EVB71122
300 to 930MHz Receiver
Evaluation Board Description
1
1.1
Theory of Operation
General
The MLX71122 receiver architecture is based on a double-conversion super-heterodyne approach. The two
LO signals are derived from an on-chip integer-N PLL frequency synthesizer. The PLL reference frequency
is derived from a crystal (XTAL). The PLL synthesizer consists of an integrated voltage-controlled oscillator
with external inductor, a programmable feedback divider chain, a programmable reference divider, a phase-
frequency detector with a charge pump and an external loop filter.
In the receiver’s down-conversion chain, two mixers MIX1 and MIX2 are driven by the internal local oscillator
signals LO1 and LO2, respectively. The second mixer MIX2 is an image-reject mixer. As the first intermedi-
ate frequency (IF1) is very high (typically above 100 MHz), a reasonably high degree of image rejection is
provided even without using an RF front-end filter. At applications asking for very high image rejections,
cost-efficient RF front-end filtering can be realized by using a SAW filter in front of the LNA.
The receiver signal chain is setup by a low noise amplifier (LNA), two down-conversion mixers (MIX1 and
MIX2), an on-chip IF filter (IFF) as well as an IF amplifier (IFA). By choosing the required modulation via an
FSK/ASK switch (at pin MODSEL), either the on-chip FSK demodulator (FSK DEMOD) or the RSSI-based
ASK detector is selected. A second order data filter (OA1) and a data slicer (OA2) follow the demodulator.
The data slicer threshold can be generated from the mean-value of the data stream or by means of the posi-
tive and negative peak detectors (PKDET+/-).
In general the MLX71122 can be set to shut-down mode, where all receiver functions are completely turned
off, and to several other operating modes. There are two global operating modes that are selectable via the
logic level at pin SPISEL:
•
•
8-channel preconfigured mode (ABC
mode)
fully programmable mode (SPI
mode).
In ABC mode the number of frequency channels is limited to eight but no microcontroller programming is
required. In this case the three lines of the serial programming interface (SPI) are used to select one of the
eight predefined frequency channels via simple 3-bit parallel programming. Pins ENRX and MODSEL are
used to enable/disable the receiver and to select FSK or ASK demodulation, respectively.
SPI mode is recommended for full programming flexibility. In this case the three lines of the SPI are config-
ured as a standard 3-wire bus (SDEN, SDTA and SCLK). This allows changing many parameters of the
receiver, for example more operating modes, channels, frequency resolutions, gains, demodulation types,
data slicer settings and more. The pin MODSEL has no effect in this mode.
Y
R
A
IN
IM
L
E
R
P
-3
1.2
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EVB Data Overview
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Total image rejection: > 65dB (with external
RF front-end filter)
!
FSK/FM deviation range: ±10 to ±50kHz
!
Spurious emission: < -70dBm
!
Linear RSSI range: > 70dB
!
FSK input frequency acceptance range:
170kHz (3dB)
!
Crystal reference frequency: 10MHz
Input frequency ranges: 300 to 930MHz
Power supply range: 3.0 to 5.5V
Temperature range: -40 to +105°C
Shutdown current: 50nA
Operating current: 11mA (typ.)
Internal IF2: 2MHz with 230kHz 3dB bandwidth
Maximum data rate: 100kbps NRZ code,
50kbps bi-phase code
!
Minimum frequency resolution: 10kHz
!
Input Sensitivity: at 4 kbps NRZ, BER = 3·10
Frequency
FSK:
±20 kHz deviation
ASK
315 MHZ
-106dBm
-108dBm
433 MHz
-104dBm
-108dBm
868 MHz
-101dBm
-106dBm
915 MHz
-101dBm
-106dBm
39012 71122 01
Rev. 001
Page 4 of 32
EVB Description
Sept/06
MELEXIS [ Melexis Microelectronic Systems ]
