Rev1.0a | 28/50
CMT2300A
4.3.8 Clock Data Recovery (CDR)
The basic task of a CDR system is to recover the clock signal that is synchronized with the symbol rate, while receiving the data. Not
only for decoding inside the chip, but also for outputting the synchronized clock to GPIO for users to sample the data. So CDR's
task is simple and important. If the recovered clock frequency is in error with the actual symbol rate, it will cause data acquisition
errors at the time of reception.
CMT2300A has designed three types of CDR systems, as follows:
1.
COUNTING system
–The system is designed for the symbol rates to be more accurate. If the symbol rate is 100% aligned,
the unlimited length of 0 can be received continuously without error.
2.
TRACING system
–The system is designed to correct the symbol rate error. It has the tracking function. It can automatically
detect the symbol rate transmitted by TX, and adjust quickly the local symbol rate of RX at the same time, so as to minimize
the error between them. The system can withstand up to 15.6% or symbol rate error. Other similar products in the industry
cannot reach this level.
3.
MANCHESTER system
–This system evolves from the COUNTING system. The basic feature is the same. The only
difference is that the system is specially designed for Manchester codec. Special processing can be done when the TX
symbol rate has unexpected changes.
4.3.9 Fast Frequency Hopping
The mechanism of fast frequency hopping is, based on the frequency configured on the RFPDFK, for instance 433.92 MHz,
during
applications the MCU can simply change 1 or 2 registers to quickly switch to another frequency channel. This simplify the
way of change the RX or TX frequency in multiple channels application.
In general, the user can configure FH_OFFSET<7:0>during the chip initialization process. And then in the application, the user
can switch the channel by changing FH_CHANNEL<7:0>.
When users need to use the fast frequency hopping in the RX mode, in some particular frequency points, one parameter of the
AFC circuit must be re-configured. Please refer to
“AN197-CMT2300A-CMT2119B-CMT2219B fast frequency hopping” and
“CMT2300A-CMT2219B frequency hopping calculation tool” for more details.