LTC2272 datasheet(30/44 Pages) LINER

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LTC2273/LTC2272

22732f

SYNC

REQUEST?

START

IS ISMODE

ENABLED?

NEGATIVE

DISPARITY?

DATA TRANSMISSION

FLOW (SEE FIGURE 18)

TRANSMIT K28.5

AS CODE GROUP 1

WAIT FOR NEXT

FRAME CLOCK

TRANSMIT K28.5

AS CODE GROUP 2

TRANSMIT K28.5

AS CODE GROUP 1

TRANSMIT D5.6

AS CODE GROUP 2

TRANSMIT K28.5

AS CODE GROUP 1

TRANSMIT D16.2

AS CODE GROUP 2

YES

(DISPARITY NOT OK)

(NEGATIVE DISPARITY)

(DISPARITY IS OK)

(POSITIVE DISPARITY)

(NEGATIVE DISPARITY)

22732 F15

YES

APPLICATIONS INFORMATION

Figure 15. Initial Synchronization Flow Diagram

Scrambling

To avoid spectral interference from the serial data output,

an optional data scrambler is added between the ADC

data and the 8B/10B encoder to randomize the spectrum

of the serial link. The scrambler is enabled by setting the

SCRAM pin to a high logic level. The polynomial used for

the scrambler is 1 + x14 + x15, which is a pseudo-random

pattern repeating itself every 215–1. Figure 16 illustrates

the LTC2273/LTC2272 implementation of this polynomial

in parallel form.

The scrambled data is converted into two valid 8B/10B

code groups, constituting a complete frame. The 8B/10B

code groups are then serialized and transmitted.

The receiver is required to deserializing the data, decode

the code-groups into octets and descramble them back

to the original octets using the self-aligning descrambler

shown in Figure 17. This descrambler is shown in 16-bit

parallel form, which is an efﬁcient implementation of the

(1 + x14 + x15) polynomial, operating at the frame clock

rate (ADC sample rate).

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