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SI4702-C19

BROADCAST FM RADIO TUNER FOR PORTABLE APPLICATIONS

Silicon Laboratories 

Si4702/03-C19

and Antenna Interface". Conformance to these

guidelines will help to ensure excellent performance

even in weak signal or noisy environments.

An image-reject mixer 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 achieves superior performance by using

digital signal processing (DSP) to perform channel

selection, FM demodulation, and stereo audio

processing compared to traditional analog

architectures.

4.3. General Purpose I/O Pins

The pins GPIO1–3 can serve multiple functions. GPIO1

and GPIO3 can be used to select between 2-wire and

3-wire modes for the control interface as the device is

brought out of reset. See Section “4.9. Reset, Powerup,

and Powerdown”. After powerup of the device, the

GPIO1–3 pins can be used as general purpose

inputs/outputs, and the GPIO2–3 pins can be used as

interrupt request pins for the seek/tune or RDS ready

functions and as a stereo/mono indicator respectively.

See register 04h, bits [5:0] in Section “6. Register

Descriptions” for information on the control of these

pins. It is recommended that the GPIO2–3 pins not be

used as interrupt request outputs until the powerup time

has completed (see Section “4.9. Reset, Powerup, and

Powerdown”). The GPIO3 pin has an internal, 1 M,

±15% pull-down resistor that is only active while RST is

low. General purpose input/output functionality is

available regardless of the state of the VA and VD

supplies, or the ENABLE and DISABLE bits.

(RDSS) and block error rate A, B, C and D (BLERA,

BLERB, BLERC, and BLERD) are unused and will read

0. This mode is backward compatible with earlier

firmware revisions.

Setting the RDS mode bit high places the device in RDS

verbose mode. The device sets RDSS high when

synchronized and low when synchronization is lost. If

the device is synchronized, RDS ready (RDSR) will be

set for a minimum of 40 ms when a RDS group has

been received. Setting the RDS interrupt enable

(RDSIEN) bit and GPIO2[1:0] = 01 will configure GPIO2

to pulse low for a minimum of 5 ms if the device is

synchronized and an RDS group has been received.

BLERA, BLERB, BLERC and BLERD provide

block-error levels for the RDS group. The number of bit

errors in each block within the group is encoded as

follows: 00 = no errors, 01 = one to two errors,

10 = three to five errors, 11 = six or more errors. Six or

more errors in a block indicate the block is

uncorrectable and should not be used.

*Note: RDS/RBDS is referred to only as RDS throughout the

remainder of this document.

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 8.

4.4. RDS/RBDS Processor and

Functionality

The Si4703 implements an RDS/RBDS* processor for

symbol decoding, block synchronization, error

detection, and error correction. RDS functionality is

enabled by setting the RDS bit. The device offers two

RDS modes, a standard mode and a verbose mode.

The primary difference is increased visibility to RDS

block-error levels and synchronization status with

verbose mode.

Setting the RDS mode (RDSM) bit low places the

device in standard RDS mode (default). The device will

set the RDS ready (RDSR) bit for a minimum of 40 ms

when a valid RDS group has been received. Setting the

RDS interrupt enable (RDSIEN) bit and GPIO2[1:0] = 01

will configure GPIO2 to pulse low for a minimum of 5 ms

when a valid RDS group has been received. If an invalid

group is received, RDSR will not be set and GPIO2 will

not pulse low. In standard mode RDS synchronization

Mono Audio

Left + Right

Stereo

Pilot

Stereo Audio

Left - Right

RDS/

RBDS

0

15 19 23

38

53 57

Frequency (kHz)

Figure 8. MPX Signal Spectrum

The Si4702/03-C19's integrated stereo decoder

automatically decodes the MPX signal. 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. Separate left and right channels are

obtained by adding and subtracting the (L+R) and (L-R)

signals, respectively. The Si4703-C uses frequency

information from the 19 kHz stereo pilot to recover the

57 kHz RDS/RBDS signal.

Adaptive noise suppression is employed to gradually

16

Rev. 1.1

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