AN207 View Datasheet(PDF) - Vishay Semiconductors

Part Name

Description

Manufacturer

AN207

12-ns DG611 Switch Family Combines Benefits of CMOS and DMOS Technologies

Vishay Semiconductors 

AN207

Vishay Siliconix

DG611

S1

S2

S3

S4

S5

S6

S7

S8

DG611

Y0 Y1 Y2 Y3

CD74HC138

Y4 Y5 Y6 Y7

VOUT

Inputs

Enable

Address

E3 E2 E1 A2 A1 A0

XXHXXX

LXXXXX

XHXXXX

HL L L L L

HL L L LH

HL L LHL

HL L LHH

HL LHL L

HL LHLH

HL LHHL

HL LHHH

H = High Level, L = Low Level

X = Don’t Care

On

Switch

None

None

None

1

2

3

4

5

6

7

8

A0 A1

A2

E1

E2

E3

FIGURE 9. High-Speed 8-Channel Multiplexer Capable of 3-MHz Sampling Rates

Analog

Input

Input Buffer

CLC111

Sample/Hold

+5 V

+12 V

S

D

IN

1/2 DG611

Output Buffer

LF356

CHOLD

650 pF Polystyrene

"4 V Output

to A/D

–5 V

FIGURE 10. High-Speed Open-Loop Sample-and-Hold

Replacing into equation (1):

fS + 8(9

18 W

1

24 pF ) 30 ns)

+ 3.7 MHz

An added benefit of this circuit is its improvement of overall

accuracy by isolating the analog and (usually noisy) digital

grounds. This is because the DG611 CMOS input stage has a

high noise immunity, allowing for differences of up to "1 V

between the analog and digital grounds.

www.vishay.com S FaxBack 408-970-5600

6-6

Sample-and-Hold Circuits

Data acquisition systems use sample-and-holds to “freeze”

fast changing analog signals so they can be presented to an

A/D converter for digitization. Accurately acquiring and holding

the signal amplitude is critical to system performance.

Figure 10 shows a basic open-loop sample-and-hold circuit.

When the switch opens, a sample is stored on the hold

capacitor.

Document Number: 70605

03-Aug-99

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