8.3.12.1 Signal Input

The analog input to the device can be either ac- or dc-coupled. In ac-coupling, the input common-mode required for device functionality can be forced with the common-mode voltage, generated internally by the device (that comes at the VCM pin) through a resistor, as shown in Figure 89. The resistor and capacitor values used for coupling determines the high-pass filter corner of the input circuit; thus, these values are chosen with the frequency of interest in mind.

Figure 89. AC Coupling

When dc-coupling the analog input, the output common-mode voltage of the driver can be set using the VCM output pin as a reference, as shown in Figure 90.

Figure 90. DC Coupling

Each input interfaces to two sets of identical sampling circuits. The electrical model of the load that each of the sampling networks present is illustrated in Figure 91. For the sake of simplification, the MOS switches can be considered as ideal switches.

As illustrated in Figure 57, Figure 58, and Figure 59, the scheme of connecting each input sampling circuit to the input pins differs across the three input modes. The time-dependent loading of the input pins therefore is different across the three input modes, and can be determined by referring to Figure 57, Figure 58, Figure 59, and Figure 91.

Figure 91. Analog Input Sampling Network