REV. B

–12–

AD8041

R2

C3

R1

C9

S1N

S1P

C7

R1

Figure 6. Small Signal Schematic

Disable Operation

The AD8041 has an active-low disable pin, which can be used

to three-state the output of the part and also lower its supply

current. If the disable pin is left floating, the part is enabled and

will perform normally. If the disable pin is pulled to 2.5 V (min)

below the positive supply, output of the AD8041 will be disabled

and the nominal supply current will drop to less than 1.6 mA.

For best isolation, the disable pin should be pulled to as low a

voltage as possible; ideally, the negative supply rail.

The disable pin on the AD8041 allows it to be configured as a 2:1

mux as shown in Figure 7 and can be used to switch many types of

high speed signals. Higher order multiplexers can also be built.

The break-before-make switching time is approximately 50 ns to

disable the output and 300 ns to enable the output.

6

4

7

3

2

AD8041

330

50

10 F

5V

330

8

6

4

7

3

2

AD8041

330

50

10 F

5V

330

8

13

12

11

10

74HC04

50

G = +2

G = +2

CH0

5MHz

CH1

10MHz

Figure 7. 2:1 Multiplexer

10

0%

100

90

200ns

1V

Figure 8. 2:1 Multiplexer Performance

Single-Supply A/D Conversion

Figure 9 shows the AD8041 driving the analog inputs of the

AD9050 in a dc-coupled system with single-ended signals. All

components are powered from a single 5 V supply. The AD820

is used to offset the ground referenced input signal to the level

required by the AD9050. The AD8041 is used to add in the offset

with the ground referenced input signal and buffer the input to

AD9050. The nominal input range of the AD9050 is 2.8 V

and 3.8 V (1 V p-p centered at 3.3 V). This circuit provides

40 MSPS analog-to-digital conversion on just 330 mW of power

while delivering 10-bit performance.

0.1 F

5V

AD8041

2.8V – 3.8V

3.3V

5V

AD9050

10

9

1k

–0.5V TO +0.5V

1k

1k

0.1 F

5V

AD820

1k

Figure 9. 10-Bit, 40 MSPS A/D Conversion

0

–10

–100

–60

–70

–80

–90

–40

–50

–30

–20

FUNDAMENTAL = 0.6dB

SECOND HARMONIC = 66.9dB

THIRD HARMONIC = 74.7dB

SNR = 55.2dB

NOISE FLOOR = – 86.1dB

ENCODE FREQUENCY = 40MHz

Figure 10. FFT Output of Circuit in Figure 9