ML2724
MODE CONTROL
The ML2724 is intended for use in TDD and TDMA radios in battery-powered equipment. To minimize power
consumption it is designed to switch rapidly from a low power mode (STANDBY) to an active mode. The ML2724 can
also make a quick transition from receive to transmit for TDD operation. Prior to transmitting or receiving, time should
be allowed for the PLL to lock and for the filters to align. When the ML2724 is operated in single-carrier TDD mode, the
LO is automatically shifted by the second (low) IF frequency when the device is switched between RECEIVE and
TRANSMIT modes.
ML2724 carrier frequency can be changed (hopped) at any time, but is usually changed between transmissions. Carrier
frequency (channel) is modified in the ML2724 by writing a corresponding new value to the PLL frequency register
(Register 1)
RECEIVE
The ML2724 uses a double-conversion super-heterodyne receiver with a nominal second IF of 1.024 MHz. The signal
flow in RECEIVE mode is from the RF input, through an RF down-conversion mixer and integrated IF filter, image reject
quadrature mixer, integrated Low IF filter, hard limiter, frequency to voltage converter, and data filter to the AOUT pin
and data slicer where the digital NRZ data is available at the DOUT pin. A 20dB step AGC extends the dynamic range
of the receiver.
The ML2724 receive chain is a Low IF receiver using advanced integrated radio techniques to eliminate external IF
filters and minimize external RF filter requirements. The precision filtering and demodulation circuits give improved
performance over conventional radio designs using external filters while providing integration comparable to advanced
direct conversion radio designs.
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
DS2724-F-01
FINAL DATASHEET
APRIL 2003
14