CMT2300A
Rev 1.0 | Page22/46
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via registers, step by step from -20dBm to +20dBm with 1dB.
When the PA is switched fast, the varying input impedance will disturb the output frequency of the VCO instantaneously. The
effect iscalled VCO pulling. It will generate the spurious and spurson the spectrumaround the desired carrier.The PA spurs can be
reduced to a minimum instantaneously by thePA output power ramping. CMT2300A has a built-in PA ramping mechanism. When
the PA Ramp is turned on, the PA output power can ramp the desired amplitude in a pre-configured rate, so as to reduce the
spurs.In FSK mode, the signal can be filtered by a Gaussian Filter before transmitted, e.g. GFSK, which can reduce the spectral
width and interference with neighboring channels.
According to different application requirements, the user can design a PA matching network to optimize the transmitting efficiency.
The typical application schematic and the required BOM is shown in Chapter 3 "Typical application schematic". For more
schematic details and layout guidelines, please refer to
“
AN141 CMT2300A Schematic and PCB Layout Design Guideline”.
The transmitter can operate in direct mode and package mode. In the direct mode, the data to be transmitted can be sent to the
chip by the DIN pin and transmitted directly. In the package mode, the data can be pre-loaded into the TX FIFO in STBY state,
and transmitted together with other package elements.
4.2 Receiver
CMT2300A has a built-in ultra-low power, high performance low-IF OOK, FSK receiver. The RF signal induced by the antennais
amplified by a low noise amplifier, and is converted to an intermediate frequency by an orthogonal mixer. The signal is filtered by
the image rejection filter, and is amplified by the limiting amplifier and then sent to the digital domain for digital demodulation.
During power on reset (POR) each analog block is calibrated to the internal reference voltage. This allows the chip to remain its
best performance at different temperatures and voltages. Baseband filtering and demodulation isdone by the digital
demodulator.The AGC loop adjust the system gain by the broadband power detector and attenuation network nearby LNA, so as
to obtain the best system linearity, selectivity, sensitivity and other performance.
LeveragingCMOSTEK's low power design technology, the receiver consumes only a very low power when it is turned on. The
periodic operation mode and wake up function can further reduce the average power consumption of the system in the
application with strict requirements of power consumption.
Similar to the transmitter, the CMT2300A receiver can operate in direct mode and packet mode.In the direct mode, the
demodulator output data can be directly output through the DOUT pin of the chip. DOUT can be assigned to GPIO1/2/3. In the
packet mode, the demodulator data output is sent to the data packet handler, get decodedand is filled in the FIFO. MCU can read
the FIFO by the SPI interface.
4.3 Auxiliary Blocks
4.3.1 Power-On Reset (POR)
The Power-On Reset circuit detect the change of the VDD power supply, and generate the reset signal for the entire CMT2300A
system. After the POR, the MCU must go through the initialization process and re-configure the CMT2300A. There are two
circumstances those will lead to the generation of POR.
The first case is a very short and sudden decrease of VDD. The POR triggering condition is, VDD dramatically decreases by 0.9V
+/- 20% (e.g. 0.72V – 1.08V) within less than 2 us. To be noticed, it detects a decreasing amplitude of the VDD, not the absolute
value of VDD.
