LTC2185CUPPBF 查看數據表（PDF） - Linear Technology

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LTC2185CUPPBF

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

Linear Technology 

LTC2185/LTC2184/LTC2183

Applications Information

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 (Figure 4

to Figure 6) should convert the signal to differential before

driving the A/D.

0.1µF

ANALOG

INPUT

T1

0.1µF

50Ω

VCM

0.1µF

T2

12Ω

25Ω 0.1µF

AIN+

LTC2185

8.2pF

25Ω 12Ω

AIN–

218543 F04

T1: MA/COM MABA-007159-000000

T2: COILCRAFT WBC1-1TL

RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE

Figure 4. Recommended Front-End Circuit for Input

Frequencies from 5MHz to 150MHz

0.1µF

ANALOG

INPUT

T1

0.1µF

50Ω

VCM

0.1µF

T2

25Ω 0.1µF

AIN+

LTC2185

1.8pF

25Ω

AIN–

T1: MA/COM MABA-007159-000000

T2: COILCRAFT WBC1-1TL

RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE

218543 F05

Figure 5. Recommended Front-End Circuit for Input

Frequencies from 150MHz to 250MHz

Reference

The LTC2185/LTC2184/LTC2183 has an internal 1.25V

voltage reference. For a 2V input range using the internal

reference, connect SENSE to VDD. For a 1V input range

using the internal reference, connect SENSE to ground.

For a 2V input range with an external reference, apply a

1.25V reference voltage to SENSE (Figure 9).

The input range can be adjusted by applying a voltage to

SENSE that is between 0.625V and 1.30V. The input range

will then be 1.6 • VSENSE.

The VREF, REFH and REFL pins should be bypassed as

shown in Figure 8. A low inductance 2.2µF interdigitated

capacitor is recommended for the bypass between REFH

and REFL. This type of capacitor is available at a low cost

from multiple suppliers.

0.1µF

ANALOG

INPUT

T1

50Ω

4.7nH

25Ω

0.1µF

VCM

0.1µF

AIN+

LTC2185

0.1µF

25Ω 4.7nH

AIN–

T1: MA/COM ETC1-1-13

RESISTORS, CAPACITORS

ARE 0402 PACKAGE SIZE

218543 F06

Figure 6. Recommended Front-End Circuit for Input

Frequencies Above 250MHz

ANALOG

INPUT

HIGH SPEED

DIFFERENTIAL

AMPLIFIER

0.1µF

++

200Ω 200Ω

25Ω

– – 0.1µF

25Ω

VCM

0.1µF

AIN+

12pF

LTC2185

AIN–

12pF

218543 F07

Figure 7. Front-End Circuit Using a High Speed

Differential Amplifier

218543f

20

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