Rainbow-electronics MAX1215 User Manual download pdf (Page 15)

MAX1215

1.8V, 12-Bit, 250Msps ADC for

Broadband Applications

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To further enhance THD and SFDR performance at high

input frequencies (>100MHz), a second transformer

(Figure 8) should be placed in series with the single-

ended-to-differential conversion transformer. This trans-

former reduces the increase of even-order harmonics at

high frequencies.

Single-Ended, AC-Coupled Analog Inputs

Although not recommended, the MAX1215 can be used

in single-ended mode (Figure 9). Analog signals can be

AC-coupled to the positive input INP through a 0.1µF

capacitor and terminated with a 49.9Ω resistor to AGND.

The negative input should be reverse terminated with

24.9Ω resistors and AC-grounded with a 0.1µF capacitor.

Grounding, Bypassing, and

Board Layout Considerations

The MAX1215 requires board layout design techniques

suitable for high-speed data converters. This ADC pro-

vides separate analog and digital power supplies. The

analog and digital supply voltage pins accept 1.7V to

1.9V input voltage ranges. Although both supply types

can be combined and supplied from one source, it is

recommended to use separate sources to cut down on

performance degradation caused by digital switching

currents, which can couple into the analog supply net-

work. Isolate analog and digital supplies (AV

and

) where they enter the PC board with separate

networks of ferrite beads and capacitors to their corre-

sponding grounds (AGND, OGND).

AGND

OGND

D0P/N–D11P/N

INP

INN

MAX1215

0.1µF

25Ω

0.1µF

ADT1-1WT

10Ω

SINGLE-ENDED

INPUT TERMINAL

AGND

OGND

D0P/N–D11P/N

INP

50Ω

25Ω

INN

MAX1215

0.1µF

SINGLE-ENDED

INPUT TERMINAL

0.1µF

Figure 8. Analog Input Configuration with Back-to-Back Transformers and Secondary-Side Termination

Figure 9. Single-Ended AC-Coupled Analog Input Configuration

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Broadband Applications 1

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