ADA4895-2ARMZ-R7 datasheet(19/24 Pages) AD

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Data Sheet

ADA4895-1/ADA4895-2

APPLICATIONS INFORMATION

USING THE ADA4895-1/ADA4895-2 AT A

GAIN < +10

The ADA4895-1/ADA4895-2 are minimum gain 10 stable when

used in normal gain configurations. However, the ADA4895-1/

ADA4895-2 can be configured to work at lower gains down to a

gain of +5. Figure 50 shows how to add a simple RC circuit (R1 =

49.9 Ω and C1 = 60 pF) to allow the ADA4895-1/ADA4895-2 to

operate at a gain of +5.

VOUT

150pF

50Ω

60pF

50Ω

VIN

Ω

200

Ω

Figure 50. Configuring the ADA4895-1/ADA4895-2 for a Gain of +5 Stable

This circuit has a gain of +9 at high frequency and a gain of +5 at

frequencies lower than the resonance frequency of 53 MHz

(1/2πR1C1). With a noise gain of approximately +9 at high

frequency, the total output noise increases unless an antialiasing

filter is used to block the high frequency content.

Figure 51 shows the small and large signal frequency response of

the circuit shown in Figure 50 into a 50 Ω analyzer (G = +5 V/V

or 14 dB). As shown in Figure 51, the circuit is very stable, and

the peaking is a little over 2 dB. This configuration is scalable to

accommodate any gain from +5 to +10, as shown in Table 11.

–1

0.1

100

1000

FREQUENCY (MHz)

VOUT = 30mV p-p

VOUT = 2V p-p

VOUT = 250mV p-p

VS = ±5V

G = +5

Figure 51. Frequency Response for G = +5

Table 11. Component Values Used with the ADA4895-1/ADA4895-2 for Gain < +10

Gain

RT (Ω)

R1 (Ω)

C1 (pF)

RG (Ω)

RF (Ω)

RO (Ω)

CL (pF)

49.9

200

49.9

150

49.9

66.5

40.2

200

49.9

150

49.9

110

37.4

226

49.9

150

49.9

205

32.4

226

49.9

120

49.9

Not applicable

30.9

249

49.9

100

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