ADC3908CSSS datasheet(25/47 Pages) TI

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7.3 Feature Description

7.3.1 Analog Input

The analog inputs of ADC3908Dx and ADC3908Sx supports differential and single-ended configuration, with

support for AC coupling and DC coupling. Analog inputs are designed for an input common mode voltage of

1.25V which must be provided externally on each input pin. DC-coupled input signals must have a common

mode voltage that meets the device input common mode voltage range.

The ADC3908Dx and ADC3908Sx has buffered analog inputs which eases design by isolating the input from the

ADC sampling operation.

7.3.1.1 Single Ended Input

The ADC3908Dx and ADC3908Sx can be configured to operate in single ended mode using just the positive

signal input. This operating mode must be enabled via pin control (Interface configuration table). The single

ended signal is connected to the positive input of the ADC and negative input must be biased to VCM as shown

in Figure 7-3.

INxP

INxM

0.475V

-0.475V

0.475V

-0.475V

INxP

INxM

Figure 7-3. Single ended analog input: AC coupled (left) and DC coupled (right)

7.3.1.2 Differential Input

The ADC3908Dx and ADC3908Sx supports differential mode with a swing of 1.9VPP as shown in Figure 7-4.

This operating mode must be enabled via pin control (Interface configuration table).

–

INxP

INxM

INxP

INxM

Figure 7-4. Differential analog input: AC coupled (left) and DC coupled (right)

7.3.1.3 Analog Input Bandwidth

Figure 7-5 shows the analog full power input bandwidth. The -3dB bandwidth is approximately 150MHz.

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ADC3908CSSS 데이터시트(PDF) 25 Page - Texas Instruments