Page 38 - Phase-Locked Loops Design, Simulation, and Applications
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MIXED-SIGNAL PLL BUILDING BLOCKS   Ronald E. Best                                       27













































                      Figure 2.16 Block diagram of the PFD with current output (charge pump).

               The dimension of K  is A/rad. I  is typically in the range 0.1 to 2 mA in commercially
                                   P
                                                P
             available PLLs, hence K  is typically in the range 0.01 to 0.5 mA/rad.
                                    P
               The question may arise now why the current output PFD should offer superior performance
             to the voltage output PFD. Assume that signal u (t) is leading u ′(t) and that both flipflops in
                                                           1              2
             Fig. 2.16 are initially reset. The next positive
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