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PDF LT5570 Data sheet ( Hoja de datos )
| Número de pieza | LT5570 | |
| Descripción | 40MHz to 2.7GHz Mean-Squared Power Detector | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
n Frequency Range: 40MHz to 2.7GHz
n Accurate RMS Power Measurement of High Crest
Factor Modulated Waveforms
n Linear DC Output vs Input Power in dBm
n Linear Dynamic Range: Up to 60dB
n Exceptional Accuracy over Temperature: ±0.3dB
n Fast Response Time: 0.5μs Rise Time,
8μs Fall Time
n Low Supply Current: 26.5mA
n Low Impedance Output Buffer Capable of Driving
High Capacitance Load
n Small 3mm × 3mm 10-Lead DFN Package
APPLICATIONS
n RMS Power Measurement
n RF Power Control
n Receive and Transmit Gain Control
n W-CDMA, CDMA2000, TD-SCDMA, WiMAX
n RF Instrumentation
LT5570
Fast Responding, 40MHz
to 2.7GHz Mean-Squared
Power Detector
DESCRIPTION
The LT®5570 is a 40MHz to 2.7GHz monolithic Logarithmic
Mean-Squared RF power detector. It is capable of RMS
measurement of an AC signal with wide dynamic range,
from –52dBm to 13dBm depending on frequency. The
power of the AC signal in an equivalent decibel-scaled
value is precisely converted into DC voltage on a linear
scale, independent of the crest factor of the waveforms. The
LT5570 is suitable for precision RF power measurement and
level control for a wide variety of RF standards, including
CDMA, W-CDMA, CDMA2000, TD-SCDMA and WiMAX.
The DC output is buffered with a low output impedance
amplifier capable of driving a high capacitance load.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 7262661, 7259620, 7268608.
TYPICAL APPLICATION
40MHz to 2.7GHz Mean-Squared Power Detector
Output Voltage, Linearity Error vs Input Power, 25°C (2140 MHz)
1MF 1nF
5V
22nF
2.4
2.0
3
2
RF
INPUT
1:4
1
VCC
2 IN+
NC 3 DEC
4 IN–
5
GND
LT5570
FLTR 10
EN 9
DNC 8
7
DNC
6
OUT
ENABLE
VOUT
5570 TA01a
1.6 1
1.2 0
0.8 –1
0.4
0
–45
–35 –25 –15
CW –2
4CH WCDMA
3CH CDMA2000
–3
–5 5 15
RF INPUT POWER (dBm)
5570 TA01b
5570f
1
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LT5570
TYPICAL PERFORMANCE CHARACTERISTICS (Test Circuits Shown in Figures 1 and 3)
Output Voltage vs Frequency
2.4 TA = 25°C
2.0
1.6
1.2
0.8
0.4
0
–55 –45
500MHz
880MHz
2140MHz
2700MHz
–35 –25 –15 –5 5
RF INPUT POWER (dBm)
15
5570 G01
Output Voltage, Linearity Error vs
RF Input Power, 500MHz
2.4 3
2.0 2
1.6 1
1.2 0
0.8 –1
0.4
0
–55 –45
–35 –25 –15
TA = –40°C –2
TA = 25°C
TA = 85°C –3
–5 5 15
RF INPUT POWER (dBm)
5570 G03
Output Voltage, Linearity Error vs
RF Input Power, 880MHz
2.4 3
2.0 2
1.6 1
1.2 0
0.8 –1
0.4
0
–55 –45
–35 –25 –15
TA = –40°C –2
TA = 25°C
TA = 85°C –3
–5 5 15
RF INPUT POWER (dBm)
5570 G05
Linearity Error vs Frequency
3 TA = 25°C
2
1
0
–1
–2
–3
–55 –45
500MHz
880MHz
2140MHz
2700MHz
–35 –25 –15 –5 5
RF INPUT POWER (dBm)
15
5570 G02
Linearity Error vs RF Input Power,
500MHz Modulated Waveforms
3 TA = 25°C
2
1
0
–1
–2
–3
–55 –45
CW
4CH WCDMA
3CH CDMA2000
–35 –25 –15 –5 5
RF INPUT POWER (dBm)
15
5570 G04
Linearity Error vs RF Input Power,
880MHz Modulated Waveforms
3 TA = 25°C
2
1
0
–1
–2
–3
–55 –45
CW
4CH WCDMA
3CH CDMA2000
–35 –25 –15 –5 5
RF INPUT POWER (dBm)
15
5570 G06
5570f
5
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LT5570
APPLICATIONS INFORMATION
The LT5570 is a mean-squared RF power detector, capable
of measuring an RF signal over the frequency range from
40MHz to 2.7GHz, independent of input waveforms with
different crest factors such as CW, CDMA, WCDMA, TD-
SCDMA and WiMAX signals. A wide dynamic range is
achieved with very stable output within the full temperature
range from –40˚C to 85˚C.
RF Inputs
The differential RF inputs are internally biased at
VCC – 1.224V. The differential impedance is about 200Ω.
These pins should be DC blocked when connected to
ground or other matching components. The impedance
vs. frequency of the differential RF input is detailed in the
following table.
Table 1. RF Differential Input Impedance
FREQUENCY DIFFERENTIAL INPUT
(MHz)
IMPEDANCE (Ω)
40 204 –j 0.6
MAG
0.606
100 204 –j 1.8 0.606
200 204 –j 3.6 0.606
400 203.5 –j 7.3 0.606
600 202.8 –j 10.9 0.605
800 201.8 –j 14.5 0.604
1000 200.6 –j17.9 0.603
1200 199.1 –j21.3 0.602
1400 197.3 –j24.7 0.601
1600 195.4 –j27.9 0.599
1800 193.2 –j31.1 0.598
2000 190.8 –j34.2 0.596
2200 188.2 –j37.4 0.593
2400 185.3 –j40.4 0.591
2600 181.9 –j43.5 0.589
2800 178.3 –j46.4 0.586
3000 174.4 –j49.3 0.582
S11
ANGLE (°)
–0.1
–0.3
–0.5
–1.1
–1.6
–2.1
–2.7
–3.2
–3.8
–4.4
–5.0
–5.6
–6.2
–6.9
–7.6
–8.4
–9.2
The LT5570’s differential inputs are optimally driven from
a fully balanced source. When the signal is from a single-
ended 50Ω source, conversion to a differential signal is
required to achieve the maximum dynamic range. This
is best achieved using a 1:4 balun to match the internal
200Ω input impedance as shown in Figures 1 and 3. This
impedance transformation results in 6dB voltage gain. At
high frequency, additional LC elements may be needed
for input impedance matching due to the parasitics of the
transformer and PCB trace.
The approximate RF input power range of the LT5570 is
60dB at frequencies up to 900MHz, even with high crest
factor signals such as a 4-carrier W-CDMA waveform.
However the minimum detectable RF power level degrades
as the input RF frequency increases.
Due to the high RF input impedance of the LT5570, a
narrow band L-C matching network can be used for the
conversion of a single-ended to balanced signal as well.
By this means, the sensitivity and overall linear dynamic
range of the detector remain the same, without using an
RF balun.
The LT5570 can also be driven in a single-ended con-
figuration. Figure 5 shows the simplified circuit of this
single-ended configuration. The DEC Pin is preferably ac-
coupled to ground via a capacitor rather than left floating.
RF
INPUT
1nF
1nF
IN+
DEC
IN–
1007
LT5570
1007
1007
5570 F05
Figure 5. Single-Ended Input Configuration
5570f
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT5570.PDF ] | |
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