AD8029AKS-R2 datasheet(17/20 Pages) AD

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AD8029/AD8030/AD8040

Rev. A | Page 17 of 20

Table 5. Effect of Load on Performance

Noninverting

Gain

(kΩ)

RLOAD

(kΩ)

–3 dB SS BW

(MHz)

Peaking

(dB)

HD2 at 1 MHz,

2 V p-p (dB)

HD3 at 1 MHz,

2 V p-p (dB)

Output Noise

(nV/√Hz)

N/A

120

0.02

–80

–72

16.5

N/A

130

0.6

–84

–83

16.5

N/A

139

–87.5

–92.5

16.5

–72

–60

33.5

2.5

44.5

0.2

–79

–72.5

34.4

–84

–86

–1

0.01

–68

–57

33.6

–1

2.5

0.05

–74

–68

–1

–78

–80

The feedback resistance (RF || RG) combines with the input

capacitance to form a pole in the amplifier’s loop response. This

can cause peaking and ringing in the amplifier’s response if the

RC time constant is too low. Figure 55 illustrates this effect.

Peaking can be reduced by adding a small capacitor (1 pF–4 pF)

across the feedback resistor. The best way to find the optimal

value of capacitor is to empirically try it in your circuit. Another

factor of higher resistance values is the impact it has on noise

performance. Higher resistor values generate more noise. Each

application is unique and therefore a balance must be reached

between distortion, peaking, and noise performance. Table 5

outlines the trade-offs that different loads have on distortion,

peaking, and noise performance. In gains of 1, 2, and 10,

equivalent loads of 1 kΩ, 2 kΩ, and 5 kΩ are shown.

With increasing load resistance, the distortion and –3 dB

bandwidth improve, while the noise and peaking degrade

slightly.

RL = 5kΩ

FREQUENCY (MHz)

–8

100

1000

–1

–2

–3

–4

–5

–6

RL = 2.5kΩ

–7

RF = RL = 5kΩ

RF = RL = 2.5kΩ

RF = RL = 1kΩ

G = +2

G = +1

RL = 1kΩ

VS = 5V

VOUT = 0.1V p-p

Figure 55. Frequency Response for Various Feedback/Load Resistances

DISABLE PIN

The AD8029 disable pin allows the amplifier to be shut down

for power conservation or multiplexing applications. When in

the disable mode, the amplifier draws only 150 µA of quiescent

current. The disable pin control voltage is referenced to the

negative supply. The amplifier enters power-down mode any

time the disable pin is tied to the most negative supply or within

0.8 V of the negative supply. If left open, the amplifier will

operate normally. For switching levels, refer to Table 6.

Table 6. Disable Pin Control Voltage

Supply Voltage

Disable Pin

Voltage

+3 V

+5 V

±5 V

Low

(Disabled)

0 V to <0.8 V

–5 V to <–4 .2 V

High

(Enabled)

1.2 V to 3 V

1.2 V to 5 V

–3.8 V to +5 V

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