lt5581 Linear Technology Corporation, lt5581 Datasheet - Page 11

• Manufacturer Part Number: lt5581
• Description: 6ghz Rms Power Detector With 40db Dynamic Range
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
OPERATION
To achieve an accurate average power measurement of
the high crest factor modulated RF signals, the LT5581
combines a proprietary high speed power measurement
subsystem with an internal 150kHz low pass averag-
ing fi lter and an output voltage buffer in a completely
integrated solution with minimal off-chip components.
The resulting output voltage is directly proportional to
the average RF input power in dBm. Figure 1 shows the
evaluation circuit schematic, and Figures 2 and 3 show
the associated board artwork. For best high frequency
performance, it is important to place many ground vias
directly under the package.
RF Input Matching
The input resistance is about 205Ω. Input capacitance
is 1.6pF. The impedance vs frequency of the RF input is
detailed in Table 1.
Figure 2. Top Side of Evaluation Board
5581 F02
Table 1. RF Input Impedance
FREQUENCY
(MHz)
1000
1500
2000
2100
2500
3000
3500
4000
5000
6000
100
200
400
500
800
900
10
50
Figure 3. Bottom Side of Evaluation Board
IMPEDANCE
199.5-j22.4
191.7-j40.3
171.1-j68.5
121.8-j95.4
100.2-j97.5
203.6-j5.5
56.8-j86.5
14.6-j41.4
13.6-j39.2
10.8-j32.1
7.3-j19.4
6.6-j14.5
48-j81.2
41.1-j76
22.2-j55
8.8-j9.6
8.6-j25
INPUT
6.4-j0
(Ω)
0.606
0.603
0.601
0.601
0.608
0.613
0.631
0.638
0.645
0.679
0.710
0.716
0.737
0.759
0.774
0.783
0.709
0.774
MAG
S11
5581 F03
LT5581
ANGLE (°)
–101.2
–112.9
–125.7
–136.9
–147.1
–157.6
–179.9
–12.3
–29.8
–46.5
–51.8
–56.8
–79.5
–97.9
–0.8
–3.4
–6.4
–24
11
5581f