EFR32FG12 Datasheet, PDF (9/183 Pages) –

EFR32FG12 Flex Gecko Proprietary Protocol SoC Family Data Sheet
System Overview
3.2.2 Fractional-N Frequency Synthesizer
The EFR32FG12 contains a high performance, low phase noise, fully integrated fractional-N frequency synthesizer. The synthesizer is
used in receive mode to generate the LO frequency used by the down-conversion mixer. It is also used in transmit mode to directly
generate the modulated RF carrier.
The fractional-N architecture provides excellent phase noise performance combined with frequency resolution better than 100 Hz, with
low energy consumption. The synthesizer has fast frequency settling which allows very short receiver and transmitter wake up times to
optimize system energy consumption.
3.2.3 Receiver Architecture
The EFR32FG12 uses a low-IF receiver architecture, consisting of a Low-Noise Amplifier (LNA) followed by an I/Q down-conversion
mixer, employing a crystal reference. The I/Q signals are further filtered and amplified before being sampled by the IF analog-to-digital
converter (IFADC).
The IF frequency is configurable from 70 kHz to 1.4 MHz. The IF can further be configured for high-side or low-side injection, providing
flexibility with respect to known interferers at the image frequency.
The Automatic Gain Control (AGC) module adjusts the receiver gain to optimize performance and avoid saturation for excellent selec-
tivity and blocking performance. The 2.4 GHz radio is calibrated at production to improve image rejection performance. The sub-GHz
radio can be calibrated on-demand by the user for the desired frequency band.
Demodulation is performed in the digital domain. The demodulator performs configurable decimation and channel filtering to allow re-
ceive bandwidths ranging from 0.1 to 2530 kHz. High carrier frequency and baud rate offsets are tolerated by active estimation and
compensation. Advanced features supporting high quality communication under adverse conditions include forward error correction by
block and convolutional coding as well as Direct Sequence Spread Spectrum (DSSS).
A Received Signal Strength Indicator (RSSI) is available for signal quality metrics, for level-based proximity detection, and for RF chan-
nel access by Collision Avoidance (CA) or Listen Before Talk (LBT) algorithms. An RSSI capture value is associated with each received
frame and the dynamic RSSI measurement can be monitored throughout reception.
3.2.4 Transmitter Architecture
The EFR32FG12 uses a direct-conversion transmitter architecture. For constant envelope modulation formats, the modulator controls
phase and frequency modulation in the frequency synthesizer. Transmit symbols or chips are optionally shaped by a digital shaping
filter. The shaping filter is fully configurable, including the BT product, and can be used to implement Gaussian or Raised Cosine shap-
ing.
Carrier Sense Multiple Access - Collision Avoidance (CSMA-CA) or Listen Before Talk (LBT) algorithms can be automatically timed by
the EFR32FG12. These algorithms are typically defined by regulatory standards to improve inter-operability in a given bandwidth be-
tween devices that otherwise lack synchronized RF channel access.
3.2.5 Wake on Radio
The Wake on Radio feature allows flexible, autonomous RF sensing, qualification, and demodulation without required MCU activity, us-
ing a subsystem of the EFR32FG12 including the Radio Controller (RAC), Peripheral Reflex System (PRS), and Low Energy peripher-
als.
3.2.6 RFSENSE
The RFSENSE module generates a system wakeup interrupt upon detection of wideband RF energy at the antenna interface, providing
true RF wakeup capabilities from low energy modes including EM2, EM3 and EM4.
RFSENSE triggers on a relatively strong RF signal and is available in the lowest energy modes, allowing exceptionally low energy con-
sumption. RFSENSE does not demodulate or otherwise qualify the received signal, but software may respond to the wakeup event by
enabling normal RF reception.
Various strategies for optimizing power consumption and system response time in presence of false alarms may be employed using
available timer peripherals.
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