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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
Check your user manual regarding your oscilloscope probes because
oscilloscopes usually have a direct input input impedance of around 1 MOhm // 15 pF a x1 probe just adds to the capacitance, say 1 MOhm // 45 pF a x10 probe has lower input capacitance, say 10 pF
so always use your probe in x10 mode, unless the signal is to low a voltage to see clearly on the 'scope. to reduce high frequency loading of the circuit being 'scoped.
before using the probe on x10 you need to adjust it using the small screwdriver slot on the body of the probe where it plugs into the 'scope, see your manual for details.
Given the above, it is quite likely that your 'scope probe in
. x1 mode loaded the circuit enough to eliminate the spikes/ringing/overshoot . x1 mode has a lower frequency response than your 'scope, e.g. 7 MHz so cannot 'see' the overshoot . x10 mode may be showing overshoot that is not actually there as the probe has not been adjusted
these things come with experience, you will soon catch up !
Registered Member #3114
Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
Sulaiman wrote ...
Check your user manual regarding your oscilloscope probes because
oscilloscopes usually have a direct input input impedance of around 1 MOhm // 15 pF a x1 probe just adds to the capacitance, say 1 MOhm // 45 pF a x10 probe has lower input capacitance, say 10 pF
so always use your probe in x10 mode, unless the signal is to low a voltage to see clearly on the 'scope. to reduce high frequency loading of the circuit being 'scoped.
before using the probe on x10 you need to adjust it using the small screwdriver slot on the body of the probe where it plugs into the 'scope, see your manual for details.
Given the above, it is quite likely that your 'scope probe in
. x1 mode loaded the circuit enough to eliminate the spikes/ringing/overshoot . x1 mode has a lower frequency response than your 'scope, e.g. 7 MHz so cannot 'see' the overshoot . x10 mode may be showing overshoot that is not actually there as the probe has not been adjusted
these things come with experience, you will soon catch up !
Thanks Sulaiman, I know how to adjust the probes with a screw driver and I had them properly tuned.
So I will switch back to x10 and just add a load resister to help dampen the output more.
Is there a better (faster or more stable) tunable schmitt-trigger oscillator that I should use or is the SN74HC14N going to be ok to drive IXDD614CI.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
An OCXO (oven controlled crystal oscillator) is overkill don't you think ? Temperature changes will alter the inductance of air core inductors much more than the frequency of the crappiest crystal oscillator
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