Datasheet LTC5505-1, LTC5505-2 (Analog Devices) - 6

LTC5505-1/LTC5505-2
U U W U APPLICATIO S I FOR ATIO Operation
voltage gain is reduced to 0.7. The compression expands the low power detector range due to higher gain. The LTC5505-X RF detector integrates several functions to provide RF power detection over frequencies ranging from
Modes of Operation
300MHz to 3.5GHz. These functions include an internally compensated buffer amplifier, an RF Schottky diode peak
MODE SHDN OPERATION
detector and level shift amplifier to convert the RF feedback Shutdown Low Disabled signal to DC, a delay circuit to avoid voltage transients at Enable High Power Detect VOUT when coming out of shutdown and a gain compres- sion circuit to extend the detector dynamic range.
Applications Buffer Amplifier
The LTC5505-1 and LTC5505-2 can be used as self- The buffer amplifier has a gain of two and is capable of standing signal strength measuring receivers for a wide driving a 2mA load. The buffer amplifier typically has an range of input signals from –32dBm to 18dBm for fre- output voltage range of 0.25V to 1.75V. quencies from 300MHz to 3.5GHz. The LTC5505-1 and LTC5505-2 can be used as demodu-
RF Detector
lators for AM and ASK modulated signals with data rates The internal RF Schottky diode peak detector and level up to 5MHz. Depending on specific application needs, the shift amplifier converts the RF input signal to a low RSSI output can be split into two branches, providing frequency signal. The detector demonstrates excellent AC-coupled data (or audio) output and DC-coupled, RSSI efficiency and linearity over a wide range of input power. output for signal strength measurements and AGC. The Schottky detector is biased at about 60µA and drives The LTC5505-1 and LTC5505-2 can be used for dual band a peak detector capacitor of 28pF. mobile phone transmitter power control (refer to Typical Application schematic on first page). The circuit uses a
Gain Compression
capacitive tap at the Tx PA outputs. For example, a 0.3pF The gain compression circuit changes the feedback ratio capacitor (C1) followed by a 100Ω resistor (R1) forms a as the RF peak-detected input voltage increases above coupling circuit with about a 20dB loss at the cellular band 100mV. Below 100mV, the voltage gain from the peak and 18dB loss at the PCS band, referenced to the LTC5505-2 detector to the buffer output is 1.5. Above 200mV, the 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 5505 TD t1 t2 t3 t4 t5 t6 t1: PART COMES OUT OF SHUTDOWN 20µs MAXIMUM PRIOR TO BURST. t4: BASEBAND CONTROLLER COMPLETES RAMP UP. t2: CIRCUITS POWER UP AND SETTLE. t5: BASEBAND CONTROLLER STARTS RF POWER RAMP DOWN AT END OF BURST. t3: BASEBAND CONTROLLER STARTS RF POWER RAMP UP AT 22µs AFTER SHDN IS ASSERTED HIGH. t6: LTC5505-X RETURNS TO SHUTDOWN MODE BETWEEN BURSTS 5505f 6