9
The external trigger input is conditioned by a precision voltage comparator before
connecting to the TRIGGER MULTIPLEXER. The reference input of the comparator
is connected to a programmable voltage source. Trigger polarity and input
impedance are programmable.
All triggers can be gated on or off by applying an asynchronous TTL-level signal to
the GATE connector. In addition, both the internal and the external triggers can be
configured to pass
n
of
m
triggers, thereby providing burst capability.
HIT FLIP-FLOP
. The Hit Flip-Flop initiates the timing cycle and enables the main
timing oscillator. The output of the Hit Flip-Flop is connected through a driver to the
T0 output. The EOD logic clears the flip-flop when all channels have completed their
output pulses, preparing the P400 for a new timing cycle.
10 MHZ CLOCK
. This temperature-compensated, crystal-controlled oscillator
(TCXO) is the timing reference for all delays. An optional ovenized oscillator (OCXO)
is also available. The OCXO is more stable over time and temperature than the
TCXO and contributes less jitter to long delays. The 10-MHz clock can be locked to
an external 10-MHz clock through the CLOCK connector on the back panel.
50-MHZ OSCILLATOR
. This oscillator provides the coarse (20-ns granularity)
component of all delays. A DSP-based phase-lock system locks the 50-MHz
oscillator to the internal crystal-controlled 10-MHz clock, making the oscillator as
accurate as the clock while preserving phase coherency to the original trigger.
DIGITAL (COARSE) COUNTERS
. The output of the 50-MHz oscillator is connected
to eight digital counters, two for each output channel. The first counter times the
leading edge of the pulse, the second counter times the trailing edge.
VERNIER DELAYS
. A fine-resolution delay circuit follows each digital counter to
interpolate delays to 1-ps resolution. The output of each vernier delay is connected to
an output driver.
OUTPUT DRIVERS
. Each of the four channels has a single output driver. The output
driver combines the leading-edge and the trailing-edge signals to produce a single
channel output. Each driver has programmable polarity, and high and low voltage
levels.
MICROPROCESSOR SYSTEM
An internal 32-bit microprocessor subsystem
manages the P400. It interacts with the front-panel controls and displays and the
external RS-232 and Ethernet interfaces.
