ADC3681IRSBT datasheet(29/91 Pages) TI2

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8.3 Feature Description

8.3.1 Analog Input

The analog inputs of ADC368x are intended to be driven differentially. Both AC coupling and DC coupling of the

analog inputs is supported. The analog inputs are designed for an input common mode voltage of 0.95 V 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 equivalent input network diagram is shown in Figure 8-1. All four sampling switches, on-resistance shown in

red are in same position (open or closed) simultaneously.

AVDD

0.6 pF

GND

2 nH

xINP/

xINM

125

1.4 pF

GND

0.15 pF

GND

0.32 pF

0.6 pF

GND

0.7 pF

GND

6.4 pF

1.6 pF

GND

Sampling Switch

Figure 8-1. Equivalent input network

8.3.1.1 Analog Input Bandwidth

Figure 8-2 shows the analog full power input bandwidth of the ADC368x with a 50 Ω differential termination.

The -3 dB bandwidth is approximately 900 MHz and the useful input bandwidth with good AC performance is

approximately 120 MHz.

The equivalent differential input resistance RIN and input capacitance CIN vs frequency are shown in Figure 8-3.

Input Frequency (MHz)

100

1000

-6

-5

-4

-3

-2

-1

ADC3

Figure 8-2. ADC Analog Input bandwidth response

Figure 8-3. Equivant RIN, CIN vs Input Frequency

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ADC3681, ADC3682, ADC3683

SBAS872B – DECEMBER 2020 – REVISED OCTOBER 2022

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