*Rate around condition
1 Answer

Rate around condition:

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  • The difficulty of both i/ps S = R = 1 is not allowed in SR flip-flops is eliminated in IK f/E by using feedback connection by o/p to i/p of gates $G_3$ and $G_4$

  • Assume that i/p to $G_3$ & $G_4$ which are coming from feedback do not change during one active high clock pulse which is not true because of feedback connection.

  • Now assume c/k = j = k = 1 & $Q_n = 0$ & $Q_n = 1$

  • After at time interval $\triangle$T (propagation delay) through two NAND gates which are in series output will change to logic 1 after another time interval $\triangle$ T & this process continues hence we conclude that for TH of pulse that o/p will oscillates between logic 0 and logic 1.

  • At the end of C/H pulse the value of new o/p is unpredictable this situation is referred to race around condition.

  • To overcome this we use master slave J.K F/F.

Master slave JK f/f:

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  • A master slave J/K F/F is called e connection of one JK and 1 SR f/f with feedback connection from o/p of 2nd stage to i/p of 1st stage.

  • Positive c/h pulse is applied to the first f/f and it is inverted before applying to 2nd f/f when c/n = 1 1st f/f is enabled and 2nd disabled and vice versa.

  • The 2nd f/f simply follows the o/p of 1st f/f hence it is referred as slave and 1st as master hence entire configuration is now as master slave. JK

  • In this cnt input to mns and mG4 do not change during the active high clock pulse hence o/p remains constant for one c/n pulse, hence rate around condition does not exist.

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