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8
Document Number: 70057
S11-0154-Rev. I, 31-Jan-11
Vishay Siliconix
DG611, DG612, DG613
TEST CIRCUITS
APPLICATIONS
High-Speed Sample-and-Hold
In a fast sample-and-hold application, the analog switch
characteristics are critical. A fast switch reduces aperture
uncertainty. A low charge injection eliminates offset (step)
errors. A low leakage reduces droop errors. The CLC111, a
fast input buffer, helps to shorten acquisition and settling
times. A low leakage, low dielectric absorption hold capacitor
must be used. Polycarbonate, polystyrene and
polypropylene are good choices. The JFET output buffer
reduces droop due to its low input bias current.
(see figure 5.)
Pixel-Rate Switch
Windows, picture-in-picture, title overlays are economically
generated using a high-speed analog switch such as the
DG613. For this application the two video sources must be
sync locked. The glitch-less analog switch eliminates halos.
(see figure 6.)
GaAs FET Drivers
Figure 7 illustrates a high-speed GaAs FET driver. To turn
the GaAs FET on 0 V are applied to its gate via S
1
, whereas
to turn it off, - 8 V are applied via S
2
. This high-speed,
low-power driver is especially suited for applications that
require a large number of RF switches, such as phased array
radars.
Figure 3. Charge Injection
C
L
1 nF
D
R
g
V
O
V+
S
V-
5 V
IN
V
L
V
g
- 3 V
GND
+ 15 V+ 5 V
Figure 4. Crosstalk
S
1
D
2
S
2
V
S
1 V, 4 V
V
O
IN
2
R
g
= 50
1 V, 4 V
X
TA L K
Isolation = 20 log
V
S
V
L
V
O
V+
IN
1
50
C = RF bypass
R
L
D
1
- 3 V
GND V-
NC
C
+ 15 V
C
+ 5 V
C
Figure 5. High-Speed Sample-and-Hold
CLC111
75
+
-
LF356
1
/
4
DG611
5 V Control
Analog
Input
Input Buffer
S
IN
D
Output Buffer
± 5 V Output
to A/D
+ 5 V + 12 V
- 5 V
C
HOLD
650 pF Polystyrene
