7

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Using a resistor in series with a reactive load will also

reduce the load’s effect on amplifier loop dynamics. For

instance, driving coaxial cables without an output series

resistor may cause peaking or oscillation.

Transmission Line Matching

One method for matching the characteristic impedance

of a transmission line is to place the appropriate resistor

at the input or output of the amplifier. Figure 7 shows the

typical circuit configurations for matching transmission

lines.

Figure 7: Transmission Line Matching

directly to ground.

transmission line or cable.

amplifier from reactive loading caused by the transmis-

sion line, or by parasitics.

The input and output matching resistors attenuate the

signal by a factor of 2, therefore additional gain is needed.

frequency range. It compensates for the increase of the op

amp’s output impedance with frequency.

Thermal Design

To calculate the power dissipation for the CLC446,

follow these steps:

1. Calculate the no-load op amp power:

2. Calculate the output stage’s RMS power:

the external load.

3. Calculate the total op amp RMS power:

To calculate the maximum allowable ambient tempera-

where

θ

Thermal Resistance section contains the thermal

resistance for various packages.

Dynamic Range (input /output protection)

ESD diodes are present on all connected pins for

protection from static voltage damage. For a signal that

may exceed the supply voltages, we recommend using

diode clamps at the amplifier’s input to limit the signals to

less than the supply voltages.

Dynamic Range (input /output levels)

The

Electrical Characteristics section specifies the

Common-Mode Input Range and Output Voltage Range;

these

voltage

ranges

scale

with

the

supplies.

Output Current is also specified in the

Electrical

Characteristics section.

Unity gain applications are limited by the Common-Mode

Input Range. At greater non-inverting gains, the Output

Voltage Range becomes the limiting factor.

Inverting

gain applications are limited by the Output Voltage

Range. For transimpedance gain applications, the sum

of

the

input

currents

injected

at

the

inverting

input pin of the op amp needs to be:

,

Gain (transimpedance) sub-section for details).

The equivalent output load needs to be large enough so

that the minimum output current can produce the

required output voltage swing. See the

DC Design (out-

put loading) sub-section for details.

Dynamic Range (noise)

In RF applications, noise is frequently specified as Noise

Figure (NF). This allows the calculation of signal to noise

ratio into a defined load. Figure 8 plots the NF for a

of 100

Ω. The minimum NF (3.9dB) occurs when the

source impedance equals 1600

Ω.

Figure 8: Noise Figure vs. Source Resistance

Figure 9: Noise Model

+

-

CLC446

+

-

I

V

R

in

max

f

≤

Source Resistance (

Ω)

20

15

0

10

100

10k

10

5

1k

100k

+

-

CLC446

+

-