SI4844-B20 Datasheet, PDF (16/27 Pages) Silicon Laboratories – BROADCAST ANALOG TUNING DIGITAL DISPLAY AM/FM/SW RADIO RECEIVER

Si4844-B20
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 Si4844-B chip.
To offer easy tuning, the Si4844-B 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. Multiple 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:
Si48xx ATDD Programming Guide" for more details.
4.9. Stereo Audio Processing
The output of the FM demodulator is a stereo
multiplexed (MPX) signal. The MPX standard was
developed in 1961, and is used worldwide. Today's
MPX signal format consists of left + right (L+R) audio,
left – right (L–R) audio, a 19 kHz pilot tone.
Mono Audio
Left + Right
Stereo
Pilot
Stereo Audio
Left - Right
RDS/
RBDS
4.6. Band Select
The Si4844-B 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. Si4844-B
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: Si4822/26/27/40/44
Antenna, Schematic, Layout, and Design Guidelines”
and "AN610: Si48xx ATDD Programming Guide".
4.7. Bass and Treble
The Si4844-B further supports Bass/Treble tone control
for superior sound quality. The Si4844-B can be set to
be default normal, or programmed by the host MCU I²C-
compatible 2-wire mode. FM has nine levels
Bass/Treble effect and AM/SW has seven levels
Bass/Treble effect. For further configuration details,
refer to "AN610: Si48xx ATDD Programming Guide."
4.8. Volume Control
The Si4844-B not only allows users to use the
traditional PVR wheel volume control through an
external speaker amplifier, it also supports digital
volume control programmed by the host MCU. Si4844-B
can be programmed to be Bass/Treble mode only or
digital volume mode only; it can also be programmed to
have the digital volume coexist with Bass/Treble in two
modes. Refer to "AN610: Si48xx ATDD Programming
Guide" and “AN602: Si4822/26/27/40/44 Antenna,
Schematic, Layout, and Design Guidelines” for more
details.
0
15 19 23
38
53 57
Frequency (kHz)
Figure 5. MPX Signal Spectrum
4.9.1. Stereo Decoder
The Si4844-B's integrated stereo decoder automatically
decodes the MPX signal using DSP techniques. The 0
to 15 kHz (L+R) signal is the mono output of the FM
tuner. Stereo is generated from the (L+R), (L–R), and a
19 kHz pilot tone. The pilot tone is used as a reference
to recover the (L–R) signal. Output left and right
channels are obtained by adding and subtracting the
(L+R) and (L–R) signals respectively.
4.9.2. Stereo-Mono Blending
Adaptive noise suppression is employed to gradually
combine the stereo left and right audio channels to a
mono (L+R) audio signal as the signal quality degrades
to maintain optimum sound fidelity under varying
reception conditions. Three metrics, received signal
strength indicator (RSSI), signal-to-noise ratio (SNR),
and multipath interference, are monitored
simultaneously in forcing a blend from stereo to mono.
The metric which reflects the minimum signal quality
takes precedence and the signal is blended
appropriately.
All three metrics have programmable stereo/mono
thresholds and attack/release rates. If a metric falls
below its mono threshold, the signal is blended from
stereo to full mono. If all metrics are above their
respective stereo thresholds, then no action is taken to
blend the signal. If a metric falls between its mono and
stereo thresholds, then the signal is blended to the level
proportional to the metric’s value between its mono and
stereo thresholds, with an associated attack and
release rate.
Rev. 1.0
16