LTC2283I View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LTC2283I

Dual 12-Bit, 125Msps Low Power 3V ADC

Linear Technology 

LTC2283

APPLICATIONS INFORMATION

ANALOG

INPUT

HIGH SPEED

DIFFERENTIAL

AMPLIFIER 25Ω

++

CM

––

25Ω

VCM

2.2μF

AIN+

LTC2283

12pF

AIN–

2283 F04

Figure 4. Differential Drive with an Amplifier

ANALOG

INPUT

0.1μF

1k 1k

25Ω

VCM

2.2μF

AIN+ LTC2283

25Ω

0.1μF

12pF

AIN–

2283 F05

Figure 5. Single-Ended Drive

Figure 4 demonstrates the use of a differential amplifier to

convert a single ended input signal into a differential input

signal. The advantage of this method is that it provides

low frequency input response; however, the limited gain

bandwidth of most op amps will limit the SFDR at high

input frequencies.

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.

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.

14

0.1μF

ANALOG

INPUT

T1

0.1μF

12Ω

25Ω 0.1μF

25Ω 12Ω

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

RESISTORS, CAPACITORS

ARE 0402 PACKAGE SIZE

VCM

2.2μF

AIN+

LTC2283

8pF

AIN–

2283 F06

Figure 6. Recommended Front End Circuit for

Input Frequencies Between 70MHz and 170MHz

0.1μF

ANALOG

INPUT

T1

0.1μF

25Ω 0.1μF

25Ω

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

RESISTORS, CAPACITORS

ARE 0402 PACKAGE SIZE

VCM

2.2μF

AIN+

LTC2283

AIN–

2283 F07

Figure 7. Recommended Front End Circuit for

Input Frequencies Between 170MHz and 300MHz

VCM

ANALOG

INPUT

0.1μF

8.2nH

2.2μF

AIN+

25Ω 0.1μF

T1

0.1μF

25Ω 8.2nH

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

AIN–

RESISTORS, CAPACITORS, INDUCTORS

ARE 0402 PACKAGE SIZE

LTC2283

2283 F08

Figure 8. Recommended Front End Circuit for

Input Frequencies Above 300MHz

2283fb

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