MLX71120_12 Datasheet, PDF (7/31 Pages) Melexis Microelectronic Systems – FSK/FM/ASK Receiver

MLX71120
300 to 930MHz
FSK/FM/ASK Receiver
1.4 Operating Modes
The receiver offers two operating modes selectable by setting the corresponding logic level at pin ENRX.
ENRX
0
1
Note: ENRX is pulled down internally.
Description
Shutdown mode
Receive mode
The receiver’s start-up procedure is controlled by a sequencer circuit. It performs the sequential activation of
the different building blocks. It also initiates the pre-charging of the data filter and data slicer capacitors in
order to reduce the overall start-up time and current consumption during the start-up phase.
At ENRX = 0, the receiver is in shutdown mode and draws only a few nA. The bias system and the reference
oscillator are activated after enabling the receiver by a positive edge at pin ENRX. The crystal oscillator (RO)
is turned on first. Then the crystal oscillation amplitude builds up from noise. After reaching a certain ampli-
tude level at pin ROI, the whole IC is activated and draws the full receive mode current consumption I_CC. This
event is used to start the pre-charging of the external data path capacitors. Pre-charging is finished after
5504 clock cycles. After that time the data output pin DTAO output is activated.
ENRX
I_CC
I _RO
I_SDN
DTAO
Hi-Z
valid data
t _{on RO}
t _SEQ
t _{on RX}
Fig. 2: Timing diagram of start-up and shutdown behavior
Hi-Z
1.5 LNA Selection
The receiver features two identical LNAs. Each LNA is a cascode amplifier with a voltage gain of approxi-
mately 18dB. The actual gain depends on the antenna matching network at the inputs and the LC tank net-
work between the LNA outputs and mixer input. LNA operation can be controlled by the LNASEL pin.
LNASEL
0
Hi-Z
1
Description
LNA1 active, LNA2 shutdown
LNA1 and LNA2 active
LNA1 shutdown, LNA2 active
Pin LNASEL is internally pulled to VCC/2 during receive mode. Therefore both LNAs are active if LNASEL is
left floating (Hi-Z state).
39010 71120
Rev. 008
Page 7 of 31
Data Sheet
Jun/12