SI4840-A10 Datasheet, PDF (15/26 Pages) Silicon Laboratories – BROADCAST ANALOG TUNING DIGITAL DISPLAY AM/FM/SW RADIO RECEIVER

Si4840/44-A10
4.7. Bass and Treble
The Si4840/44-A10 further supports Bass/Treble tone
control for superior sound quality. The Si4840/44-A10
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: Si484x-A Programming Guide."
4.8. Volume Control
The Si4840/44-A10 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.
Si4840/44-A10 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: Si484x-A
Programming Guide" and "AN602: Si484x-A Antenna,
Schematic, Layout, and Design Guidelines" 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
0
15 19 23
38
53 57
Frequency (kHz)
Figure 5. MPX Signal Spectrum
4.9.1. Stereo Decoder
The Si4840/44-A10'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.
4.10. Stereo DAC
High-fidelity stereo digital-to-analog converters (DACs)
drive analog audio signals onto the LOUT and ROUT
pins. The audio output may be muted.
4.11. Soft Mute
The soft mute feature is available to attenuate the audio
outputs and minimize audible noise in very weak signal
conditions. Advanced algorithm is implemented to get a
better analog tuning experience. The soft mute feature
is triggered by the SNR metric. The SNR threshold for
activating soft mute is programmable, as are soft mute
attenuation levels and attack and decay rates.
4.12. Reference Clock
The Si4840/44-A10 supports RCLK input (to XTALI pin)
with the spec listed in Table 7. It can be shared with the
host MCU to save extra crystal.
An onboard crystal oscillator is available to generate the
32.768 kHz reference when an external crystal and
load capacitors are provided. Refer to "AN602: Si484x-
A Antenna, Schematic, Layout, and Design Guidelines"
for more details.
4.13. Memorizing Status
The Si4840/44-A10 provides the feature to memorize
status from the last power down with a simple design on
PCB, including frequency of the FM/AM/SW station.
Refer to "AN602: Si484x-A Antenna, Schematic,
Layout, and Design Guidelines" for details.
Rev.1.0
15