Layout Considerations

A properly designed PC board is an essential part of

any RF/microwave circuit. On the PA output, use con-

trolled-impedance lines and keep them as short as

possible to minimize losses and radiation. At high fre-

quencies, trace lengths that are on the order of

λ/10 or

longer can act as antennas.

Keeping the traces short also reduces parasitic induc-

tance. Generally, 1in of PC board trace adds about

20nH of parasitic inductance. The parasitic inductance

can have a dramatic effect on the effective inductance.

For example, a 0.5in trace connecting a 100nH induc-

tor adds an extra 10nH of inductance, or 10%.

To reduce the parasitic inductance, use wider traces

and a solid ground or power plane below the signal

traces. Using a solid ground plane can reduce the par-

asitic inductance from approximately 20nH/in to 7nH/in.

Also, use low-inductance connections to ground on all

GND pins, and place decoupling capacitors close to all

300MHz-to-450MHz Low-Power, Crystal-Based

ASK Transmitter

8

_______________________________________________________________________________________

PA

AND

GATE

PAOUT

PAGND

GND

CRYSTAL-

OSCILLATOR

DRIVER

32 x PLL

LOCK DETECT

MAX1472

DATA

ENABLE

XTAL1

XTAL2

Functional Diagram

Chip Information

TRANSISTOR COUNT: 1430

PROCESS: CMOS