LTC2274 Linear Technology, LTC2274 Datasheet - Page 26

• Manufacturer Part Number: LTC2274
• Description: 105Msps Serial Output ADC
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
LTC2274
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 + x
pattern repeating itself every 2
the LTC2274 implementation of this polynomial in parallel
form.
26
14
FLOW (SEE FIGURE 18)
DATA TRANSMISSION
+ x
15
, which is a pseudo-random
15
NO
–1. Figure 16 illustrates
AS CODE GROUP 1
AS CODE GROUP 2
TRANSMIT K28.5
TRANSMIT K28.5
WAIT FOR NEXT
FRAME CLOCK
REQUEST?
START
Figure 15. Initial Synchronization Flow Diagram
SYNC
NO
(NEGATIVE DISPARITY)
(NEGATIVE DISPARITY)
(DISPARITY NOT OK)
YES
IS ISMODE
ENABLED?
AS CODE GROUP 1
AS CODE GROUP 2
TRANSMIT K28.5
TRANSMIT D5.6
NO
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 deserialize 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 effi cient implementation of the
(1 + x
rate (ADC sample rate).
DISPARITY?
YES
NEGATIVE
14
+ x
AS CODE GROUP 1
AS CODE GROUP 2
TRANSMIT K28.5
TRANSMIT D16.2
15
YES
) polynomial, operating at the frame clock
(DISPARITY IS OK)
(POSITIVE DISPARITY)
(NEGATIVE DISPARITY)
2274 F15
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