LTC5507

5

5507f

APPLICATIO S I FOR ATIO

Operation

The LTC5507 integrates several functions to provide RF

power detection over frequencies up to 1000MHz. These

functions include an internally compensated buffer ampli-

fier, an RF Schottky diode peak detector and level shift

amplifier to convert the RF signal to DC, a delay circuit to

down, and a gain compression 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

RF Detector

The internal RF Schottky diode peak detector and level

shift amplifier converts the RF input signal to a low

frequency signal. The frequency range of the RF pin is

typically up to 1000MHz. The detector demonstrates ex-

cellent operation over a wide range of input power. The

Schottky detector is biased at about 70

µA. The hold

capacitor is external.

Gain Compression

The gain compression circuit changes the feedback ratio

as the RF peak-detected input voltage increases above

60mV. Below 60mV, the DC voltage gain from the peak

detector to the buffer output is 4. Above 140mV, the DC

voltage gain is reduced to 0.75. 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 LTC5507 can be used as a self-standing signal strength

measuring receiver for a wide range of input signals from

–34dBm to 14dBm for frequencies up to 1000MHz.

The LTC5507 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.

C1, C2 Capacitor Selection (Refer to Figure 3)

C2 will affect the slew rate and bandwidth. Typically C1 can

equal C2. Ceramic capacitors are recommended for C1

and C2. The values for C1 and C2 are dependent on the

operating RF frequency. The capacitive reactance should

be less than 5

Ω to minimize ripple on C2.

C2(

µF) ≥ 1/(30 • f) where f is the lowest RF input

frequency (MHz)

C1 = C2

In general, select C1 and C2 large enough to pass the

lowest expected RF signal frequency, as described by the

above formulas. But optimize C1 and C2, subject to this

constraint, to improve output slew rate and bandwidth,

and to enable good AC performance for the highest

expected RF signal frequency.