Avtech AVR-G5-B, Instructions Manual

Page: 23 / 43

GATING MODES
Triggering can be suppressed by a TTL-level signal on the rear-panel GATE connector.
The instrument can be set to stop triggering when this input high or low, using the front-
panel gate menu or the appropriate programming commands. This input can also be
set to act synchronously or asynchronously. When set to asynchronous mode, the
GATE will disable the output immediately. Output pulses may be truncated. When set to
synchronous mode, the output will complete the full pulse width if the output is high,
and then stop triggering. No pulses are truncated in this mode.
OUTPUT IMPEDANCE
The AVR-G5-B has an output impedance (i.e., an internal resistance in series with the
output) of 50 Ohms, to provide transmission line back-matching and short-circuit
protection.
The rise and fall times are fixed at less than 20 ns. However, since the output
impedance is 50Ω, the rise and fall times will degrade if cable lengths longer than 1
meter (3 feet) are used on the output, due to the cable capacitance. The maximum
usable cable length is 2 meters (6 feet).
LOAD IMPEDANCE
The AVR-G5-B can drive load impedances of 100 kΩ or higher.
The AVR-G5-B is NOT designed to drive 50 Ω loads or highly capacitive loads. The
AVR-G5-B is tested with capacitive loads of 100 pF. Load capacitance should not
exceed 100 pF.
PREVENTING OUTPUT STAGE FAILURE
The output stage is protected against overload conditions by an overload circuit and
fuses on the main frame back panel. However, the output switching elements may fail if
the unit is triggered at a PRF exceeding 100 kHz or if the load impedance is too low (<
100 kΩ or > 100 pF). Heating and subsequent possible failure of the output stage is
reduced if the following action is taken where possible:

PRF is kept to a minimum, i.e. operate in a low PRF range when possible rather
than in a high PRF range.

Keep the output PW to a minimum.

Never apply an externally generated voltage to the output port.
23