If one is feeling paranoid about ground loop noise (and wishes to avoid
transformers, optoisolators , or fibre optics), etc one could always use
an LVDS driver with a batter powered(?) LVDS to CMOS receiver/translator
right at the 5370A/B input BNC connector.
This may be useful for a DMTD system that uses a 5370A/B.
Bruce
Bob Camp wrote:
Hi
AC cmos will easily drive an L pad to match a 50 ohm cable at these levels.
That's true at either 3.3 or at 5.0 volts. There are a lot of cmos families out
there that beat AC for speed and match the output drive capability.
Bob
On Feb 27, 2010, at 9:12 PM, Bruce Griffiths wrote:
1) One method with 5V CMOS is to add a resistive voltage divider at the CMOS
driver output with a 50 ohm output impedance at the tap that drives the 5370A/B
input.
2) If one has a 5V 50 ohm driver (eg Thunderbolt PPS output) use a 50 ohm
attenuator at the 5370A/B input.
For a 5370A an attenuation of at least 11dB is required.
For a 5370B an attenuation of at least 3dB is required.
3) One can always use the 10x input attenuation setting built in to the 5370A/B
however this reduces the signal swing to 0.5V at the trigger amplifier input
(5V CMOS input).
4) Attenuate the output of the logic signal by a factor of 2 and use an npn
emitter follower to drive the 50 ohm load.
5) Use 3.3V CMOS signal levels for the 5370B.
6) Use a current mode emitter or source coupled switch to drive the 5370A/B
input.
The switching jitter of the above drivers will be much lower than the internal
noise of the 5370A/B as long as HCMOS or faster logic is employed.
Bruce
Bob Camp wrote:
Hi
Which *still* carefully avoids the issue of how .....
Bob
On Feb 27, 2010, at 8:52 PM, Bruce Griffiths wrote:
Oops! a small correction (2nd paragraph):
For the 5370A attenuating the 5V CMOS signal to a 1V swing with the threshold
set to 0.5V is close to optimum.
An input signal with limits of 0V and +1.4V with a trigger threshold of 0.7V is
the maximum usable (for high performance).
An input signal with limits of 0V and +0.3V with a trigger threshold of 0.15V
is the minimum usable (for high performance).
For the 5370B attenuating the 5V CMOS signal to a 2V swing with the threshold
set to 1V is close to optimum.
An input signal with limits of 0V and +3.5V with a trigger threshold of 0.7V is
the maximum usable (for high performance).
An input signal with limits of 0V and +0.3V with a trigger threshold of 0.15V
is the minimum usable (for high performance).
Thus using the PPS output (~270 ohm is series with a 5V 74AC04 output) from a
Synergy evaluation board that uses an M12M or M12+ GPS timing receiver to drive
the inputs (with a 0-750mV signal) of a 5370A or 5370B is well within the
recommended input signal range for high performance.
This avoids having to adding an external 5V 50 ohm driver that some would use.
Bruce
Bob Camp wrote:
Hi
So exactly how did you know that I bought a (cheap) 5370B a few hours ago on
the e-place and was just about to ask about how best to use it.
Hmmmm.......
Bob
On Feb 27, 2010, at 7:01 PM, Bruce Griffiths wrote:
The attached excerpts from the 5370A and 5370B manuals indicate that for best
performance, that the common practice of driving the 5370A/B 1x inputs directly
from a 5V CMOS logic signal is a bad idea.
For the 5370A attenuating the 5V CMOS signal to a 1V swing with the threshold
set to 0.5V is close to optimum.
An input signal with limits of 0V and +1.4V with a trigger threshold of 0.7V is
the maximum usable (for high performance).
An input signal with limits of 0V and +0.3V with a trigger threshold of 0.15V
is the minimum usable (for high performance).
For the 5370A attenuating the 5V CMOS signal to a 2V swing with the threshold
set to 1V is close to optimum.
An input signal with limits of 0V and +3.5V with a trigger threshold of 0.7V is
the maximum usable (for high performance).
An input signal with limits of 0V and +0.3V with a trigger threshold of 0.15V
is the minimum usable (for high performance).
Bruce
<5370ATriggering.png><5370BTriggering.png>_______________________________________________
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