General Design Considerations

The CLC430 is a general purpose current-feedback ampli-

fier for use in a variety of small- and large-signal applica-

tions. Use the feedback resistor to fine tune the gain

flatness and -3dB bandwidth for any gain setting. Com-

linear provides information for the performance at a gain of

+2 for small and large signal bandwidths. The plots show

feedback resistor values for selected gains.

Gain

Use the following equations to set the CLC430's non-

inverting or inverting gain:

Non -Inverting Gain = 1+

R

R

f

g

Inverting Gain = -

R

R

f

g

Choose the resistor values for non-inverting or inverting

gain by the following steps.

CLC430

+

-

Fig. 0 Component Identification

1)

to plot in the plot section entitled

2)

3)

4)

High Gains

Current feedback closed-loop bandwidth is independent of

gain-bandwidth-product for small gain changes. For larger

gain changes the optimum feedback register R

by the following:

As gain is increased, the feedback resistor allows bandwidth

to be held constant over a wide gain range. For a more

complete explanation refer to application note OA-25 Stabil-

ity Analysis of Current-Feedback Amplifiers.

Resistors have varying parasitics that affect circuit perfor-

mance in high-speed design. For best results, use leaded

metal-film resistors or surface mount resistors. A SPICE

model for the CLC430 is available to simulate overall

circuit performance.

Enable / Disable Function

The CLC430 amplifier features an enable/disable function

that changes the output and inverting input from low to high

impedance. The pin 8 enable/disable logic levels are as

follows:

±15V

±5V

Enable

>12.7V

>2.7V

Disable

<10.0V

<0.8V

The amplifier is enabled with pin 8 left open due to the 2k

Ω

pull-up resistor, shown in Fig. 1.

To CLC430

Bias network

2k

Ω

Pin 8 DISABLE

8k

Ω

Fig. 1 Pin 8 Equivalent Disable Circuit

Open-collector or CMOS interfaces are recommended to

drive pin 8. The turn-on and off time depends on the speed

of the digital interface.

The equivalent output impedance when disabled is shown

ance. To raise the output impedance in the disabled state,

connect the CLC430 as a unity-gain voltage follower by

circuit layouts consider using the dual CLC431 (with

disable) or the dual CLC432 (without disable).

Equivalent Impedance

in Disable

300k

Ω

8pF

+

-

Fig. 2 Equivalent Disabled Output Impedance

To meet low distortion requirements, recognize the effect

of the feedback resistor. Increasing the feedback resistor

will decrease the loop gain and increase distortion. De-

Differential Gain and Differential Phase

The CLC430 has low DG and DP errors for video applica-

tions. Add an external pulldown resistor to the CLC430’s

output to improve DG and DP as seen in Fig.3. A 604

ΩR

P

will improve DG and DP to 0.01% and 0.02°.

5

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RA

f

v

=−

⋅

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724

60

ΩΩ