LTC2228 datasheet(18/28 Pages) LINER

18 / 28 page

LTC2228/LTC2227/LTC2226

222876fb

APPLICATIONS INFORMATION

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

seen by the analog inputs should be matched. This circuit

is not recommended if low distortion is required.

The 25Ω resistors and 12pF capacitor on the analog

inputs serve two purposes: isolating the drive circuitry

from the sample-and-hold charging glitches and limiting

the wideband noise at the converter input.

25Ω

12pF

2.2μF

VCM

LTC2228/27/26

222876 F04

–

ANALOG

INPUT

HIGH SPEED

DIFFERENTIAL

AMPLIFIER

AIN

–

Figure 4. Differential Drive with an Ampliﬁer

25Ω

0.1μF

ANALOG

INPUT

VCM

AIN

–

12pF

222876 F05

2.2μF

25Ω

0.1μF

LTC2228/27/26

Figure 5. Single-Ended Drive

For input frequencies above 70MHz, the input circuits of

Figure 6, 7 and 8 are recommended. The balun transformer

gives better high frequency response than a ﬂux coupled

center tapped transformer. The coupling capacitors 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.

25Ω

12Ω

0.1μF

AIN

–

8pF

2.2μF

VCM

LTC2228/27/26

ANALOG

INPUT

0.1μF

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

RESISTORS, CAPACITORS

ARE 0402 PACKAGE SIZE

222876 F06

Figure 6. Recommended Front-End Circuit for

Input Frequencies Between 70MHz and 170MHz

25Ω

0.1μF

AIN

–

2.2μF

VCM

LTC2228/27/26

ANALOG

INPUT

0.1μF

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

RESISTORS, CAPACITORS

ARE 0402 PACKAGE SIZE

222876 F07

Figure 7. Recommended Front-End Circuit for

Input Frequencies Between 170MHz and 300MHz

25Ω

0.1μF

AIN

–

2.2μF

VCM

LTC2228/27/26

ANALOG

INPUT

0.1μF

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

RESISTORS, CAPACITORS, INDUCTORS

ARE 0402 PACKAGE SIZE

222876 F08

6.8nH

Figure 8. Recommended Front-End Circuit for

Input Frequencies Above 300MHz

LTC2228 Datasheet(PDF) 18 Page - Linear Technology

LTC2228 Datasheet(HTML) 18 Page - Linear Technology

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