> long time to turn OFF once saturated. The faster
 RS> the IC is switched, the higher the current because
 RS> of this.

 RS> That's why they added Schottky diodes from base
 RS> to collector inside some IC's. The voltage drop
 RS> across a Schottky diode is .3V. This "pulls" the
 RS> base voltage down as the collector tries to go
 RS> below .3 to .4V (approaches saturation) preventing
 RS> saturation and speeding up turn Off.

I think there is another factor in the choice of using Schottky diodes.
Ask yourself the question why not simply use a low forward voltage diode
such as Germanium? The problem is that the capacitance of a diode
increases as its reverse bias voltage becomes smaller. The diode
capacitance actually becomes a maximum just as it starts to conduct. The
choice of Schottky diodes is because they have a low forward voltage and
can be made very tiny with very little capacitance.

 Mike
 ****

... High Voltage Electronics:  Life's a glitch, then you fry.
--- Blue Wave/DOS v2.30