STV8217 datasheet(65/149 Pages) STMICROELECTRONICS

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STV82x7

SQTH1

Channel 1 FM Squelch Threshold Register

CAROFFSET1

Channel 1 DCO Carrier Offset Compensation

Bit Name

Reset

Function

CETH1[7:0]

00100000

This register is used to compare the carrier level in the channel and the threshold value. This

level is measured after the channel filter and is relative to the full scale reference level (0 dB).

This is used as part of the validation of an FM signal, if the carrier level is below the threshold,

the signal is considered to be non-valid.

CETH

Threshold (dB)

CETH

Threshold (dB)

FFh

-6

10h

-32 (Recommended Value)

80h

-12

08h

-38

40h

-18

00h

OFF (all carrier levels are accepted)

20h

-24 (Default)

Address: 21h

Type: R/W

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

SQTH1[7:0]

Bit Name

Reset

Function

SQTH1[7:0]

00111100

The squelch detector measures the level of high frequency noise (> 40 kHz) and compares it to

the threshold level (SQTH). If the level is below this value, the S/N of the FM signal is

considered to be acceptable. Values are given for FM with standard deviation.

SQTH

S/N (dB)

FAh

77h

3Ch

15 (Default)

23h

19h

Address: 22h

Type: R/W

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

CAROFFSET1[7:0] (S)

Bit Name

Reset

Function

CAROFFSET1[7:0]

00000000

This value is used to correct the carrier frequency offset of the incoming IF signal. Automatic

frequency control in FM mode can be implemented by registers DC_REMOVAL_L and

DC_REMOVAL_R.

A DCO frequency offset (in two’s complement format) is added to the pre-programming value

by AUTOTSD in the CARFQ1 registers (corresponding to the standard IF carrier frequency).

The programmable carrier offset ranges from -192 kHz to +190.5 kHz with a resolution of

1.5 kHz.

For standard FM deviation, the value displays by DC_REMOVAL_L and DC_REMOVAL_R can

be directly loaded in CAROFFSET1 to exactly compensate the carrier offset on Channel 1

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