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Superheterodyne ASK/FSK receiver

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article image Receives ASK and FSK data simultaneously.

MAXIM Integrated Products, represented in Australia by Arrow Electronics , has released the MAX1471, a dual-channel receiver that can receive both ASK and FSK data simultaneously. This eliminates switching lag time between modes.

It is designed for low-cost systems where both encoding schemes are present and includes a discontinuous receive (DRX) feature for low-power duty-cycle operation. The DRX feature is user-configurable through a serial interface (SPI) bus. The DRX mode also allows self-polling. It can stay in sleep mode as long as eight minutes and can also be used to wake the system microprocessor. This offers additional cost and power savings.

The receiver operates from 300MHz to 450MHz and includes an on-chip 45dB (typ) image-rejection mixer, which eliminates the need for SAW filters in many applications. The device operates from either a 3.3V or 5V supply, down to 2.4V.

It has sensitivities of -114dBm (ASK) and -108dBm (FSK). It has a low-noise amplifier, an image-reject mixer, a fully integrated phase locked loop, and a local oscillator. It also has a 10.7MHz IF limiting amplifier with received signal strength indicator, a low-noise FM demodulator, and a 3.0V voltage regulator. Differential peak-detecting data demodulators are included for both FSK and ASK analog baseband data recovery.

The receiver is designed to operate in a wide variety of power-sensitive applications such as remote keyless-entry systems, car alarms, tyre pressure monitoring systems, home-security systems, remote controls, and garage-door openers.

The part draws less than 1.1μA in shutdown mode and only 7.0mA in receive mode. Depending on the components selected, the MAX1471 is capable of receiving data rates up to 33kbps (Manchester) or 66kbps (NRZ) and transitions from shutdown to valid data out in less than 250μs. In power-cycled applications, this quick transition minimises how long the system needs to be in receive mode.

The MAX1471 comes in a 32-pin thin TQFN, and operates over the automotive temperature range from -40°C to 125°C.

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