| 摘要 |
PURPOSE:To transmit and receive sound signals of good quality without attenuating the high band part of a low-side band signal by a low pass filter even in case of the change of a subcarrier frequency by changing the cut-off frequency of the low pass filter synchronously with the subcarrier frequency fs in the same direction as this frequency fs. CONSTITUTION:In a handset 1, a subcarrier signals Ss having the prescribed frequency fs is supplied to a modulating cirucit 14 and a signal Sa is modulated to a balanced-modulated signal Sb, and this signal Sb is supplied to a low pass filter 15 to take out a low-side band signal Si. The low pass filter 15 consists of a switched capacitor filter, and a pulse P1 is supplied to the filter 15 as the clock. Thus, the cut-off frequency of the filter 15 is changed synchro nously with the subcarrier frequency fs in the same direction as the subcarrier frequency fs, and therefore, only the signal Si is taken out from the signal Sb by the filter 15, and the high band part of the signal Si is not attenuated then. |
