LTC2289 datasheet(14/24 Pages) LINER

14 / 24 page

LTC2289

2289fa

Figure 5 shows a single-ended input circuit. The imped-

ance seen by the analog inputs should be matched. This

circuit is not recommended if low distortion is required.

APPLICATIO S I FOR ATIO

Figure 6. Recommended Front End Circuit for

Input Frequencies Between 70MHz and 170MHz

Figure 8. Recommended Front End Circuit for

Input Frequencies Above 300MHz

Figure 7. Recommended Front End Circuit for

Input Frequencies Between 170MHz and 300MHz

Ω

0.1

µF

AIN

–

8pF

2.2

µF

VCM

ANALOG

INPUT

0.1

µF

0.1

µF

T1 = MA/COM, ETC 1-1-13

RESISTORS, CAPACITORS

ARE 0402 PACKAGE SIZE

2289 F06

LTC2289

Figure 5. Single-Ended Drive

Figure 4. Differential Drive with an Amplifier

Ω

12pF

2.2

µF

VCM

2289 F04

–

ANALOG

INPUT

HIGH SPEED

DIFFERENTIAL

AMPLIFIER

AIN

–

LTC2289

Ω

0.1

µF

ANALOG

INPUT

VCM

AIN

–

12pF

2289 F05

2.2

µF

Ω

0.1

µF

LTC2289

The 25

Ωresistorsand12pFcapacitorontheanaloginputs

serve two purposes: isolating the drive circuitry from the

sample-and-hold charging glitches and limiting the

wideband noise at the converter input.

For input frequencies above 70MHz, the input circuits of

Figure 6, 7 and 8 are recommended. The balun trans-

former gives better high frequency response than a flux

coupled center tapped transformer. The coupling capaci-

tors allow the analog inputs to be DC biased at 1.5V. In

Figure 8, the series inductors are impedance matching

elements that maximize the ADC bandwidth.

Ω

0.1

µF

AIN

–

2.2

µF

VCM

ANALOG

INPUT

0.1

µF

0.1

µF

T1 = MA/COM, ETC 1-1-13

RESISTORS, CAPACITORS

ARE 0402 PACKAGE SIZE

2289 F07

LTC2289

Ω

0.1

µF

AIN

–

2.2

µF

VCM

ANALOG

INPUT

0.1

µF

0.1

µF

T1 = MA/COM, ETC 1-1-13

RESISTORS, CAPACITORS, INDUCTORS

ARE 0402 PACKAGE SIZE

2289 F08

6.8nH

LTC2289

LTC2289 Datasheet(PDF) 14 Page - Linear Technology

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