AN207 Vishay Intertechnology, AN207 Datasheet - Page 6

• Manufacturer Part Number: AN207
• Description: 15-ns DG611 Switch Family Combines Benefits of CMOS And Dmos
• Manufacturer: Vishay Intertechnology

AN207
Vishay Siliconix
Replacing into equation (1):
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
between the analog and digital grounds.
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6-6
S
S
S
S
S
S
S
S
1
2
3
4
5
6
7
8
f
S
8(9
Analog
Y
Input
0
18
DG611
A
0
Y
1
Y
A
2
1
1
24 pF
FIGURE 9. High-Speed 8-Channel Multiplexer Capable of 3-MHz Sampling Rates
Input Buffer
Sample/Hold
Y
3
A
CD74HC138
CLC111
2
30 ns)
E
FIGURE 10. High-Speed Open-Loop Sample-and-Hold
1
IN
E
3.7 MHz
S
Y
2
4
DG611
Y
E
5
3
1
+5 V
/
2
Y
6
DG611
1 V
Y
7
–5 V
+12 V
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.
D
V
OUT
C
650 pF Polystyrene
HOLD
Output Buffer
LF356
H = High Level, L = Low Level
X = Don’t Care
E
X
L
X
H
H
H
H
H
H
H
H
3
Enable
E
X
X
H
L
L
L
L
L
L
L
L
2
E
Inputs
H
X
X
L
L
L
L
L
L
L
L
1
A
X
X
X
H
H
H
H
L
L
L
L
2
Address
Document Number: 70605
to A/D
4 V Output
A
X
X
X
H
H
H
H
L
L
L
L
1
A
H
H
H
H
X
X
X
L
L
L
L
0
Switch
03-Aug-99
None
None
None
O
On
On
1
2
3
4
5
6
7
8