Suppression of limit cycles in digital filters by random dither

The use of random dither to suppress limit cycles in 2nd-order direct-form digital filter sections is discussed. Experimental comparisons are made, for binary random dither and uniformly distributed random dither, of the average time taken to suppress limit cycles and of the increase in output noise caused by the dither. A new form of dither is introduced, termed bandstop dither. This has the advantage of suppressing limit cycles about as quickly as binary dither yet it causes an increase in output noise of less than 2 dB.