ltc5587 Linear Technology Corporation, ltc5587 Datasheet - Page 15

• Manufacturer Part Number: ltc5587
• Description: Ltc5587 6 Ghz Rms Power Detector With Digital Output Features
• Manufacturer: Linear Technology Corporation

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 6. Residual Ripple, Output Transient Response for RF
Pulse with WCDMA 4-Carrier Modulation
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.
Figure 7. Residual Ripple for 2.6GHz WiMax OFDM 802.16-2004
4000
3500
3000
2500
2000
1500
1000
3500
3000
2500
2000
1500
1000
500
500
0
0
0
0
T
T
A
A
0.1
0.2
= 25°C
= 25°C
0.4
0.2
0.3
0.6
TIME (msec)
0.4
TIME (msec)
0.8
0.5
1
0.6
1.2
1.4
0.7
1.6
0.8
NO CAP
0.047μF
NO CAP
0.047μF
0.9 1.0
1.8 2
5587 F06
5587 F07
3400
3300
3200
3100
3000
2900
2800
2700
2600
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.
Figure 8. Residual Ripple, Output Transient Times for RF Pulse
with WCDMA 4-Carrier Modulation vs External Filter Capacitor C4
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.
Figure 9. RF Pulse Response Rise Time and Fall Time vs RF
Input Power
0
9
8
6
5
4
0.001
7
3
2
1
9
8
7
6
3
2
1
0
5
4
–30
T
A
= 25°C
–25
RIPPLE
RISE
FALL
EXTERNAL CAPACITOR (μF)
–20
INPUT POWER (dBm)
0.01
–15
RISE TIME
FALL TIME
–10
0.1
–5
T
A
= 25°C
0
5587 F09
LTC5587
5587 F08
5
1
1000
10
1
100
15
5587f