The ADS54T01 analog signal input is designed to be driven differentially. The analog input pins have internal analog buffers that drive the sampling circuit. As a result of the analog buffer, the input pins present a high impedance input across a very wide frequency range to the external driving source which enables great flexibility in the external analog filter design as well as excellent 50 Ω matching for RF applications. The buffer also helps isolate the external driving circuit from the internal switching currents of the sampling circuit which results in a more constant SFDR performance across input frequencies.

The common-mode voltage of the signal inputs is internally biased to 1.9 V using 500-Ω resistors which allows for AC coupling of the input drive network. Each input pin (INP, INM) must swing symmetrically between (VCM + 0.25 V) and (VCM – 0.25 V), resulting in a 1.0 Vpp (default) differential input swing. The input sampling circuit has a 3-dB bandwidth that extends up to 1.2 GHz.

Figure 8-5 Analog Input Internal Circuitry