THS4501CDG4 datasheet(25/48 Pages) TI1

25 / 48 page

THS4500

THS4501

www.ti.com

SLOS350F

– APRIL 2002 – REVISED OCTOBER 2011

For more detailed information about balance in fully

voltage regardless of the load impedance present.

differential amplifiers, see the application report, Fully

Terminating the output of a fully differential

Differential Amplifiers (SLOA054), referenced at the

amplifier with a heavy load adversely affects the

end of this data sheet.

amplifier linearity.

•

Comprehend the VOCM input drive requirements.

INTERFACING TO AN ANALOG-TO-DIGITAL

Determine if the ADC voltage reference can

CONVERTER

provide the required amount of current to move

VOCM to the desired value. A buffer may be

The THS4500 family of amplifiers are designed

needed.

specifically

interface

today's

•

Decouple the VOCM pin to eliminate the antenna

highest-performance ADCs. This section highlights

effect. VOCM is a high-impedance node that can

the key concerns when interfacing to an ADC and

act as an antenna. A large decoupling capacitor

provides example interface circuits.

on this node eliminates this problem.

There

are

several

key

design

concerns

when

•

Know the input common-mode range. If the input

interfacing to an analog-to-digital converter:

signal

referenced

around

the

negative

•

Terminate

the

input

source

properly.

power-supply rail (for example, around ground on

high-frequency receiver chains, the source that

a single 5 V supply), then the THS4500/1

feeds the fully differential amplifier requires a

accommodates the input signal. If the input signal

specific load impedance (that is, 50

Ω).

referenced

around

midrail,

choose

the

•

Design a symmetric printed circuit board (PCB)

THS4502/3 for the best operation.

layout. Even-order distortion products are heavily

•

Packaging

makes

difference

higher

influenced by layout, and careful attention to a

frequencies. If possible, choose the smaller,

symmetric

layout

minimizes

these

distortion

thermally-enhanced MSOP package for the best

products.

performance.

rule,

lower

junction

•

Minimize inductance in power-supply decoupling

temperatures

provide

better

performance.

traces

and

components.

Poor

power-supply

possible, use a thermally-enhanced package,

decoupling can have a dramatic effect on circuit

even if the power dissipation is relatively small

performance. Since the outputs are differential,

compared to the maximum power dissipation

differential currents exist in the power-supply pins.

rating to achieve the best results.

Thus, decoupling capacitors should be placed in a

•

Understand the effect of the load impedance seen

manner that minimizes the impedance of the

by the fully differential amplifier when performing

current loop.

system-level intercept point calculations. Lighter

•

Use separate analog and digital power supplies

loads (such as those presented by an ADC) allow

and grounds. Noise (bounce) in the power

smaller intercept points to support the same level

supplies (created by digital switching currents) can

of intermodulation distortion performance.

couple

directly

into

the

signal

path,

and

power-supply noise can create higher distortion

EXAMPLE ANALOG-TO-DIGITAL

products as well.

CONVERTER DRIVER CIRCUITS

•

Use care when filtering. While an RC low-pass

The THS4500 family of devices is designed to drive

filter may be desirable on the output of the

high-performance ADCs with extremely high linearity,

amplifier to filter broadband noise, the excess

allowing for the maximum effective number of bits at

can

negatively

impact

the

amplifier

the output of the data converter. Two representative

linearity. Filtering in the feedback path does not

circuits shown below highlight single-supply operation

have this effect.

and split supply operation, respectively. Specific

•

AC-coupling

allows

easier

circuit

design.

feedback

resistor,

gain

resistor,

and

feedback

dc-coupling is required, be aware of the excess

capacitor values are not shown, as these values

power

dissipation

that

can

occur

due

depend on the frequency of interest. Information on

level-shifting

the

output

through

the

output

calculating

these

values

can

found

the

common-mode voltage control.

applications material above.

•

Do not terminate the output unless required. Many

open-loop,

class-A

amplifiers

require

50-

Ω

termination for proper operation, but closed-loop

fully differential amplifiers drive a specific output

Submit Documentation Feedback

Product Folder Link(s): THS4500 THS4501

THS4501CDG4 датащи(PDF) 25 Page - Texas Instruments

THS4501CDG4 датащи(HTML) 25 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

датащи скачать

ссылки URL