LTC6404 datasheet(24/28 Pages) LINER

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LTC6404

6404f

Figure 8. LTC6404 Filter Topology Modiﬁed for 1/2x Filter

Bandwidth (3 External Capacitors)

capacitor solution of 12pF from each ﬁltered output to

ground plus a 12pF capacitor between the ﬁltered outputs

would also halve the ﬁlter bandwidth (Figure 8).

Noise Considerations

The LTC6404’s input referred voltage noise is on the

order of 1.5nV/√Hz. Its input referred current noise is on

the order of 3pA/√Hz. In addition to the noise generated

by the ampliﬁer, the surrounding feedback resistors also

contribute noise. A noise model is shown in Figure 9.

The output noise generated by both the ampliﬁer and the

feedback components is governed by the equation:

⎛

⎝⎜

⎞

⎠⎟

⎛

⎝⎜

⎞

⎠⎟

() +

••

•

nRF

••

⎛

⎝⎜

⎞

⎠⎟

⎛

⎝⎜

⎞

⎠⎟

A plot of this equation, and a plot of the noise generated

by the feedback components for the LTC6404 is shown

in Figure 10.

APPLICATIONS INFORMATION

Figure 9. Noise Model of the LTC6404

–

OUT+

OUTF+

OUT–

OUTF–

V–

6404 F08

LTC6404

FILTERED OUTPUT

(44.25MHz)

50Ω

12pF

50Ω

12pF

–

SHDN

IN–

OUT+

OUTF+

IN+

OUT–

OUTF–

eno

RF2

V+

V–

V+

V–

V+

V–

VOCM

V–

V+

V–

6404 F09

LTC6404

enof

enRI2

SHDN

RF1

RI2

RI1

V–

V+

V–

enRF2

enRI1

encm

eni

enRF1

–2

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