| 摘要 |
PURPOSE:To simplify a circuit constitution considerably by measuring the power ratio before and after a cam filter for decision to decide whether a specific frequency exists or not. CONSTITUTION:Non-linear PCM signals and linear PCM signals are inputted from terminal 3 and terminal 3a respectively, and the former is converted to a linear PCM signal by expander EXP. Expander EXP is connected to spectrum inverter INV and low-pass filter LPF. Then, cam filters CF1 and CF2, filters CF1a and CF2a for decision, and power calculators P1-P4 are provided, and calculators P1 and P2 measure power Pt1 before input of filter CF2a and power Pt2 after output of it respectively. Similarly, calculators P3 and P4 measure power Pt3 before input of filter CF1a and power Pt4 after output of it respectively. Then, it is decided with powers Pt1-Pt4 and number ZCt1 of zero crossing as data by decision equipment DC1 whether tone signals exist or not. |
