A modulator for differentially encoded phase-shift keyed digital data is implemented entirely by digital means. Baseband serial binary data are illustratively transformed into dibit pairs which are assigned discrete quaternary carrier-wave phase shifts. A "staircasing" shift register whose weighted outputs are combined to form a quantized phase-modulated carrier wave is advanced by a relatively high-speed counter through a frequency divider network. The division rate of the divider is selectively accelerated in each baud interval in accordance with the assigned dibit coding. The resultant quantized carrier wave is then lowpass filtered prior to application to a telephone transmission line. By controlling the division rate of the divider rather than the advancement rate of the shift register, gradual transitions are imparted to the output carrier wave with minimal harmonic distortion.
A digitalized phase modulating means in which a two level binary modulated sequence from a data source of bit rate f.sub.s is supplied to a pulse add/delete circuit. Also supplied to such pulse add/delete circuit is a train of clock pulses of frequency C.sub.a, and a train of add/delete pulses having a repetition rate mkf.sub.s, where m and k are integers. The pulse add/delete circuit responds to a binary bit of value 1 or 0 to add or delete the said add/delete pulses to the train of clock pulses at a given rate, such as mk pulses per data bit period 1/f.sub.s. The altered clock pulse train is then supplied to a divider which divides by 4k to produce a cyclical output whose phase is advanced or retarded by 1/4k of 360.degree. each time a pulse is added or deleted from the clock pulse train C.sub.a. By changing the value of k and by either only adding pulses to, or by only deleting pulses from, the clock pulse train, or by both adding and deleting pulses, several different forms of phase modulation can be effected.
An improved four-phase differential phase shift keyed modulator for use in a modem is shown. A microprocessor (15) generates two vectors of equal frequency and equal magnitude, but different relative phases, by reference to a cyclic sine table contained in a read only memory (22). Values of the two vectors are summed and provided as an output (32) to a digital to analog converter (35). The phase shift of the carrier in a phase plane with reference to a predetermined reference phase (86) shows that the path taken by a vector in the phase plane defines a straight line (88) between two phase values by which dibits are encoded. The result is lower out-of-band transmitted signals resulting in a relatively simple transmit filter (37).
4764940 - Modem for RF subscriber telephone system - Owned by International Mobile Machines Corporation (Philadelphia, PA) [*] Notice:The portion of the term of this patent subsequent to February 17, 2004 has been disclaimed.
A modulator for a modem, said modulator being adapted to convert a bit stream, wherein each given number of successive bits defines a symbol, into a phase modulated intermediate frequency (IF) signal, the symbols in the modulator section being phase modulated DPSK conversion. The phase modulated symbols are then digitally filtered to provide a filtered signal comprising time shared, digital in-phase and quadrature phase components that, when converted into an analog signal, provides a modulation signal of a frequency that is centered about a predetermined frequency and deviates therefrom in accordance with the value of the phase modulated symbol. The filtered signal, after being converted to an analog signal is then filtered and passed to a mixer for up conversion to an IF signal.
A line protocol format with a low bit overhead provides for the high accuracy, asynchronous exchange of digital signal information between processing units in a supervisory control system having a central processing unit (CPU) and at least one remote processing unit (RPU).
A radio FM receiver is provided with a voltage-controlled oscillator which can be connected via a frequency 2-divider to a quadrature combination circuit for transforming down the frequencies of received radio signals and for supplying quadrature output signals. The receiver is further provided with detection and sound reproduction circuitry connected to this combination circuit. A frequency 3-divider is also present as well as a switching circuit for selectively connecting the mixer element to the oscillator either through the 2-divider or through the 3-divider.
