CLC1606 datasheet(13/18 Pages) EXAR

13 / 18 page

Data Sheet

13/18

Rev 1D

Application Information

Basic Operation

Figures 3, 4, and 5 illustrate typical circuit configurations for

non-inverting, inverting, and unity gain topologies for dual

supply applications. They show the recommended bypass

capacitor values and overall closed loop gain equations.

Figure 3. Typical Non-Inverting Gain Circuit

Figure 4. Typical Inverting Gain Circuit

Figure 5. Typical Unity Gain (G=1) Circuit

CFB amplifiers can be used in unity gain configurations.

Do not use the traditional voltage follower circuit, where

the output is tied directly to the inverting input. With a CFB

amplifier, a feedback resistor of appropriate value must be

used to prevent unstable behavior. Refer to figure 5 and

Table 1. Although this seems cumbersome, it does allow a

degree of freedom to adjust the passband characteristics.

Feedback Resistor Selection

One of the key design considerations when using a CFB

amplifier is the selection of the feedback resistor, Rf. Rf is

used in conjunction with Rg to set the gain in the traditional

non-inverting and inverting circuit configurations. Refer to

figures 3 and 4. As discussed in the Current Feedback

Technology section, the value of the feedback resistor has

a pronounced effect on the frequency response of the

circuit.

Table 1, provides recommended Rf and associated Rg

values for various gain settings. These values produce

the optimum frequency response, maximum bandwidth

with minimum peaking. Adjust these values to optimize

performance for a specific application. The typical

performance characteristics section includes plots that

illustrate how the bandwidth is directly affected by the

value of Rf at various gain settings.

Gain

(V/V

Rf (Ω)

Rg (Ω)

±0.1dB BW

(MHz)

-3dB BW

(MHz)

390

136

1300

270

150

1200

270

67.5

115

750

Table 1: Recommended Rf vs. Gain

In general, lowering the value of Rf from the recommended

value will extend the bandwidth at the expense of

additional high frequency gain peaking. This will cause

increased overshoot and ringing in the pulse response

characteristics. Reducing Rf too much will eventually

cause oscillatory behavior.

Increasing the value of Rf will lower the bandwidth.

Lowering the bandwidth creates a flatter frequency

response and improves 0.1dB bandwidth performance.

This is important in applications such as video. Further

increase in Rf will cause premature gain rolloff and

adversely affect gain flatness.

0.1μF

6.8μF

Output

G = - (Rf/Rg)

For optimum input offset

voltage set R1 = Rf || Rg

Input

+Vs

-Vs

0.1μF

6.8μF

0.1μF

6.8μF

Output

G = 1

Rf is required for CFB amplifiers

Input

+Vs

-Vs

0.1μF

6.8μF

0.1μF

6.8μF

Output

G = 1 + (Rf/Rg)

Input

+Vs

-Vs

0.1μF

6.8μF

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