OPA690IDBVT datasheet(15/37 Pages) TI1

15 / 37 page

OutputPull-DownCurrent(mA)

V =2V

,10MHz

OPA690

402W

50W

402W

59W

698W

+5V

DIS

0.1 F

30W

50pF

0.1 F

2.5VDC

±1VAC

ADCInput

Power-supplydecouplingnotshown.

OPA690

www.ti.com

SBOS223F – DECEMBER 2001 – REVISED FEBRUARY 2010

Again, an additional resistor (50

Ω in this case) is

The OPA690 in the circuit of Figure 39 provides

included directly in series with the noninverting input.

> 200MHz bandwidth for a 2VPP output swing.

This minimum recommended value provides part of

Minimal

3rd-harmonic

distortion

two-tone,

the

source

resistance

matching

for

the

3rd-order intermodulation distortion will be observed

noninverting input bias current. It is also used to form

due to the very low crossover distortion in the

a simple parasitic pole to roll off the frequency

OPA690

output

stage.

The

limit

output

response at very high frequencies ( > 500MHz) using

Spurious-Free Dynamic Range (SFDR) will be set by

the input parasitic capacitance to form a bandlimiting

the 2nd-harmonic distortion. Without RB, the circuit of

pole. The gain resistor (RG) is ac-coupled, giving the

Figure 39 measured at 10MHz shows an SFDR of

circuit a dc gain of +1, which puts the input dc bias

57dBc. This may be improved by pulling additional dc

voltage (2.5V) at the output as well. The output

bias current (IB) out of the output stage through the

voltage can swing to within 1V of either supply pin

optional RB resistor to ground (the output midpoint is

while

delivering

100mA

output

current.

at 2.5V for Figure 39). Adjusting IB gives the

demanding 100

Ω load to a midpoint bias is used in

improvement in SFDR shown in Figure 38. SFDR

this characterization circuit. The new output stage

improvement is achieved for IB values up to 5mA,

circuit used in the OPA690 can deliver large bipolar

with worse performance for higher values.

output currents into this midpoint load with minimal

crossover distortion, as shown in the +5V supply,

3rd-harmonic distortion plots.

SINGLE-SUPPLY ADC INTERFACE

Most modern, high performance ADCs (such as the

TI ADS8xx and ADS9xx series) operate on a single

+5V (or lower) power supply. It has been a

considerable challenge for single-supply op amps to

deliver a low distortion input signal at the ADC input

for signal frequencies exceeding 5MHz. The high

slew rate, exceptional output swing, and high linearity

of the OPA690 make it an ideal single-supply ADC

driver. The circuit on the front page shows one

possible (inverting) interface. Figure 39 shows the

test circuit of Figure 37 modified for a capacitive

(ADC) load and with an optional output pull-down

Figure 38. SFDR vs IB

resistor (RB).

Figure 39. SFDR versus IB Test Circuit

Product Folder Link(s): OPA690

OPA690IDBVT Datasheet(PDF) 15 Page - Texas Instruments

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