SI4735-D60-GM Silicon Laboratories Inc, SI4735-D60-GM Datasheet - Page 26

• Manufacturer Part Number: SI4735-D60-GM
• Description: IC RAD RX AM/FM/SW/LW/AUX 20QFN
• Manufacturer: Silicon Laboratories Inc
• Series: -r

Specifications of SI4735-D60-GM

• Frequency: 153kHz ~ 279kHz, 520kHz ~ 1.71MHz, 2.3MHz ~ 26.1MHz, 64MHz ~ 108MHz
• Sensitivity: -
• Data Rate - Maximum: -
• Modulation Or Protocol: AM, FM, SW-LW
• Applications: General Purpose
• Current - Receiving: 10.5mA
• Data Interface: PCB, Surface Mount
• Memory Size: -
• Antenna Connector: PCB, Surface Mount
• Features: RSSI Equipped
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -20°C ~ 85°C
• Package / Case: *
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Si4730/31/34/35-D60
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, and
RDS/RBDS data as shown in Figure 11 below.
4.9.1. Stereo Decoder
The Si473x'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
simultaneously in forcing a blend from stereo to mono.
The metric which reflects the minimum signal quality
takes
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.
26
0
multipath
precedence
Figure 11. MPX Signal Spectrum
Mono Audio
Left + Right
15
Stereo
Pilot
19
interference,
Frequency (kHz)
and
23
the
Stereo Audio
Left - Right
38
signal
are
is
53
monitored
RBDS
RDS/
blended
57
Rev. 1.0
4.10. Received Signal Qualifiers
The quality of a tuned signal can vary depending on
many factors including environmental conditions, time of
day, and position of the antenna. To adequately manage
the audio output and avoid unpleasant audible effects to
the end-user, the Si473x monitors and provides
indicators of the signal quality, allowing the host
processor to perform additional processing if required
by the customer. The Si473x monitors signal quality
metrics including RSSI, SNR, and multipath interference
on FM signals. These metrics are used to optimize
signal processing and are also reported to the host
processor. The signal processing algorithms can use
either Silicon Labs' optimized settings (recommended)
or be customized to modify performance.
4.11. Volume Control
The audio output may be muted. Volume is adjusted
digitally by the RX_VOLUME property.
4.12. 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.
4.13. Soft Mute
The soft mute feature is available to attenuate the audio
outputs and minimize audible noise in very weak signal
conditions. 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 release rates.
4.14. FM Hi-Cut Control
Hi-cut control is employed on audio outputs with
degradation of the signal due to low SNR and/or
multipath interference. Two metrics, SNR and multipath
interference, are monitored concurrently in forcing hi-cut
of the audio outputs. Programmable minimum and
maximum thresholds are available for both metrics. The
transition frequency for hi-cut is also programmable with
up to seven hi-cut filter settings. A single set of attack
and release rates for hi-cut are programmable for both
metrics from a range of 2 ms to 64 s. The level of hi-cut
applied can be monitored with the FM_RSQ_STATUS
command. Hi-cut can be disabled by setting the hi-cut
filter to audio bandwidth of 15 kHz.