PRODUCT DESCRIPTION
The AD8309 is a complete IF limiting amplifier, providing both an accurate logarithmic (decibel) measure of the input signal (the RSSI function) over a dynamic range of 100 dB, and a programmable limiter output, useful from 5 MHz to 500 MHz.
It is easy to use, requiring few external components. A single supply voltage of +2.7 V to +6.5 V at 16 mA is needed, corresponding to a power consumption of under 50 mW at 3 V, plus the limiter bias current, determined by the application and typically 2 mA, providing a limiter gain of 100 dB when using 200 Ω loads. A CMOS-compatible control interface can enable the AD8309 within about 500 ns and disable it to a standby current of under 1 µA.
The six cascaded amplifier/limiter cells in the main path have a small signal gain of 12.04 dB (×4), with a –3 dB bandwidth of 850 MHz, providing a total gain of 72 dB. The programmable output stage provides a further 18 dB of gain. The input is fully differential and presents a moderately high impedance (1 kΩ in parallel with 2.5 pF). The input-referred noise-spectral-density, when driven from a terminated 50 Ω, source is 1.28 nV/√Hz, equivalent to a noise figure of 3 dB. The sensitivity of the AD8309 can be raised by using an input matching network.
Each of the main gain cells includes a full-wave detector. An additional four detectors, driven by a broadband attenuator, are used to extend the top end of the dynamic range by over 48 dB.

FEATURES
   Complete Multistage Log-Limiting IF Amplifier
   100 dB Dynamic Range: –78 dBm to +22 dBm (Re 50 V)
   Stable RSSI Scaling Over Temperature and Supplies:
      20 mV/dB Slope, –95 dBm Intercept
      60.4 dB RSSI Linearity up to 200 MHz
   Programmable Limiter Gain and Output Current
      Differential Outputs to 10 mA, 2.4 V p-p
      Overall Gain 100 dB, Bandwidth 500 MHz
      Constant Phase (Typical 680 ps Delay Skew)
   Single Supply of +2.7 V to +6.5 V at 16 mA Typical
   Fully Differential Inputs, RIN = 1 kV, CIN = 2.5 pF
   500 ns Power-Up Time, <1 mA Sleep Current
  
APPLICATIONS
   Receivers for Frequency and Phase Modulation
   Very Wide Range IF and RF Power Measurement
   Receiver Signal Strength Indication (RSSI)
   Low Cost Radar and Sonar Signal Processing
   Instrumentation: Network and Spectrum Analyzers