參數(shù)資料
型號(hào): AD9648BCPZRL7-125
廠商: Analog Devices Inc
文件頁數(shù): 21/44頁
文件大?。?/td> 0K
描述: IC ADC 14BIT 125MSPS 64LFCSP
標(biāo)準(zhǔn)包裝: 750
位數(shù): 14
采樣率(每秒): 125M
數(shù)據(jù)接口: LVDS,并聯(lián),串行,SPI
轉(zhuǎn)換器數(shù)目: 2
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: 64-VFQFN 裸露焊盤,CSP
供應(yīng)商設(shè)備封裝: 64-LFCSP-VQ(9x9)
包裝: 帶卷 (TR)
輸入數(shù)目和類型: 4 個(gè)單端,2 個(gè)差分
AD9648
Rev. 0 | Page 28 of 44
External Reference Operation
The use of an external reference may be necessary to enhance
the gain accuracy of the ADC or improve thermal drift charac-
teristics. Figure 51 shows the typical drift characteristics of the
internal reference in 1.0 V mode.
4
3
2
1
0
–1
–2
–3
–4
–5
–6
–40
–20
0
20
40
60
80
TEMPERATURE (°C)
V
R
E
F
E
RR
O
R
(m
V)
VREF ERROR (mV)
09975-
079
Figure 51. Typical VREF Drift
When the SENSE pin is tied to AVDD, the internal reference is
disabled, allowing the use of an external reference. An internal
reference buffer loads the external reference with an equivalent
7.5 k load (see Figure 41). The internal buffer generates the
positive and negative full-scale references for the ADC core.
Therefore, the external reference must be limited to a maximum
of 1.0 V.
CLOCK INPUT CONSIDERATIONS
For optimum performance, clock the AD9648 sample clock
inputs, CLK+ and CLK, with a differential signal. The signal
is typically ac-coupled into the CLK+ and CLK pins via a
transformer or capacitors. These pins are biased internally
(see Figure 52) and require no external bias.
0.9V
AVDD
2pF
CLK–
CLK+
09975-
058
Figure 52. Equivalent Clock Input Circuit
Clock Input Options
The AD9648 has a very flexible clock input structure. The clock
input can be a CMOS, LVDS, LVPECL, or sine wave signal.
Regardless of the type of signal being used, clock source jitter is
of the most concern, as described in the Jitter Considerations
section.
Figure 53 and Figure 54 show two preferred methods for clock-
ing the AD9648 (at clock rates up to 1 GHz prior to internal CLK
divider). A low jitter clock source is converted from a single-
ended signal to a differential signal using either an RF
transformer or an RF balun.
The RF balun configuration is recommended for clock frequencies
between 125 MHz and 1 GHz, and the RF transformer is recom-
mended for clock frequencies from 10 MHz to 200 MHz. The
back-to-back Schottky diodes across the transformer/balun
secondary limit clock excursions into the AD9648 to
approximately 0.8 V p-p differential.
This limit helps prevent the large voltage swings of the clock
from feeding through to other portions of the AD9648 while
preserving the fast rise and fall times of the signal that are critical
to a low jitter performance.
0.1F
SCHOTTKY
DIODES:
HSMS2822
CLOCK
INPUT
50
100
CLK–
CLK+
ADC
Mini-Circuits
ADT1-1WT, 1:1 Z
XFMR
09975-
059
Figure 53. Transformer-Coupled Differential Clock (Up to 200 MHz)
0.1F
1nF
CLOCK
INPUT
1nF
50
CLK–
CLK+
SCHOTTKY
DIODES:
HSMS2822
ADC
09975-
060
Figure 54. Balun-Coupled Differential Clock (Up to 1 GHz)
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