comparator problem

Hey
I'm actually designing a comparator circuit


|--------feedback resistor------|
| |
| |---------------------| |
RC CIRCUIT ----|------|+ | |
| COMPARATOR CIRCUIT | |
INPUT----------|- |--|---------OUT
|---------------------|
The task is to design this cirucit in such a way that when an input
pulse (0.5,-2.5) with a pulse width of 8micro seconds is given it
should produce me an output which remains high for atleast like
64micro seconds..i tried using R=2248.5k and C=8500pF and the feedback
resistor i used was 90k..i was able to get an o/p which remains high
for 64microseconds but when looked at it carefuly i was able to figure
out that the outout remained high just beacuse of the large difference
between the resistors(the storage capacitance is not much observed in
the o/p graph)...it should basically work like a monostable
multivibrator (without using ic 555 timer though)...it would be of
great help to me if u could give me some suggestions as how could i do
this..

thanks
sk

 

Homework or not, I needed a rest from programming a damned PIC and as a
starter, suggest this ...
Should give a -repeatable- timed pulse of about 65uS.

+5V +5V +5V +5V +5V +5V
| | | | | |
.-. | --- .-. | |
| | | --- | | | |
| |1k | 1n| | | | .-.
'-' | | '-'10k | | |
|| | ___ |< | | | | |1k
o--||--o-|___|--| BC556 | | | '-'
IN || 10k |\ | | |\| |
o 1n | | o----|-\ |
| | | | | >--o---o
| '------o----------|+/ OUT
| | | |/|LM393 o
| | | | |
| .-. .-. | |
| | | | | | |
| | | | | | |
| 56k'-' '-'6k8 | |
=== | | | |
GND === === === ===
GND GND GND GND

(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)

 

[clip]

No good. Belay that. I Didn't read the question. The 8uS input pulse is the
critical feature.