Datasheet

AD810
REV. A
–15–
N:1 MULTIPLEXER
A multiplexer of arbitrary size can be formed by combining the
desired number of AD810s together with the appropriate
selection logic. The schematic in Figure 58 shows a
recommendation for a 4:1 mux which may be useful for driving
a high impedance such as the input to a video A/D converter
(such as the AD773). The output series resistors effectively
compensate for the combined output capacitance of the OFF
channels plus the input capacitance of the A/D while
maintaining wide bandwidth. In the case illustrated, the –0.1 dB
bandwidth is about 20 MHz with no peaking. Switching time
and OFF channel isolation (for the 4:1 mux) are about 250 ns
and 60 dB at 10 MHz, respectively.
–0.5
–3.0
1 10 100
–1.0
–1.5
–2.0
–2.5
0
0.5
0
–45
–90
–135
–180
–225
PHASE
GAIN
CLOSED-LOOP GAIN – dB
PHASE SHIFT – Degrees
FREQUENCY – MHz
V
S
= ±15V
R
L
= 10kΩ
C
L
= 10pF
Figure 56. 4:1 Mux ON Channel Gain and Phase vs.
Frequency
–50
1 10 100
–60
–70
–40
–30
FEEDTHROUGH – dB
FREQUENCY – MHz
Figure 57. 4:1 Mux OFF Channel Feedthrough vs.
Frequency
AD810
75Ω
7
2
3
0.1µF
+V
S
6
1kΩ
–V
S
4
0.1µF
8
SELECT A
AD810
7
2
3
0.1µF
+V
S
6
–V
S
4
0.1µF
8
SELECT D
AD810
7
2
3
0.1µF
+V
S
6
–V
S
4
0.1µF
8
SELECT C
AD810
7
2
3
0.1µF
+V
S
6
–V
S
4
0.1µF
8
SELECT B
33Ω
V
OUT
R
L
C
L
V
IN
, A
V
IN
, B
V
IN
, C
V
IN
, D
75Ω
1kΩ
33Ω
75Ω
1kΩ
33Ω
75Ω
1kΩ
33Ω
Figure 58. A 4:1 Multiplexer Driving a High Impedance