T
Tim Williams
- Jan 1, 1970
- 0
Reading through AN47 by Jim Williams, I *knew* I had to build a pulse
generator. I mean it's just too fucking simple.
So I thought, what low voltage, fast BJTs do I have, and I realized I have
some PH2369's pulled from a monitor video drive board (they were the bottom
of a cascode gain stage driving a class B emitter follower, of all things).
Coincidentially, the transistor Jim used is a *2N*2369...
So I grabbed a 47 ohm resistor, 2.2k, 10k and 100k (so a bit more rapid than
Jim's ;-). Discovering my bench supply tops out at 36V, a bit too low for
avalanche breakdown, I wired up a MOSFET, inductor and fast diode to my
signal generator for a quick 100V booster.
The results:
http://webpages.charter.net/dawill/Images/Pulse_1.jpg
Simple layout, tight; note red wire going under 47 ohm resistor and signal
lead as quasi-ground plane.
Reponse:
http://webpages.charter.net/dawill/Images/Pulse_2.jpg
5V/div vertical, 500ns/div horizontal. Note uncertainty in repetition
rate -- okay, so the supply has a bit of hum on it...
Maximum sweep rate, 10ns/div:
http://webpages.charter.net/dawill/Images/Pulse_3.jpg
X10 button (1ns/div):
http://webpages.charter.net/dawill/Images/Pulse_4.jpg
Now this is with my Tek 475, which is "only" 200MHz, so this pulse ought to
be considerably taller and thinner than shown.
And not to forget the second most important element: the transmission line
is a 3' 50 ohm BNC cable from pulse generator to scope input. A tee and 50
ohm (looks solid enough) terminator complete the scope end.
Pretty bouncy after the pulse, could be a number of things. I'm not
complaining, since this is the fastest thing I've observed, or generated for
that matter.
Tim
generator. I mean it's just too fucking simple.
So I thought, what low voltage, fast BJTs do I have, and I realized I have
some PH2369's pulled from a monitor video drive board (they were the bottom
of a cascode gain stage driving a class B emitter follower, of all things).
Coincidentially, the transistor Jim used is a *2N*2369...
So I grabbed a 47 ohm resistor, 2.2k, 10k and 100k (so a bit more rapid than
Jim's ;-). Discovering my bench supply tops out at 36V, a bit too low for
avalanche breakdown, I wired up a MOSFET, inductor and fast diode to my
signal generator for a quick 100V booster.
The results:
http://webpages.charter.net/dawill/Images/Pulse_1.jpg
Simple layout, tight; note red wire going under 47 ohm resistor and signal
lead as quasi-ground plane.
Reponse:
http://webpages.charter.net/dawill/Images/Pulse_2.jpg
5V/div vertical, 500ns/div horizontal. Note uncertainty in repetition
rate -- okay, so the supply has a bit of hum on it...
Maximum sweep rate, 10ns/div:
http://webpages.charter.net/dawill/Images/Pulse_3.jpg
X10 button (1ns/div):
http://webpages.charter.net/dawill/Images/Pulse_4.jpg
Now this is with my Tek 475, which is "only" 200MHz, so this pulse ought to
be considerably taller and thinner than shown.
And not to forget the second most important element: the transmission line
is a 3' 50 ohm BNC cable from pulse generator to scope input. A tee and 50
ohm (looks solid enough) terminator complete the scope end.
Pretty bouncy after the pulse, could be a number of things. I'm not
complaining, since this is the fastest thing I've observed, or generated for
that matter.
Tim