Preliminary Technical Data
UG-1828
Rev. PrC | Page 275 of 338
RF AND CLOCK SYNTHESIZER SUPPLIES
The noise performance of the power domain used to power the RF blocks will directly affect the overall TRx phase noise. Power domains
should be powered using separate traces with extra isolation using a low DCR ferrite bead such as the Murata BLM18KG121TN1D or
similar device:
The power supply noise rejection on the synthesizer power input pins is very low. This means that any noise ripple on these pins will
affect the synthesizer performance. The RF synthesizer requires more critical supply decoupling because any noise or variation in voltage
that occurs during operation is directly imposed on the RF channel. Refer to Figure 259 for an example of how the power supply
connections are made on the ADRV9001 evaluation card.
The synthesizers are more susceptible to low frequency noise than other supplies because they have programmable loop filters. The loop
filter bandwidth directly affects the supply noise rejection on the synthesizers. For example, if the loop filter bandwidth is 50 kHz, then
any noise on the supply below 50 kHz will not be filtered. The roll-off of the loop filter provides the noise rejection above 50 kHz.
For each power domain, a ferrite bead with high isolation at the frequency of operation is recommended to help isolate the pin from the
supply source for best performance. This is especially important when operating in TDD mode. Such high isolation ferrite beads tend to
also have high dc resistance. This tradeoff is acceptable for the synthesizer power inputs because their low current draws will result in
relatively small voltage drops that are well within the supply tolerance range.
For domains that consume higher amount of current care should be taken to ensure that voltage drop on in-series Ferrite Bead does not
exceed power domain voltage tolerances. Good candidates for such Ferrite Beads with low DCR are PANASONIC EXC-ML20A390U
39OHM or MURATA, BLM15AX300SN1D or BLM18KG121TN1D.
For power domains which does not consume higher amount of current and at the same time higher level of isolation is desire a Ferrite
Beads with higher DCR are recommended. An example of recommended high DCR Ferrite Bead would be Taiyo Yuden, BK1005LL470-T
