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參數(shù)資料
| 型號(hào)： | LTC2222CUK#TR |
| 廠商： | Linear Technology |
| 文件頁數(shù)： | 9/28頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC ADC 12BIT 105MSPS SAMPL 48QFN |
| 標(biāo)準(zhǔn)包裝： | 2,000 |
| 位數(shù)： | 12 |
| 采樣率（每秒）： | 105M |
| 數(shù)據(jù)接口： | 并聯(lián) |
| 轉(zhuǎn)換器數(shù)目： | 1 |
| 功率耗散（最大）： | 535mW |
| 電壓電源： | 單電源 |
| 工作溫度： | 0°C ~ 70°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 48-WFQFN 裸露焊盤 |
| 供應(yīng)商設(shè)備封裝： | 48-QFN-EP（7x7） |
| 包裝： | 帶卷 (TR) |
| 輸入數(shù)目和類型： | 1 個(gè)單端，雙極; 1 個(gè)差分，雙極 |
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LTC2222/LTC2223
17
22223fb
APPLICATIONS INFORMATION
During the sample phase when ENC is low, the transistors
connect the analog inputs to the sampling capacitors and
they charge to, and track the differential input voltage.
When ENC transitions from low to high, the sampled input
voltage is held on the sampling capacitors. 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.
Single-Ended Input
For cost sensitive applications, the analog inputs can be
driven single-ended. With a single-ended input the har-
monic distortion and INL will degrade, but the SNR and
DNL will remain unchanged. For a single-ended input, AIN+
should be driven with the input signal and AIN– should be
connected to 1.6V or VCM.
Common Mode Bias
For optimal performance the analog inputs should be driven
differentially. Each input should swing ±0.5V for the 2V
range or ±0.25V for the 1V range, around a common mode
voltage of 1.6V. The VCM output pin (Pin 44) may be used
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 a 2.2μF or greater capacitor.
Input Drive Impedance
As with all high performance, high speed ADCs, the
dynamic performance of the LTC2222/LTC2223 can be
inuenced by the input drive circuitry, particularly the
second and third harmonics. Source impedance and in-
put reactance can inuence SFDR. At the falling edge of
ENC, the sample-and-hold circuit will connect the 1.6pF
sampling capacitor to the input pin and start the sampling
period. The sampling period ends when ENC rises, hold-
ing 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 recommended to have a
source impedance of 100Ω or less for each input. The
source impedance should be matched for the differential
inputs. Poor matching will result in higher even order
harmonics, especially the second.
Input Drive Circuits
Figure 3 shows the LTC2222/LTC2223 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. Terminating on
the transformer secondary is desirable, as this provides
a common mode path for charging glitches caused by
the sample and hold. Figure 3 shows a 1:1 turns ratio
transformer. Other turns ratios can be used if the source
impedance seen by the ADC does not exceed 100Ω for each
ADC input. A disadvantage of using a transformer is the loss
of low frequency response. Most small RF transformers
have poor performance at frequencies below 1MHz.
Figure 3. Single-Ended to Differential Conversion
Using a Transformer
25Ω
0.1μF
AIN
+
AIN
–
12pF
2.2μF
VCM
LTC2222/23
ANALOG
INPUT
0.1μF
T1
1:1
T1 = MA/COM ETC1-1T
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
22223 F03
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| LTC2222IUK | 功能描述:IC ADC 12BIT 105MSPS SAMPL 48QFN RoHS:否 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 模數(shù)轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:1 系列:- 位數(shù):14 采樣率（每秒）:83k 數(shù)據(jù)接口:串行，并聯(lián) 轉(zhuǎn)換器數(shù)目:1 功率耗散（最大）:95mW 電壓電源:雙 ± 工作溫度:0°C ~ 70°C 安裝類型:通孔 封裝/外殼:28-DIP（0.600"，15.24mm） 供應(yīng)商設(shè)備封裝:28-PDIP 包裝:管件 輸入數(shù)目和類型:1 個(gè)單端，雙極 |
| LTC2222IUK#PBF | 功能描述:IC ADC 12BIT 105MSPS SAMPL 48QFN RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 模數(shù)轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:1 系列:- 位數(shù):14 采樣率（每秒）:83k 數(shù)據(jù)接口:串行，并聯(lián) 轉(zhuǎn)換器數(shù)目:1 功率耗散（最大）:95mW 電壓電源:雙 ± 工作溫度:0°C ~ 70°C 安裝類型:通孔 封裝/外殼:28-DIP（0.600"，15.24mm） 供應(yīng)商設(shè)備封裝:28-PDIP 包裝:管件 輸入數(shù)目和類型:1 個(gè)單端，雙極 |
| LTC2222IUK#TR | 功能描述:IC ADC 12BIT 105MSPS SAMPL 48QFN RoHS:否 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 模數(shù)轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:1 系列:- 位數(shù):14 采樣率（每秒）:83k 數(shù)據(jù)接口:串行，并聯(lián) 轉(zhuǎn)換器數(shù)目:1 功率耗散（最大）:95mW 電壓電源:雙 ± 工作溫度:0°C ~ 70°C 安裝類型:通孔 封裝/外殼:28-DIP（0.600"，15.24mm） 供應(yīng)商設(shè)備封裝:28-PDIP 包裝:管件 輸入數(shù)目和類型:1 個(gè)單端，雙極 |
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