SI4840-A10 Datasheet, PDF (14/26 Pages) Silicon Laboratories – BROADCAST ANALOG TUNING DIGITAL DISPLAY AM/FM/SW RADIO RECEIVER

Si4840/44-A10
4.2. FM Receiver
The Si4840/44-A10 integrates a low noise amplifier
(LNA) supporting the worldwide FM broadcast band (64
to 109 MHz).
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: Si484x-A Antenna, Schematic,
Layout, and Design Guidelines."
The Si4840/44-A10 also has advanced stereo blending
that employs adaptive noise suppression. As a signal
quality degrades, the Si4840/44-A10 gradually
combines the stereo left and right audio channels to a
mono audio signal to maintain optimum sound fidelity
under varying reception conditions. The Si4840/44-A10
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: Si484x-A Antenna,
Schematic, Layout, and Design Guidelines." The user
can also refer to the “AN610: Si484x-A Programming
Guide” for those who want to configure the value by
host MCU.
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. Refer to
“AN610: Si484x-A Programming Guide” and "AN602:
Si484x-A Antenna, Schematic, Layout, and Design
Guidelines" for more details.
4.4. SW Receiver
The Si4844 supports short wave band receptions from
2.3 to 28.5 MHz in 5 kHz step size increments. Si4844
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: Si484x-A Programming
Guide” and "AN602: Si484x-A Antenna, Schematic,
Layout, and Design Guidelines."for more details.
4.5. Frequency Tuning
A valid channel can be found by tuning the
potentiometer that is connected to the TUNE1 and
TUNE2 pin of the Si4840/44-A10 chip.
To offer easy tuning, the Si4840/44-A10 also outputs the
tuned information to the MCU with LCD/LED driver to
display. It will light up the icon on display if the RF signal
quality passes a certain threshold when tuned to a valid
station. Four tuning preferences are available. The user
can choose to have the best performance (volume,
stereo/mono effect) only at the exact channel, or the
best performance in a larger range. Refer to "AN610:
Si484x-A Programming Guide" for more details.
4.3. AM Receiver
The highly integrated Si4840/44-A10 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 Si4840/44-A10
optimizes sensitivity and rejection of strong interferers,
allowing better reception of weak stations.
4.6. Band Select
The Si4840/44-A10 supports worldwide AM band with
five sub-bands, US/Europe/Japan/China FM band with
five sub-bands, and SW band with 16 sub-bands.
Si4840/44-A10 provides the flexibility to configure the
band and band properties at either the MCU side or the
Tuner side, enabling masked MCU for multiple projects.
For details on band selection, refer to "AN602: Si484x-A
Antenna, Schematic, Layout, and Design Guidelines"
and "AN610: Si484x-A Programming Guide".
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Rev.1.0