CLC418 datasheet(9/12 Pages) NSC

9 / 12 page

http://www.national.com

SPICE Models

SPICE models provide a means to evaluate op amp

designs. Free SPICE models are available that:

Support Berkeley SPICE 2G and its many

derivatives

Reproduce typical DC, AC, Transient, and

Noise performance

Support room temperature simulations

The

readme file that accompanies the models lists the

released models, and provides a list of modeled

parameters.

The

application

note

Simulation

SPICE Models for Comlinear’s Op Amps

contains

schematics and detailed information.

Differential Line Driver With Load

Impedance Conversion

The circuit shown in the

Typical Application schematic

on the front page operates as a differential line driver.

The transformer converts the load impedance to

a value that best matches the CLC418’s output

capabilities.

The

single-ended

input

signal

converted to a differential signal by the CLC418. The

line’s characteristic impedance is matched at both the

input and the output. The schematic shows Unshielded

Twisted Pair for the transmission line; other types of lines

can also be driven.

Set up the CLC418 as a difference amplifier:

Make the best use of the CLC418’s output drive

capability as follows:

where Req is the transformed value of the load

impedance, Vmax is the Output Voltage Range, and Imax

is the maximum Output Current.

Match the line’s characteristic impedance:

Select the transformer so that it loads the line with a

value very near Zo over your frequency range. The out-

put impedance of the CLC418 also affects the match.

With an ideal transformer we obtain:

where Zo(418)(jω) is the output impedance of the CLC418,

and |Zo(418)(jω)| << Rm.

The load voltage and current will fall in the ranges:

The CLC418’s high output drive current and low

distortion make it a good choice for this application.

Lowpass Anti-aliasing Filter

with Delay Equalization

The circuit shown in Figure 7 is a 5th-order Butterworth

lowpass filter with group delay equalization. Vin needs to

be a voltage source with low output impedance. Section

simple

single-pole

filter.

Section

provides a single-pole allpass function for group delay

equalization. Sections C and D are Sallen-Key lowpass

biquad sections.

Figure 7: Lowpass Anti-aliasing Filter

The filter specifications we built to are:

fc = 10MHz

(passband corner frequency)

fs = 20MHz

(stopband corner frequency)

Ap = 3.01dB (maximum passband attenuation)

As = 30dB

(minimum stopband attenuation)

Ho = 0dB

(DC gain)

The designed component values are in the table below.

The pre-distorted values compensate for the finite band-

width of the CLC418.

CLC418 Applications

2 1

= ⋅ +











 = ⋅

2 V

max

= ⋅

Return Loss

-20 log

(j )

, dB

o(418)

≈

⋅

n V

max

≤ ⋅

≤

418 Fig7

1/2

CLC418

RfA

VoA

Vin

R1A

C2A

1/2

CLC418

RfB

VoB

R1B

C2B

R3B

1/2

CLC418

RfC

VoC

R3C

R1C

C4C

1/2

CLC418

RfD

R3D

C4D

C5C

U1A

U1B

U2C

U2D

C5D

RgD

R1D

αD

R1D

αD

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