поискавой системы для электроныых деталей
  Russian  ▼
ALLDATASHEETRU.COM

X  

AD7984 датащи(PDF) 7 Page - Analog Devices

номер детали AD7984
подробное описание детали  Devices Connected
Download  12 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
производитель  AD [Analog Devices]
домашняя страница  http://www.analog.com
Logo AD - Analog Devices

AD7984 датащи(HTML) 7 Page - Analog Devices

Back Button AD7984 Datasheet HTML 3Page - Analog Devices AD7984 Datasheet HTML 4Page - Analog Devices AD7984 Datasheet HTML 5Page - Analog Devices AD7984 Datasheet HTML 6Page - Analog Devices AD7984 Datasheet HTML 7Page - Analog Devices AD7984 Datasheet HTML 8Page - Analog Devices AD7984 Datasheet HTML 9Page - Analog Devices AD7984 Datasheet HTML 10Page - Analog Devices AD7984 Datasheet HTML 11Page - Analog Devices Next Button
Zoom Inzoom in Zoom Outzoom out
 7 / 12 page
background image
Circuit Note
CN-0269
Rev. 0 | Page 7 of 12
During the conversion phase, the switch is open and the REXT
and CEXT time constant determines the input settling time.
When the switch is closed and the ADC enters the acquisition
phase, the internal RIN and CIN is connected in parallel with the
external network, and a charge transient can be injected onto
the input.
In this circuit, with a 0.4× gain of the AD8475 and a 20 V
single-ended input step, the voltage step into the AD7984 is 4 V
single-ended and 8 V differential.
When the step voltage is initially applied, the AD8475 is in the
conversion mode, and the switch is open. The REXT and CEXT
time constant is 22 ns, and 12.48 time constants is 275 ns (time
required to settle to 18 bits shown in Table 1), which is less than
the 500 ns allowable conversion time when sampling at 1 MSPS.
When the AD7984 enters the acquisition mode at the end of the
500 ns interval, the switch closes. At this point, the voltage at the
RC filter input can be positive full-scale, and the voltage on CIN
can be negative full-scale, or vice-versa. The settling time of the
voltage across CIN is now a function of REXT, CEXT, RIN, and CIN.
The settling time for this circuit can be simulated by the Multisim
and is shown in Figure 11. The SIN is a component of Multisim
named PULSE_VOLTAGE which provides the 4 V step input with
50% duty cycle. Another PULSE_VOLTAGE in Figure 11 is
SW_ADC. This PULSE_VOLTAGE combined with ideal switch
A1 controls the CONVERSION and ACQUISITION cycle
timing of the SAR ADC. The pulse is 500 ns wide which equals
the CONVERSION time of the AD7984. The 5 μs is the half-
period of the input switching signal. The SIN and SW_ADC are
controlled by the same phase of the clock. The switch A1 is
open during the first 500 ns after SIN is switched. Switch A1
then closes, allowing the capacitive DAC to acquire the input
signal from the external RC filter.
Figure 11. Multisim Settling Time Model of the AD7984 Front End
The simulation result is shown in Figure 12. The blue label
shows that the voltage on CIN settled to 4 V with 18-bit accuracy
469 ns after the input step signal. Therefore the total settling
time of the front end of the AD7984 is tSRC = 469 ns.
Figure 12. Settling Time Waveforms for AD7984 Front End Simulation Model
Table 1 is useful and shows the number of time constants
required to settle to a given accuracy for a simple RC network.
Table 1. Number of Time Constants Required to Settle to a
Given Accuracy for an Simple RC Network
Resolution,
No. of Bits
LSB (%FS)
No. of Time Constants =
−In (%Error/100)
6
1.563
4.16
8
0.391
5.55
10
0.0977
6.93
12
0.0244
8.32
14
0.0061
9.70
16
0.00153
11.09
18
0.00038
12.48
20
0.000095
13.86
22
0.000024
15.25
The total settling time of the entire circuit shown in Figure 1
can now be estimated:
2
_
2
_
2
_
2
_
_
RC
S
ATN
S
BUF
S
MUX
S
ALL
S
t
t
t
t
t
ns
2270
469
200
600
2129
2
2
2
2
Therefore for settling to 18 bits, the maximum switching rate of
this circuit is:
fS < 1/(2270 ns + 147 ns) = 414 kHz
Noise Analysis
The Noise of the AD8065 Buffer Stage
The noise sources in the signal chain of this circuit are the
thermal noise from resistors and the voltage and current noise
from the AD8065 and the AD8475. The on resistance of the two
switches is small enough to ignore.
A simplified noise analysis model for the AD8065 circuit is
shown in Figure 13.
XSC1
AB C D
G
T
NOT
U1
RIN
400Ω
CIN
30pF
4.5V, 0.5V
SW_ADC
0V, 5V
500ns, 5µs
SIN
0.5V, 4.5V
5µs, 10µs
A1
REXT
10Ω
CEXT
2.2nF
RC FILTER
ADCINPUT
14
15
16
910
TIME (µs)
11
12
13
2
1
SIN
SW_ADC
RCEXT
OUT
(11.0469µ 4)


Аналогичный номер детали - AD7984

производительномер деталидатащиподробное описание детали
logo
Analog Devices
AD7984 AD-AD7984 Datasheet
722Kb / 24P
   18-Bit, 1.33 MSPS PulSAR 10.5 mW ADC in MSOP/QFN
REV. 0
AD7984 AD-AD7984 Datasheet
469Kb / 24P
   16-Bit Lower Power
REV. B
AD7984 AD-AD7984 Datasheet
926Kb / 32P
   Ultralow Power, Low Distortion
REV. B
AD7984 AD-AD7984 Datasheet
814Kb / 24P
   18-Bit, 5 MSPS PulSAR Differential ADC
REV. 0
AD7984 AD-AD7984 Datasheet
554Kb / 24P
   Precision, Selectable Gain, Fully Differential Funnel Amplifier
REV. B
More results

Аналогичное описание - AD7984

производительномер деталидатащиподробное описание детали
logo
Analog Devices
CN0221 AD-CN0221 Datasheet
418Kb / 5P
   Devices Connected
CN0216 AD-CN0216 Datasheet
603Kb / 5P
   Devices Connected
CN0385 AD-CN0385 Datasheet
532Kb / 13P
   Devices Connected
CN0253 AD-CN0253 Datasheet
135Kb / 4P
   Devices Connected
CN0357 AD-CN0357 Datasheet
223Kb / 5P
   Devices Connected
CN0388 AD-CN0388 Datasheet
503Kb / 5P
   Devices Connected
CN0267 AD-CN0267 Datasheet
336Kb / 8P
   Devices Connected
CN0287 AD-CN0287 Datasheet
476Kb / 9P
   Devices Connected
CN0326 AD-CN0326 Datasheet
519Kb / 7P
   Devices Connected
CN0336 AD-CN0336 Datasheet
301Kb / 7P
   Devices Connected
More results


Html Pages

1 2 3 4 5 6 7 8 9 10 11 12


датащи скачать

Go To PDF Page


ссылки URL




Конфиденциальность
ALLDATASHEETRU.COM
Вашему бизинису помогли Аллдатащит?  [ DONATE ] 

Что такое Аллдатащит   |   реклама   |   контакт   |   Конфиденциальность   |   обмен ссыками   |   поиск по производителю
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn
Indian : Alldatasheet.in  |   Mexican : Alldatasheet.com.mx  |   British : Alldatasheet.co.uk  |   New Zealand : Alldatasheet.co.nz
Family Site : ic2ic.com  |   icmetro.com