AD9361 Reference Manual
UG-570
| Page 125 of 128
Rx and Tx Synthesizer Supplies
The power supply noise rejection on the VDDA1P3_
Rx_SYNTH and VDDA1P3_Tx_SYNTH power domains is
very low. This means that any noise ripple on these balls will
affect the synthesizer performance. The supply noise on the
synthesizers will degrade the phase noise. For the best
performance, in the FDD mode, VDDA1P3_RX_SYNTH,
VDDA1P3_TX_SYNTH, VDDA1P3_RX_LO,
VDDA1P3_RX_VCO_LDO, VDDA1P3_TX_LO,
VDDA1P3_TX_VCO_LDO can be powered up with a
separate low noise LDO. This will also help in mitigating
effects of transients on the 1.3 V analog supply. The evalua-
tion board uses this power design.
Tx Balun DC Feed Supplies
Each transmitter requires 150 mA of current that the DC feed
of the balun supplies. To reduce switching transients when
attenuation settings change, the balun DC feed must be
powered directly by the 1.3 V plane. A 10 μF and a 0.1 μF
capacitors are helpful on the DC feed pin to eliminate spurs on
the Tx spectrum and dampen the transients.
Figure 91. Power Supply Fingers
1
166
8-
0
92
Rev. A