DN1030 - RF Input Impedance Matching Data for the LTC5564 Schottky Detector

RF Input Impedance Matching Data for the LTC5564
Schottky Detector – Design Note 1030
John Chung, Bruce Hemp
Introduction
File Links
The LTC 5564 is an UltraFast™ RF power detector
for applications in the 600MHz to 15GHz frequency
range. It combines a temperature compensated
Schottky diode peak detector, a gain selectable
operational amplifier and a fast comparator in a
16-lead 3mm × 3mm package.
FILE NAME
CONTENTS
LTC5564_-10dBm.S1P
Input Reflection Coefficient, S11,
PIN = –10dBm, Touchstone Format.
101 Freq. Points, 0.5GHz to 16.5GHz.
LTC5564_0dBm.S1P
Input Reflection Coefficient, S11,
PIN = 0dBm, Touchstone Format. 101
Freq. Points, 0.5GHz to 16.5GHz.
®
Performance of the RF detector, specifically detector response and bandwidth, depends on proper
impedance matching into the detector RF input. The
impedance measurements presented here can be
used in conjunction with a CAD simulation tool to
simplify the task of RF input impedance matching.
GND
RF INPUT
SMA
CONNECTOR
The phase reference plane for the measurement is
1.1mm away from the edge of the QFN package.
This distance was chosen to give a comfortable
margin against typical DFM rules regarding the
distance between components.
For higher frequencies, the accuracy of the S11
measurement becomes diminished by various
factors specific to each individual PCB design,
such as ground via inductance, the quality of the
microstrip transitions, etc. Nonetheless, the S1P
data helps in producing the first cut design, saving
development time.
05/13/1030
GND
GND
RF Input Impedance Measurement
Input impedance was measured on a LTC5564
demo board DC1646A, modified for minimal RF
trace length as shown in Figure 1. For the purpose
of this measurement, the detector input DC block
was omitted since the test equipment supports DC
voltage at its input. In a real world application, a
DC block function must be included as part of the
matching network design. The measured LTC5564
input impedance is shown in Figure 2 and Table 1.
Cu CONNECTING TRACE:
18 MIL WIDTH, TAPERED
AT IC PAD
N4000-13 SUBSTRATE:
THICKNESS IS 17 MILS
BETWEEN LAYER 1 AND
GROUND LAYER 2
1.1mm
REFERENCE
PLANE
DN1030 F01
Figure 1. Test Setup Showing Location
of the Reference Plane
Note that the input impedance to the Schottky detector is a slight function of RF drive level, as seen in
Figure 2. There is no measurable input impedance
variation over the specified supply voltage range
of 3V to 5.5V.
Refer to the DC1646A demo board manual for several LTC5564 RF input matching circuit examples.
Conclusion
The LTC5564 RF input impedance was measured
and converted to a 1-port S-parameter file, which
can be read by most industry-standard RF CAD
programs, expediting the matching process.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks
and UltraFast is a trademark of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
0dBm
–10dBm
PHASE REFERENCE PLANE:
1.1mm FROM THE EDGE OF
THE QFN PACKAGE
Figure 2. Measured S11 for the LTC5564
Table 1. LTC5564 Input Impedance, PIN = –10dBm
INPUT IMPEDANCE
(SERIES EQUIV.)
VOLT. REFL. COEFF.
(ZO = 50Ω)
INPUT IMPEDANCE
(SERIES EQUIV.)
VOLT. REFL. COEFF.
(ZO = 50Ω)
RS
jXS
MAG
ANG
FREQUENCY
(GHz)
RS
jXS
MAG
ANG
0.5
126.2
–59.8
0.521
–19.4
9.3
50.7
91.2
0.671
47.4
1.3
65.9
–58.6
0.468
–48.0
10.1
63.7
109.7
0.700
38.9
2.1
40.7
–40.3
0.416
–79.0
10.9
92.0
132.1
0.715
29.4
2.9
31.0
–22.5
0.350
–114.7
11.7
120.8
143.3
0.717
23.7
3.7
28.5
–11.2
0.305
–144.2
12.5
170.8
143.6
0.712
16.9
4.5
24.1
–0.1
0.350
–179.7
13.3
211.7
78.6
0.658
9.2
5.3
20.9
12.8
0.442
146.0
14.1
197.7
3.7
0.596
0.6
6.1
21.9
27.1
0.508
115.3
14.9
115.7
–22.0
0.415
–11.0
6.9
26.6
40.9
0.542
91.7
15.7
95.8
46.1
0.425
27.6
7.7
30.3
57.7
0.617
73.1
16.5
168.9
83.8
0.621
14.2
8.5
38.4
76.7
0.663
57.7
FREQUENCY
(GHz)
Note: For a less granular version of this data, use the
S1P data file (101 frequency points)
Data Sheet Download
www.linear.com/LTC5564
Linear Technology Corporation
For applications help,
call (408) 432-1900
dn1030f 0513
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
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 LINEAR TECHNOLOGY CORPORATION 2013
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