ML2726 Datasheet, PDF (12/25 Pages) SIRENZA MICRODEVICES – 2.4GHz Low-IF 2.0Mbps FSK Transceiver

ML2726
FUNCTIONAL DESCRIPTION
The ML2726 is a fully integrated 2.0Mbps frequency shift keyed (FSK) transceiver that operates in the unlicensed
2.4GHz ISM frequency band. The device has been optimized for digital cordless telephone applications and includes all
the frequency generation, receive and transmit functions for a raw data rate of 2.0Mbps. This high data rate allows for
data spreading, such as Direct Sequence Spread Spectrum (DSSS) modulation, which improves range. The ML2726
receiver architecture is a dual conversion Low IF, which has all of the sensitivity and selectivity advantages of a
traditional super-heterodyne receiver without requiring costly, bulky external filters.
The RF mixer down-converts the 2.4GHz RF input signal to the first intermediate frequency (IF), where it is filtered to
remove adjacent channel signals. An active image reject mixer converts this signal down to a Low IF frequency, where
the data is limited, filtered, and demodulated. This architecture provides all the benefits of direct conversion to
baseband while maintaining the stability and robustness of a traditional super-heterodyne.
A single synthesizer is used for both the receiver and the FSK transmitter. The phase locked loop (PLL) is completely
integrated, including the voltage controlled oscillator (VCO), tuning circuits, and VCO resonator.
In RECEIVE MODE, the ML2726 is a dual conversion Low IF receiver. No external SAW filters are required. The
integrated image reject mixer gives sufficient rejection in this channel. All channel filtering and demodulation is
performed using active filters, which are automatically aligned. A matched bit rate filter and a data slicer follow the
demodulator. The sliced data is provided at the DOUT pin, and the analog data is available at AOUT.
In TRANSMIT MODE, the ML2726 generates a 2.4GHz output using the transmit mixer. An auto-aligned transmit data
filter and modulation compensation circuit results in an adjustment-free transmitter. The VCO is modulated by the
transmit data, which is put through a sigma-delta fractional-N PLL ensuring modulation accuracy. This modulation
occurs while the phase locked loop is closed, thus allowing practically infinite transmit or receive times with excellent
frequency accuracy and stability. A 3dBm FSK-modulated differential signal is output at the TXO/TXOB pins at the
2.4GHz carrier frequency.
The integrated PLL frequency synthesizer includes a fully integrated VCO, prescaler, phase detector and charge pump.
The reference frequency is generated from the incoming signal at the FREF pin, which can be 9.216MHz, 12.288MHz,
18.432MHz, or 24.576MHz. The loop filter is external to allow customers to optimize their loop bandwidth to their
system’s lock time and in-band phase noise requirements. This frequency-agile synthesizer allows the ML2726 to be
used in frequency hopped spread spectrum (FHSS) applications with nominal channel spacing of 3.072MHz. Carrier
frequency is programmed via the configuration registers and 3-wire serial interface. The VCO tank circuit (inductor and
varactor) is fully integrated.
RXI
2.4 GHz
Receive Input
TXO/TXOB
2.4 GHz
Output
Transmit
Mixer
2
Bandgap
Quadrature
Downmixers
Filter
Alignment
Divide
by 2
Quadrature
Divider
F
to
V
RSSI
Test Mux
Mode
Control
Two-port
Modulator
1.6 GHz
VCO
PLL
Divider
P.D.
Control
Registers
Ref.
Divider
AOUT
DOUT
Receive Data
Out
RSSI
TPC
PAON
RXON
XCEN
Parallel
control lines
DIN
Transmit Data In
DATA _Serial
CLK _{Control Bus}
EN
FREF
Frequency
Reference
VTUNE
QPO
PLL Loop
Filter
PRELIMINARY DATASHEET
OCT 2007
12
EDS-105982 REV P01