internal 100-Ω termination with several biasing options. At POR, the EVM automatically applies a weak 1.3-V
common mode bias to the SYSREFREQ pins. However, the default EVM profile configures the SYSREF input
for DC-coupled input.
In DC-coupled mode, the common mode bias on the SYSREFREQ pins must be
between 1 V and 2 V.
The input common mode requirements can be fulfilled with a standard LVDS output
buffer.
For evaluating SYNC mode and SYSREF windowing, it is critical to have a SYSREFREQ input source capable
of consistently meeting setup and hold requirements for a single cycle of the input clock. This can become very
challenging at higher frequencies where setup and hold requirements can be < 50 ps. Another device capable of
picosecond-precision timed pulses, such as LMX2820 or LMX2594, could be used as a reference input to both
CLKIN and SYSREF for evaluating these features.
2.4 Output Connections
Connect any of the CLKOUT SMA connectors to a signal analyzer. All CLKOUT connections are AC-coupled at
the LMX1204EVM and can be connected directly to RF instruments with 0VDC requirements; an additional DC
block is not required. The unused CLKOUT SMA connector must be terminated with a 50-Ω load, or a differential
connection may be used if a balun with a suitable frequency range is available.
If additional hardware such as a high-speed oscilloscope and phase noise analyzer are available, they may also
be connected to the output SMA connectors. Recommended oscilloscope connections include one CLKOUT and
one SYSREF output from the same channel, as well as the one LOGICLK and one LOGISYS output.
Other unused CLKOUT SMA connectors should be terminated with 50-Ω single-ended or 100-Ω differential load,
or alternately should be disabled in software, to minimize unterminated output effects on performance.
2.5 Programming Interface
After the 2.5-V power supply has been connected and power has been applied to the EVM, connect the USB
cable from the PC to the EVM. The USB interface will provide the necessary power to enable the onboard
USB2ANY controller. A firmware update may be required; if prompted, see
for more details.
Run TICS Pro software and open the device profile:
1. From the top-menu, click
Select Device → Clock Distribution with Divider → LMX1204
EVM Connections
SNAU266 – JULY 2021
LMX1204EVM User's Guide
5
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