LTC5509
6
5509f
APPLICATIO S I FOR ATIO
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Operation
The LTC5509 RF detector integrates several functions to
provide RF power detection over frequencies ranging from
300MHz to 3GHz. These functions include an internally
compensated buffer amplifier, an RF Schottky diode peak
detector and level shift amplifier to convert the RF feedback
signal to DC and a delay circuit to avoid voltage transients
at V
OUT
when coming out of shutdown. The LTC5509 does
not incorporate gain compression. Consequently, it offers
a linear transfer relationship between RF input voltage and
DC output voltage.
Buffer Amplifier
The buffer amplifier is capable of driving a 2mA load. The
buffer amplifier typically has an output voltage range of
0.25V to 3V with V
CC
= 3.6V. At lower supply voltages the
maximum output swing is reduced.
RF Detector
The internal RF Schottky diode peak detector and level
shift amplifier converts the RF input signal to a low
frequency signal. The detector demonstrates excellent
efficiency and linearity over a wide range of input power.
The Schottky detector is biased at about 60µA and drives
a peak detector capacitor of 28pF.
Modes of Operation
MODE SHDN OPERATION
Shutdown Low Disabled
Enable High Power Detect
Applications
The LTC5509 can be used as a self-standing signal strength
measuring receiver for a wide range of input signals from
–30dBm to 6dBm for frequencies from 300MHz to 3GHz.
The LTC5509 can be used as a demodulator for AM and
ASK modulated signals with data rates up to 1.5MHz.
Depending on specific application needs, the RSSI output
can be split into two branches, providing AC-coupled data
(or audio) output and DC-coupled, RSSI output for signal
strength measurements and AGC.
The LTC5509 can be used for RF power detection and
control. Refer to Application Note 91, “Low Cost Coupling
Methods for RF Power Detectors Replace Directional
Couplers.”
Demo Board Schematic
SHDN
GND
V
OUT
RF
GND
V
CC
LTC5509
1
2
3
JP1
V
CC
V
CC
V
CC
R2
68Ω
(OPT)
R1
68Ω
(OPT)
C5
(OPT)
C2
0.1µF
C3
100pF
C1
33pF
RF
IN
J1
E1
E5
E2
E4
E3
GND
V
OUT
GND
SHDN
R3
22k
ENABLE
DISABLE
5509 AI01
