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DIFFERENTIAL RECEIVER/DRIVER

SINGLE-SUPPLY MFB DIFFERENTIAL

p ´

f =

R =R =0.65

R =0.375

C =C

C =2

50W

-VI

750W

50W

1/2

OPA2890

1/2

OPA2890

=1+

DIFF

(

- -V )

Frequency(Hz)

10k

100k

10M

-3

-6

-12

-9

OPA2890

SBOS364A – DECEMBER 2007 – REVISED DECEMBER 2007

ACTIVE FILTER: 2MHz BUTTERWORTH

A very versatile application for a dual operational

CONFIGURATION

amplifier is the differential amplifier configuration

shown in Figure 56. With both amplifiers of the

The active filter circuit illustrated in Figure 58 can be

OPA2890 connected for noninverting operation, the

easily implemented using the OPA2890. In this

circuit provides a high input impedance, while the

configuration,

each

amplifier

the

OPA2890

gain can easily be set by just one resistor, RG. When

operates as an integrator. For this reason, this type of

operated in low gains, the output swing may be

application is also called an infinite gain filter

limited as a result of the common-mode input swing

implementation.

Butterworth

filter

can

limits of the amplifier itself. An interesting modification

implemented using the following component ratios:

of this circuit is to place a capacitor in series with RG.

Now the dc gain for each side is reduced to +1V/V;

the ac gain follows the standard transfer function of G

2RF/RG.

This

configuration

might

advantageous for applications processing only a

frequency band that excludes dc or very low

frequencies. An input dc voltage resulting from input

bias currents is not amplified by the ac gain and can

be kept low. This circuit can be used as a differential

The frequency response for a 2MHz Butterworth filter

line receiver, driver, or as an interface to a differential

is shown in Figure 57. One advantage for using this

input ADC.

type of filter is the independent setting of

o and Q. Q

can be easily adjusted by changing the R3A, B

resistors without affecting

Figure 56. High-Speed Differential Receiver

Figure 57. Multiple Feedback Filter Frequency

Response

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