Digitally controlled oscillator

Claim 1

A digitally controlled oscillator for use in a sonar transmitter/receiver comprising: a memory, storing the half periods T i (i=1,2,...,n) of corresponding frequencies f i =1/(2T i ) to be generated; a digital feedback circuit connected to said memory; said circuit decreasing each of the half periods taken from memory after a fixed time interval τby the value τon a time sharing basis; n counters to count residual values; said digital feedback circuit connected to said n residual value counters, each counter being supplied with a series of residual values Δ i ,j ; in which circuit as soon as the residual values Δ i ,1 i,=T i -k i ,1 <τ, where k i ,1 is an integer are obtained, said residual values are increased by the corresponding half periods T i also on a time sharing basis, and each value so increased is repeatedly decreased after a fixed time interval τ by the value τ whereby after the process of increasing by T i and repeatedly decreasing by τ has been performed j times the residual values can be expressed by: Δ i ,j =T i +Δ i ,j-1 -k i ,j τ, where each k i ,j is so large that 0≦Δ i ,j <τ; a conversion circuit; said counters on reaching a fixed value after writing of a residual value from the respective series, delivering a signal to said conversion circuit connected to the respective counter, which circuit converts the applied signals into a square-wave signal of frequency f i .