The ACSPCIE module is a clock buffer circuit, which has both receive (RX) and transmission (TX) mode. This clock buffer is used to provide low jitter input clock to APLL. In receive mode it takes in an external differential clock and converts it to single-ended CMOS level clock signal. In transmission mode it takes in an internal single-ended clock and converts it to differential HCSL[1] level (in presence of external terminations). The I/O pins of ACSPCIE are ljcb_clkp and ljcb_clkn differential pair.
- Receive mode: RX is a clock slicer that receives HCSL or LVDS differential clock (typically from on-board Crystal Oscillator) between ljcb_clkp and ljcb_clkn and converts it to CMOS single-ended output CLKREF_ACSPCIE. This CMOS clock signal is the input clock for APLL.
- Transmission mode: TX is a current switching driver that receives CMOS single-ended clock CLKREF_ADPLL at it's input pin from DPLL_PCIE_REF and converts it to HCSL differential-ended output ljcb_clkp and ljcb_clkn. The termination for TX is on-board and 50 Ohms single-ended or 100 Ohms differential.
The ACSPCIE module has two modes of operation:
- Functional mode: The module is powered up automatically and acts as either an input or output buffer.
- Power-down mode: The module is powered down. RX output is held low and TX output is tri-stated/terminated.