Apparatus is depicted which enables the sampling of the phase angle of a modulated signal and manipulates the sample signals to demodulate the same. The apparatus is particularly adaptable for use in demodulating the I and Q channel signals of a zero IF receiver. The system contains an angle sensing circuit which combines the I and Q channel signals in differential form to produce a series of output signals of an angular range indicative of the present value of the instanteous phase. The signals from the angle detector are coupled to an octant decoder which operates to determine the particular octant that the angle is to be included in. In the present system eight octants are used, each comprising 45°. The octant decoder determines which octant the angle belongs in and assigns a predetermined angle value to that angle. In one embodiment, the assigned angle values are 0°, 45°, 90°, 135°, 180°, 225°, 270° or 315°. The value of the assigned angles are then sampled by means of a clock at a high frequency rate whereby the resultant pulses indicative of the angles are then processed as differentiated to produce an output signal indicative of the information content on the original signal.

Zero IF receiver AM/FM/PM demodulator using sampling techniques

A coherent signal detector for extracting analog and digital information from a received AM-compatible digital broadcast waveform is provided. The waveform can have an in-phase component and a quadrature component. The detector can include a down converter for shifting the in-phase and quadrature components in phase, frequency, or both, in response to a phase word, thereby providing a recovered in-phase output and a recovered quadrature output. The signal detector also includes an integration circuit for integrating a portion of the recovered quadrature output over a first preselected time interval, which can be one digital time frame.

Coherent signal detector for AM-compatible digital audio broadcast waveform recovery

The present invention provides for a receiver addressable AM compatible digital broadcast system and method. The digital broadcast signal includes a plurality of digitally modulated signals and an analog signal. A transmitter useable within the system includes a data combiner for generating an aggregate digital data signal, and a waveform generator for forming the digital broadcast signal. A receiver useable within the system comprises a waveform detector for separating the signals and a data parser for separating the digitally modulated signals. The present invention further provides for a method of selectively transmitting data via a digital broadcast signal. The method includes forming the digital broadcast signal from an analog signal and a plurality of digitally modulated signals, transmitting and receiving the digital broadcast signal. The method further includes the steps of separating the analog signal from the digitally modulated signals, separating the digitally modulated signals, comparing a destination identification signal with an identification code, and passing a user defined message signal responsive to the destination identification digital signal corresponding to the identification code.

Receiver addressable AM compatible digital broadcast system

A demodulator for coherent demodulation of a π/4 shifted QPSK signal includes a -π/4 phase-shift circuit in a conventional QPSK signal decision/feedback type Costas loop to alternately rotate the phase of an inputted π/4 shifted QPSK signal by 0 and -π/4 for each symbol period interval from a timing controller, thus eliminating the π/4 shift component of the π/4 shifted QPSK signal. Thus, coherent detection demodulation for the π/4 shifted QPSK signal having stable points at intervals of π/2 phase angles is enabled.

Coherent demodulator for π/4 shifted QPSK signal

A digitally-controlled quadrature signal generator is provided having a frequency synthesizer for receiving a digital input signal and in response thereto generating an output signal having a predetermined frequency. The output signal is split to produce an in-phase (I) signal and a quadrature-phase (Q) signal. A first table look-up memory is provided for generating a predetermined phase correction signal for use in cancelling any phase error in the quadrature-phase signal. A mixer receives the phase correction signal and the in-phase signal and in response thereto generates a phase error signal. The phase error signal is then added to the quadrature-phase signal to thereby cancel the undesirable phase error. Moreover, programmable attenuator circuits or limiter circuits are provided to limit the in-phase and quadrature-phase signals and thereby cancel any undesirable amplitude error components therein.

Quadrature signal generator having digitally-controlled phase and amplitude correction

An n (=8, 9)-valued polyphase modulation system having circuit construction for carrier regeneration in which not only correct phase demodulation is effected but also any AM components of the regenerated carrier wave are effectively compensated for and in which the decision circuit is adapted to produce a signal output having no phase ambiguity which is coupled to a π/4 phase modulator unit of the carrier generator to serve as a drive signal therefor.

Carrier regeneration circuit for polyphase modulation system

PURPOSE:To reproduce the carrier wave of the orthogonal partial response modulation system by causing the small number of circuit element to perform stable leading-in at every pi/4 and eliminating noise components CONSTITUTION:QPRS input signal S is subjected to envelop detection 5 and has AM components extracted, and signals a1 to a4 of amplitude beta and signals b1 to b4 of amplitude gamma are distinguished from each other in 6 and are pi/4-phase-modulated by output G1 Simultaneously, when the amplitude is reduced to 1/12 , signals a1 to a2 agree with signals b1 to b4, and AM components of the difference between beta and gamma are compensated to obtain signals like a 4 PSK wave This wave is multiplied by four in 8 for the purpose of eliminating 4 PSK wave components and is subjected to phase comparison in 9 to obtain phase error signals Then, when these signals have noise components eliminated through LPF 10 and are supplied to VCO 11, the reference carrier whose phase is synchronized with the input signal is obtained Then, this carrier is given to detector 1 and is given to detector 2 after pi/2 phase shift to detect signal S synchronously, and demodulated signals S1 and S2 are obtained In this constitution, since pi/4 phase modulation is performed in 4 by signal G1 which is directly detected from the input signal, a leading-in stable point exists only at every pi/4

Yasuharu Yoshida

Papers

Carrier regeneration circuit for polyphase modulation system

Carrier wave reproducing circuit