The ADC3644 can be operated using a differential or a single ended clock input where the single ended clock consumes less power consumption. However clock amplitude impacts the ADC aperture jitter and consequently the SNR. For maximum SNR performance, a large clock signal with fast slew rates needs to be provided.

• Differential Clock Input: The clock input can be AC coupled externally. The ADC3644 provides internal biasing for that use case.
• Single Ended Clock Input: This mode needs to be configured using SPI register (0x0E, D2 and D0) or with the REFBUF pin. In this mode there is no internal clock biasing and thus the clock input needs to be DC coupled around a 0.9 V center. The unused input needs to be AC coupled to ground.

Figure 8-9 External and internal connection using differential (left) and single ended (right) clock input