Rainbow-electronics MAX1211 Manual de usuario descargar pdf (Pagina 25)

MAX1211

65Msps, 12-Bit, IF Sampling ADC

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Single-Ended AC-Coupled Input Signal

Figure 11 shows an AC-coupled, single-ended input

application. The MAX4108 provides high speed, high

bandwidth, low noise, and low distortion to maintain the

input signal integrity.

Buffered External Reference Drives

Multiple ADCs

The buffered external reference mode allows for more

control over the MAX1211 reference voltage and allows

multiple converters to use a common reference. The

REFIN input impedance is >50MΩ.

Figure 12 shows the MAX6062 precision bandgap ref-

erence used as a common reference for multiple con-

verters. The 2.048V output of the MAX6062 passes

through a one-pole, 10Hz, lowpass filter to the

MAX4250. The MAX4250 buffers the 2.048V reference

before its output is applied to the REFIN input of the

MAX1211. The MAX4250 provides a low offset voltage

(for high gain accuracy) and a low noise level.

Unbuffered External Reference Drives

Multiple ADCs

The unbuffered external reference mode allows for pre-

cise control over the MAX1211 reference and allows

multiple converters to use a common reference.

Connecting REFIN to GND disables the internal refer-

ence, allowing REFP, REFN, and COM to be driven

directly by a set of external reference sources.

Figure 13 shows the MAX6066 precision bandgap ref-

erence used as a common reference for multiple con-

verters. The 2.500V output of the MAX6066 is followed

by a 10Hz lowpass filter and precision voltage-divider.

The MAX4254 buffers the taps of this divider to provide

the +2.000V, +1.500V, and +1.000V sources to drive

REFP, REFN, and COM. The MAX4254 provides a low-

offset voltage and low-noise level. The individual volt-

age followers are connected to 10Hz lowpass filters,

which filter both the reference voltage and amplifier

noise to a level of 3nV/√Hz. The 2.000V and 1.000V ref-

erence voltages set the differential full-scale range of

the associated ADCs at ±1.000V.

The common power supply for all active components

removes any concern regarding power-supply

sequencing when powering up or down.

With the outputs of the MAX4254 matching better than

0.1%, the buffers and subsequent lowpass support as

many as eight ADCs.

MAX1211

0.1µF

100Ω

5.6pF

INP

INN

COM

0.1µF

MAX4108

24.9Ω

2.2µF

Figure 11. Single-Ended, AC-Coupled Input Drive

MAX1211

N.C.

5.6pF

0.1µF

0Ω*

49.9Ω

0.5%

49.9Ω

0.5%

0Ω*

MINICIRCUITS

ADT1-1WT

N.C. N.C.

MINICIRCUITS

ADT1-1WT

INP

COM

INN

*0Ω RESISTORS CAN BE REPLACED WITH

LOW-VALUE RESISTORS TO LIMIT THE

INPUT BANDWIDTH.

0.1µF4.7µF

49.9Ω

0.5%

49.9Ω

0.5%

Figure 10. Transformer-Coupled Input Drive for Input Frequencies Beyond Nyquist

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Rainbow-electronics MAX1211 Manual de usuario Pagina 25

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