SI4844-B20 Datasheet, PDF (15/27 Pages) Silicon Laboratories – BROADCAST ANALOG TUNING DIGITAL DISPLAY AM/FM/SW RADIO RECEIVER

Si4844-B20
4.2. FM Receiver
The Si4844-B integrates a low noise amplifier (LNA)
supporting the worldwide FM broadcast band (64 to
109 MHz) and the TV audio stations within the fre
quency range in China are also supported. The FM
band can also be configured to be a wider range such
as 64–108 MHz in one band.
Pre-emphasis and de-emphasis is a technique used by
FM broadcasters to improve the signal-to-noise ratio of
FM receivers by reducing the effects of high frequency
interference and noise. When the FM signal is
transmitted, a pre-emphasis filter is applied to
accentuate the high audio frequencies. All FM receivers
incorporate a de-emphasis filter which attenuates high
frequencies to restore a flat frequency response. Two
time constants are used in various regions. The de-
emphasis time constant can be chosen to be 50 or
75 μs. Refer to “AN602: Si4822/26/27/40/44 Antenna,
Schematic, Layout, and Design Guidelines.”
The Si4844-B also has advanced stereo blending that
employs adaptive noise suppression. As a signal
quality degrades, the Si4844-B gradually combines the
stereo left and right audio channels to a mono audio
signal to maintain optimum sound fidelity under varying
reception conditions. The Si4844-B can output a stereo
signal to MCU with LCD/LED driver to display on the
LCD/LED so that the user can easily discern the signal
quality.
The stereo on signal is defined using both RSSI and the
Left and Right separation levels as these two
specifications are the primary factors for stereo
listening. The criteria can be set between two
conditions: the Left and Right channels are separated
by more than 6 dB with RSSI at >20 dB or Left and
Right channels are separated by more than 12 dB with
RSSI at >28 dB. The selection can be set up using
different values of the external resistor or configured by
the host MCU. Refer to “AN602: Si4822/26/27/40/44
Antenna, Schematic, Layout, and Design Guidelines.”
The user can also refer to the “AN610: Si48xx ATDD
Programming Guide” for those who want to configure
the value by host MCU.
4.3. AM Receiver
The highly integrated Si4844-B supports worldwide AM
band reception from 504 to 1750 kHz with five sub-
bands using a digital low-IF architecture with a minimum
number of external components and no manual
alignment required. This patented architecture allows
for high-precision filtering, offering excellent selectivity
and SNR with minimum variation across the AM band.
Similar to the FM receiver, the Si4844-B optimizes
sensitivity and rejection of strong interferers, allowing
better reception of weak stations.
To offer maximum flexibility, the receiver supports a
wide range of ferrite loop sticks from 180–450 μH. An
air loop antenna is supported by using a transformer to
increase the effective inductance from the air loop.
Using a 1:5 turn ratio inductor, the inductance is
increased by 25 times and easily supports all typical AM
air loop antennas, which generally vary between 10 and
20 μH.
A 9, 10 kHz tuning step can be chosen by the external
resistor or host MCU according to the different regions,
and AM soft mute level can be programmed by the host
MCU to have different tuning experiences. One of the
AM bands can be configured as a universal AM band
that simultaneously supports 9 kHz and 10 kHz channel
spaces for all regional AM standards worldwide. Refer
to “AN610: Si48xx ATDD Programming Guide” and
“AN602: Si4822/26/27/40/44 Antenna, Schematic,
Layout, and Design Guidelines” for more details.
4.4. SW Receiver
The Si4844-B supports short wave band receptions
from 2.3 to 28.5 MHz in 5 kHz step size increments. It
can also be configured to have a wide SW band that
can be used in SW radio with 1 or 2 SW banks. Si4844-
B supports extensive short wave features such as
minimal discrete components and no factory
adjustments. The Si4844 supports using the FM
antenna to capture short wave signals. Refer to
“AN610: Si48xx ATDD Programming Guide” and
“AN602: Si4822/26/27/40/44 Antenna, Schematic,
Layout, and Design Guidelines” for more details.
Rev. 1.0
15