LTC5505-1 データシートの表示（PDF） - Linear Technology

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LTC5505-1

RF Power Detector with Buffered Output and >40dB Dynamic Range

Linear Technology 

LTC5505-1/LTC5505-2

APPLICATIO S I FOR ATIO

Operation

The LTC5505-X RF detector integrates several functions to

provide RF power detection over frequencies ranging from

300MHz to 3.5GHz. 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, a delay circuit to avoid voltage transients at

VOUT 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

100mV. Below 100mV, the voltage gain from the peak

detector to the buffer output is 1.5. Above 200mV, the

voltage gain is reduced to 0.7. The compression expands

the low power detector range due to higher gain.

Modes of Operation

MODE

Shutdown

Enable

SHDN

Low

High

OPERATION

Disabled

Power Detect

Applications

The LTC5505-1 and LTC5505-2 can be used as self-

standing signal strength measuring receivers for a wide

range of input signals from –32dBm to 18dBm for fre-

quencies from 300MHz to 3.5GHz.

The LTC5505-1 and LTC5505-2 can be used as demodu-

lators for AM and ASK modulated signals with data rates

up to 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 LTC5505-1 and LTC5505-2 can be used for dual band

mobile phone transmitter power control (refer to Typical

Application schematic on first page). The circuit uses a

capacitive tap at the Tx PA outputs. For example, a 0.3pF

capacitor (C1) followed by a 100Ω resistor (R1) forms a

coupling circuit with about a 20dB loss at the cellular band

and 18dB loss at the PCS band, referenced to the LTC5505-2

IC RF input pin. For improved coupling accuracy, the C1

capacitor should be a high tolerance component (±0.05pF.)

Example of LTC5505-X GSM/DCS Power Control Timing Diagram

20µs

2µs

28µs

543µs

28µs

SHDN

VOUT

RF INPUT

POWER

t1

t2 t3

t4

5505 TD

t5

t6

t1: PART COMES OUT OF SHUTDOWN 20µs MAXIMUM PRIOR TO BURST.

t2: CIRCUITS POWER UP AND SETTLE.

t3: BASEBAND CONTROLLER STARTS RF POWER RAMP UP AT 22µs AFTER SHDN IS ASSERTED HIGH.

t4: BASEBAND CONTROLLER COMPLETES RAMP UP.

t5: BASEBAND CONTROLLER STARTS RF POWER RAMP DOWN AT END OF BURST.

t6: LTC5505-X RETURNS TO SHUTDOWN MODE BETWEEN BURSTS

5505f

6

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