MLX71122_16 Datasheet, PDF (35/59 Pages) Melexis Microelectronic Systems – 300 to 930MHz FSK/FM/ASK Receiver

MLX71122
300 to 930MHz FSK/FM/ASK Receiver
Datasheet
3.4.4. Output Comparator
The output comparator or data slicer decides whether the incoming signal is a digital LOW or HIGH by using
the reference voltage at SLC (pin 32). If the internal voltage is larger than the reference then the output is
HIGH and vice versa. Nevertheless, the polarity of the output comparator can be inverted. The driving
capability of the comparator output is ±2mA and in standby mode the tri-state output is at high
impedance.
Pin DTAO must not be connected by a low impedance to a fixed voltage supply or a stronger driver output!
We recommend using a series resistance of 10kΩ to connect DTAO.
3.5. Frequency Acceptance Range
The frequency acceptance range is defined as
the bandwidth where the input sensitivity can
be degraded by 3dB at a maximum, compared
to the sensitivity at the center frequency of
the channel.
Typically, the frequency acceptance range of
the MLX71122 is about 180kHz, see Fig.16.
The frequency acceptance range is mainly
depending on the frequency deviation, and
slightly on the modulation frequency. The
larger the frequency deviation the smaller the
acceptance range.
-92
-95
-98
-101
-104
180kHz
-107
-110
433.7
433.8
433.9
434.0
frequency / MHz
Fig. 16: Measured sensitivity characteristic
(BER=3·10^-3, 4kbps, Δf=±20kHz)
434.1
3.6. Biasing System
The biasing system needs an external 30kΏ resistor that is connected between RBIAS (pin 10) and the PCB
ground. The band-gap voltage at RBIAS causes a reference current flow of about 42µA through this
reference current resistor. The accuracy of the external resistor should be within ±2%. To minimize the
temperature dependency it is recommended to use a metal film resistor.
3.7. Operating Modes
The MLX71122 has four operating modes having an impact on the receiver’s current consumption. The
OPMODE bits in register R0 (see 4.1.1) determine the operating mode. Selections are:
 00 – Shutdown
all blocks deactivated, only SPI active (default)
 01 – Receive
receiving data from LNAI at selected frequency
 10 – RO and bias only only biasing system and reference oscillator are working
 11 – Synthesizer only only biasing system, reference oscillator and PLL are working
The first operating mode consumes virtually no current. The circuit is dead except of the SPI that can listen
to commands. In Receive mode all necessary blocks are turned on in order to receive data at the
programmed frequency.
REVISION 014 – AUGUST, 2016
390 10 71122 01
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