Products > Test Equipment
Cheap Fast Rise Time Oscillator
jonpaul:
Bonjour, topic seems off a bit this is a fast rise pulse generator, an oscillator is normaly a sinne wave output.
See this related EEVBLOG thread re probes, many tests and shots of fast rise pulsers, DIY, Leo B with various scopes and probes.
https://www.eevblog.com/forum/testgear/probe-into-probes-whats-up/50/
The Leo Bodnar 40 pS BNC pulse gen is low cost, high developed and very fine performance. Was ~~ L 50
http://www.leobodnar.com/shop/index.php?main_page=product_info&products_id=295
Our Leo B has give fine service for many years.
Here are my 2019 Tektronix 7104/&A29/LeoB 40 pS shots with Mini Ckts 20 db 50 Ohm atten.
After selection of 7A29 and transient response adjustment both 7A29 and 7104, perhaps the best I can do.
Your thoughts appreciated!
Lower pix BNC inline atten and 50 Ohm term collection.
Vive l'ANALOG! Vive TEKTRONIX! !
Jon
BillyO:
So I maybe not following you 100%, but what I'm getting is that the LB pulser gave you a 10ns rise time when directly connected, but a .79 ns when connected via a 20 db attenuator. Is that correct?
Just a bit of confusion.
In my experience, the rise time improves with increased current in the load.
jonpaul:
Rebonjour, BillyO:
1/ Leo Bodnar 40 pS is designed to drive a 50 Ohm termination or 50 Ohm scope input.
There is no spec for other Zo, so current is the same with and without the attenuator, and load not the issue.
See the spec sheet of the LB 40 pS.
2/ A constant impedance atten is a resistive T or Pi network designed to attenuate with same Zo input/output eg 50 Ohms.
See spec sheet of Mini Circuits HAT-20 wideband 50 Ohm attenuator.
See Tee /Pi attenuator
Thus the load on the LeoB pulser is 50 Ohms with or sans the HAT-20 attenuator.
3/ Purpose of the attenuator is to the reduce reflected energy from scope t pulser due to VSWR or Zo mismatch.
Thus pulse aberrations due to reflections from scope to pulser are reduced and the test aberration is reduced.
Pix: Leo B USB utility , allows Vo adjust 50 mV>>1.5 V set at 1.0V P-P into 50 Ohm.
Yokogawa DL7440 500 MHz BW, FS = equv 100 G/sec, sweep at 1 nS/div
Upper trace LeoB40 direct to scope 50 Ohm input
Lower trace LeoB40>>Mini Ckts HAT-20 atten>scope 50 Ohm input
Many previous old EEVBLOG threads on similar like "show us your squarewave" TD pulser, Avalanche pulser, etc.
Hope all is now clear!
Jon
David Hess:
One way to get a cleaner pulse is to use the output of the logic gate to drive the emitter/source of a common base/gate transistor with then has a pull-up or pull-down on its collector/drain to produce the output. Then on the rising or falling edge, the transistor "disconnects" the gate from the output and only the pull-up or pull-down in parallel with a very small capacitance is connected to the transmission line. This essentially duplicates how an ECL output from a differential pair works.
Some designs may use a microwave diode in place of the transistor.
magic:
Do you expect that ordinary 3904 could be good enough to compete with "bare" LVC logic in terms of rise/fall time?
Or are we talking some special RF transistors?
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