Method for calibrating variable delay circuit and a variable delay

Abstract

In a variable delay circuit calibrating method in which the state of connection of M delay stages connected in cascade through multiplexers and weighted differently is controlled by a control signal value to generate a calibrated amount of delay corresponding to a nominal amount of delay D.sub.s which varies in a predetermined minimum nominal delay step d.sub.s, the method comprises the steps of: dividing an amount of delay D.sub.i measured for each given control signal value CC.sub.i by the minimum nominal delay step d.sub.s of a variable delay circuit; calculating first and second errors, R.sub.k =D.sub.i -d.sub.s k and R.sub.k+1 =d.sub.s -R.sub.k, between the value k of an integral part of the resulting quotient and two adjoining nominal amounts of delay D.sub.sk and D.sub.sk+1 ; making a check to determine if the first error R.sub.k is smaller than an error held in a k-th row of a calibration table in correspondence with a nominal set signal value CS=k; if so, writing the first error R.sub.k and the corresponding control signal value CC.sub.i over the existing values in the column of the k-th row of the calibration table; making a check to determine if the second error R.sub.k+1 is smaller than an error held in a (k+1)-th row of the calibration table in correspondence with a nominal setting signal value CS=k+1; and, if so, writing the second error R.sub.k+1 and the corresponding control signal value CC.sub.i over the existing values in the column of the (k+1)-th row of the calibration table. By repeatedly executing these steps for i=0 to i=2.sup.M -1, control signal values, which minimize errors between delay times of the variable delay circuit and the nominal amounts of delay, are generated in O-th to K-th rows of the calibration table in correspondence with the respective nominal setting signal values CS.