ADF7901

Preliminary Technical Data

Rev. PrD | Page 10 of 12

3pF

8pF

22nH

27nH

5.6pF

DVDD

RFOUT

RSET

3.6k

Ω

CREG2

2.2mF

220nF

CVCO

CPOUT

VCOIN

VCOIN

FSK1

FSK2

FSK3

OOK_SEL

TxDATA

CE

9.8304MHz

33pF

33pF

GND

OSC2

OSC1

ANTENNA

ADF7901

PA_EN

RSET_FSK

RSET_OOK

3.6k

Ω

3.6k

Ω

CREG1

2.2mF

3pF

1.5pF

22nH

36nH

MATCHING 50 V

TO ANTENNA

5TH ORDER LOW PASS FILTER

MATCHING RFOUT TO 50V

NOTES

1. DECOUPLING CAPACITORS HAVE

BEEN OMITTED FOR CLARITY.

Figure 8. Applications Diagram for the ADF7901 in a Remote Control System

LAYOUT GUIDELINES

The layout of the board is crucial to ensuring low levels of

spurious and harmonics.

Decoupling

Decoupling capacitors (high frequency 22 pF, low frequency

100 nF) should be placed as close as possible to the supply pins

on the part. Low size 0402 and 0603 components are recom-

mended for the high frequency rejection on the supply.

Regulator Stability

stability. An additional 22 pF capacitor can be added to reject

higher frequency noise. Since many of the internal block run off

the regulator it is critical to reduce the noise on this. Low size

0402 and 0603 components are recommended for the high

frequency rejection on the supply.

Grounding

Emphasis should be placed on the grounding once the

decoupling capacitors have been added. The PA stage switches

currents of 15 mA in max power mode. This will cause changes

in the ground resulting in large return currents which can

radiate to other parts of the board. The shortest and least

obstructed ground from RFGND back to the ground of the

battery should be ensured. A 4-layer board will help, as well as

flooding of the top layer. The ground paths should not have any

vias, and should be wide tracks.

Supply

The supply tracks can be routed through vias, as these act as

free inductors on the board and make layout easier on a 2-layer

board. See the Decoupling section. Tracks should be wide.

Digital Lines

Any digital lines should contain a large resistor in series. This

impedance will block signals of many frequencies including

harmonics and the carrier frequency. Long control lines can act

as an antenna. It can be useful to add capacitance to ground.

There will be some capacitance to ground provided by the lines,

and at the input of the digital pins.