Study of noise reduction by 3 multiple decoupling capacitors with series resistors

Multiple decoupling capacitors with series resistors are effective for noise reduction at higher radio frequency bands. The resistance plays a part in preventing impedance from increasing at the resonant frequency. A clock speed of a digital circuit has easily exceeded more than 100 MHz. Therefore, 3 or more decoupling capacitors are often needed to suppress the radiation noise from such a digital circuit. So we have studied the relation of the impedance and the radiation noise in case of 3 decoupling capacitors with series resistors. In this report, we show the calculated optimum value of the resistor to minimize the impedance by circuit simulator and the results are proved by measurement.