The output pulse width from a 74121 OS is given by the approximate formula tp ≈ 0.7R_TC_T where R_T is the resistance connected between the R_EXT/C_EXT pin and V_CC, and C_T is the capacitance connected between the C_EXT pin and the R_EXT/C_EXT pin. The value for R_T can be varied between 2 and 40 kΩ, and C_T can be as large as 1000 μF.

(a) Show how a 74121 can be connected to produce a negative-going pulse with a 5-ms duration whenever either of two logic signals (E or F) makes a NGT. Both E and F are normally in the HIGH state.

(b) Modify the circuit so that a control input signal, G, can disable the OS output pulse, regardless of what occurs at E or F.