Algorithms for quickly and efficiently detecting a periodic signal such as a DTMF signal in a telephone system are described. The algorithms, implemented in a tone detector, detect the periodicity of the input data and do not require an estimation of the tone frequency.

A tone detector includes at least one circuit (hereinafter "single phase reference matcher") that not only performs a convolution of an input signal with a reference signal, but also compares the result of convolution with a threshold to determine if there is a match, and if so drives a signal active indicating that tone is present. If there is no match, another circuit (hereinafter "phase shifter") delays the reference signal by a fraction (e.g. 1/8) of the measuring period, thereby to introduce a phase shift (e.g. .pi./8) between the input signal and the reference signal. The "single phase reference matcher" again performs the just-described operation, this time with a delayed reference signal, and repeats the operation as often as necessary (e.g. eight times) to cycle through the entire measuring period, thereby to ensure that tone (if present in the input signal) is detected irrespective of phase, during one of the operations. The smaller the phase shift, the greater the number of times the operation is repeated, and vice versa. A tone detector of the type described herein can include more than one "single phase reference matcher," each of which performs one of the above-described operations in parallel, thereby to reduce the total time required to perform all operations. The number of samples over a measurement period is selected to minimize the noise, e.g. by selecting a number based on the input frequency and difference in frequency with the nearest adjacent frequency at which another tone may be present.

Systems and techniques for communication over telephony wireline. A command interface and control device may include a wireline input configured to connect the device to an operative line of a wireline telephony network (such as the PSTN) and to transmit voice signals to and receive voice signals from the wireline telephony network. The device may also include a cellular module configured to transmit signals to and receive signals from a cellular telephony network and a system controller to control communications on the wireline input and the cellular module. One or more wireline adapter modules may be configured to provide control functionality local to a telecommunications device.

The disclosed filter structure employs parallel first and second input signal data paths. The first data path includes a digital Finite Impulse Response (FIR) filter having a small number of non-zero multiplier coefficients to define its theoretical impulse frequency response. The second data path includes plural series filters including (1) a digital FIR or Infinite Impulse Response (IIR) filter including a reduced-number of designer-chosen non-zero multiplier coefficients that tend to introduce error sources in the physical-realized filter structure's impulse frequency response and (2) a set of one or more frequency stop filters, each of which permits zero signal transmission therethrough at a different selected frequency. This arrangement anchors the frequency response value of the filter structure near each of the different selected frequencies of the set substantially at the corresponding theoretical impulse frequency response value of the digital FIR filter of the first data path near that one of the plurality of different selected frequencies of the set. The summed outputs of the first and second data paths is the filter output.

A signal detector for detecting a narrow-band signal of a desired frequency, using an adaptive type FIR filter having two filter coefficients, is disclosed. Using this filter, the input signal of a shift register which delays the signal, is estimated by referring to the output therefrom. A narrow-band signal of a desired frequency is detected by comparing each filter coefficient of this filter with a known filter coefficient corresponding to the frequency which is the object of detection.