RMPA2271 데이터 시트보기 (PDF) - Fairchild Semiconductor
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RMPA2271
Fairchild Semiconductor
RMPA2271 Datasheet PDF : 9 Pages
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PRELIMINARY
Application Note
Due to the varying amplitude envelope of WCDMA signal, a filter is required at the Pdet pin in order to minimize the ripple noise of the
detector output voltage (Pdet). RMPA2271 has no integrated filter for the Pdet pin. Therefore, an external low-pass filter, comprising a
shunt resistor (R) and a shunt capacitor (C), is required to detect the WCDMA signal properly. The filter bandwidth is determined by
the RC time constant of the filter, and can be reduced by increasing the values of the resistor and/or capacitor. A narrower filter band-
width has the advantage of lower voltage ripple noise, but it comes at the expense of increased response time. A tradeoff needs to be
made between the ripple noise and response time for the optimal system performance.
SMA1
RF IN
3.3 µF
1000 pF
1000 pF
3.3 µF
Vcc1
1
2
50 ohm
TRL
3
8
50 ohm
7 TRL
6
Vcc2
Vmode
1000 pF
4
Vref
5
0.1 µF
9
(package
R
base)
Pdet
C
SMA2
RF OUT
The detector output voltage (Pdet) range can be adjusted by the value of the external shunt resistor (R). The following figure shows
the dependence of Pdet voltage as a function of R. The maximum Pdet voltage can be increased by raising the value of R. This pro-
vides the added flexibility to handset designers to change the detector range to meet the system requirements.
RMPA2271 3x3 WCDMA PAM with Power Detector
Vcc=3.4V, Vref=2.85V, Vmode=0V, Freq=1950MHz, Temp=25°C
2.0
1.8
R=9.1k Ohm
1.6
R=5.1k Ohm
1.4
R=2.4k Ohm
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-10 -5
0
5
10
15
20
25
30
Pout (dBm)
It is recommended that the value of the resistor R is first determined depending on the desired detector output voltage range. Then
the value of the shunt capacitor C is selected for the required detector output voltage ripple level, and response time.
RMPA2271 Rev. B
4
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