LT5581IDDB-PBF LINER [Linear Technology], LT5581IDDB-PBF Datasheet - Page 13

• Manufacturer Part Number: LT5581IDDB-PBF
• Description: 6GHz RMS Power Detector with 40dB Dynamic Range
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
the output pin, to form an RC lowpass fi lter. The internal
300Ω resistor in series with the output pin enables fi lter-
ing of the output signal with just the addition of C
Figure 7 shows the effect of the external fi lter capacitor
on the residual ripple level for a 4-carrier WCDMA signal
at 2.14GHz with –10dBm. Adding a 10nF capacitor to the
output decreases the peak-to-peak output ripple from
135mV
can be calculated with the following equation:
Figure 8 shows the transient response for a 2.6GHz WiMAX
signal, with preamble and burst ripple reduced by a factor
Figure 8. Residual Ripple for 2.6GHz WiMAX OFDM 802.16-2004
LT5581
INPUT
Figure 6. Simplifi ed Circuit Schematic of the Output Interface
f
C
=
P-P
2
π
to 50mV
C
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
LOAD
0
T
A
0.2
= 25°C
(
1
300
0.4
P-P
0.6
. The fi lter –3dB corner frequency
40μA
+
0.8
R
V
TIME (ms)
CC
SS
300Ω
1
)
1.2
1.4
V
1.6
OUT
NO CAP
0.047μF
3
1.8
5581 F08
R
2
SS
C
LOAD
LOAD
V
(FILTERED)
OUT
.
Figure 9. Residual Ripple, Output Transient Times for RF Pulse
with WCDMA 4-Carrier Modulation vs External Filter Capacitor C4
of 3, using a 0.047μF external fi lter capacitor. The aver-
age power in the preamble section is –10dBm, while the
burst section has a 3dB lower average power. With the
capacitor, the ripple in the preamble section is about 0.5dB
peak-to-peak. The modulation used was OFDM (WiMAX
802.16-2004) MMDS band, 1.5MHz BW, with 256 size FFT
and 1 burst at QPSK
Figure 9 shows how the peak-to-peak ripple decreases with
increasing external fi lter capacitance value. Also shown is
how the RF pulse response will have longer rise and fall
times with the addition of this lowpass fi lter cap.
Figure 7. Residual Ripple, Output Transient Response
for RF Pulse with WCDMA 4-Carrier Modulation
1.4
1.2
0.8
0.6
0.4
0.2
1.0
0.001
0
9
8
7
6
3
2
1
0
5
4
0
T
A
10
= 25°C
NO CAP
0.01μF
20
RIPPLE
RISE
FALL
EXTERNAL CAPACITOR (μF)
3
30
0.01
/
4
.
40
TIME (μs)
50
60
0.1
70
T
80
A
= 25°C
90
5581 F09
5581 F07
100
1
LT5581
1.25
1.20
1.10
1.05
1.00
0.95
0.90
1.15
1000
100
10
1
13
5581f