SI4844-A10-GU【PDF 15/26 页】IC AM/FM RX FOR DIGITAL RADIOS

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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 I 2 C-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 .

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

Mono Audio

Left + Right

Stereo

Pilot

Stereo Audio

Left - Right

RDS/

RBDS

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.

15 19 23 38

Frequency (kHz)

4.12. Reference Clock

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.

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

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