LTC5587IDD View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC5587IDD' PDF : 20 Pages View PDF
LTC5587
APPLICATIONS INFORMATION
Figure 6 shows the effect of the external filter capacitor on
the residual ripple level for a 4-carrier WCDMA downlink
signal at 2.14GHz with –10dBm. Adding a 0.047μF capaci-
tor to the output decreases the peak-to-peak output ripple
from 150LSB to about 60LSB.
Figure 8 shows how the peak-to-peak ripple decreases with
increasing external filter capacitance value. Also shown is
how the RF pulse response will have longer rise and fall
times with the addition of this lowpass filter cap.
4000
TA = 25°C
3500
3400
NO CAP
0.047μF 3300
3000
3200
2500
3100
2000
3000
1500
2900
1000
2800
500
2700
0
2600
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
TIME (msec)
5587 F06
Figure 6. Residual Ripple, Output Transient Response for RF
Pulse with WCDMA 4-Carrier Modulation
9
8
7
6
5
4
3
2
1
0
0.001
RIPPLE
RISE
FALL
1000
TA = 25°C
100
10
0.01
0.1
EXTERNAL CAPACITOR (μF)
1
1
5587 F08
Figure 8. Residual Ripple, Output Transient Times for RF Pulse
with WCDMA 4-Carrier Modulation vs External Filter Capacitor C4
Figure 7 shows the transient response for a 2.6GHz WiMax
signal with preamble and burst ripple reduced by a fac-
tor of three using a 0.047μF external filter capacitor. The
average power in the preamble section is –10dBm, while
the burst section has 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 ¾.
3500
TA = 25°C
3000
NO CAP
0.047μF
2500
2000
1500
1000
500
0
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
TIME (msec)
5587 F07
Figure 7. Residual Ripple for 2.6GHz WiMax OFDM 802.16-2004
Figure 9 shows the rise time and fall time is a strong
function of the RF input power when the filter capacitor
is not present.
9
TA = 25°C
8
7
FALL TIME
6
5
4
3
2
RISE TIME
1
0
–30 –25 –20 –15 –10 –5
INPUT POWER (dBm)
05
5587 F09
Figure 9. RF Pulse Response Rise Time and Fall Time vs RF
Input Power
5587f
15
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