Icom Incorporated

Michio Nakajima

Weimin Sun

Hirofumi Yamauchi

An angle demodulator in which an FM modulated wave is converted into an IF signal (SI) in the form of digital so as the signal is supplied to a Hilbert transformer ( ) and to an outer product calculation section ( ). The Hilbert transformer ( ) allows the phase of the IF signal (SI) to shift ninety degrees and supplied it to the outer product calculation section ( ). An integrator ( ) calculates a phase of a cosine wave of an angular frequency that a frequency control unit ( ) designates. A phase converter ( ) calculates the cosine wave and an instantaneous value of a signal in which the cosine wave shifts ninety degrees out of phase so as to supply the value to the outer product calculation section ( ). The outer product calculation section ( ) supplies to the frequency control unit ( ) an outer product of a vector including a value of the IF signal and of a signal from the Hilbert transformer ( ) and a vector including a value supplied from the phase converter ( ). The frequency control unit ( ) performs a proportion integral control to the outer product so as to determine an updated value of an angular frequency, and supplies the determined value to the integrator ( ). A digital signal representing the value of the angular frequency is converted into an analog signal as a result of D/A conversion and is reproduced as a voice.

Apparatus and method for demodulating an angle-modulated signal

An input analog signal is sampled at a sampling frequency f.sub.s, which is four times a carrier frequency f.sub.c. A demultiplexer 11 outputs supplied data to four systems sequentially, and generates four zero carriers whose frequencies and amplitudes are equal to each other, with only the phases being different. The delay circuits 12 to 15 delay each one of the zero carriers, and supply delayed signals to adaptive filters 16 to 19. Data output from the four adaptive filters 16 to 19 are selected by a multiplexer 22, and the multiplexer 22 outputs the selected signals as a single signal. The difference between a first zero carrier and an output signals of the first adaptive filter 16 is obtained, and tap coefficients of the adaptive filters 16 to 19 are controlled in accordance with an LMS algorithm based on the difference. A signal output by the multiplexer 22 is output as a reproduced carrier.

Digital filter system, carrier reproduction circuit using the digital

Constants {P.sub.b00i, Q.sub.b00j, . . . , P.sub.ak2i, Q.sub.ak2j, P.sub.ci, Q.sub.cj, P.sub.di, and Q.sub.dj } for calculating each of filter coefficients {a.sub.k1, a.sub.k2, b.sub.00, b.sub.k1, b.sub.k2, c and d} for a digital filter 15 by using non-linear polynomials for pass band position data x and pass band width data y are stored in a memory 13. The constants {P.sub.b00i, Q.sub.b00j, . . . , P.sub.ak2i, Q.sub.ak2j, P.sub.ci, Q.sub.cj, P.sub.di, and Q.sub.dj } are determined by using the least square method so that the sum of the square of the errors between the filter coefficients calculated by using non-liner polynomials and the filter coefficients of digital filter having known characteristics becomes the least or the minimum. A CPU 11 calculates the filter coefficients non-linearly by using the constants stored in the memory 13, and sets the results to the digital filter 15 when new pass band position data x or pass band width data y is input at knobs SC and SW.

Digital filter system

Data from an A/D converter is supplied to a fixed-point DSP. The fixed-point DSP adjusts the level of the data x so that computed results do not exceed .+-.1. In succession, for the i-th data x.sub.i, the fixed-point DSP computes cos .pi..multidot.x.sub.i when i=1, 5, . . . , -sin .pi..multidot.x.sub.i when i=2, 6, . . . , -cos .pi..multidot.x.sub.i when i=3, 7, . . . and sin .pi..multidot.x.sub.i when i=4, 8, . . . and outputs a digital phase modulated signal y(t) by outputting the computed results in order. Trigonometrical functions are computed by expanding them to a series so that the intermediate computed results do not exceed .+-.1.

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Osaka, Japan

Michio Nakajima