RF31
2. Functional Description
The RF31 is a 100% CMOS ISM wireless receiver with continuous frequency tuning over the complete 240–960 MHz
band. The wide operating voltage range of 1.8–3.6 V and low current consumption makes the RF31 and ideal
solution for battery powered applications.
The RF31 receiver uses a single-conversion, image-reject mixer to downconvert the 2-level FSK/GFSK/OOK
modulated receive signal to a low IF frequency. Following a programmable gain amplifier (PGA) the signal is
converted to the digital domain by a high performance △∑ ADC allowing filtering, demodulation, slicing, error
correction, and packet handling to be performed in the built-in DSP increasing the receiver‘s performance and
flexibility versus analog based architectures. The demodulated signal is then output to the system MCU through a
programmable GPIO or via the standard SPI bus by reading the 64-byte RX FIFO.
A high precision local oscillator (LO) is generated by an integrated VCO and △∑ Fractional-N PLL synthesizer. The
synthesizer is designed to support configurable data rates, output frequency, frequency deviation, and Gaussian
filtering at any frequency between 240–960 MHz.
The RF31 supports frequency hopping and antenna diversity switch control to extend the link range and improve
performance. Antenna diversity is completely integrated into the RF31 and can improve the system link budget by
8–10 dB, resulting in substantial range increases depending on the environmental conditions.
The RF31 is designed to work with a microcontroller, crystal, and a few passives to create a very low cost system.
Voltage regulators are integrated on-chip which allow for a wide range of operating supply voltage conditions from
+1.8 to +3.6 V. A standard 4-pin SPI bus is used to communicate with the microcontroller. Three configurable
general purpose I/Os are available for use to tailor towards the needs of the system. A more complete list of the
available GPIO functions is shown in "8. Auxiliary Functions" but just to name a few, microcontroller
clock output, Antenna Diversity, Antenna SwitchPOR, and specific interrupts. A limited number of passive
components are needed to match the LNA. Figure 25, ―Receiver—Schematic,‖
The application shown in Figure 1 is designed for a system with . The Antenna Diversity Control Algorithm is
completely integrated into the chip.
Figure 1. RX Application Example
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