
CMT2380F17
Rev0.1 | 35/347
www.cmostek.com
4 Sub-GHz Transceiver
4.1
Transmitter
The CMT2380F17
transmitter is based on direct RF synthesizer. Its carrier frequency is generated by a low noise fractional
frequency synthesizer. The modulated data is transmitted by an efficient single-ended power amplifier (PA). The output power
can be read and written by registers, which is configurable ranging from -20dBm to +20dBm with 1dB step.
When the PA switches quickly, its changed input impedance instantaneously interferes with the output frequency of the VCO.
This effect becomes a VCO pull that produces spectral spurs and glitches near the target carrier. By ramping the PA output power,
it can minimize the instantaneous glitch of the PA. The CMT2380F32 has a built-in ramping mechanism. When the PA ramp is
enabled, the PA output power can be ramped to the required value by the configured speed in order to reduce the undesired
spectral spectrum. In FSK mode, the transmitter supporting signal is transmitted after Gaussian filtering, meaning GFSK, to make
the transmitting spectrum more concentrated.
Users can design a PA matching network based on specific application requirements to optimize the transmission efficiency
at the required output power. Typical application schematics and required BOMs are detailed above. For more application
schematic details and layout guidelines, please refer toAN141 CMT2300A Schematic and PCB Layout Guide.
The transmitter can work in pass-through mode and packet mode respectively. In pass-through mode, data is sent to the chip
directly through the DIN pin of the chip and transmitted directly. In packet mode, data is preloaded into the FIFO of the chip in
STBY status and transmitted then along with other packet elements.
4.2
Receiver
An ultra-low power, high performance low IF OOK, FSK receiver is built in the CMT2380F17. It follows processing steps as: 1)
The RF signal sensed by the antenna is amplified by the low noise amplifier. 2) The signal is down-converted to the intermediate
frequency by the quadrature mixer and then filtered by the image rejection filter. 3) The signal is further amplified by the limiting
amplifier. 4) The signal is sent to the digital domain for digital demodulation processing. Each analog module is calibrated to an
internal reference voltage during power-on reset (POR). This allows the chip to perform better at different temperatures and
voltages. Baseband filtering and demodulation is done by a digital demodulator. When the chip is working in an environment with
strong out-of-band interference, the automatic gain control loop adjusts the gain of the system through the wideband power
detector and attenuation network next to the LNA to achieve optimal system linearity, selectivity, sensitivity, etc.
Following the low-power design techniques of CMOSTEK, an ultra-low power is consumed even when the receiver keeps
operating for long period. Its periodic operating mode and air wakeup feature further reduce the average power consumption of
the system, serving well in applications where power consumption is critical.
Similar to the transmitter, the CMT2380F17 receiver can operate in pass-through mode and packet mode respectively. In the
pass-through mode, the data output by the demodulator can be directly output through the DOUT pin of the chip. DOUT can be
configured from GPIO1/2/3. In the packet mode, data processing follows steps as: 1)The data output of the demodulator is firstly
sent to the packet processor for decoding. 2)The data is filled into the FIFO. 3)The controller portion of the CMT2380F17 reads
the FIFO through the SPI interface.
4.3
Transceiver Power-on Reset (POR)
The power-on reset circuit assists in power supply change detection and generates a corresponding reset signal to reset the
entire RF system (the RF portion of the CMT2380F32). The CMT2380F32 controller can reinitialize the RF system after POR.
The two cases for POR reset generation are as follows:
1.
A rapid power supply mutation triggers POR reset under the condition that RF-VDD (RF system power supply, the
same below) drops 0.9V±20% (0.72V
– 1.08V) within less than 2 us. Note that it monitors RF-VDD decrease instead of its
absolute value as shown inthe below figure.
Содержание CMT2380F17
Страница 27: ...CMT2380F17 Rev0 1 27 347 www cmostek com 1 25 Phase Noise...
Страница 111: ...CMT2380F17 Rev0 1 111 347 www cmostek com INT2IS 1 0 Selected Port Pin of nINT2 00 P4 4 01 P3 0 10 P1 1 11 P1 6...
Страница 131: ...CMT2380F17 Rev0 1 131 347 www cmostek com Figure 16 1 Timer 0 Mode 0 Structure Figure15 2 Timer 1 Mode 0 Structure...
Страница 161: ...CMT2380F17 Rev0 1 161 347 www cmostek com Figure 16 32 Split Timer 3 Mode 1 Structure AR with Ex INT...
Страница 177: ...CMT2380F17 Rev0 1 177 347 www cmostek com Figure 17 3 PCA Interrupt System...
Страница 239: ...CMT2380F17 Rev0 1 239 347 www cmostek com Figure 19 5 8 bit Timer Mode Configuration for S1BRG S1TME 1...
Страница 246: ...CMT2380F17 Rev0 1 246 347 www cmostek com SnMIPS S0MI S1MI 1 P3 3 P4 7...
Страница 289: ...CMT2380F17 Rev0 1 289 347 www cmostek com...