參數(shù)資料
型號(hào): AD9266BCPZRL7-20
廠商: Analog Devices Inc
文件頁(yè)數(shù): 14/32頁(yè)
文件大?。?/td> 0K
描述: IC ADC 16BIT 20MSPS 32LFCSP
標(biāo)準(zhǔn)包裝: 1,500
位數(shù): 16
采樣率(每秒): 20M
數(shù)據(jù)接口: 串行,SPI?
轉(zhuǎn)換器數(shù)目: 1
功率耗散(最大): 63mW
電壓電源: 模擬和數(shù)字
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 32-WFQFN 裸露焊盤(pán),CSP
供應(yīng)商設(shè)備封裝: 32-LFCSP-WQ(5x5)
包裝: 帶卷 (TR)
輸入數(shù)目和類型: 2 個(gè)單端,單極;1 個(gè)差分,單極
Data Sheet
AD9266
Rev. A | Page 21 of 32
Input Clock Divider
The AD9266 contains an input clock divider with the ability
to divide the input clock by integer values between 1 and 8.
Optimum performance can be obtained by enabling the internal
duty cycle stabilizer (DCS) when using divide ratios other than
1, 2, or 4.
Clock Duty Cycle
Typical high speed ADCs use both clock edges to generate
a variety 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.
The AD9266 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 AD9266. Noise and distortion perform-
ance are nearly flat for a wide range of duty cycles with the DCS on,
as shown in Figure 51.
80
79
78
77
76
70
71
72
73
74
75
30
35
40
45
50
55
60
65
70
S
NR
(
d
BF
S
)
POSITIVE DUTY CYCLE (%)
DCS OFF
DCS ON
08678-
064
Figure 51. SNR vs. DCS On/Off
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 s to 5 s
is required after a dynamic clock frequency increase or decrease
before the DCS loop is relocked to the input signal.
Jitter Considerations
High speed, high resolution ADCs are sensitive to the quality of
the clock input. The degradation in SNR from the low frequency
SNR (SNRLF) at a given input frequency (fINPUT) due to jitter
(tJRMS) can be calculated by
SNRHF = 10 log[(2π × fINPUT × tJRMS)2 + 10
)
10
/
(
LF
SNR
]
In the previous equation, the rms aperture jitter represents the
clock input jitter specification. IF undersampling applications
are particularly sensitive to jitter, as illustrated in Figure 52.
80
75
70
65
60
55
50
45
1
10
100
1k
FREQUENCY (MHz)
S
NR
(
d
BF
S
)
0.5ps
0.2ps
0.05ps
1.0ps
1.5ps
2.0ps
2.5ps
3.0ps
08678-
022
Figure 52. SNR vs. Input Frequency and Jitter
The clock input should be treated as an analog signal when
aperture jitter may affect the dynamic range of the AD9266. To
avoid modulating the clock signal with digital noise, keep power
supplies for clock drivers separate from the ADC output driver
supplies. Low jitter, crystal-controlled oscillators make the best
clock sources. If the clock is generated from another type of source
(by gating, dividing, or another method), it should be retimed by
the original clock at the last step.
For more information, see the AN-501 Application Note and
the AN-756 Application Note available at www.analog.com.
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