| 摘要 |
PURPOSE:To obtain an output signal having good flat characteristics although the frequency characteristics of an LPF is not steep, by giving a D/A conversion to the output signal of a digital filter, turning on and off the output of the D/A conversion with a double frequency and supplying the obtained output signal to the LPF. CONSTITUTION:An analog switch 2 is turned on and off with the frequency 2fs which is double as high as the sampling frequency fs used to a D/A converter 1. Thus a PAM wave fp2(t2n-1) corresponding to the odd-numbered time and a PAM wave fp2(t2n) corresponding to the even-numbered time axis are obtained at the output side of the switch 2. Then ta(t)=cosomega3t is satisfied for the synthesized PAM wave fp2(t) with fp2(t2n-1)=fp2(t2n) to obtain equation I. Here a digital filter 5 and an LPF6 are set before the converter 1 and after the switch 2 respectively. Thus the signal having the flat transmission characteristics can be transmitted to an output terminal 4. |
