LTC2274 Linear Technology, LTC2274 Datasheet - Page 23

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

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APPLICATIONS INFORMATION
SERIALIZED DATA FRAME
Prior to serialization, the ADC data is encoded into the
8B/10B format, which is DC balanced, and run-length
limited. The receiver is required to lock onto the data
and recover the clock with the use of a PLL. The 8B/10B
format requires that the ADC data be broken up into 8-bit
blocks (octets), which is encoded into 10-bit code groups
applying the 8B/10B rules (refer to IEEE Std 802.3-2002
Part 3, for a complete 8B/10B description).
ANALOG
BIT
INPUT
a
0
AIN
AIN
BIT
b
1
+
–
BIT 0 OF CODE GROUP 1 IS TRANSMITTED FIRST
Figure 12. Evolution of One Transmitted Frame (Compare to IEEE Std 802.3-2002 Part 3, Figure 36-3)
BIT
BIT
BIT
H
7
H
7
2
c
LTC2274
MSB
BIT
15
CLOCK/DUTY
ENC
BIT
BIT
BIT
G
G
CONTROL
6
6
d
3
AMP
8B/10B CODE GROUP 1
S/H
CYCLE
BIT
14
+
BIT
BIT
BIT
FIRST SCRAMBLED OCTET
F
5
F
5
e
4
ENC
Figure 11. Functional Equivalent Block Diagram of Internal Dither Circuit
BIT
13
–
FIRST OCTET
BIT
BIT
BIT
E
4
E
4
5
i
BIT
12
BIT
BIT
BIT
D
D
3
3
6
f
BIT
11
BIT
BIT
BIT
C
C
2
2
g
7
BIT
10
PRECISION
PIPELINED
ADC CORE
BIT
BIT
BIT
16-BIT
B
1
B
1
h
8
DAC
BIT
9
ADC OUTPUT WORD
BIT
BIT
BIT
A
0
A
0
9
j
ONE FRAME
SERIAL OUT
BIT
8
BIT
7
SUMMATION
BIT
BIT
BIT
H
H
7
7
a
0
DIGITAL
Figure 12 illustrates the generation of one complete 8B/10B
frame. The 8 most signifi cant bits of the ADC are assigned
to the fi rst half of the frame, and the remaining 8 bits
to the second half of the frame. Next, the two resulting
octets are optionally scrambled and encoded into their
corresponding 8B/10B code. Finally, the two 10-bit code
groups are serialized and transmitted beginning with Bit
0 of code group 1.
BIT
6
BIT
BIT
BIT
G
G
b
6
6
1
BIT
5
SECOND SCRAMBLED OCTET
BIT
BIT
BIT
F
5
F
5
c
2
PSEUDO-RANDOM
HIGH = DITHER ON
LOW = DITHER OFF
MULTIBIT DEEP
BIT
DITHER ENABLE
4
GENERATOR
SECOND OCTET
NUMBER
BIT
BIT
BIT
ENCODER
E
4
E
4
d
3
DITH
8B/10B CODE GROUP 2
8b10b
BIT
3
BIT
BIT
BIT
D
3
D
3
e
4
BIT
2
BIT
BIT
BIT
C
2
C
2
5
i
BIT
1
BIT
BIT
BIT
SERIALIZER
B
1
B
1
6
f
LSB
BIT
0
BIT
BIT
BIT
A
A
0
0
g
7
BIT
h
8
2274 F11
LTC2274
BIT
2274 F12
9
j
CMLOUT
CMLOUT
OCTET
ASSIGNMENT
OPTIONAL
SCRAMBLER
8B/10B
ENCODER
23
+
–
2274f