ADA4855-3

Rev. 0 | Page 15 of 20

APPLICATIONS INFORMATION

GAIN CONFIGURATIONS

The ADA4855-3 is a single-supply, high speed, voltage feedback

amplifier. Table 6 provides a convenient reference for quickly

determining the feedback and gain set resistor values and

bandwidth for common gain configurations.

Table 6. Recommended Values and Frequency Performance1

Gain

−3 dB SS

BW (MHz)

Large Signal 0.1 dB

Flatness (MHz)

1

0 Ω

N/A

200

53

2

1 kΩ

1 kΩ

120

50

5

1 kΩ

200 Ω

45

6

Figure 47 and Figure 48 show the typical noninverting and

inverting configurations and recommended bypass capacitor values.

0.1µF

10µF

10µF

0.1µF

0.1µF

ADA4855-3

–

+

Figure 47. Noninverting Gain Configuration

0.1µF

10µF

10µF

0.1µF

0.1µF

ADA4855-3

+

–

Figure 48. Inverting Gain Configuration

20 MHz ACTIVE LOW-PASS FILTER

The ADA4855-3 triple amplifier lends itself to higher order

active filters. Figure 49 shows a 20 MHz, 6-pole, Sallen-Key

low-pass filter.

U1

OP AMP

OUT1

+

–

R1

232Ω

R2

1.69kΩ

C2

6.6pF

C1

15pF

R8

261Ω

R7

1kΩ

R9

1kΩ

U2

OP AMP

OUT2

+

–

R3

309Ω

R4

1.87kΩ

C4

4.3pF

C3

15pF

U3

OP AMP

OUT3

+

–

R5

261Ω

R6

1.43kΩ

C6

3pF

C5

33pF

R10

261Ω

R11

1kΩ

R12

261Ω

Figure 49. 20 MHz, 6-Pole Low-Pass Filter

The filter has a gain of approximately 6 dB and flat frequency

response out to 14 MHz. This type of filter is commonly used at

the output of a video DAC as a reconstruction filter. The frequency

response of the filter is shown in Figure 50.

10

0

–10

–20

–30

–40

–50

–60

–70

1

200

10

100

FREQUENCY (MHz)

OUT1

OUT3

OUT2

Figure 50. 20 MHz, Low-Pass Filter Frequency Response