Products > Test Equipment
Cheap Fast Rise Time Oscillator
blackdog:
Hi,
I tested and few years ago different cmos logic ICs for a nice fast pulse with few abberations.
I never managed to get it really nice due to such things as the length of the bonding wire in the IC and the various decoupling capacitors.
But the SO enclosure you still get and somewhat better result and think about your PCB pathways, make the output 50 Ohm with multiple resistors of different outputs, e.g. 4x a 200 Ohm resistor in parallel.
In the end I bought the Leo Bodnar pulser.
PS
And just like jonpaul pointed out, use an attenuator 10 a 20dB to get the SWR as good as possible.
Kind regards,
Bram
mawyatt:
--- Quote from: magic on February 03, 2023, 10:57:17 pm ---....
Maybe it's the Chinese chip being better than original AC logic.
One pattern I have seen in knockoff ICs is that they are often die shrinks on more advanced processes; apparently it saves them money somehow.
....
--- End quote ---
Recurring chip cost to the Original Chip Manufacture (OCM) is directly related to the chip area, smaller chip lower cost. Think many generic chips are now fabbed in smaller feature size processes which yields smaller chips, wether the OCM offers this at a lower cost depends on the chip, market, technology and so on but their recurring cost is lower because of the smaller chip area. Of course these chips also benefit from a faster process which may benefit the end user!!
Best,
BillyO:
--- Quote from: jonpaul on February 03, 2023, 09:59:03 pm ---Please compare to Leo Bodnar 40ps pulser, BNC and 30 pS SMA versions
--- End quote ---
I don't have the SMA version, just the BNC version.
The Bodnar is the lower trace. Twice as fast as mine and less ringing.
tggzzz:
--- Quote from: BillyO on February 04, 2023, 12:36:40 am ---
--- Quote from: jonpaul on February 03, 2023, 09:59:03 pm ---Please compare to Leo Bodnar 40ps pulser, BNC and 30 pS SMA versions
--- End quote ---
I don't have the SMA version, just the BNC version.
The Bodnar is the lower trace. Twice as fast as mine and less ringing.
--- End quote ---
The amplitude of the overshoot is pretty similar.
The frequency of your "oscillation" is much lower; as best as I can see, the peak-to-trough is 0.3div vs 1.1div.
Since it is the same scope, I think that points to your construction and components. "Excess" inductance or capacitance somewhere would, of course, lower the frequency; 10* capacitance or 10* inductance would be necessary to see that. I doubt the capacitance has changed that much, so my bet is on the inductance. That would be consistent with long leads between chip, PCB and decoupling capacitors.
magic:
--- Quote from: Bud on February 03, 2023, 11:03:48 pm ---Actually the logo looks familiar, but can't remember who it was.
--- End quote ---
Of course it does. It's the logo of WanHungLo Semiconductor Shenzhen :P
Found an example: https://www.eevblog.com/forum/projects/watch-out-for-fake-74ls-logic-ics
They do analog too: https://www.eevblog.com/forum/beginners/lm741-testing/msg4466656/#msg4466656
All DIP8 chips here are also fakes.
--- Quote from: blackdog on February 03, 2023, 11:23:03 pm ---I tested and few years ago different cmos logic ICs for a nice fast pulse with few abberations.
I never managed to get it really nice due to such things as the length of the bonding wire in the IC and the various decoupling capacitors.
--- End quote ---
:-+
That's why I always advocate for using the smallest available package and most compact layout whenever this topic recurs.
The mikrocontroller.net thread clearly shows what's possible with a single LVC gate in SOT23.
Those things aren't any more expensive or harder to get, so why bother with DIP?
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version