50 MHz, 80 dB Demodulating Logarithmic Amplifier with Limiter Output AD606 a loadable output voltage of +0.1 V dc to +4 V dc. The logarithmic scaling is such that the output is +0.5 V for a sinusoidal input of –75 dBm and +3.5 V at an input of +5 dBm; over this range the logarithmic linearity is typically within ± 0.4 dB. All scaling parameters are proportional to the supply voltage.
FEATURES Logarithmic Amplifier Performance –75 dBm to +5 dBm Dynamic Range ≤1.5 nV/√Hz Input Noise Usable to >50 MHz 37.5 mV/dB Voltage Output On-Chip Low-Pass Output Filter Limiter Performance ؎1 dB Output Flatness over 80 dB Range ؎3؇ Phase Stability at 10.7 MHz over 80 dB Range Adjustable Output Amplitude Low Power +5 V Single Supply Operation 65 mW Typical Power Consumption CMOS Compatible Power-Down to 325 W typ <5 s Enable/Disable Time
The AD606 can operate above and below these limits, with reduced linearity, to provide as much as 90 dB of conversion range. A second low-pass filter automatically nulls the input offset of the first stage down to the submicrovolt level. Adding external capacitors to both filters allows operation at input frequencies as low as a few hertz. The AD606’s limiter output provides a hard-limited signal output as a differential current of ± 1.2 mA from open-collector outputs. In a typical application, both of these outputs are loaded by 200 Ω resistors to provide a voltage gain of more than 90 dB from the input. Transition times are 1.5 ns, and the phase is stable to within ± 3° at 10.7 MHz for signals from –75 dBm to +5 dBm.
APPLICATIONS Ultrasound and Sonar Processing Phase-Stable Limiting Amplifier to 100 MHz Received Signal Strength Indicator (RSSI) Wide Range Signal and Power Measurement
The logarithmic amplifier operates from a single +5 V supply and typically consumes 65 mW. It is enabled by a CMOS logic level voltage input, with a response time of <5 µs. When disabled, the standby power is reduced to <1 mW within 5 µs.
The AD606J is specified for the commercial temperature range of 0°C to +70°C and is available in 16-pin plastic DIPs or SOICs. Consult the factory for other packages and temperature ranges.
The AD606 is a complete, monolithic logarithmic amplifier using a 9-stage “successive-detection” technique. It provides both logarithmic and limited outputs. The logarithmic output is from a three-pole post-demodulation low-pass filter and provides
FUNCTIONAL BLOCK DIAGRAM INHI
REFERENCE AND PO WER UP
OFFSET-NULL LOW-PASS FILTER
MAIN SIGNAL PATH 11.15 dB/STAGE
HIGH-END DETECTORS ONE-POLE FILTER
2 µ A/dB
TWO-POLE SALLEN-KEY FILTER X2
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