We have discovered some poorly-documented "features" of the MQT200F
time-to-charge converter from LeCroy. It should be noted that other
than these problems the chip performs as advertised.
These comments will probably not mean much to you unless you have read
and understood in detail the data sheet for the MQT200F.
Run-Up Current Limitation
About 30% of the chips we have tested don't work with a run-up current
(IRU) larger than 100uA. According to the data sheet, currents up to
250uA should work.
TIME Signal Leading Edge Uncertainty
The TIME signal (logic output from the MQT200F) produces a pulse whose
width is supposedly proportional to the charge integrated during the
gate. The leading edge of the TIME signal occurs after delay of about
200-450ns from the leading edge of the GATE input. This delay varies
from chip to chip.
TIME Signal Termination
The TIME signal is advertised as a TTL-compatible logic output. In
fact it performs very poorly driving TTL; a Thevenin-equivalent
termination to about 1V and discriminator are required for good
performance. Please see our daughtercard schematic for a working
example.