This equation is rearranged to find the location of the two

poles:

(1)

As shown in Equation (1), as values of R

increased, the magnitude of the poles is reduced, which in

turn decreases the bandwidth of the amplifier. Whenever

possible, it is best to choose smaller feedback resistors.

Figure 3 shows the effect of feedback resistor on the

LMP7701/LMP7702/LMP7704 bandwidth.

Equation (1) has two poles. In most cases, it is the presence

of pairs of poles that causes gain peaking. In order to elimi-

nate this effect, the poles should be placed in Butterworth

position, since poles in Butterworth position do not cause

gain peaking. To achieve a Butterworth pair, the quantity

under the square root in Equation (1) should be set to equal

−1. Using this fact and the relation between R

−A

shown in Equation (2).IfR

optimum value, gain peaking will occur.

(2)

In Figure 2,C

and to increase stability. Additionally, C

nates the gain peaking that can be caused by having a larger

feedback resistor. Figure 4 shows how C

peaking.

DIODES BETWEEN THE INPUTS

The LMP7701/LMP7702/LMP7704 have a set of anti-parallel

diodes between the input pins, as shown in Figure 5. These

diodes are present to protect the input stage of the amplifier.

At the same time, they limit the amount of differential input

voltage that is allowed on the input pins. A differential signal

larger than one diode voltage drop might damage the di-

odes. The differential signal between the inputs needs to be

20127354

FIGURE 3. Closed Loop Gain vs. Frequency

20127355

FIGURE 4. Closed Loop Gain vs. Frequency with

Compensation

20127325

FIGURE 5. Input of LMP7701

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