AD8027ART-R2 datasheet(18/24 Pages) AD

18 / 24 page

AD8027/AD8028

Rev. B | Page 18 of 24

WIDEBAND OPERATION

Voltage feedback amplifiers can use a wide range of resistor

values to set their gain. Proper design of the application’s feed-

back network requires consideration of the following issues:

•

Poles formed by the amplifier’s input capacitances

with the resistances seen at the amplifier’s input

terminals

•

Effects of mismatched source impedances

•

Resistor value impact on the application’s voltage noise

•

Amplifier loading effects

The AD8027/AD8028 has an input capacitance of 2 pF. This

input capacitance will form a pole with the amplifier’s feedback

network, destabilizing the loop. For this reason, it is generally

desirable to keep the source resistances below 500 Ω, unless

some capacitance is included in the feedback network. Likewise,

keeping the source resistances low will also take advantage of

the AD8027/AD8028’s low input referred voltage noise of

4.3 nV/√Hz.

With a wide bandwidth of over 190 MHz, the AD8027/AD8028

has numerous applications and configurations. The

AD8027/AD8028 shown in Figure 57 is configured as a nonin-

verting amplifier. The inverting configuration is shown in

Figure 58 and an easy selection table of gain, resistor values,

bandwidth, slew rate, and noise performance is presented in

Table 5.

–V

µF

0.1

µF

0.1

µF

VOUT

SELECT

VIN

R1 = RF||RG

AD8027/

AD8028

–

03327-A-056

Figure 57. Wideband Noninverting Gain Configuration

–V

µF

0.1

µF

0.1

µF

VOUT

R1 = RF||RG

VIN

SELECT

AD8027/

AD8028

–

03327-A-057

Figure 58. Wideband Inverting Gain Configuration

Table 5. Component Values, Bandwidth, and Noise

Performance (VS = ±2.5 V)

Noise Gain

(Noninverting)

RSOURCE

(Ω)

–3 dB

SS BW

(MHz)

Output

Noise with

Resistors

(nV/√Hz)

N/A

190

4.4

499

54.9

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