поискавой системы для электроныых деталей |
|
AD7984 датащи(PDF) 5 Page - Analog Devices |
|
AD7984 датащи(HTML) 5 Page - Analog Devices |
5 / 12 page Circuit Note CN-0269 Rev. 0 | Page 5 of 12 Settling Time Analysis When the circuit shown in Figure 1 is operating in the continuous switching mode, all the 16-channel signal-ended or 8-channel differential signal streams are merged into a time- division multiplexed signal by the two stage multiplexer, the ADG5208 and ADG5236. The signal is then buffered by the AD8065 that has a high impedance, low capacitance input. Then the low impedance output of AD8065 buffer drives the AD8475 stage that attenuates, level shifts, and performs the single-ended to differential conversion. An RC (10 Ω, 2.2 nF) filter is placed at the input of the AD7984 ADC in order to limit out-of-band noise and attenuate the kickback from the switched capacitor input of the ADC. The −3 dB bandwidth of the filter is 7.2 MHz. (See Front-End Amplifier and RC Filter Design for a Precision SAR Analog-to-Digital Converters, Analog Dialogue 46-12, December 2012). For the purposes of calculating settling time, the circuit can be divided into four parts as shown in Figure 5. Figure 5. Sub-Stage Block Diagram for Settling Time Analysis Then the total settling time is estimated to be the root sum square (rss) of settling time of each stage 2 _ 2 _ 2 _ 2 _ _ RC S ATN S BUF S MUX S ALL S t t t t t + + + = In order to settle to within a specific error band at a sampling rate, fS , the relationship below must be satisfied. tS_ALL + tDD + tMD < 1/fS Or, fS <1/(tS_ALL + tDD + tMD) Settling Time for the Multiplexer Stage The equivalent circuit for a CMOS switch can be approximated as an ideal switch in series with a resistor (RON) and in parallel with two capacitors (CS, CD). The multiplexer stage and associated filters can therefore be modeled as shown in Figure 6. Figure 6. First-Order Model for Input Pre-Filter, Multiplexer, and AD8065 Input Note that the ADG5236 model does not show the series switch because it only switches when changing from single-ended to differential mode inputs. The pre-filter in front of multiplexer is not shown in Figure 1. This pre-filter is used for noise suppression. Also, the RP resistor combined with protection diodes and the TVS provides additional transient and over-voltage protection for hostile environments. The protection components are shown in the complete circuit schematic contained in the CN-0269 Design Support Package. The RS is the 1 kΩ resistor in series with non-inverting input of the AD8065, and CIN is the input capacitance of AD8065. The input impedance of AD8065 is 1 GΩ||2.2 pF, and the 1 GΩ resistance can be ignored. The circuit in Figure 6 was simulated using NI Multisim™ as shown in Figure 7, with the following component values: Pre-filter: RP = 300 Ω; CP = 120 pF; ADG5208: RON =160 Ω; CS = 5.5 pF; CD = 52 pF; ADG5236: RON =160 Ω; CS = 2.5 pF; CD = 12 pF; AD8065: RS =1 kΩ; CIN = 2.2 pF; Figure 7. NI Multisim Simulation Circuit for the Pre-Filter, Multiplexer, and AD8065 Input PART 3 ATTENUATION AD8475 PART 1 tS_MUX tS_BUF tS_ATN MUX ADG5208 ADG5236 PART 4 RC + ADC AD7984 tS_RC PART 2 BUFFER AD8065 D CS CS CD VSS CS VSS VSS CD VSS VSS VSS VSS VSS SW1 SW2 RP RP ADG5208 ADG5236 RON RON RON CP CP AI 1 AI 2 PRE-FILTER RS CIN AD8065 SW1 SW2 RP1 300Ω RP2 300Ω CP1 120pF CD1 52pF RON3 160Ω CD2 15pF V1 259kHz 4V RS 1kΩ CIN 2.2pF CA1 10pF CS1 5.5pF CS2 5.5pF ADG5208 CS3 2.5pF ADG5236 S1 10V S2 –10V RON1 160Ω RON2 160Ω FIRST RC SECOND RC THIRD RC FOURTH RC XSC1 A B C D G T CP2 120pF CA2 10pF |
Аналогичный номер детали - AD7984 |
|
Аналогичное описание - AD7984 |
|
|
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 |
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 |