hi,,
i have a diff way of answer for this.
assume u have opamp with 60db openloop gain.now you use this opamp in unity gain buffer mode and give 1v to positive pin of opamp..idealy you are suppose to get 1v at o/p..but u get 999m only..diff b/w inputs of opamp is 1mv(static volatage diff)...this is becuase of finite open loop gain of opamp.if u want to reduce this,u have to increase the AV of opamp.
similarly in PLL,instead of voltage,you will get constant phase diff at pll input even after pll is locked.this static phase error phase error will give spurious tones(=near ref input freq)..so if u want to reduce this error,then u may have to increase the gain of ur pll.
hope it helps you..
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kamal.