LTC5508
7
5508fa
APPLICATIO S I FOR ATIO
WUU
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Operation
The LTC5508 RF detector integrates several functions to
provide RF power detection over frequencies ranging from
300MHz to 7GHz. These functions include an internally
compensated buffer amplifier, an RF Schottky diode peak
detector and level shift amplifier to convert the RF input
signal to DC, a delay circuit to avoid voltage transients at
V
OUT
when coming out of shutdown and a gain compres-
sion circuit to extend the detector dynamic range.
Buffer Amplifier
The buffer amplifier has a gain of two and is capable of
driving a 2mA load. The buffer amplifier typically has an
output voltage range of 0.25V to 1.75V.
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.
Gain Compression
The gain compression circuit changes the feedback ratio
as the RF peak-detected input voltage increases above
60mV. Below 60mV, the voltage gain from the peak
detector to the buffer output is 4. Above 120mV, the
voltage gain is reduced to 0.85. The compression expands
the low power detector range due to higher gain.
Modes of Operation
MODE SHDN OPERATION
Shutdown Low Disabled
Enable High Power Detect
Applications
The LTC5508 can be used as a self-standing signal strength
measuring receiver for a wide range of input signals from
–32dBm to 12dBm for frequencies from 300MHz to 7GHz.
The LTC5508 can be used as a demodulator for AM and
ASK modulated signals with data rates up to 2MHz.
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 LTC5508 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
LTC5508
1
2
3
JP1
V
CC
V
CC
V
CC
R2
68Ω
(OPT)
R1
68Ω
(OPT)
C5
(OPT)
C2
0.1µF
C3
100pF
C1
18pF
RF
IN
J1
E1
E5
E2
E4
E3
GND
V
OUT
GND
SHDN
R3
22k
ENABLE
DISABLE
5508 AI01
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
