adl5504 Analog Devices, Inc., adl5504 Datasheet - Page 16

• Manufacturer Part Number: adl5504
• Description: 450 Mhz To 6000 Mhz Trupwr Detector
• Manufacturer: Analog Devices, Inc.

ADL5504
OUTPUT DRIVE CAPABILITY AND BUFFERING
The ADL5504 is capable of sourcing a VRMS output current of
approximately 3 mA. The output current is sourced through the
on-chip, 100 Ω series resistor; therefore, any load resistor forms
a voltage divider with this on-chip resistance. It is recommended
that the ADL5504 VRMS output drive high resistance loads to
preserve output swing. If an application requires driving a low
resistance load (as well as in cases where increasing the nominal
conversion gain is desired), a buffering circuit is necessary.
SELECTING THE SQUARE-DOMAIN FILTER AND
OUTPUT LOW-PASS FILTER
The internal filter capacitor of the ADL5504 provides averaging
in the square domain but leaves some residual ac on the output.
Signals with high peak-to-average ratios, such as W-CDMA or
CDMA2000, can produce ac residual levels on the ADL5504
VRMS dc output. To reduce the effects of these low frequency
components in the waveforms, some additional filtering is
required.
The square-domain filter capacitance of the ADL5504 can be
augmented by connecting a capacitor between Pin 1 (FLTR) and
Pin 2 (VPOS). In addition, the VRMS output of the ADL5504 can
be filtered directly by placing a capacitor between VRMS (Pin 5)
and ground. The combination of the on-chip, 100 Ω output
series resistance and the external shunt capacitor forms a low-
pass filter to reduce the residual ac.
Figure 39 and Figure 40 show the effects on the residual ripple
vs. the output and square-domain filter capacitor values at two
communication standards with high peak-to-average ratios.
Note that there is a trade-off between ac residual and response
time. Large filter capacitances increase the turn-on and pulse
response times (see Figure 28 to Figure 33). Figure 41 shows the
effect of the two filtering options, the output filter and the
square-domain filter capacitor, on the pulse response time of
the ADL5504. For more information on the effects of the filter
capacitances on the response, see the Power Consumption,
Enable, and Power-On/Power-Off Response Time section.
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Figure 41. C
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W-CDMA Forward Link (11.7 dB CF) Waveform
W-CDMA Reverse Link (5.8 dB CF) Waveform
Figure 39. AC Residual vs. C
Figure 40. AC Residual vs. C
FLTR
and C
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CAPACITANCE (nF)
CAPACITANCE (nF)
CAPACITANCE (nF)
OUT
C
C
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C
FLTR
OUT
OUT
FLTR
Response Time vs. Capacitance
C
FLTR
FLTR
FLTR
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and C
and C
C
OUT
OUT
OUT
,
,
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