ML2724 View Datasheet(PDF) - Micro Linear Corporation
Part Name
Description
MFG CO.
'ML2724' PDF : 26 Pages View PDF
ML2724
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 ML2724 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 ML2724. 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.
PLL PROGRAMMING & CHANNEL SELECTION
The ML2724 PLL is programmed via control register 2 to the set RF center frequency of operation of the radio. The PLL
does not need to be (though it can be) reprogrammed between RECEIVE and TRANSMIT modes. Nominal channel
separation is 2.048MHz, allowing for over 40 non-overlapping channels in any given location. With careful planning,
channels can be programmed in 1024kHz steps as long as care is exercised to insure that two radio links will not share
spectrum at any one time. The equation to determine channel center frequency from the ML2724 control register word
is:
fC = CHQ<0:11>*1.024MHz
DS2724-F-03
FINAL DATASHEET
DECEMBER 2005 14
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