Superheterodyne ASK Receiver – with integrated image rejection

Maxim introduced the MAX7033 , the newest 300MHz to 450MHz superheterodyne ASK receiver. This devices features a high sensitivity of -114dBm, user-selectable center-frequency image rejection of better than 42dB, and the option of running from either a 3V or 5V supply. In addition, the MAX7033 includes a one-step AGC circuit that drops the LNA gain by 35dB when the RF input signal is greater than -62dBm.

An AGC feature locks the AGC in its current state, and prevents it from switching in the middle of a data stream. The receiver uses a 10.7MHz IF filter with received-signal-strength indicator (RSSI) and has an on-chip, phase-locked loop and VCO, and analog baseband data-recovery circuitry.

The MAX7033 consists of a low-noise amplifier (LNA), a fully differential image-rejection mixer, a 10.7MHz IF limiting amplifier stage with received-signal-strength indicator (RSSI), and analog baseband recovery circuitry. A fully self-contained PLL requires no external components. The PLL block contains a phase detector, charge pump/integrated loop filter, VCO, asynchronous 32x or 64x clock divider, and crystal oscillator. The quadrature VCO is centered at the nominal LO frequency of 304.3MHz. For an input RF frequency of 315MHz, a reference frequency of 9.5194MHz; 4.7547MHz is needed for a 10.7MHz IF frequency (low side injection is required).

The MAX7033 is designed to operate in a wide variety of power-sensitive applications such as remote keyless-entry systems, car alarms, home-security systems, remote controls, and garage-door openers. The part draws less than 1.6&microA in shutdown mode and only 5.2mA in receive mode. The center frequency of the fully differential image-rejection mixer can be selected at 315MHz, 375MHz, or 433MHz.

Depending on the components selected, the MAX7033 can receive data rates up to 66kbps (NRZ coded) and transitions from shutdown to valid data out in less than 250 microseconds. In power-cycled applications, this quick transition minimizes the time the system needs to be in receive mode. The MAX7033 comes in a 28-pin SSOP and operates over the -40&degC to +105&degC temperature range. Prices start at $1.84 (10,000-up, FOB USA).

Maxim Integrated Products Ltd , Theale, Berks RG7 4XX, UK.

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