CSAMPLE 7pF
參數(shù)資料
型號: LTC1743IFW#TR
廠商: Linear Technology
文件頁數(shù): 5/24頁
文件大小: 0K
描述: IC ADC 12BIT 50MSPS SMPL 48TSSOP
標準包裝: 1,800
位數(shù): 12
采樣率(每秒): 50M
數(shù)據(jù)接口: 并聯(lián)
轉換器數(shù)目: 1
功率耗散(最大): 1.2W
電壓電源: 單電源
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 48-TFSOP(0.240",6.10mm 寬)
供應商設備封裝: 48-TSSOP
包裝: 帶卷 (TR)
輸入數(shù)目和類型: 2 個單端,雙極;1 個差分,雙極
13
LTC1743
1743f
APPLICATIO S I FOR ATIO
WU
U
Figure 2. Equivalent Input Circuit
CSAMPLE
7pF
CPARASITIC
8pF
VDD
LTC1743
AIN
+
1743 F02
CSAMPLE
7pF
8pF
BIAS
VDD
5V
AIN
ENC
2V
6k
2V
6k
When ENC is low, the analog input is sampled differentially
directly onto the input sample-and-hold capacitors, inside
the “Input S/H” shown in the block diagram. At the instant
that ENC transitions from low to high, the sampled input
is held. While ENC is high, the held input voltage is
buffered by the S/H amplifier which drives the first pipelined
ADC stage. The first stage acquires the output of the S/H
during this high phase of ENC. When ENC goes back low,
the first stage produces its residue which is acquired by
the second stage. At the same time, the input S/H goes
back to acquiring the analog input. When ENC goes back
high, the second stage produces its residue which is
acquired by the third stage. An identical process is re-
peated for the third stage, resulting in a third stage residue
that is sent to the fourth stage ADC for final evaluation.
Each ADC stage following the first has additional range to
accommodate flash and amplifier offset errors. Results
from all of the ADC stages are digitally delayed such that
the results can be properly combined in the correction
logic before being sent to the output buffer.
SAMPLE/HOLD OPERATION AND INPUT DRIVE
Sample Hold Operation
Figure 2 shows an equivalent circuit for the LTC1743
CMOS differential sample-and-hold. The differential ana-
log inputs are sampled directly onto sampling capacitors
(CSAMPLE) through CMOS transmission gates. This direct
capacitor sampling results in lowest possible noise for a
given sampling capacitor size. The capacitors shown
attached to each input (CPARASITIC) are the summation of
all other capacitance associated with each input.
During the sample phase when ENC/ENC is low, the
transmission gate connects the analog inputs to the sam-
pling capacitors and they charge to and track the differen-
tial input voltage. When ENC/ENC transitions from low to
high the sampled input voltage is held on the sampling
capacitors. During the hold phase when ENC/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/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.
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