US 5,862,210 A · Signal detection circuit and telephone apparatus

Abstract

A signal detection circuit includes band pass filters for detecting frequency components of a Call Alert signal (CAS) signal, a tone detection circuit for detecting whether or not a signal component is present in the output signals of the band pass filters, and two types of guard time setting circuits that have different guard times. When the CAS signal component is present, a transmitting speech signal is muted. Thereafter, with the guard time setting circuit having the normal guard time, it is determined whether or not the signal component lasts for a predetermined time period. Since the CAS signal is detected with two types of guard times, even if the transmitting speech signal contains a frequency component of the CAS signal, the transmitting speech signal is not mis-detected as the CAS signal.

Claims6

Dependent claims

A signal detection circuit for determining whether a multi-frequency signal exists for a predetermined period on a signal line on which a transmitting speech signal and a receiving speech signal are carried, the signal detection circuit comprising:

frequency detection means for detecting the multi-frequency signal on the signal line and for producing a detection signal;
a controllable speech network for muting the transmitting speech signal carried by the signal line;
a first guard time setting circuit for producing an output signal when the detection signal from the frequency detection means exists for a first period, the first period being shorter than the predetermined period;
determination means for controlling the controllable speech network for muting the transmitting speech signal in response to the output from the first guard time setting circuit;
and
a second guard time setting circuit for producing an output signal when the detection signal from the frequency detection means exists for the predetermined period while the transmitting speech signal is muted.

3 more elements

A telephone apparatus usable for a call-waiting service in which a telephone number of a calling party is transmitted to said telephone apparatus from a central office, said telephone apparatus having a transmitting and receiving speech circuit, a signal detection circuit for determining whether a first multi-frequency signal exists for a predetermined period on a signal line on which a transmitting speech signal and a receiving speech signal are carried, and a signal generation circuit for generating a second multi-frequency signal that is transmitted to said central office when said signal detection circuit determines that the first multi-frequency signal exists for the predetermined period, said signal detection circuit comprising:

frequency detection means for detecting the first multi-frequency signal on the signal line and for producing a detection signal;
a controllable speech network for muting the transmitting speech signal carried by the signal line;
a first guard time setting circuit for producing an output signal when the detection signal from the frequency detection means exists for a first period, the first period being shorter than the predetermined period;
determination means for controlling said controllable speech network for muting the transmitting speech signal in response to the output from the first guard time setting circuit;
and
a second guard time setting circuit for producing an output signal when the detection signal from the frequency detection means exists for the predetermined period while the transmitting speech signal is muted.

3 more elements

Dependencies are inferred from the claim text.

Signal detection circuit and telephone apparatus

Life of this patent

Signal detection circuit and telephone apparatus

Life of this patent

Abstract

Claims6