MAX9268 datasheet(23/35 Pages) MAXIM

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Gigabit Multimedia Serial Link Deserializer

with LVDS System Interface

______________________________________________________________________________________ 23

Line Equalizer

The MAX9268 includes an adjustable line equalizer to

further compensate cable attenuation at high frequencies.

The cable equalizer has 12 selectable levels of compensa-

tion, from 2.1dB to 13dB (Table 6). The EQS input selects

the default equalization level at power-up. The state of EQS

is latched upon power-up or when resuming from power-

down mode. To select other equalization levels, set the

corresponding register bits in the MAX9268 (0x05 D[3:0]).

Use equalization in the MAX9268, together with preempha-

sis in the GMSL serializer, to create the most reliable link

for a given cable.

Spread Spectrum

To reduce the EMI generated by the transitions on the serial

link and outputs of the MAX9268, both the GMSL serial-

izer and MAX9268 support spread spectrum. Turning on

spread spectrum on the GMSL serializer spreads the serial

data and the MAX9268 outputs. Do not enable spread for

both the GMSL serializer and the MAX9268. The two select-

able spread-spectrum rates at the MAX9268 outputs are

2% and Q4% (Table 7).

Set the MAX9268 SSEN input high to select 2% spread

at power-up, and SSEN input low to select no spread at

power-up. The state of SSEN is latched upon power-up or

when resuming from power-down mode.

Turning on spread spectrum on the GMSL serializer or the

MAX9268 does not affect the audio data stream. Changes

in the GMSL serializer spread settings only affect the

MAX9268 MCLK output if it is derived from TXCLKOUT_

(MCLKSRC = 0).

The MAX9268 includes a sawtooth divider to control the

spread-modulation rate. Autodetection or manual program-

ming of the TXCLKOUT_ operation range guarantees a

spread-spectrum modulation frequency within 20kHz to

40kHz. Additionally, manual configuration of the sawtooth

divider (SDIV, 0x03 D[4:0]) allows the user to set a modula-

tion frequency according to the TXCLKOUT_ frequency.

Always keep the modulation frequency between 20kHz to

40kHz to ensure proper operation.

Manual Programming of the

Spread-Spectrum Divider

The modulation rate for the MAX9268 relates to the

TXCLKOUT_ frequency as follows:

(

) TXCLKOUT_

1 DRS

MOD SDIV

= +

where:

fM = Modulation frequency

DRS = DRS input value (0 or 1)

fTXCLKOUT_ = LVDS clock frequency

MOD = Modulation coefficient given in Table 8

SDIV = 5-bit SDIV setting, manually programmed by the FC

To program the SDIV setting, first look up the modulation

coefficient according to the spread-spectrum settings.

Table 6. Cable Equalizer Boost Levels

Table 7. LVDS and Control Output Spread

Rates

Table 8. Modulation Coefficients and

Maximum SDIV Settings

BOOST SETTING

(0x05 D[3:0])

TYPICAL BOOST GAIN (dB)

0000

2.1

0001

2.8

0010

3.4

0011

4.2

0100

5.2

Power-up default

(EQS = high)

0101

6.2

0110

0111

8.2

1000

9.4

1001

10.7

Power-up default

(EQS = low)

1010

11.7

1011

SPREAD (%)

No spread spectrum.

Power-up default when SSEN = low.

2% spread spectrum.

Power-up default when SSEN = high.

No spread spectrum

4% spread spectrum

SPREAD-

SPECTRUM

SETTING (%)

MODULATION

COEFFICIENT

(dec)

SDIV UPPER

LIMIT (dec)

208

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