Typical applications involving transformer-coupled circuits are discussed in this section. To achieve good phase and amplitude balances at the ADC input, surface-mount transformers can be used (for example transformers such as ADT1-1WT or WBC1-1 can be used for frequencies up to 300 MHz and TC1-1-13M+ for higher frequencies) to achieve good phase and amplitude balances at the ADC inputs. When designing dc-driving circuits, the ADC input impedance must be considered. Figure 9-15 and Figure 9-16 show the impedance (Z_IN = R_IN || C_IN) across the ADC input pins.

Figure 9-15 R_IN vs Input Frequency

Figure 9-16 C_IN vs Input Frequency

By using the simple drive circuit of Figure 9-17, uniform performance can be obtained over a wide frequency range. The buffers present at the analog inputs of the device help isolate the external drive source from the switching currents of the sampling circuit.

Figure 9-17 Input Drive Circuit