Design a circuit using a 74121 to convert a 33-kHz, 30% duty cycle waveform to a 33-kHz, 60% duty cycle waveform.

• Rint = 2 kΩ, Cext = 0.012 nF
• Rint = 2 kΩ, Cext = 0.012 µF
• Rint = 4 kΩ, Cext = 0.012 nF
• Rint = 4 kΩ, Cext = 0.012 µF