参数资料
型号: DC1369A-C
厂商: Linear Technology
文件页数: 14/34页
文件大小: 0K
描述: BOARD DEMO 80MSPS LTC2259-14
软件下载: QuikEval II System
设计资源: DC1369A Design Files
标准包装: 1
系列: *
相关产品: DC890B-ND - BOARD USB DATA COLLECTION
21
226114fc
LTC2261-14
LTC2260-14/LTC2259-14
For more information www.linear.com/LTC2261-14
applicaTions inForMaTion
Encode Input
The signal quality of the encode inputs strongly affects
the A/D noise performance. The encode inputs should
be treated as analog signals—do not route them next to
digital traces on the circuit board. There are two modes
of operation for the encode inputs: the differential encode
mode (Figure 10) and the single-ended encode mode
(Figure 11).
The differential encode mode is recommended for sinu-
soidal, PECL or LVDS encode inputs (Figures 12, 13). The
encode inputs are internally biased to 1.2V through 10k
equivalent resistance. The encode inputs can be taken
above VDD (up to 3.6V), and the common mode range
is from 1.1V to 1.6V. In the differential encode mode,
ENCshould stay at least 200mV above ground to avoid
falsely triggering the single-ended encode mode. For good
jitter performance ENC+ and ENCshould have fast rise
and fall times.
Thesingle-endedencodemodeshouldbeusedwithCMOS
encode inputs. To select this mode, ENCis connected
to ground and ENC+ is driven with a square wave encode
input. ENC+ can be taken above VDD (up to 3.6V) so 1.8V
to3.3VCMOSlogiclevelscanbeused.TheENC+threshold
is 0.9V. For good jitter performance ENC+ should have fast
rise and fall times.
Clock Duty Cycle Stabilizer
For good performance the encode signal should have a
50%(±5%) duty cycle. If the optional clock duty cycle
stabilizer circuit is enabled, the encode duty cycle can
vary from 30% to 70% and the duty cycle stabilizer will
maintain a constant 50% internal duty cycle. If the encode
signal changes frequency or is turned off, the duty cycle
stabilizer circuit requires one hundred clock cycles to lock
onto the input clock. The duty cycle stabilizer is enabled
by mode control register A2 (serial programming mode),
or by CS (parallel programming mode).
VDD
LTC2261-14
226114 F10
ENC
ENC+
15k
VDD
DIFFERENTIAL
COMPARATOR
30k
Figure 10. Equivalent Encode Input Circuit
for Differential Encode Mode
30k
ENC+
ENC
226114 F11
0V
1.8V TO 3.3V
LTC2261-14
CMOS LOGIC
BUFFER
Figure 11. Equivalent Encode Input Circuit
for Single-Ended Encode Mode
100
25
D1
ENC+
ENC
0.1F
T1: COILCRAFT WBC4 - 1WL
D1: AVAGO HSMS - 2822
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
226114 F12
LTC2261-14
T1
1:4
Figure 12. Sinusoidal Encode Drive
ENC+
ENC
PECL OR
LVDS
CLOCK
0.1F
226114 F13
LTC2261-14
Figure 13. PECL or LVDS Encode Drive
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