
2000 Sep 29
7
Philips Semiconductors
Product specication
SDH/SONET STM16/OC48 main ampliers
OQ2538HP; OQ2538U
An external 200
resistor between IN and INQ is
recommended in order to match the inputs to a differential
transmission line, coupled microstrip or stripline with an
odd mode impedance Zo(odd) =50 , as shown in Fig.4.
For single-ended excitation, separate matching networks
on IN and INQ, as depicted in Fig.5, achieve optimum
matching. Care should be taken to avoid DC loading, since
the OQ2538HP controls its own DC input voltage.
The resistors on the unused input INQ may be combined
for convenience.
In both cases, the essence of good matching is the equity
of the circuitry on both input pins. The impedance seen on
pins IN and INQ should be as equal as possible. For more
information see
“Application Note AN96051” describing
the OM5801 STM16 demo board.
RF output matching circuit
Matching of the main amplifier outputs, OUT and OUTQ, is
not mandatory. In most applications, the receiving end of
the transmission line will be properly matched, so very little
reflection will occur. Matching the transmitting end to
absorb these reflections is only recommended for very
sensitive applications. In such cases, 100
pull-up
resistors should be connected from OUT and OUTQ to
ground, as close as possible to the IC pins. These
matching resistors will not be needed in most applications,
however. The output circuit of the OQ2538HP is depicted
in Fig.6. For more information see
“Application Note
AN96051” describing the OM5801 STM16 demo board.
Fig.4 Differential input matching.
handbook, halfpage
differential line
Zo(odd) = 50
MGM115
200
IN
INQ
22 nF
Fig.5 Single-ended input matching.
handbook, halfpage
MGM116
100
100
50
IN
INQ
22 nF
Zo = 50
transmission line
Fig.6 RF output topology.
handbook, halfpage
MGM117
OUT
OUTQ
GND
100
100