Instrument Design and Function Description CMU
1100.4903.82 3.8 E-4
REARPANEL BOARD2
The REARPANEL BOARD2 is mounted to the right of the integrated
and unscrewable rear panel plate and accommodates the interfaces
SERVICE, AUX, AUX4 as well as further spare interfaces. For
connection with MOTHERBOARD1 two 34-pin ribbon cables are used.
REFERENCE BOARD
The REFERENCE BOARD provides all required clock signals (NETCLK1/2) and reference frequencies
(110.8 MHz) as well as the +5 VDC reference voltage for the CMU. The REFERENCE BOARD is a
plug-in module in HVC design.
Design
At the top of the module, nine MMCX connectors are attached, which
serve as inputs or outputs for various clock signals and are routed to the
respective modules or the integrated rear panel with appropriate coax
cables.
Two holes in the HVC panel at the top are used for adjusting the
+5 VDC reference voltage and the 10 MHz TCXO reference frequency.
Connection
The plug-in module REFERENCE BOARD is inserted in the CMU on the
right side on MOTHERBOARD2 using a 48-pin FUTURE-bus connector.
REFERENCE
frequency generation
All frequencies provided by the CMU are derived from internal high-
precision 10-MHz reference elements (TCXO or optional OCXO) or from
externally applied frequencies.
A 110.8-MHz crystal oscillator is coupled in locked phase relation in a
PLL loop with the selected reference.
The reference element TCXO is used as standard on the reference
board. If the option OCXO (CMU-B11 or -B12) is installed in the CMU, it
is automatically used as reference element and the standard TCXO is
switched off.
It is additionally possible to switch over to external synchronization (see
operating manual, 4.34 Connection Control-Synch.) and use the signal
fed in at the BNC connector REFIN at the rear of the CMU as reference
signal.
At the BNC connector REFOUT1 at the rear of the CMU, either the
internal 10-MHz reference frequency or the signal applied at REFIN can
be buffered and tapped depending on the selected reference element.
The 110.8-MHz sinewave signal of the crystal oscillator passes a
harmonics filter, is buffered and provided at three MMXC connectors,
serving as reference frequency for the RXTX BOARD1/2 and the
DIGITAL BOARD.
At a further MMCX connector, the TTL signal RESFREQ is available with
27.7 MHz (110.8 MHz / 4) for the option CMU-B41
AUDIO-GEN. + ANA. as clock signal.
Netclock generation
The REFERENCE BOARD is also used for netclock generation,
providing adjustable TTL clock frequencies from 21 MHz to 84 MHz with
a very fine frequency resolution of 0.1 Hz. This function is provided twice
so that two independent netclock frequencies are available at the same
time.
The signal generated by the 110.8-MHz crystal oscillator is divided by
three and applied to a DDS circuit (Direct Digital Synthesis). The DDS
circuit is used as a fine-adjustable frequency divider and generates a
divided signal from 9 MHz to 12 MHz.
This signal is then used in a further PLL as nominal value for the phase
detector in order to tune a VCO (Voltage Controlled Oscillator) with a
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