OPA694 datasheet(12/31 Pages) TI2

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OPA694

+5V

50W

430W

50W

-5V

OPA694

SAW

Filter

+12V

Matching

Network

=12dB

(SAWLoss)

50W

Source

50W

400W

50W

0.1 F

1000pF

5kW

-3

-6

-9

-12

10M

100M

Frequency(Hz)

G=+1,Figure1

G=+1,Figure6

OPA694

SBOS319G – SEPTEMBER 2004 – REVISED JANUARY 2010

www.ti.com

SAW FILTER BUFFER

small-signal frequency response for the unity gain

buffer of Figure 31 compared to the improved

One common requirement in an IF strip is to buffer

approach shown in Figure 36. Either approach gives

the output of a mixer with enough gain to recover the

low-power

unity-gain

buffer

with

1.56GHz

insertion loss of a narrowband SAW filter. Figure 35

bandwidth.

shows one possible configuration driving a SAW filter.

The Two-Tone, Third-Order Intermodulation Intercept

plot

(Figure

14)

shown

the

Typical

Characteristics curves. Operating in the inverting

mode at a voltage gain of –8V/V, this circuit provides

a 50

Ω input match using the gain set resistor, has the

feedback optimized for maximum bandwidth (250MHz

in this case), and drives through a 50

Ω output resistor

into the matching network at the input of the SAW

filter. If the SAW filter gives a 12dB insertion loss, a

net gain of 0dB to the 50

Ω load at the output of the

SAW (which could be the input impedance of the next

IF amplifier or mixer) will be delivered in the

passband of the SAW filter. Using the OPA694 in this

Figure 36. Improve Unity Gain Buffer

application will isolate the first mixer from the

impedance of the SAW filter and provide very low

two-tone, 3rd-order spurious levels in the SAW filter

bandwidth.

Figure 35. IF Amplifier Driving SAW Filter

Figure 37. Gain of +1 Frequency Response

WIDEBAND UNITY GAIN BUFFER WITH

IMPROVED FLATNESS

DESIGN-IN TOOLS

The unity gain buffer configuration of Figure 31

shows

peaking

the

frequency

response

DEMONSTRATION FIXTURES

exceeding 2dB. This gives the slight amount of

overshoot and ringing apparent in the gain of +1V/V

Two printed circuit boards (PCBs) are available to

pulse response curves. A similar circuit that holds a

assist in the initial evaluation of circuit performance

flatter frequency response, giving improved pulse

using the OPA694 in its two package options. Both of

fidelity, is shown in Figure 36.

these are offered free of charge as unpopulated

PCBs, delivered with a user’s guide. The summary

This circuit removes the peaking by bootstrapping out

information for these fixtures is shown in Table 1.

any parasitic effects on RG. The input impedance is

still set by RM as the apparent impedance looking into

Table 1. Demonstration Fixtures by Package

RG is very high. RM may be increased to show a

higher input impedance, but larger values will start to

ORDERING

LITERATURE

impact DC output offset voltage. This circuit creates

PRODUCT

PACKAGE

NUMBER

an additional input offset voltage as the difference in

DEM-OPA-

OPA694ID

SO-8

SBOU026

the two input bias currents times the impedance to

SO-1B

ground at VI. Figure 37 shows a comparison of

DEM-OPA-

OPA694IDBV

SOT23-5

SBOU027

SOT-1B

Product Folder Link(s): OPA694

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