| 摘要 |
PURPOSE:To shorten the time required for the trimming of an active filter, by using a phase synchronous loop and digital phase detector. CONSTITUTION:A rectiangular-wave signal obtained by comparator 15 from an input signal and a rectangular signal obtained by comparator 13 from the output of active filter 12 are both inputted to phase detector 14, which outputs a difference in phase between both the signals. Further, phase synchronous loop 19 supplies a signal, obtained by multiplying the output of comparator 15 by N, to gate circuit 18. Circuit 18 gates the phase-difference output and passess the N-multiplication signal. This penetrating signal is counted by counter 20 and trimming is carried on until its content reaches a fixed value. Consequently, rapid trimming can be performed. |
