Silicon Laboratories SI4734/35-B20 Stereo Audio Processing De-emphasis, Stereo DAC, Soft Mute

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Mono Audio Left + Right
Modulation Level

 

Si4734/35-B20

4.8. Stereo Audio Processing

4.9. De-emphasis

The output of the FM demodulator is a stereo

Pre-emphasis and de-emphasis is a technique used by

multiplexed (MPX) signal. The MPX standard was

FM broadcasters to improve the signal-to-noise ratio of

developed in 1961, and is used worldwide. Today's

FM receivers by reducing the effects of high-frequency

MPX signal format consists of left + right (L+R) audio,

interference and noise. When the FM signal is

left – right (L–R) audio, a 19 kHz pilot tone, and

transmitted, a pre-emphasis filter is applied to

RDS/RBDS data as shown in Figure 13.

accentuate the high audio frequencies. The Si4734/35

 

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.

 

Stereo

Stereo Audio

 

RDS/

 

 

Pilot

 

 

 

 

 

Left - Right

 

RBDS

 

 

 

 

 

0

15

19

23

38

53

57

Frequency (kHz)

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. Volume is adjusted digitally with the RX_VOLUME property.

Figure 13. MPX Signal Spectrum

 

 

4.11. Soft Mute

 

 

 

 

 

 

4.8.1. Stereo Decoder

 

 

 

 

 

The soft mute feature is available to attenuate the audio

The Si4734/35's integrated stereo decoder

outputs and minimize audible noise in very weak signal

automatically decodes the MPX signal using DSP

conditions. The softmute attenuation level is adjustable

techniques. The 0 to 15 kHz (L+R) signal is the mono

using the FM_SOFT_MUTE_MAX_ATTENUATION and

output of the FM tuner. Stereo is generated from the

AM_SOFT_MUTE_MAX_ATTENUATION properties.

(L+R), (L–R), and a 19 kHz pilot tone. The pilot tone is

4.12. RDS/RBDS Processor (Si4735 Only)

used as a reference to recover the (L–R) signal. Output

The Si4735 implements an RDS/RBDS* processor for

left and

right channels are obtained

by adding

and

symbol

decoding,

block

synchronization,

error

subtracting the (L+R) and (L–R) signals respectively.

detection, and error correction.

 

 

 

 

The Si4735 uses frequency information from the 19 kHz

 

 

 

 

stereo pilot to recover the 57 kHz RDS/RBDS signal.

The Si4735 device is user configurable and provides an

4.8.2. Stereo-Mono Blending

 

 

 

 

optional

interrupt

when

RDS

is

synchronized,

loses

 

 

 

 

synchronization, and/or the user configurable RDS

Adaptive noise suppression is employed to gradually

FIFO threshold has been met.

 

 

 

 

combine the stereo left and right audio channels to a

The Si4735 reports RDS decoder synchronization

mono (L+R) audio signal as the signal quality degrades

status, and detailed bit errors in the information word for

to maintain optimum

sound

fidelity

under

varying

each RDS block with the FM_RDS_STATUS command.

reception

conditions.

Stereo/mono

status

can

be

The range of reportable block errors is 0, 1–2, 3–5, or

monitored with the FM_RSQ_STATUS command. Mono

6+.

More than

six

errors

indicates

that

the

operation

can

be

forced

with

 

the

 

corresponding block

information word contains six or

FM_BLEND_MONO_THRESHOLD property.

 

 

 

 

more

non-correctable

errors,

or that

the

block

 

 

 

 

 

 

 

checkword contains errors.

*Note: RDS/RBDS is referred to only as RDS throughout the remainder of this document.

