LTC4263IDE View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LTC4263IDE

14-Bit, 65Msps ADC

Linear Technology 

LTC2205-14

APPLICATIONS INFORMATION

Center-tapped transformers provide a convenient means

of DC biasing the secondary; however, they often show

poor balance at high input frequencies, resulting in large

2nd order harmonics.

Figure 4a shows transformer coupling using a transmission

line balun transformer. This type of transformer has much

better high frequency response and balance than flux

coupled center tap transformers. Coupling capacitors are

added at the ground and input primary terminals to allow

the secondary terminals to be biased at 1.25V. Figure

4b shows the same circuit with components suitable for

higher input frequencies.

Direct Coupled Circuits

Figure 5 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 any op amp or closed-loop amplifier

will degrade the ADC SFDR at high input frequencies.

Additionally, wideband op amps or differential amplifiers

tend to have high noise. As a result, the SNR will be

degraded unless the noise bandwidth is limited prior to

the ADC input.

VCM

5Ω

10Ω

T1

0.1μF

10Ω

2.2μF

5Ω AIN+

8.2pF

LTC2205-14

35Ω

8.2pF

35Ω

5Ω AIN–

T1 = MA/COM ETC1-1T

RESISTORS, CAPACITORS

ARE 0402 PACKAGE SIZE

EXCEPT 2.2μF

8.2pF

220514 F03

Figure 3. Single-Ended to Differential Conversion Using a Transformer.

Recommended for Input Frequencies from 5MHz to 150MHz

0.1mF

ANALOG

INPUT

T1

1:1

0.1mF

10Ω

25Ω 0.1μF

25Ω 10Ω

T1 = MA/COM ETC1-1-13

RESISTORS, CAPACITORS

ARE 0402 PACKAGE SIZE

EXCEPT 2.2mF

VCM

2.2μF

5Ω AIN+

LTC2205-14

4.7pF

4.7pF

5Ω AIN–

4.7pF

220514 F04a

Figure 4a. Using a Transmission Line Balun Transformer.

Recommended for Input Frequencies from 150MHz to 250MHz

ANALOG

INPUT

0.1μF

T1

0.1μF 1:1

25Ω 0.1μF

25Ω

T1 = MA/COM ETC1-1-13

RESISTORS, CAPACITORS

ARE 0402 PACKAGE SIZE

EXCEPT 2.2μF

VCM

2.2μF

5Ω AIN+

LTC2205-14

2.2pF

5Ω AIN–

2.2pF

22054 F04b

Figure 4b. Using a Transmission Line Balun Transformer.

Recommended for Input Frequencies from 250MHz to 500MHz

220514fb

17

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