Rainbow Electronics RF22 - Manual (Page 6)

RF22
Version: 0.1 Date: 12/23/2008
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Test Notes:
All electrical parameters with Min/Max values are guaranteed by one (or more) of the following test methods.
Electrical parameters shown with only typical values are not guaranteed.
■ Guaranteed by design and/or simulation but not tested.
■ Guaranteed by Engineering Qualification testing at Extreme Test Conditions.
■ Guaranteed by 100% Production Test Screening at Production Test Conditions.
2. Functional Description
The RF22 is a 100% CMOS ISM wireless transceiver with continuous frequency tuning over the complete 240–930
MHz band. The wide operating voltage range of 1.8–3.6 V and low current consumption makes the RF22 and ideal
solution for battery powered applications.
The RF22 operates as a time division duplexing (TDD) transceiver where the device alternately transmits and receives
data packets. The receiver uses a singleconversion, 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 Δ-Σ 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 single high precision local oscillator (LO) is used for both transmit and receive modes since the transmitter and
receiver do not operate at the same time. The LO is generated by an integrated VCO and Δ-Σ Fractional-N PLL
synthesizer. The synthesizer is designed to support configurable data rates, output frequency, frequency deviation,
and Gaussian filtering at any frequency between 240–930 MHz. The transmit FSK data is modulated directly into the
Δ-Σ data stream and can be shaped by a Gaussian low-pass filter to reduce unwanted spectral content.
The PA output power can be configured between +11 and +20 dBm in 3 dB steps. The PA is single-ended to allow for
easy antenna matching and low BOM cost. The PA incorporates automatic ramp-up and rampdown control to reduce
unwanted spectral spreading. This RF22 supports frequency hopping, TX/RX switch control, and antenna diversity
switch control to extend the link range and improve performance. Antenna diversity is completely integrated into the
RF22 and can improve the system link budget by 8–10 dB (according to published papers on Antenna Diversity)
resulting in substantial range increases depending on the environmental conditions. The +20 dBm power amplifier can
also be used to compensate for the reduced performance of a lower cost antenna or antenna with size constraints due
to a small form-factor. Competing solutions require large and expensive external PAs to achieve comparable
performance.
The RF22 is designed to work with a microcontroller, crystal, and a few passives to create a very low cost system as
shown Figure 1. 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 3 or 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" on page 53 but just to name a few, microcontroller
clock output, Antenna Diversity, TRSW control, POR, and specific interrupts. A limited number of passive components
are needed to match the LNA and PA; refer to "9. Reference Design" on page 70 for the required component values at
different frequency ranges.
The application shown in Figure 1 is designed for a system with Antenna Diversity. The Antenna Diversity Control
Algorithm is completely integrated into the chip and is discussed further in "8.9. Antenna-Diversity" on page 66.
For a simpler application example not using Antenna Diversity see the "9. Reference Design" on page 70.