OPA141 datasheet(13/25 Pages) TI

13 / 25 page

100k

SourceResistance,R (W)

100

10k

100

+(i R ) +4kTR

ResistorNoise

OPA211

OPA141

OPA2141

OPA4141

www.ti.com

SBOS510B – MARCH 2010 – REVISED MAY 2010

APPLICATION INFORMATION

with total circuit noise calculated. The op amp itself

The OPA141, OPA2141, and OPA4141 are unity-gain

contributes both a voltage noise component and a

stable, operational amplifiers with very low noise,

current noise component. The voltage noise is

input

bias

current,

and

input

offset

voltage.

commonly modeled as a time-varying component of

Applications with noisy or high-impedance power

the offset voltage. The current noise is modeled as

supplies require decoupling capacitors placed close

the time-varying component of the input bias current

to the device pins. In most cases, 0.1mF capacitors

and reacts with the source resistance to create a

are adequate. Figure 1 shows a simplified schematic

voltage component of noise. Therefore, the lowest

of the OPA141.

noise op amp for a given application depends on the

source

impedance.

For

low

source

impedance,

OPERATING VOLTAGE

current

noise

negligible,

and

voltage

noise

generally dominates. The OPA141, OPA2141, and

The OPA141, OPA2141, and OPA4141 series of op

OPA4141 family has both low voltage noise and

amps can be used with single or dual supplies from

extremely low current noise because of the FET input

an operating range of VS = +4.5V (±2.25V) and up to

of the op amp. As a result, the current noise

VS = +36V (±18V). These devices do not require

contribution of the OPAx141 series is negligible for

symmetrical supplies; they only require a minimum

any practical source impedance, which makes it the

supply voltage of +4.5V (±2.25V). For VS less than

better choice for applications with high source

±3.5V, the common-mode input range does not

impedance.

include midsupply. Supply voltages higher than +40V

can

permanently

damage

the

device;

see

the

The equation in Figure 31 shows the calculation of

Absolute Maximum Ratings table. Key parameters

the total circuit noise, with these parameters:

are specified over the operating temperature range,

•

en = voltage noise

TA = –40°C to +125°C. Key parameters that vary over

•

In = current noise

the supply voltage or temperature range are shown in

the Typical Characteristics section of this data sheet.

•

RS = source impedance

•

k = Boltzmann's constant = 1.38 × 10–23 J/K

CAPACITIVE LOAD AND STABILITY

•

T = temperature in degrees Kelvin (K)

The dynamic characteristics of the OPAx141 have

For more details on calculating noise, see the section

been optimized for commonly encountered gains,

on Basic Noise Calculations.

loads, and operating conditions. The combination of

low closed-loop gain and high capacitive loads

decreases the phase margin of the amplifier and can

lead to gain peaking or oscillations. As a result,

heavier capacitive loads must be isolated from the

output. The simplest way to achieve this isolation is to

add a small resistor (ROUT equal to 50Ω, for example)

in series with the output.

Figure

and

Figure

illustrate

graphs

Small-Signal

Overshoot

Capacitive

Load

for

several values of ROUT. Also, refer to Applications

Bulletin

AB-028

(literature

number

SBOA015,

available for download from the TI web site) for

details of analysis techniques and application circuits.

NOISE PERFORMANCE

Figure 31. Noise Performance of the OPA141 and

Figure 31 shows the total circuit noise for varying

OPA211 in Unity-Gain Buffer Configuration

source impedances with the operational amplifier in a

unity-gain configuration (with no feedback resistor

network

and

therefore

additional

noise

contributions). The OPA141 and OPA211 are shown

Product Folder Link(s): OPA141 OPA2141 OPA4141

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