Si4731-A-EVB Silicon Laboratories Inc, Si4731-A-EVB Datasheet - Page 17

• Manufacturer Part Number: Si4731-A-EVB
• Description: WiFi / 802.11 Modules & Development Tools Si4731 Eval Board
• Manufacturer: Silicon Laboratories Inc

Specifications of Si4731-A-EVB

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

4.3. FM Receiver
The Si4730/31 FM receiver is based on the proven
Si4700/01 FM tuner. The receiver uses a digital low-IF
architecture
components and factory adjustments. The Si4730/31
integrates a low noise amplifier (LNA) supporting the
worldwide FM broadcast band (76 to 108 MHz). An
automatic gain control (AGC) circuit controls the gain of
the LNA to optimize sensitivity and rejection of strong
interferers. For testing purposes, the AGC can be
disabled. Refer to Section "5. Commands and
Properties" on page 21 for additional programming and
configuration
downconverts the RF signal to low-IF. The quadrature
mixer output is amplified, filtered, and digitized with high
resolution analog-to-digital converters (ADCs). This
advanced architecture allows the Si4730/31 to perform
channel selection, FM demodulation, and stereo audio
processing to achieve superior performance compared
to traditional analog architectures.
4.4. AM receiver
The highly integrated Si4730/31 supports worldwide AM
band reception from 520 to 1710 kHz using a digital low-
IF architecture with a minimum number of external
components and no manual alignment required. This
digital low-IF architecture allows for high-precision
filtering
suppression. The DSP also provides 9 or 10 kHz
channel selection, AM demodulation, soft mute, and
additional
bandwidth settings. Similar to the FM receiver, the
integrated LNA and AGC optimize sensitivity and
rejection of strong interferers allowing better reception
of weak stations.
The Si4730/31 provides highly accurate digital AM
tuning without factory adjustments. To offer maximum
flexibility, the receiver supports a wide range of ferrite
loop sticks from 180–600 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 25x easily
supporting all typical AM air loop antennas which
generally vary between 10 and 20 µH.
4.5. 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 9 below.
offering
features
allowing
information.
excellent
such
the
An
as
elimination
selectivity
adjustable
image-reject
of
and
external
channel
mixer
noise
Rev. 1.0
4.5.1. Stereo Decoder
The
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.
The Si4731 uses frequency information from the 19 kHz
stereo pilot to recover the 57 kHz RDS/RBDS signal.
4.5.2. 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. Stereo/mono status can be
monitored with the FM_RSQ_STATUS command. Mono
operation
FM_BLEND_MONO_THRESHOLD property.
4.6. De-emphasis
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. The Si4730/31
incorporates 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 is programmable to 50 or 75 µs
and is set by the FM_DEEMPHASIS property.
4.7. 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. Volume is
adjusted digitally with the RX_VOLUME property.
0
Mono Audio
Left + Right
Si4730/31's
Figure 9. MPX Signal Spectrum
can
15
Stereo
Pilot
19
Frequency (kHz)
23
Si4730/31-A10
integrated
be
Stereo Audio
forced
Left - Right
38
stereo
with
decoder
53
RBDS
RDS/
57
the
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