MICRF221 datasheet(20/26 Pages) MICREL

20 / 26 page

Micrel Inc.

MICRF221

October 2008

M9999-100108

(408) 955-1690

PCB LAYOUT RECOMMENDATIONS

PCB Considerations and Layout

Figures 19 to 22 below, show some of the printed

circuit layers for the QR221BPF board, refer to Figure

5. Use the Gerber files provided (downloadable from

the Micrel Website at: www.micrel.com ), which have

the remaining layers needed to fabricate this board.

When copying or making one’s own boards, make

traces as short as possible. Long traces alter the

matching network and the values suggested are no

longer valid. Suggested Matching Values may vary

due to PCB variations. A PCB trace 100 mills (2.5mm)

long has about 1.1nH inductance.

Optimization should always be done with exhaustive

range tests.

Make individual ground connections to the ground

plane with a VIA for each ground connection. Do not

share VIAs with ground connections. Each ground

connection = one or more VIAs. The ground plane

must be solid and, if possible, without interruptions.

Avoid a ground plane on the top layer next to the

matching element, as it will normally add additional

stray capacitance, which changes the matching.

Do not use phenolic material; use only FR4 or better

materials, since phenolic material is conductive above

200MHz.

The RF path should be as straight as possible,

avoiding loops and unnecessary turns.

Separate the ground and VDD lines from other circuits

(microcontroller, etc).

Known sources of noise should be positioned as far

as possible from the RF circuits.

Avoid thick traces. The higher the frequency, the

thinner the trace should be to minimize losses in the

RF path.

Figure 19. QR221BPF Top Layer

Figure 20. QR221BPF Bottom Layer, Mirror Image

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