ADA4895-1/ADA4895-2

Data Sheet

HIGH GAIN BANDWIDTH APPLICATION

The circuit in Figure 52 shows cascaded dual amplifier stages

using the ADA4895-1/ADA4895-2. Each stage has a gain of +10

(20 dB), making the output 100 times (40 dB) the input. The total

gain bandwidth product is approximately 9 GHz with the device

operating on 6 mA of quiescent current (3 mA per amplifier).

50

Ω

1k

Ω

226

Ω

2pF

C1

5pF

25.5

Ω

226

Ω

2pF

25.5

Ω

R1

249

Ω

Figure 52. Cascaded Amplifier Stages for High Gain Applications (G = +100)

Figure 53 shows the large signal frequency response for two cases.

the second case is without these capacitors. Removing the 2 pF

feedback capacitors from this circuit increases the bandwidth,

but adds about 0.5 dB of peaking.

0

4

8

12

16

20

24

28

32

36

40

44

0.1

1

10

100

1000

FREQUENCY (MHz)

G = +100

To better balance the second stage and remove the current offset

contribution, an R1C1 circuit can be sized to correct for any

mis-match between the source impedance and the feedback

network impedance on the input amplifier. (In the example

shown in Figure 52, R1 = 249 Ω and C1 = 5 pF.) The offset of

each amplifier is within the same statistical range. As configured,

the offset of the output amplifier is not statistically significant to

the overall offset of the system.

Figure 53 was captured using a ±5 V supply; however, this circuit

also operates with supplies from ±1.5 V to ±5 V as long as the

input and output headroom values are not violated.

FEEDBACK CAPACITOR APPLICATION

For applications where frequency response flatness is necessary,

or a larger feedback resistor value is desired, a small feedback

capacitor in parallel with the feedback resistor can be used to

reduce peaking and increase flatness.

Figure 54 shows the small signal frequency response with and

without a feedback capacitor.

–15

–12

–9

–6

–3

0

3

6

1

10

100

1000

FREQUENCY (MHz)

G = +10

ADA4895-1 SOIC

Figure 54. Small Signal Frequency Response With and Without a Feedback

Capacitor

Rev. B | Page 20 of 24