OPA659 datasheet(12/32 Pages) NSC

12 / 32 page

APPLICATION INFORMATION

Wideband, Noninverting Operation

OPA659

OUT

0.1 F

10 F

0.1 F

10 F

Load

Source

OUT

+6V

OPA659

OUT

0.1 F

10 F

0.1 F

10 F

Load

Source

OUT

+6V

OPA659

SBOS342B – DECEMBER 2008 – REVISED AUGUST 2009 ............................................................................................................................................ www.ti.com

Voltage-feedback op amps can use a wide range of

resistor values to set the gain. To retain a controlled

The OPA659 is a very broadband, unity-gain stable,

frequency response for the noninverting voltage

voltage-feedback amplifier with a high impedance

amplifier of Figure 35, the parallel combination of RF

JFET-input stage. Its very high gain bandwidth

|| RG should always be less than 200Ω. In the

product (GBP) of 350MHz can be used to either

noninverting configuration, the parallel combination of

deliver high signal bandwidths for low-gain buffers, or

RF || RG forms a pole with the parasitic input and

to deliver broadband, low-noise, transimpedance

board layout capacitance at the inverting input of the

bandwidth to photodiode-detector applications. The

OPA659. For best performance, this pole should be

OPA659 is designed to to provide very low distortion

frequency

greater

than

the

closed-loop

and accurate pulse response with low overshoot and

bandwidth for the OPA659. For this reason, a direct

ringing. To achieve the full performance of the

short from the output to the inverting input is

OPA659, careful attention to printed circuit board

recommended for the unity-gain follower application.

(PCB) layout and component selection are required,

Table 1 lists several recommended resistor values for

as discussed in the remaining sections of this data

noninverting gains with a 50

Ω input/output match.

sheet.

Figure 34 shows the noninverting gain of +1 circuit;

Figure 35 shows the more general circuit used for

other noninverting gains. These circuits are used as

the basis for most of the noninverting gain Typical

Characteristics graphs. Most of the graphs were

characterized using signal sources with 50

Ω driving

impedance,

and

with

measurement

equipment

presenting a 50

Ω load impedance. In Figure 34, the

shunt resistor RT at VIN should be set to 50Ω to

match the source impedance of the test generator

and cable, while the series output resistor, ROUT, at

VOUT should also be set to 50Ω to provide matching

impedance for the measurement equipment load and

cable.

Generally,

data

sheet

voltage

swing

Figure 35. General Noninverting Test Circuit

specifications are measured at the output pin, VOUT,

in Figure 34 and Figure 35.

Table 1. Resistor Values for Noninverting Gains

with 50

Ω Input/Output Match

NONINVERTING

GAIN

ROUT

Open

49.9

249

49.9

249

61.9

49.9

+10

249

27.4

49.9

Figure 34. Noninverting Gain of +1 Test Circuit

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