Application Division

Description

The CLC420 is a high-speed, slew-boosted, voltage feed-

back amplifier with unity-gain stability. These features along

with matched inputs, low input bias and noise currents, and

excellent CMRR render the CLC420 very attractive for active

filters, differential amplifiers, log amplifiers, and transimped-

ance amplifiers.

DC accuracy

Unlike current-feedback amplifiers, voltage-feedback ampli-

fiers have matched inputs. This means that the non-inverting

and inverting input bias current are well matched and track

over temperature, etc. As a result, by matching the resis-

tance looking out of the two inputs, these errors can be re-

duced to a small offset current term.

Gain bandwidth product

Since

the

CLC420

is

a

voltage-feedback

op-amp,

closed-loop bandwidth is approximately equal to the

gain-bandwidth product (typically 100MHz) divided by the

noise gain of the circuit (for noise gains greater than 5). At

lower noise gains, higher-order amplifier poles contribute to

higher closed-loop bandwidth. At low gains use the fre-

quency response performance plots given in the data sheet.

Another point to remember is that the closed-loop bandwidth

is determined by the noise gain, not the signal gain of the cir-

cuit. Noise gain is the reciprocal of the attenuation in the

feedback network enclosing the op amp. For example, a

CLC420

setup

as

a

non-inverting

amplifier

with

a

closed-loop gain of +1 (a noise gain of 1) has a 300MHz

bandwidth. When used as an inverting amplifier with a gain

of −1 (a noise gain of 2), the bandwidth is less, typically only

100MHz.

Full-power bandwidth, and slew-rate

The CLC420 combines exceptional full-power bandwidths

(40MHz, V

A

and slew rates (1100V/µs,

A

tive results are achieved by using slew-boosting circuitry to

keep the slew rates high while consuming very little power.

In non-slew boosted amplifiers, full-power bandwidth can be

easily determined from slew-rate measurements, but in

slew-boosting amplifiers, such as the CLC420, you can’t. For

this reason we provide data for both.

Slew rate is also different for inverting and non-inverting con-

figurations. This occurs because common-mode signal volt-

ages are present in non-inverting circuits but absent in in-

verting circuits. Once again data is provided for both.

DS012752-16

FIGURE 1. Recommended Non-Inverting Gain Circuit

DS012752-17

FIGURE 2. Recommended Inverting Gain Circuit

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