The Power Amplifier (PA) has an open-collector differential output and can directly drive different PCB antennas, like loop or dipole, with a programmable output power level during signal transmission.
A built-in, automatic antenna tuning circuit is used to avoid the manual tuning and trimming procedures during production process, they are called “hand effect”
Low Noise Amplifier:
The Low Noise Amplifier (LNA) has approximately 250Ω of differential input impedance which functions well with the proposed antenna during signal transmission.
The LNA, when connected to the 50Ω device, needs an external matching circuit (Balun) for correct matching and to minimize the noise figure of the receiver.
The LNA gain can be selected in four steps for different gain factors (between 0 and -20 dB relative to the highest gain) based on the required RF signal strength.
A suitable bandwidth should be used to achieve various FSK deviation, data rate and crystal tolerance requirements.
The filter structure is a 7th order, Butterworth low-pass with 40 dB suppression at twice the bandwidth frequency.
Offset cancellation is done by using a high-pass filter, with a cut-off frequency below 7 kHz, in order to achieve the best possible frequency response in baseband and a good flat response in the pass band
FSK Modulated Deviation
Data Quality Indicator DIO Logic Block Diagram
The Data Quality Indicator (DQI) is the digital processing part of the radio connected to the demodulator and functions when the receiver is on.
The DIO signal goes high if the internally calculated data quality value exceeds the DIO threshold parameter, for five consecutive data bits, for both high and low periods.
The signal goes high if the received signal strength exceeds a given pre-programmed level.
The settling time of digital RSSI depends on the external filter capacitor.
The digital RSSI is basically a sensitive comparator behind an analog RSSI block. The comparator threshold can be set using the three bits and the comparator output can be read out through the Status Read register.