Abstract: An enhanced telephony call waiting feature is provided wherein identifying information related to a third party wishing to converse with a first party already engaged in a conversation with a second party is spontaneously provided to the first party. The method comprises the steps of the local office sending a call waiting tone having predetermined characteristics to the first party and its apparatus responding thereto by muting its associated handset for a predetermined interval of time. The local office then transmits the identification data relating to the third party and the first party apparatus receives and displays to the first party the identification information related to the third party thereby allowing the first party to either accept or reject the waiting call in the conventional manner but also based on the displayed information.

Abstract: A digital signal processing apparatus is disclosed. The apparatus is particularly suited for detecting a digital signal containing a frequency component in a noisy environment. It uses a distributed arithmetic concept for hardware realization. The use of specific coefficients and hardware arrangement has resulted in a reduction of memory location requirement. The invention finds the main application in the area of telephony in which detection of a variety of signal tones is required for various operations of telephone functions.

Abstract: Digital FSK demodulators to be used in the telephone environment are disclosed. The demodulator according to one embodiment uses the sequential processing of a digital signal encoded in the fractional two's complement numeric representation. The use of multipliers is largely eliminated, thus enabling extensive use of simple shift registers and adders. Consequently the hardware complexity requirement is greatly reduced, thus resulting in very low cost products.

Abstract: An electret microphone has a metal shield around it in order to guard against electromagnetic interference. Acoustic waves reach the electret element through a passage in the shield. The electret response is undesirably affected by an electric field produced by body capacitance when the microphone is brought close to a user's mouth. To overcome this effect, the microphone has a conductive film, transparent to acoustic waves, positioned between the passage and the electret element, the film contacting a grounded part of the casing. The conductive film can form an integral part of a microphone moisture barrier.

Abstract: A porcelain coated metal substrate bearing a printed circuit and in which a capacitive coupling is created between the substrate and the circuit to eliminate unwanted frequencies. This coupling is formed by the inclusion of a conductive element on the porcelain. The conductive element is out of direct electrical contact with the printed circuit and has a means to connect the element to ground. Connection to ground provides the desired capacitive coupling and another capacitive coupling from the metal substrate to the conductive element, the two couplings being in series.

Abstract: Telephone circuit using a transconductance switch in a high current line with the voice network, and a dial network in a low current line with the control input of the switch to provide dial input signals at the control input and send dial pulse signalling along the high current line through the voice network. The voice network includes a current clamp to stabilize the high current through the switch to the voice network sufficiently quickly to establish the desired waveform during dialling.