AD810ARZ datasheet(20/22 Pages) AD

20 / 22 page

AD810

Data Sheet

Rev. B | Page 20 of 22

4:1 MULTIPLEXER

A multiplexer of arbitrary size can be formed by combining the

desired number of AD810 devices together with the appropriate

selection logic. The schematic in Figure 63 shows a recommenda-

tion for a 4:1 mux, which can be useful for driving a high

impedance such as the input to a video ADC. The output series

resistors effectively compensate for the combined output

capacitance of the off channels plus the input capacitance of the

ADC while maintaining wide bandwidth. In the case illustrated

in Figure 63, 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.

–2.5

–1.5

–0.5

–3.0

–2.0

–1.0

0.5

10M

100M

–45

–90

–135

–180

–225

–270

FREQUENCY (Hz)

PHASE

GAIN

VS = ±15V

RL = 10kΩ

CL = 10pF

Figure 61. Closed-Loop Gain and Phase Shift vs. Frequency for 4:1 Mux,

On Channel

–70

–60

–50

–45

–40

–35

–30

–25

–75

–65

–55

10M

100M

FREQUENCY (Hz)

Figure 62. Isolation vs. Frequency for 4:1 Mux, Off Channel

1kΩ

75Ω

AD810

+VS 0.1µF

SELECT A

–VS

0.1µF

VINA

33Ω

1kΩ

75Ω

AD810

+VS 0.1µF

SELECT B

–VS

0.1µF

VINB

33Ω

1kΩ

75Ω

AD810

+VS 0.1µF

SELECT C

–VS

0.1µF

VINC

33Ω

1kΩ

75Ω

AD810

+VS 0.1µF

SELECT D

–VS

0.1µF

VIND

33Ω

VOUT

Figure 63. 4:1 Multiplexer Driving a High Impedance

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