ADRF6801 datasheet(21/36 Pages) AD

21 / 36 page

ADRF6801

Rev. 0 | Page 21 of 36

APPLICATIONS INFORMATION

BASIC CONNECTIONS

The basic circuit connections for a typical ADRF6801 application

are shown in Figure 40.

SUPPLY CONNECTIONS

The ADRF6801 has several supply connections and on-board

regulated reference voltages that should be bypassed to ground

using low inductance bypass capacitors located in close proximity

to the supply and reference pins of the ADRF6801. Specifically

Pin 1, Pin 2, Pin 9, Pin 10, Pin 17, Pin 22, Pin 27, Pin 29, Pin 34,

and Pin 40 should be bypassed to ground using individual bypass

capacitors. Pin 40 is the decoupling pin for the on-board VCO

LDO, and for best phase noise performance, several bypass

capacitors ranging from 100 pF to 10 μF may help to improve

phase noise performance. For additional details on bypassing the

supply nodes, see the evaluation board schematic in Figure 42.

SYNTHESIZER CONNECTIONS

The ADRF6801 includes an on-board VCO and PLL for LO

synthesis. An external reference must be applied for the PLL to

operate. A 1 V p-p nominal external reference must be applied

to Pin 6 through an ac coupling capacitor. The reference is

compared to an internally divided version of the VCO output

frequency to create a charge pump error current to control and

lock the VCO. The charge pump output current is filtered and

converted to a control voltage through the external loop filter

that is then applied to the VTUNE pin (Pin 39). ADIsimPLL™

can be a helpful tool when designing the external charge pump

loop filter. The typical Kv of the VCO, the charge pump output

current magnitude, and PFD frequency should all be considered

when designing the loop filter. The charge pump current magnitude

can be set internally or with an external RSET resistor connected to

Pin 5 and ground, along with the internal digital settings applied to

the PLL (see the Register 4—Charge Pump, PFD, and Reference

Path Control section for more details).

RFIN

GND

VCCBB

GND

GNDRF

VCCRF

GND

VCCBB

MUXOUT

GND

RSET

DECL3

GND

CPOUT

VCC2

REFIN

VCC1

DECL2

ADRF6801

+5V

RF INPUT

+5V

EXTERNAL

REFERENCE

MONITOR

OUTPUT

OPEN

+5V

SPI CONTROL

IF Q-OUTPUT

BALUN

IF Q-OUTPUT

IF I-OUTPUT

BALUN

IF I-OUTPUT

CHARGE PUMP

LOOP FILTER

+5V

Figure 40. Basic Connections

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