Which of the waveforms shown below can be generated by the output QB of the
synchronous counter shown? (QA is least significant)
CLOCK _-__-__-__-__-__-__-__-__-__-__-__-__-__-__-__-__-_
QB1 __---------_________---------_________---------____
QB2 __---___---___---___---___---___---___---___---___-
QB3 __------------____________------------____________-
QB4 __------______------______------______------______-
QB5 __------------------------________________________-
4 is CORRECT. The counter outputs frequency divide the basic clock frequency (multiply clock period) in the following manner:
QA: f=fc/2 T = 2Tc fc = clock frequency
QB: f=fc/4 T = 4Tc Tc = 1/fc = clock period
QC: f=fc/8 T = 8Tc
QD: f=fc/16 T =16Tc
Considering output QB, we must find that output waveform which
oscillates at a frequency f = fc/4, or alternatively T = 4Tc.
Waveform 4 has a period which is four times that of the clock.