POWER-SUPPLY DECOUPLING

_

+

4

5

3

7

2

6

VOCM

V

S

PwrPad

VS

PD

1

8

R0805

R4

C4

C0805

R5

R0805

C3

C0805

R6

R7

R0805

R0805

C5

C6

C0805

C0805

C7

C0805

J2

J3

J2

J3

R2

R0805

R3

R0805

C1

C0805

C2

C0805

R1

R1206

J1

3

1

4

5

6

R11

R1206

R9

R0805

R8

R9

R0805

R0805

J2

J3

J4

T1

U1

THS450X

EVALUATION FIXTURES, SPICE MODELS,

THS4504

THS4505

www.ti.com ......................................................................................................................................................... SLOS363D – AUGUST 2002 – REVISED MAY 2008

TECHNIQUES AND RECOMMENDATIONS

Power-supply decoupling is a critical aspect of any

high-performance amplifier design process. Careful

decoupling provides higher quality ac performance

(most notably improved distortion performance). The

following guidelines ensure the highest level of

performance.

1. Place decoupling capacitors as close to the

power-supply inputs as possible, with the goal of

minimizing the inductance of the path from

ground to the power supply.

2. Placement priority should be as follows: smaller

capacitors should be closer to the device.

3. Use of solid power and ground planes is

recommended to reduce the inductance along

power-supply return current paths.

Figure 93. Simplified Schematic of the Evaluation

4. Recommended

values

for

power

supply

Board. Power-Supply Decoupling, VOCM, and

Power-Down Circuitry not Shown

decoupling include 10-

µF and 0.1-µF capacitors

for each supply. A 1000-pF capacitor can be

used across the supplies as well for extremely

Computer simulation of circuit performance using

high-frequency return currents, but often is not

SPICE

is

often

useful

when

analyzing

the

required.

performance of analog circuits and systems. This is

particularly true for video and RF amplifier circuits

where parasitic capacitance and inductance can have

AND APPLICATIONS SUPPORT

a major effect on circuit performance. A SPICE model

for the THS4500 family of devices is available

Texas Instruments is committed to providing its

through the Texas Instruments web site (www.ti.com).

customers with the highest quality of applications

The Product Information Center (PIC) is available for

support. To support this goal, an evaluation board

design assistance and detailed product information.

has been developed for the THS4500 family of fully

These

models

do

a

good

job

of

predicting

differential amplifiers. The evaluation board can be

small-signal ac and transient performance under a

obtained by ordering through the Texas Instruments

wide variety of operating conditions. They are not

web site, www.ti.com, or through your local Texas

intended to model the distortion characteristics of the

Instruments sales representative. The schematic for

amplifier, nor do they attempt to distinguish between

the evaluation board is shown in Figure 93 with

the

package

types

in

their

small-signal

ac

default component values. Unpopulated footprints are

performance. Detailed information about what is and

shown to provide insight into design flexibility.

is not modeled is contained in the model file itself.

Copyright © 2002–2008, Texas Instruments Incorporated

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Product Folder Link(s): THS4504 THS4505