AD8309ARUZ

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1. DESCRIPTION

The AD8309ARUZ 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. The overall dynamic range for this combination extends from –91 dBV (–78 dBm at the 50 Ω level) to a maximum permissible value of +9 dBV, using a balanced drive of antiphase inputs each of 2 V in amplitude, which would correspond to a sine wave power of +22 dBm if the differential input were terminated in 50 Ω. The slope of the RSSI output is closely controlled to 20 mV/dB, while the intercept is set to –108 dBV (–95 dBm re 50 Ω). These scaling parameters are determined by a bandgap voltage reference and are substantially independent of temperature and supply. The logarithmic law conformance is typically within ±0.4 dB over the central 80 dB of this range at any frequency between 10 MHz and 200 MHz, and is degraded only slightly at 500 MHz. The RSSI response time is nominally 67 ns (10%–90%). The averaging time may be increased without limit by the addition of an external capacitor. The full output of 2.34 V at the maximum input of +9 dBV can drive any resistive load down to 50 Ω and this interface remains stable with any value of capacitance on the output. The AD8309 is fabricated on an advanced complementary bipolar process using silicon-on-insulator isolation techniques and is available in the industrial temperature range of –40°C to +85°C, in a 16-lead TSSOP package.

2. Feature

    1. Complete multi-stage logarithmic limit IF amplifier

    2. 100 dB dynamic range: -78 dBm to +22 dBm (Re 50 V)

    3. Stable RSSI scaling within the temperature and power range:

        - 20 mV/dB slope, –95 dBm intercept

        - 60.4 dB RSSI linearity up to 200 MHz

    4. Programmable limiter gain and output current

    5. Differential output to 10 mA, 2.4 V p-p

    6. Total gain 100 dB, bandwidth 500 MHz

    7. Constant phase (typical 680 ps delay offset)

    8. +2.7 V to +6.5 V single power supply, 16 mA typical

    9. Fully differential input, RIN = 1 kV, CIN = 2.5 pF

  10. 500 ns power-on time, <1 mA sleep current

3. APPLICATIONS

    1. Receivers for Frequency and Phase Modulation

    2. Very Wide Range IF and RF Power Measurement

    3. Receiver Signal Strength Indication (RSSI)

    4. Low Cost Radar and Sonar Signal Processing

    5. Instrumentation: Network and Spectrum Analyzers

4. PIN CONFIGURATION

5. PIN FUNCTION DESCRIPTIONS