JAJSCV8B May 2016 – December 2021 ADC32RF80 , ADC32RF83
PRODUCTION DATA
The ADC32RF8x analog signal inputs are designed to be driven differentially. The analog input pins have internal analog buffers that drive the sampling circuit. The ADC32RF8x provides on-chip, differential termination to minimize reflections. The buffer also helps isolate the external driving circuit from the internal switching currents of the sampling circuit, thus resulting in a more constant SFDR performance across input frequencies.
The common-mode voltage of the signal inputs is internally biased to CM using the 32.5-Ω termination resistors that allow for ac-coupling of the input drive network. Figure 8-1 and Figure 8-2 show SDD11 at the analog inputs from dc to 5 GHz with a 100-Ω reference impedance.
The input impedance of analog inputs can also be modeled as parallel combination of equivalent resistance and capacitance. Figure 8-3 and Figure 8-4 show how equivalent impedance (CIN and RIN) vary over frequency.
Each input pin (INP, INM) must swing symmetrically between (CM + 0.3375 V) and (CM – 0.3375 V), resulting in a 1.35-VPP (default) differential input swing. As shown in Figure 8-5, the input sampling circuit has a 3-dB bandwidth that extends up to approximately 3.2 GHz.