The Counter

Some digital circuits are programmed to change state every so-many clock pulses. Such type of circuit is called as counter. It is also called as divider, as if the output

                                                             Figure--Schematic symbol for a J-K flip-flop.

changes state after every n input pulses, output frequency is 1/n of the input frequency. Counters are built up by interconnecting several flip-flops.A special type of counter is instructed to divide by any desired positive integer n. This is a programmable divider. It forms heart of a digital frequency synthesizer, an oscillator whose frequency is digitally set.