ML2726
Receive Signal Strength Indication (RSSI)
RSSI is an indication of field strength. It can be used to control transmit power to conserve battery life or it may be used
to determine if a given channel is occupied. See Figure 3.
Figure 3: RSSI Voltage vs. Input Signal Level
Automatic Filter Alignment
When the ML2726 is placed in RECEIVE mode, it automatically tunes all the internal filters using the reference
frequency from the FREF pin. When the chip is powered up (VDD first applied), the tuning information is reset to mid-
range. This self-calibration sets:
Discriminator center frequency
IF filter center frequency and bandwidth
Receiver data low-pass filter bandwidth
Transmit data low-pass filter bandwidth
TRANSMIT MODE
In TRANSMIT mode, the PLL is closed to eliminate frequency drift. A two-port modulator modulates both the VCO and
the fractional-N PLL. The VCO is directly modulated with filtered FSK transmit data. The PLL is driven by a sigma-delta
modulator, which ensures that the PLL follows the mean frequency of the modulated VCO.
The transmit modulation filter is automatically tuned during every RECEIVE time, alleviating the need for production
alignment. Asserting RXON enables the ML2726. The rising edge of XCEN triggers a complete calibration of all the on-
chip filters, which takes up to 256μs, which ensures the modulation filters are aligned to prevent unwanted spurious
emissions.
PRELIMINARY DATASHEET
OCT 2007
14
EDS-105982 REV P01
SIRENZA [ SIRENZA MICRODEVICES ]
