参数资料
| 型号： | LTC2205IUK-14#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 8/28页 |
| 文件大小： | 0K |
| 描述： | IC ADC 14BIT 65MSPS 48-QFN |
| 标准包装： | 52 |
| 位数： | 14 |
| 采样率（每秒）： | 65M |
| 数据接口： | 并联 |
| 转换器数目： | 1 |
| 功率耗散（最大）： | 776mW |
| 电压电源： | 单电源 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 48-WFQFN 裸露焊盘 |
| 供应商设备封装： | 48-QFN-EP（7x7） |
| 包装： | 管件 |
| 输入数目和类型： | 1 个差分 |
| 配用： | DC890B-ND - BOARD USB DATA COLLECTION |
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LTC2205-14
16
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During the hold phase when ENC is high, the sampling
capacitors are disconnected from the input and the held
voltage is passed to the ADC core for processing. As ENC
transitions from high to low, the inputs are reconnected to
the sampling capacitors to acquire a new sample. Since
the sampling capacitors still hold the previous sample,
a charging glitch proportional to the change in voltage
between samples will be seen at this time. If the change
between the last sample and the new sample is small,
the charging glitch seen at the input will be small. If the
input change is large, such as the change seen with input
frequencies near Nyquist, then a larger charging glitch
will be seen.
Common Mode Bias
The ADC sample-and-hold circuit requires differential
drive to achieve specied performance. Each input should
swing ±0.5625V for the 2.25V range (PGA = 0) or ±0.375V
for the 1.5V range (PGA = 1), around a common mode
voltage of 1.25V. The VCM output pin (Pin 2) is designed
to provide the common mode bias level. VCM can be tied
directly to the center tap of a transformer to set the DC
input level or as a reference level to an op amp differential
driver circuit. The VCM pin must be bypassed to ground
close to the ADC with 2.2μF or greater.
Input Drive Impedence
As with all high performance, high speed ADCs the
dynamic performance of the LTC2205-14 can be inuenced
by the input drive circuitry, particularly the second and
third harmonics. Source impedance and input reactance
can inuence SFDR. At the falling edge of ENC the
sample-and-hold circuit will connect the 4.9pF sampling
capacitor to the input pin and start the sampling period.
The sampling period ends when ENC rises, holding the
sampled input on the sampling capacitor. Ideally, the
input circuitry should be fast enough to fully charge
the sampling capacitor during the sampling period
1/(2FENCODE); however, this is not always possible and the
incomplete settling may degrade the SFDR. The sampling
glitch has been designed to be as linear as possible to
minimize the effects of incomplete settling.
For the best performance it is recomended to have a source
impedence of 100Ω or less for each input. The source
impedence should be matched for the differential inputs.
Poor matching will result in higher even order harmonics,
especially the second.
INPUT DRIVE CIRCUITS
Input Filtering
A rst order RC lowpass lter at the input of the ADC can
serve two functions: limit the noise from input circuitry and
provide isolation from ADC S/H switching. The LTC2205-14
has a very broadband S/H circuit, DC to 700MHz; it can
be used in a wide range of applications; therefore, it is not
possible to provide a single recommended RC lter.
Figures 3, 4a and 4b show three examples of input RC
ltering at three ranges of input frequencies. In general
it is desirable to make the capacitors as large as can be
tolerated—this will help suppress random noise as well as
noise coupled from the digital circuitry. The LTC2205-14
does not require any input lter to achieve data sheet
specications; however, no ltering will put more stringent
noise requirements on the input drive circuitry.
Transformer Coupled Circuits
Figure 3 shows the LTC2205-14 being driven by an RF
transformer with a center-tapped secondary. The secondary
center tap is DC biased with VCM, setting the ADC input
signal at its optimum DC level. Figure 3 shows a 1:1 turns
ratio transformer. Other turns ratios can be used; however,
as the turns ratio increases so does the impedance seen by
the ADC. Source impedance greater than 50Ω can reduce
the input bandwidth and increase high frequency distortion.
A disadvantage of using a transformer is the loss of low
frequency response. Most small RF transformers have
poor performance at frequencies below 1MHz.
APPLICATIONS INFORMATION
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC2205IUK-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:16-Bit, 65Msps/40Msps |
| LTC2205IUK-TR | 制造商:LINER 制造商全称:Linear Technology 功能描述:16-Bit, 65Msps/40Msps |
| LTC2205IUK-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:16-Bit, 65Msps/40Msps |
| LTC2205UK | 制造商:LINER 制造商全称:Linear Technology 功能描述:16-Bit, 65Msps/40Msps |
| LTC2205UK-14 | 制造商:LINER 制造商全称:Linear Technology 功能描述:14-Bit, 65Msps ADC |
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