MLX71121_15 Datasheet, PDF (4/29 Pages) Melexis Microelectronic Systems – FSK/OOK Receiver

MLX71121
300 to 930MHz
FSK/OOK Receiver
1 Theory of Operation
1.1 General
The MLX71121 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). As the first intermediate frequency (IF1) is very high, a reasonably high
degree of image rejection is provided even without using an RF front-end filter. At applications OOKing 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 second mixer MIX2 is an image-reject mixer.
The receiver signal chain can be setup by one or two low noise amplifiers (LNA1, LNA2), two down-
conversion mixers (MIX1, MIX2), an on-chip IF filter (IFF) as well as an IF amplifier (IFA). By choosing the
required modulation via an FSK/OOK switch (at pin MODSEL), either the on-chip FSK demodulator (FSK
DEMOD) or the RSSI-based OOK 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 positive and negative peak detectors (PKDET+/-). Some post-processing of the
data output signal can be performed by means a noise cancellation filter (NCF).
The dual LNA configuration can be used for antenna space diversity or antenna frequency diversity or to
setup an LNA cascade (to further improve the input sensitivity). Another option is to set up the two LNAs for
feeding the RF signal differentially.
A sequencer circuit (SEQ) controls the timing during start-up. This is to reduce start-up time and to minimize
power dissipation.
A clock output, which is a divide-by-8 version of the crystal oscillator signal, can be used to drive a microcon-
troller. The clock output is an open drain and gets activated only if a loading resistor is connected to positive
supply.
1.2 Technical Data Overview
 Input frequency ranges: 300 to 470MHz

610 to
930MHz
 Power supply range: 2.1 to 5.5V
 Temperature range: -40 to +125°C
 Shutdown current: 50 nA
 Operating current: 10.0 to 11.1mA
 FSK input sensitivity: -107dBm* (433MHz)
 OOK input sensitivity: -112dBm* (433MHz)
 Internal IF: 1.8MHz with 300kHz 3dB bandwidth
 FSK deviation range: ±10kHz to ±100kHz
 Image rejection:
 65dB 1^st IF (with external RF front-end filter)
 25dB 2^nd IF (internal image rejection)
 Maximum data rate: 50kps RZ (bi-phase) code,

100kps NRZ
 Spurious emission: < -54dBm
 Usable RSSI range: 45 to 55dB
 Crystal frequency: 16 to 27MHz
 MCU clock frequency: 2.0 to 3.4MHz
* at 4kbps NRZ, BER = 310^-3, at LNA input pins
39010 71121
Rev. 012
Page 4 of 29
Data Sheet
Mar/15