Data Sheet

©2007-2013 Exar Corporation

10/15

Rev 1C

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 fig-

ure 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

tional non-inverting and inverting circuit configurations.

Refer to figures 3 and 4. As discussed in the Current Feed-

back Technology section, the value of the feedback resis-

tor has a pronounced effect on the frequency response of

the circuit.

ues for various gain settings. These values produce the

optimum frequency response, maximum bandwidth with

minimum peaking. Adjust these values to optimize perfor-

mance for a specific application. The typical performance

characteristics section includes plots that illustrate how

various gain settings.

Gain

(V/V

±0.1dB BW

(MHz)

-3dB BW

(MHz)

1

1240

-

129

300

2

510

510

140

230

5

200

50

18

111

mended 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

cause oscillatory behavior.

Increasing the value of Rf will lower the bandwidth. Low-

ering the bandwidth creates a flatter frequency response

and improves 0.1dB bandwidth performance. This is im-

portant in applications such as video. Further increase in

Rf will cause premature gain rolloff and adversely affect

gain flatness.

+

-

0.1μF

6.8μF

Output

For optimum input offset

Input

0.1μF

6.8μF

+

-

0.1μF

6.8μF

Output

G = 1

Input

0.1μF

6.8μF

+

-

0.1μF

6.8μF

Output

Input

0.1μF

6.8μF