Datasheet

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LTC6430-15

643015f

Figure 3. Wideband ADC Driver, LTC6430-15 Directly Driving the LTC2158 ADC

Figure 4. Wideband ADC Driver, LTC6430-15 Directly Driving the LTC2158 ADC—Alternative Using Mini Circuits 2:1 Balun

applicaTions inForMaTion

the presence of multi GHz mixing products, it will distort.

A band limiting filter would provide suppression from

those products beyond the capability of the amplifier, as

well as limit the noise bandwidth, however the settling of

the filter can be an issue. The LTC2158, at 310Msps only

allows 1.5ns settling time for any driver that is disturbed

by these transients.

This approach of removing the filter between the ADC

and driver amplifier offers many advantages. It opens

the opportunity to precede the amplifier with switchable

bandpass filters, without any need to change the critical

network between the drive amplifier and ADC. The trans-

mission line distances shown in the schematic are part

of the design, and are devised such that there are no

impedance discontinuities, and therefore no reflections,

in the distances between 75ps to 200ps from the ADC.

End termination can be immediately prior to, or preferably

after the ADC, and the amplifier should either be within

the 75ps inner boundary, or outside the 200ps distance.

Similarly, any shunt capacitor or

resonator, including the

large pads required

by some inductors with more than a

small fraction of 1pF, incorporated into a filter, should not

be in this range of distances from the ADC where reflec-

tions will impair performance. Transformers with large

= 5V

350Ω

643015 F03

49.9Ω

560nH

0402AF

100nH

0402CS

150Ω

1nF

GUANELLA

BALUN

MA/COM

ETC1-1-13

60pF

LTC6430-15 LTC2158

•

200ps