Rev. 1.0

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Contents Description FeaturesFunctional Block Diagram ApplicationsSi4734/35-B20 Table of Contents Recommended Operating Conditions Electrical SpecificationsParameter Symbol Test Condition Min Typ Max Unit Parameter Symbol Value UnitSupplies and Interface DC CharacteristicsParameter Symbol Test Condition Min Typ Max Unit FM Mode AM/SW/LW ModeGPO1, GPO2/INT Parameter Symbol Min Typ Max UnitRST Start Wire Control Interface Characteristics1,2,3Sclk Sdio Sclk SENSPI Control Interface Write Timing Parameters Dclk DFS Dout Fmdeemphasis = FM Receiver Characteristics1,2RDS Bler 5% Si4734/35-B20 KHz Long Wave LW 153 279 Crystal Oscillator RefclkprescaleRefclk Si4734/35-GM Typical Application SchematicOptional Components Bill of MaterialsComponents Value/Description Supplier 3.6V Functional DescriptionOverview 5.5SW Receiver Operating ModesFM Receiver AM ReceiverAudio Sample Rates Digital Audio Interface Si4735 OnlyAudio Data Formats I2S Digital Audio Format RDS/RBDS Processor Si4735 Only Stereo Audio Processing De-emphasisStereo DAC Soft MuteReference Clock TuningBus Mode Select on Rising Edge SeekSPI Control Interface Mode GPO Outputs Firmware UpgradesReset, Power Up, and Power Down Programming with CommandsDescription Commands and PropertiesSi473x Command Summary CmdSi473x Property Summary Prop Name Description DefaultAmchannelfilter RdsconfigRxvolume AmdeemphasisPin Numbers Name Description Pin Descriptions Si4734/35-GMRDS/RBDS Ordering GuidePart Number Description Package Operating QFNTop Mark Explanation Package Markings Top MarksSi4734/35 Top Mark Package Outline Si4734/35 QFN Symbol Millimeters Min Nom MaxPCB Land Pattern PCB Land Pattern Si4734/35 QFNBSC PCB Land Pattern DimensionsSymbol Millimeters Min Max Additional Reference Resources Revision 0.4 to Revision Document Change ListContact Information

SI4734/35-B20 specifications

Silicon Laboratories SI4734/35-B20 is an advanced, highly integrated broadcast radio receiver designed for various consumer applications. Hailed for its compactness and versatility, the SI4734/35-B20 offers extensive features that enable radio reception across multiple frequency bands, including AM, FM, and shortwave. It caters to the needs of manufacturers looking to incorporate reliable radio capabilities into their devices, ensuring quality sound and performance without the cumbersome designs typically associated with traditional radio receivers.

At the heart of the SI4734/35-B20 are performance-optimized technologies. One standout feature is the device's ability to support digital and analog processing simultaneously, utilizing Silicon Labs’ proprietary digital signal processing (DSP) technology. This architecture not only enhances signal clarity but also helps in mitigating noise, enabling users to experience a superior audio quality across varied environments.

Another notable characteristic of the SI4734/35-B20 is its low power consumption, making it ideal for battery-operated devices. The receiver employs sophisticated power management techniques that allow it to operate efficiently, prolonging battery life while maintaining optimal performance. In this context, the “sleep” mode and fast wake-up times contribute to significant energy savings, affirming its suitability for portable applications.

The SI4734/35-B20 is designed with a robust set of features for ease of integration into various systems. The device supports multiple programmable interfaces, including I2C, providing flexibility in communication with microcontrollers and facilitating straightforward integration into existing designs. Because of its programmable architecture, developers can customize the receiver’s capabilities according to the specific needs of their applications.

Additional features include automatic frequency control (AFC) for stability in tuning, allowing seamless transitions while listening to programs. The built-in AGC (automatic gain control) optimizes the receiver's sensitivity to ensure clear reception even in weak signal conditions.

The SI4734/35-B20 also possesses a wide frequency range, accommodating both standard and niche applications. Its compact form factor and surface-mount technology (SMT) footprint further enhance its appeal to developers seeking to maximize board space in their designs.

In conclusion, the Silicon Laboratories SI4734/35-B20 is a significant advancement in radio receiver technology, combining advanced DSP, low power consumption, and ease of integration. These attributes make it a preferred choice for engineers and manufacturers looking to deliver high-quality audio experiences across a range of consumer electronics, from radios to multifunctional smart devices.
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