摘要 |
An apparatus and method provide for filtering of voiceband and specified tone frequencies of a mixed voice/data signal, such as an Asymmetric Digital Subscriber Line (ADSL) signal. A lowpass filter section passes voiceband content of the mixed signal and suppresses mixed signal content having frequencies falling within a databand of the mixed signal. A bandpass filter section is coupled to or integral with the lowpass filter section and passes the specified tone frequency, such as a metering or billing tone frequency. The lowpass and bandpass filter sections exhibit a combined frequency response that provides for a stopband between the voiceband and the metering tone frequency. The bandpass filter section effectively detunes a frequency response of the lowpass filter section to provide for the stopband. The stopband preferably provides for an insertion loss of 3 dB or greater between the voiceband and the metering tone frequency, and suppresses undesirable mixed signal content having frequencies falling within the stopband. The lowpass filter section and the bandpass filter section may each be implemented to include only passive components, such as passive magnetic components. |