Analog Devices AD9253 Evaluation Board AD9253-125EBZ AD9253-125EBZ 데이터 시트
제품 코드
AD9253-125EBZ
Data Sheet
AD9253
Rev. 0 | Page 25 of 40
80
55
40
60
S
NRF
S
(
d
B
F
S
)
DUTY CYCLE (%)
10
065
-06
9
60
65
70
75
42
44
46
48
50
52
54
56
58
SNRFS (DCS OFF)
SNRFS (DCS ON)
bypass the CLK− pin to ground with a 0.1 μF capacitor (see
Figure 67).
Figure 67).
Input Clock Divider
contains an input clock divider with the ability
to divide the input clock by integer values between 1 and 8.
clock divider can be synchronized using the
external SYNC input. Bit 0 and Bit 1 of Register 0x109 allow the
clock divider to be resynchronized on every SYNC signal or
only on the first SYNC signal after the register is written. A
valid SYNC causes the clock divider to reset to its initial state.
This synchronization feature allows multiple parts to have their
clock dividers aligned to guarantee simultaneous input sampling.
clock divider to be resynchronized on every SYNC signal or
only on the first SYNC signal after the register is written. A
valid SYNC causes the clock divider to reset to its initial state.
This synchronization feature allows multiple parts to have their
clock dividers aligned to guarantee simultaneous input sampling.
Clock Duty Cycle
Figure 64. SNR vs. DCS On/Off
Typical high speed ADCs use both clock edges to generate a vari-
ety of internal timing signals and, as a result, may be sensitive to
clock duty cycle. Commonly, a ±5% tolerance is required on the
clock duty cycle to maintain dynamic performance characteristics.
ety of internal timing signals and, as a result, may be sensitive to
clock duty cycle. Commonly, a ±5% tolerance is required on the
clock duty cycle to maintain dynamic performance characteristics.
Jitter in the rising edge of the input is still of concern and is not
easily reduced by the internal stabilization circuit. The duty
cycle control loop does not function for clock rates less than
20 MHz, nominally. The loop has a time constant associated
with it that must be considered in applications in which the
clock rate can change dynamically. A wait time of 1.5 μs to 5 μs
is required after a dynamic clock frequency increase or decrease
before the DCS loop is relocked to the input signal.
easily reduced by the internal stabilization circuit. The duty
cycle control loop does not function for clock rates less than
20 MHz, nominally. The loop has a time constant associated
with it that must be considered in applications in which the
clock rate can change dynamically. A wait time of 1.5 μs to 5 μs
is required after a dynamic clock frequency increase or decrease
before the DCS loop is relocked to the input signal.
contains a duty cycle stabilizer (DCS) that retimes
the nonsampling (falling) edge, providing an internal clock
signal with a nominal 50% duty cycle. This allows the user to
provide a wide range of clock input duty cycles without affecting
the performance of the
signal with a nominal 50% duty cycle. This allows the user to
provide a wide range of clock input duty cycles without affecting
the performance of the
. Noise and distortion perform-
ance are nearly flat for a wide range of duty cycles with the DCS
on, as shown in Figure 64.
on, as shown in Figure 64.
100Ω
0.1µF
0.1µF
0.1µF
0.1µF
240Ω
240Ω
50kΩ
50kΩ
CLK–
CLK+
CLOCK
INPUT
CLOCK
INPUT
ADC
AD951x
PECL DRIVER
100
65-
066
Figure 65. Differential PECL Sample Clock (Up to 1 GHz)
100Ω
0.1µF
0.1µF
0.1µF
0.1µF
50kΩ
50kΩ
CLK–
CLK+
ADC
CLOCK
INPUT
CLOCK
INPUT
AD951x
LVDS DRIVER
100
65-
067
Figure 66. Differential LVDS Sample Clock (Up to 1 GHz)
OPTIONAL
100Ω
0.1µF
0.1µF
0.1µF
50Ω
1
1
50Ω RESISTOR IS OPTIONAL.
CLK–
CLK+
ADC
V
CC
1kΩ
1kΩ
CLOCK
INPUT
AD951x
CMOS DRIVER
100
65-
0
68
Figure 67. Single-Ended 1.8 V CMOS Input Clock (Up to 200 MHz)