9

A second method illustrated in Figure 21b, is to use for-

ward-biased diodes in series with the power supply. For

example, three silicon diodes connected in series will drop

a 5-volt supply to approximately 3 volts.

The use of the series diode approach has the advantage

of less dependency on current variation in the amplifiers

since the forward voltage drop of a diode is somewhat

current independent.

Reverse breakdown diodes (e.g., Zener diodes) could also

be used as in Figure 21c. However, care should be taken

to ensure that the noise generated by diodes in either Ze-

ner or reverse breakdown is adequately filtered (e.g., by-

passed to ground) such that the diode’s noise is not added

to the amplifier’s signal.

SOT-363 PCB Footprint

A recommended PCB pad layout for the miniature SOT-

363 (SC-70) package used by the MGA-81563 is shown in

Figure 22 (dimensions are in inches). This layout provides

ample allowance for package placement by automated

assembly equipment without adding parasitics that could

impair the high frequency RF performance of the MGA-

81563. The layout is shown with a nominal SOT-363 pack-

age footprint superimposed on the PCB pads.

0.026

0.079

0.018

0.039

Dimensions in inches.

Figure 22. Recommended PCB Pad Layout for Avago’s SC70 6L/SOT-363

Products.