CLC446AMC datasheet(8/12 Pages) NSC

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The CLC446 noise model in Figure 9 is used to develop

this equation for NF:

where:

RS is the source resistance at the non-

inverting input

There is no matching resistor from the input

to ground

eni, ibn, and ibi are the voltage and current

noise density terms (see the

Electrical

Characteristics section)

Rf is the feedback resistor, and Rg is the

gain-setting resistor

To achieve a low Noise Figure while matching the source,

use a matching transformer or the

Low Noise

Composite Amp With Input Matching circuit found in

the

CLC446 Applications section.

Dynamic Range (distortion)

The distortion plots in the Typical Performance

Characteristics section show distortion as a function of

load resistance, frequency, and output amplitude.

Distortion places an upper limit on the CLC446’s

dynamic range.

Realized output distortion is highly dependent upon the

external circuit.

Some of the common external circuit

choices that can improve distortion are:

Short and equal return paths from the load to

the supplies

De-coupling capacitors of the correct value

Higher load resistance

A lower ratio of the output voltage swing to

power supply voltage

Printed Circuit Board Layout

High Frequency op amp performance is strongly depen-

dent on proper layout, proper resistive termination and

adequate power supply decoupling. The most important

layout points to follow are:

Use a ground plane

Bypass power supply pins with:

ceramic capacitors of about 0.1

µF placed

less than 0.1" (3mm) from the pin

tantalum capacitors of about 6.8

µF for large

signal current swings or improved power

supply noise rejection; we recommend a

minimum of 2.2

µF for any circuit

Minimize trace and lead lengths for components

between the inverting and output pins

Remove ground plane underneath the amplifier

package and 0.1" (3mm) from all input/output

pads

For prototyping, use flush-mount printed circuit

board pins; never use high profile DIP sockets

Evaluation Board

Separate evaluation boards are available for prototyping

and measurements. Additional information is available in

the evaluation board literature.

Low Noise Composite Amp With Input Matching

The composite amp shown in Figure 10 eliminates the

need for a matching resistor to ground at the input. By

connecting two amplifiers in series, the first non-

inverting and the second inverting, an overall inverting

gain is realized. The feedback resistor (Rf) closes the

loop, and generates a set input resistance (Rin) that can

be matched to RS. Rf generates less noise than a

matching resistor to ground at the input.

Figure 10: Composite Amplifier

The input resistance and DC voltage gain of the

amplifier are:

Match the source resistance by setting: Rin = RS.

The voltage noise produced by Rf, referred to the source

VS, is:

The noise of a simple input matching resistor connected to

ground can be calculated by setting G to 0 in this equation.

Thus, this circuit reduces the thermal noise power

produced by the matching resistor by a factor of (1+G).

Rectifier Circuit

Wide bandwidth rectifier circuits have many applications.

Figure 11 shows a 200MHz wideband full-wave rectifier

circuit using a CLC446 and a CLC522 amplifier. Schottky

or PIN diodes are used for D1 and D2. They produce an

active half-wave rectifier whose signals are taken at the

feedback diode connection. The CLC522 takes the

difference of the two half-wave rectified signals,

producing a full-wave rectifier. The CLC522 is used at a

gain of 5 to achieve high differential bandwidth. For best

NF 10log

i R

4 TR

4 T R

4TR

bn s

() ++ ⋅

() +⋅

















4 T

16.0 x 10

290 K

, T is in K

()⋅









−

CLC446 Applications

CLC446

Rg2

Ω

CLC446

Rf2

Rf1

Rg1

Rin

, where G

ff1











 ⋅













=− ⋅









e4 TR

R1 G

=⋅

⋅+

()









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