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參數(shù)資料
型號: LTC2222CUK#TR
廠商: Linear Technology
文件頁數(shù): 17/28頁
文件大?。?/td> 0K
描述: IC ADC 12BIT 105MSPS SAMPL 48QFN
標準包裝: 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
供應商設備封裝: 48-QFN-EP(7x7)
包裝: 帶卷 (TR)
輸入數(shù)目和類型: 1 個單端,雙極; 1 個差分,雙極
LTC2222/LTC2223
24
22223fb
APPLICATIONS INFORMATION
High quality ceramic bypass capacitors should be used at
the VDD, OVDD, VCM, REFHA, REFHB, REFLA and REFLB
pins as shown in the block diagram on the front page of
this data sheet. Bypass capacitors must be located as
close to the pins as possible. Of particular importance are
the capacitors between REFHA and REFLB and between
REFHB and REFLA. These capacitors should be as close to
the device as possible (1.5mm or less). Size 0402 ceramic
capacitors are recommended. The 2.2μF capacitor between
REFHA and REFLA can be somewhat further away. The
traces connecting the pins and bypass capacitors must be
kept short and should be made as wide as possible.
The LTC2222/LTC2223 differential inputs should run
parallel and close to each other. The input traces should
be as short as possible to minimize capacitance and to
minimize noise pickup.
HEAT TRANSFER
Most of the heat generated by the LTC2222/LTC2223 is
transferred from the die through the bottom-side exposed
pad and package leads onto the printed circuit board. For
good electrical and thermal performance, the exposed
pad should be soldered to a large grounded pad on the
PC board. It is critical that all ground pins are connected
to a ground plane of sufcient area.
Clock Sources for Undersampling
Undersampling raises the bar on the clock source and the
higher the input frequency, the greater the sensitivity to
clock jitter or phase noise. A clock source that degrades
SNR of a full-scale signal by 1dB at 70MHz will degrade
SNR by 3dB at 140MHz, and 4.5dB at 190MHz.
In cases where absolute clock frequency accuracy is
relatively unimportant and only a single ADC is required,
a 3V canned oscillator from vendors such as Saronix
or Vectron can be placed close to the ADC and simply
connected directly to the ADC. If there is any distance to
the ADC, some source termination to reduce ringing that
may occur even over a fraction of an inch is advisable.
You must not allow the clock to overshoot the supplies or
performance will suffer. Do not lter the clock signal with
a narrow band lter unless you have a sinusoidal clock
source, as the rise and fall time artifacts present in typical
digital clock signals will be translated into phase noise.
The lowest phase noise oscillators have single-ended
sinusoidal outputs, and for these devices the use of a lter
close to the ADC may be benecial. This lter should be
close to the ADC to both reduce roundtrip reection times,
as well as reduce the susceptibility of the traces between
the lter and the ADC. If you are sensitive to close-in phase
noise, the power supply for oscillators and any buffers
must be very stable, or propagation delay variation with
supply will translate into phase noise. Even though these
clock sources may be regarded as digital devices, do not
operate them on a digital supply. If your clock is also used
to drive digital devices such as an FPGA, you should locate
the oscillator, and any clock fan-out devices close to the
ADC, and give the routing to the ADC precedence. The
clock signals to the FPGA should have series termination
at the source to prevent high frequency noise from the
FPGA disturbing the substrate of the clock fan-out device.
If you use an FPGA as a programmable divider, you must
re-time the signal using the original oscillator, and the re-
timing ip-op as well as the oscillator should be close to
the ADC, and powered with a very quiet supply.
For cases where there are multiple ADCs, or where the
clock source originates some distance away, differential
clock distribution is advisable. This is advisable both from
the perspective of EMI, but also to avoid receiving noise
from digital sources both radiated, as well as propagated in
the waveguides that exist between the layers of multilayer
PCBs. The differential pairs must be close together, and
distanced from other signals. The differential pair should
be guarded on both sides with copper distanced at least
3x the distance between the traces, and grounded with
vias no more than 1/4 inch apart.
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