BRUSSELS — The latest members of a highly integrated RF receiver family, the MLX71120 and MLX71121, from Melexis are both automotive qualified ICs with dual RF inputs. They have been specifically designed for low cost antenna diversity applications in the unlicensed Industrial-Scientific-Medical (ISM) and Short-Range-Devices (SRD) frequency bands.
The low-power ICs can address the European 863 to 870 MHz SRD bands or the ISM bands at 902 to 928 MHz in North America. At the same time the receiver chips are applicable for the lower frequency bands at 315 MHz (e.g. in the US) or at 433 MHz (e.g. in Europe and China).
Manufacturers of world-wide equipment for automotive Remote Keyless Entry (RKE) and Tire Pressure Monitoring Systems (TPMS) as well as consumer and industrial system makers benefit through the simplification of their production logistics and the indirect reduction in cost. A simple crystal change adapts the system for different application frequencies.
The dual RF input feature allows the user to very easily set up an antenna diversity scheme previously found only in high-end wireless systems. This can significantly improve the reliability of the RF communications link by selecting the RF input with the best signal quality. Another interesting feature of both receivers' is the dual-band approach. This allows switching the RF inputs between two applications, one at 433 MHz and a second at 868 MHz.
The MLX71120 receiver features a fully integrated FSK and ASK demodulator. The IC provides the freedom to select an external intermediate frequency (IF) filter, operating at one of the two common frequencies 455 kHz or 10.7 MHz. This way the receiver can be easily adapted to very narrow band or medium bandwidth applications. The sister component MLX71121 also features a fully internal demodulator, and it comes additionally with an on-chip IF filter offering a 230-kHz bandwidth. This means no external IF filter is required for the MLX71121.
The small 32 lead QFN package with a footprint of 5 mm x 5 mm and the fact that no bulky external ceramic filter and discriminator components are necessary make the RF receiver ICs the ideal choice for systems requiring the smallest PCB footprint and the lowest circuit cost.
The MLX71120/71121 operates over a wide supply voltage range from 2.1 to 5.5 V with a typical current consumption of 6.5 to 11 mA. In standby mode the current draw is below 50 nA. The receiver input sensitivity is as low as -113 dBm for ASK and -112 dBm (MLX71120) and -107 dBm (MLX71121) for FSK signals, respectively.
Both receivers combine flexibility with high levels of circuit complexity. They dramatically reduce system costs thanks to the internal IF filter and FM/FSK demodulator. In addition, an AFC feature can tolerate frequency uncertainties of the input signal.
The extended operating temperature range of -40 to +125 °C makes the parts suitable for automotive applications such as RKE, TPMS or car alarm systems. Other typical applications for the receivers include security systems, home automation, garage door openers, wireless door bells, baby monitors and wireless headsets.
Datasheets for the
MLX71121 and
MLX71120
are available on the Melexis website.
