Low Power Mixer/Limiter/RSSI 3V Receiver IF Subsystem
The AD608 provides a low power, low distortion, low noise mixer as well as a complete, monolithic logarithmic/limiting amplifier that uses a successive-detection technique. In addition, the AD608 provides both a high speed received signal strength indicator (RSSI) output with 80 dB dynamic range and a hard-limited output. The RSSI output is from a two-pole postdemodulation low-pass filter and provides a loadable output voltage of 0.2 V to 1.8 V. The AD608 operates from a single 2.7 V to 5.5 V supply at a typical power level of 21 mW at 3 V.
The RF and local oscillator (LO) bandwidths both exceed 500 MHz. In a typical IF application, the AD608 can accept the output of a 240 MHz surface acoustic wave (SAW) filter and down-convert it to a nominal 10.7 MHz IF with a conversion gain of 24 dB (ZIF = 165 Ω). The AD608 logarithmic/limiting amplifier section handles any IF from low frequency (LF) up to 30 MHz.
The mixer is a doubly balanced gilbert-cell mixer and operates linearly for RF inputs spanning −95 dBm to −15 dBm. It has a nominal −5 dBm third-order intercept. An on-board LO preamplifier requires only −16 dBm of LO drive. The current output of the mixer drives a reverse-terminated, industry-standard 10.7 MHz, 330 Ω filter.
The nominal logarithmic scaling is such that the output is +0.2 V for a sinusoidal input to the IF amplifier of −75 dBm and +1.8 V at an input of +5 dBm; over this range, the logarithmic conformance is typically ±1 dB. The logarithmic slope is proportional to the supply voltage. A feedback loop automatically nulls the input offset of the first stage down to the submicrovolt level.
The AD608 limiter output provides a hard-limited signal output at 400 mV p-p. The voltage gain of the limiting amplifier to this output is more than 100 dB. Transition times are 11 ns and the phase is stable to within ±3° at 10.7 MHz for signals from −75 dBm to +5 dBm.
The AD608 is enabled by a CMOS logic-level voltage input, with a response time of 200 ns. When disabled, the standby power is reduced to 300 μW within 400 ns.
The AD608 is specified for the industrial temperature range of −25°C to +85°C for 2.7 V to 5.5 V supplies and −40°C to +85°C for 3.0 V to 5.5 V supplies. This device comes in a 16-lead plastic SOIC.
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At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
EVAL-AD608EBZ is a fully populated, 4-layer, FR4-based evaluation board. RF input, LO input, limiter output, detector input, RSSI output, and power up connections with single ended setups are featured. Access to the +3V/7.3 mA supply is achieved with clip leads to the VPOS and GND testpoints; it has a range from +2.7 to +5.5V.
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The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Analog Devices, Inc. sales office or authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.