在电话自动交换网中,频分或时分复用的局间中继电路上的占用、拆线、应答、挂机等信号,有使用带内单频脉冲线路信号方式的。在数字网中,此单频脉冲以数字信号传送,因此,必须设置检测数字单频脉冲信号的专用单元。对这种数字单频信号的检测,可以有多种方法。本文介绍一种用正交复解调加FIR数字滤波的方法,给 In the automatic telephone exchange network, frequency division or time division multiplexing on the trunk circuit occupancy, stitches, answering, hang up and other signals, there is the use of single-band pulse line signal within the band. In the digital network, this single-frequency pulse is transmitted as a digital signal. Therefore, a dedicated unit for detecting the digital single-frequency pulse signal must be set. There are many ways to test this digital single-frequency signal. This article describes a quadrature demodulation method to increase the FIR digital filter