OPA861IDBVT datasheet(21/34 Pages) TI2

21 / 34 page

e =

+(R i ) +4kTR +(R i ) +4kTR ]

S BN

G BI

G +

√4kTR

Frequency (Hz)

10k

100k

10M

100M

Input−Referred

OPA861

www.ti.com

SBOS338G – AUGUST 2005 – REVISED MAY 2013

NOISE PERFORMANCE

The OTA noise model consists of three elements: a

voltage noise on the B-input; a current noise on the

B-input; and a current noise on the E-input. Figure 51

shows the OTA noise analysis model with all the

noise terms included. In this model, all noise terms

are taken to be noise voltage or current density terms

in either nV/

√Hz or pA/√Hz.

Figure 50. CMRR of the ADC Driver

DESIGN-IN TOOLS

Figure 51. OTA Noise Analysis Model

DEMONSTRATION BOARDS

The total output spot noise voltage can be computed

A printed circuit board (PCB) is available to assist in

as the square root of the sum of all squared output

the initial evaluation of circuit performance using the

noise voltage contributors. Equation 8 shows the

OPA861. This module is available free, as an

general form for the output noise voltage using the

unpopulated

PCB

delivered

with

descriptive

terms shown in Figure 51.

documentation. The summary information for the

board is shown below:

LITERATURE

BOARD PART

REQUEST

PRODUCT

PACKAGE

NUMBER

(8)

OPA861ID

SO-8

DEM-OTA-SO-1A

SBOU035

THERMAL ANALYSIS

The

board

can

requested

the

Texas

Instruments web site (www.ti.com).

Maximum desired junction temperature will set the

maximum allowed internal power dissipation as

MACROMODELS AND APPLICATIONS

described below. In no case should the maximum

SUPPORT

junction temperature be allowed to exceed 150°C.

Computer simulation of circuit performance using

Operating junction temperature (TJ) is given by

SPICE

often

useful

when

analyzing

the

TA + PD ×

θ JA. The total internal power dissipation

performance of analog circuits and systems. This

(PD) is the sum of quiescent power (PDQ) and

principle is particularly true for Video and RF amplifier

additional power dissipated in the output stage (PDL)

circuits where parasitic capacitance and inductance

to deliver output current. Quiescent power is simply

can have a major effect on circuit performance. A

the specified no-load supply current times the total

SPICE model for the OPA861 is available through the

supply voltage across the part. PDL will depend on the

Texas Instruments web page (www.ti.com). These

required output signal and load but would, for the

models do a good job of predicting small-signal AC

OPA861 be at a maximum when the maximum IO is

and transient performance under a wide variety of

being driven into a voltage source that puts the

operating conditions. They do not do as well in

maximum voltage across the output stage. Maximum

predicting the harmonic distortion. These models do

IO is 15mA times a 9V maximum across the output.

not attempt to distinguish between the package types

Note that it is the power in the output stage and not

in their small-signal AC performance.

into

the

load

that

determines

internal

power

dissipation.

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