DQS Data strobe enable circuitry

[promach]

For Data strobe enable circuitry , in Figures 4 and 5 , how exactly does the DQS_Clean being phase-shifted 90 degrees with reference to DQS_P and DQS_N ? Why do we need the COUNTER module in which the circuit is described in Figure 5 ? What value should I assign for Vref ?

 

[BradtheRad]

how exactly does the DQS_Clean being phase-shifted 90 degrees with reference to DQS_P and DQS_N ?

Possibly so incoming Data settles at a high or low voltage, just before the moment a clock signal arrives to gate the flip-flop.

What value should I assign for Vref ?

At the op amps... The other inputs have labels containing P & N. Probably the incoming signals are positive or negative (high vs low). My surmise is that Vref is the voltage which determines the difference between high and low.

 

[promach]

I try to replicate the circuit, it is not working yet. Any advices ?