LTC2193C Просмотр технического описания (PDF) - Linear Technology

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LTC2193C

16-Bit, 125/105/80Msps Low Power Dual ADCs

Linear Technology 

LTC2195

LTC2194/LTC2193

APPLICATIONS INFORMATION

50Ω

ANALOG

INPUT

0.1µF T1

1:1

25Ω

25Ω 0.1µF

25Ω 25Ω

T1: MA/COM MABAES0060

RESISTORS, CAPACITORS

ARE 0402 PACKAGE SIZE

VCM

0.1µF

AIN+

12pF

AIN–

LTC2195

219543 F03

Figure 3. Analog Input Circuit Using a Transformer.

Recommended for Input Frequencies from 5MHz to 70MHz

50Ω

VCM

0.1µF

ANALOG

INPUT

T1

0.1µF

T2

25Ω 0.1µF

25Ω

0.1µF

AIN+

1.8pF

AIN–

T1: MA/COM MABA-007159-000000

T2: COILCRAFT WBC1-1TL

RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE

LTC2195

219543 F05

Figure 5. Recommended Front-End Circuit for Input Frequencies

from 150MHz to 250MHz

50Ω

VCM

0.1µF

ANALOG

INPUT

T1

0.1µF

12Ω

T2

25Ω 0.1µF

25Ω 12Ω

0.1µF

AIN+

8.2pF

AIN–

T1: MA/COM MABA-007159-000000

T2: COILCRAFT WBC1-1TL

RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE

LTC2195

219543 F04

Figure 4. Recommended Front-End Circuit for Input Frequencies

from 5MHz to 150MHz

0.1µF

ANALOG

INPUT

T1

50Ω

4.7nH

25Ω

0.1µF

VCM

0.1µF

AIN+

LTC2195

0.1µF

25Ω 4.7nH

AIN–

T1: MA/COM ETC1-1-13

RESISTORS, CAPACITORS

ARE 0402 PACKAGE SIZE

219543 F06

Figure 6. Recommended Front-End Circuit for Input Frequencies

Above 250MHz

tap is biased with VCM, setting the A/D input at its optimal

DC level. At higher input frequencies a transmission line

balun transformer (Figures 4 to 6) has better balance,

resulting in lower A/D distortion.

Amplifier Circuits

Figure 7 shows the analog input being driven by a high

speed differential amplifier. The output of the amplifier is AC

coupled to the A/D so the amplifier’s output common mode

voltage can be optimally set to minimize distortion.

At very high frequencies an RF gain block will often have

lower distortion than a differential amplifier. If the gain

block is single ended, then a transformer circuit (Figures  4

to 6) should convert the signal to differential before driv-

ing the A/D.

ANALOG

INPUT

HIGH SPEED

DIFFERENTIAL

AMPLIFIER

0.1µF

+

200Ω 200Ω

25Ω

–

0.1µF

25Ω

VCM

0.1µF

AIN+

12pF

LTC2195

AIN–

12pF

219543 F07

Figure 7. Front-End Circuit Using a High Speed

Differential Amplifier

219543f

18

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