Frequency sensing and control circuit

Abstract

In construction of a digital phase locked loop for detection of the angular displacement of a mobile object depending on input signals from an encoder, is provided a bit number control circuit so that working bit numbers of A/D converters and a counter in the loop are automatically reduced as the frequency of the input signals rise and, in accordance with such reduction in working bit number, a function generating ROM of a smaller bit number is selected from a group of function generating ROMs of different bit numbers for supply of address data to multipliers connected to the A/D converters, thereby the signal processing speed of the loop is significantly raised to face up to current speed-up in the mobile object displacement.