ADRF6821 datasheet(32/61 Pages) AD

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ADRF6821

Data Sheet

Rev. A | Page 32 of 61

POWER SUPPLY CONFIGURATION

The ADRF6821 incorporates two main supply domains, namely

RF/IF and PLL/VCO. The RF/IF supply domain includes the

supplies related to the RF switch, the DSA, the mixer, the mixer

LO drivers, and the IF amplifier. The PLL/VCO supply domain

includes the PFD/CP, the VCO, the dividers, and the output

drivers.

RF/IF Supply Domain

Connect the RF/IF supply domain pins together with beads in

between and decoupling capacitors specific to each pin as shown

in Figure 62. The RF/IF supply pins draw a combined 350 mA

approximately. For the RF/IF supply domain, the ADRF6821

evaluation board employs the ADM7170, a low noise and high

power supply rejection ratio (PSRR) linear regulator that is

capable of delivering 500 mA.

The power supply rejection (PSR) of the RF/IF supply pins allow

the use of a switching supply to reduce the power consumption

on the linear regulators. The ADRF6821 evaluation board includes

the ADP2370 switching regulator and allows the observation of

the operation with a switching supply. The ADP2370 is a low

quiescent current buck regulator capable of delivering an output

current of 800 mA with a selectable switching frequencies of

600 kHz and 1.2 MHz. See the ADRF6821-EVALZ user guide

on how to configure the switching supply for RF/IF domain.

PLL/VCO Supply Domain

The PLL/VCO supply domain requires specific attention;

otherwise, performance degradation can result. The ADRF6821

incorporates an ultralow noise PLL and VCO that are sensitive

to any noise and/or frequency component at the supply pins.

These unwanted noise and frequency components degrade

the performance of the overall system. To avoid performance

degradation, the ADRF6821 evaluation board employs the

PLL/VCO supply domain circuit shown in Figure 63. The supply

circuit in Figure 63 uses the HMC1060, an ultralow noise, LDO

with four isolated outputs. Noise performance and isolated outputs

make the HMC1060 an ideal solution for the PLL/VCO supply

domain. For additional configuration options, refer to the

ADRF6821-EVALZ user guide.

0.1µF

10µF

100pF

VCC_3V3_I

0.1µF

100pF

VCC_3V3_Q

0.1µF

100pF

VCC_LO1

0.1µF

10µF

100pF

VCC_LO2

0.1µF

100pF

VCC_IFMIX_I

0.1µF

100pF

0.1µF

100pF

0.1µF

100pF

VCC_IFMIX_Q

VCC_IFMIX_I

VCC_IFMIX_Q

BEAD

ADM7170

Figure 62. RF/IF Domain Power Supply Circuit

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