STW81101 datasheet(39/48 Pages) STMICROELECTRONICS

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STW81101

Application information

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Alternatively, you can combine the two outputs in other ways. A first topology for the direct

output (3.3GHz to 4.4GHz) is suggested in

Figure 29. It basically consists of a simple LC

balun and a matching network to adapt the output to a 50

Ω load. The two LC networks shift

output signal phase of -90° and +90°, thus combining the two outputs. This topology,

designed for a center frequency of 4GHz, is intrinsically narrow-band since the LC balun is

tuned at a single frequency. If the application requires a different sub-band, the LC combiner

can be easily tuned to the frequency of interest.

Figure 29.

LC lumped balun and matching network (MATCH_LC_LUMP_4G.dsn)

The 1.9nH shunt inductor works as a DC feed for one of the open collector terminals as well

as a matching element along with the other components. The 1.9nH series inductors are

used to resonate the parasitic capacitance of the chip.

For optimum output matching, it is recommended to use 0402 Murata or AVX capacitors and

0403 or 0604 HQ Coilcraft inductors. It is also advisable to use short interconnection paths

to minimize losses and undesired impedance shift.

An alternative topology that permits a more broadband matching as well as balanced to

unbalanced conversion, is shown in

Figure 30.

50 ohm

1.9nH

0.8pF

1.9nH

0.8pF

2.5pF

Vcc

OUTP

OUTN

STW81101 Datasheet(PDF) 39 Page - STMicroelectronics