
UG-1548 EV-ADF4372SD2Z User Guide
Rev. 0 | Page 4 of 21
EVALUATION BOARD HARDWARE
The EV-ADF4372SD2Z requires the SDP-S platform that uses
the EVAL-SDP-CS1Z. The SDP-B is not recommended.
The EV-ADF4372SD2Z schematics are shown in Figure 9,
Figure 10, Figure 11, and Figure 12. The silkscreens for the
evaluation board are shown in Figure 13 and Figure 14.
POWER SUPPLIES
The EV-ADF4372SD2Z board is powered by a 6 V power supply
connected to the VSUPPLY SMA, or the red banana plug, P2.
Connect GND to the black banana plug, P4.
The power supply circuitry has two LT3045, high performance, low
noise, and low dropout (LDO) regulators.
One LT3045 is used to generate 5 V to drive the VCO supply pins.
The remaining supplies are powered from the other LT3045, which
is set to 3.3 V voltage.
Use Switch S1 to switch the 6 V to the EV-ADF4372SD2Z on
and off.
RF OUTPUT
The EV-ADF4372SD2Z has three pairs of SMA, 3.5 mm output
connectors: RF8P/RF8N, RFAUX8P/RFAUX8N, and
RF16P/RF16N (differential outputs). Because these ports are
sensitive to impedance mismatch, connect the radio frequency
(RF) outputs to equal load impedances.
If only one port of a differential pair is used, terminate the
complementary port with an equal load terminator (in general,
a 50 Ω terminator).
LOOP FILTER
The loop filter schematic is included in the board schematic in
Figure 9. Figure 2 shows the loop filter component placement. The
loop filter on the evaluation board is optimized for fractional mode
performance with a phase frequency detector (PFD) frequency of
100 MHz and 1.8 mA charge pump current. The values of the loop
filter components are as follows:
• Resistors: RCPOUT = 91 Ω, R2 = 400 Ω, R4 = 200 Ω,
R15 = 0 Ω
• Capacitors: C20 = 220 pF, C19 = 0.018 μF, C23 = 330 pF
C22 C20
R15
RCPOUT
RVTUNE
C12 C1T C1
C9C8
C3
R2
R4 C23
C19
20393-002
Figure 2. Loop Filter Component Placement
The lowest rms jitter is achieved in integer mode by using a high
PFD frequency. This jitter can be tested by using the same filter
with a PFD frequency of 200 MHz (enabling the doubler) and
2.4 mA charge pump current. Additional optimization is still
possible depending on target frequency and integration limits.
In general, narrower loop filter bandwidths have lower spurious
signals. Wide loop filters in Integer N mode can achieve <50 fs
jitter with very clean reference frequency input (REFIN) signals.
ADDITIONAL OPTIMIZATION ON LOOP FILTER
The PLL loop bandwidth can be optimized for different
parameters like reference spurs or VCO noise, depending on
the system requirements.
Reducing Σ-Δ Modulator (SDM) Noise
In fractional mode, SDM noise becomes apparent and starts to
contribute to overall phase noise. This noise can be reduced to
insignificant levels by using a series resistor between the CPOUT
pin and the loop filter. Place this resistor close to the CPOUT pin.
Select a reasonable resistor value that does not affect the loop
bandwidth and phase margin of the designed loop filter. In most
cases, a 91 Ω resistor value produces the best results. This resistor
is not required in Integer N mode (SDM not enabled) or when a
narrow-band loop filter (SDM noise attenuated) is used. This
resistor is labeled as RCPOUT in schematics.
Optimizing Spurious Signals
The loop filter is placed at the secondary side of the EV-
ADF4372SD2Z to create a more compact layout and so that the
board is more tolerant to external signals. Using a capacitor
on the same side with the ADF4372 (the primary side) results in
higher isolation on internally generated spurious signals. For this
purpose, a small valued capacitor (C26 = 10 pF) is placed close
to the VTUNE pin on the primary side.
REFERENCE SOURCE
The EV-ADF4372SD2Z board is supplied with a low noise
100 MHz crystal oscillator (XO) from Crystek (CCHD-575-50-
100.000).
To us e an external single-ended REFIN, connect a low
noise reference source to the REFP SMA connector. Remove
Resistor R19 (0 Ω) and Resistor R20 (0 Ω) to remove power
from the crystal and break the connection to the REFP input.
DEFAULT CONFIGURATION
All components necessary for local oscillator (LO) generation are
inserted on the EV-ADF4372SD2Z board. The EV-ADF4372SD2Z
board is shipped with a 100 MHz XO, the ADF4372 synthesizer
with an integrated VCO, and a 180 kHz loop filter (charge
pump current (ICP) = 1.8 mA).
DOUBLER OUTPUT
The ADF4372 contains a frequency doubler to double the 4 GHz
to 8 GHz VCO signal on RF16P and RF16N.