Hi All.
We are working on a project where we need a very stable monostable to
produce 5 microsecond pulses every time an input pulses arrive. We
have tried IC 74123 and 74221 integrated circuits but the pulse width
is not stable enough. Does anyone know a circuit or integrated circuit
that produce high stable pulse width?. We need 5 microsecond pulses +-
0.01%. Actually we work in a range from 1 to 10 microsecond pulse
width.
As has been pointed out, 0.01% of 5usec is 500psec.
Alan Peake suggested using a 100MHz clock; if you built your timing
circuit with ON-Semiconductor's ECLinPS logic, you sould be able to
get up to 700MHz. Vectron you can order a 700MHz crystal-controlled
oscillator from Vectron
http://www.vectron.com/products/xo/co437457.htm
and there were other sources when I last looked (quite a few years
ago).
700MHz crystals aren't all that stable. If you want real stability,
use a 700MHz voltage-pullable crystal-controlled oscillator such as
this
http://www.vectron.com/products/vcxo/c5310.pdf
divide the ouptput down to 10MHz and use phase-locked loop to lock the
700MHz to a high-stability 10MHz source.
Getting 0.01% stability on the pulse width in such a system is a
breeze.
Obviously, the simple version of such a system can only start the 5
microsecon pulse on the next clock edge after your trigger pulse,
giving you a 1.43nsec jitter on the leading and trailing edges.
I've built a system around an 800MHz clock, where we used a time to
voltage converter to measure the off-set between the trigger and the
clock, digitised it eight bits (5psec) and used a programmable delay
to make the leading and trailing edges synchronous with the trigger to
5nsec (in principle - in practice, the jitter through the system was
about 100psec).
It took some 40nsec before the digital data was available to correct
the leading edge of the pulse.
The scheme we used to generate the programmable delay involved
discharging a capacitor and setting up a threshold with a D/A
converter; today you might use an ECLinPS digitally programmable delay
http://www.onsemi.com/pub_link/Collateral/MC10E195-D.PDF
http://www.onsemi.com/pub_link/Collateral/MC10EP195-D.PDF
The actual delays generated are temperature dependent; you'd probably
have to build in automatic self-calibration (we did) but you might be
able to getting away with putting it into a crystal oven, or
stabilising the temperature closer to room temperature by putting a
Peltier junction on the top of the package.