Patent ID: 9106505
Filing Date: 2015-08-11
Classification: H04B,H04L

Abstract:
1. A digital filter for removing a PWM (pulse width modulation) noise from a sampling data comprising: an averaging filter, wherein the sampling data is obtained by sampling control amounts driving an electrical device at a sampling frequency, wherein the control object is driven at a driving frequency in a pulse width modulation (PWM) control method, wherein the PWM noise includes a fundamental wave component having the driving frequency and a harmonic wave component of the fundamental wave component having a harmonic wave frequency, wherein the sampling data is input into the averaging filter over a predetermined sampling time period, the averaging filter calculates an average of the sampling data over the predetermined sampling time period, and the averaging filter outputs an averaging number of the sampling data for the predetermined sampling time period, wherein the sampling frequency and the averaging number are determined to satisfy a relationship that an absolute value of a difference between the sampling frequency multiplied by a predetermined first integer and the harmonic wave frequency is equal to the sampling frequency divided by the averaging number and multiplied by a predetermined second integer in a frequency range between zero and a Nyquist frequency when the fundamental wave component and the harmonic wave component in the PWM noise are removed from the sampling data, and wherein the predetermined first integer is equal to or larger than zero, and the predetermined second integer is equal to or larger than one.