参数资料
型号: LTC2145IUP-14#TRPBF
厂商: Linear Technology
文件页数: 13/38页
文件大小: 0K
描述: IC ADC DUAL 14BIT 125MSPS 64-QFN
标准包装: 2,000
位数: 14
采样率(每秒): 125M
数据接口: 并联,串行,SPI
转换器数目: 2
功率耗散(最大): 360mW
电压电源: 模拟和数字
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 64-WFQFN 裸露焊盘
供应商设备封装: 64-QFN(9x9)
包装: 带卷 (TR)
输入数目和类型: 2 个差分
配用: DC890B-ND - BOARD USB DATA COLLECTION
LTC2145-14/
LTC2144-14/LTC2143-14
20
21454314fa
CONVERTER OPERATION
The LTC2145-14/LTC2144-14/LTC2143-14 are low power,
two-channel, 14-bit, 125Msps/105Msps/80Msps A/D
converters that are powered by a single 1.8V supply. The
analog inputs should be driven differentially. The encode
input can be driven differentially, or single ended for lower
power consumption. The digital outputs can be CMOS,
double data rate CMOS (to halve the number of output
lines), or double data rate LVDS (to reduce digital noise
in the system.) Many additional features can be chosen
by programming the mode control registers through a
serial SPI port.
ANALOG INPUT
The analog inputs are differential CMOS sample-and-hold
circuits (Figure 2). The inputs should be driven differen-
tially around a common mode voltage set by the VCM1 or
VCM2 output pins, which are nominally VDD/2. For the 2V
input range, the inputs should swing from VCM – 0.5V
to VCM + 0.5V. There should be 180° phase difference
between the inputs.
The two channels are simultaneously sampled by a shared
encode circuit (Figure 2).
Single-Ended Input
For applications less sensitive to harmonic distortion, the
AIN+ input can be driven single-ended with a 1VP-P signal
centered around VCM. The AIN– input should be connected
to VCM and the VCM bypass capacitor should be increased
to 2.2μF. With a single-ended input, the harmonic distortion
and INL will degrade, but the noise and DNL will remain
unchanged.
INPUT DRIVE CIRCUITS
Input Filtering
If possible, there should be an RC lowpass filter right at
the analog inputs. This lowpass filter isolates the drive
circuitry from the A/D sample-and-hold switching, and
also limits wideband noise from the drive circuitry. Figure 3
shows an example of an input RC filter. The RC component
values should be chosen based on the application’s input
frequency.
Transformer Coupled Circuits
Figure 3 shows the analog input being driven by an RF
transformer with a center-tapped secondary. The center
tap is biased with VCM, setting the A/D input at its optimal
DC level. At higher input frequencies a transmission line
balun transformer (Figure 4 to Figure 6) has better balance,
resulting in lower A/D distortion.
CSAMPLE
5pF
RON
15Ω
RON
15Ω
VDD
LTC2145-14
AIN
+
21454314 F02
CSAMPLE
5pF
VDD
AIN
ENC
ENC+
1.2V
10k
1.2V
10k
CPARASITIC
1.8pF
CPARASITIC
1.8pF
10Ω
25Ω
50Ω
0.1μF
AIN
+
AIN
12pF
0.1μF
VCM
LTC2145-14
ANALOG
INPUT
0.1μF
T1
1:1
T1: MA/COM MABAES0060
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
21454314 F03
Figure 2. Equivalent Input Circuit. Only One of the Two
Analog Channels Is Shown
Figure 3. Analog Input Circuit Using a Transformer.
Recommended for Input Frequencies from 5MHz to 70MHz
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