Abstract: Arrangement for decoding a stereo multiplex signal, having a baseband stero signal (L+R), a stereo difference signal (L-R) which is amplitude-modulated on a suppressed sub-carrier, and a pilot signal having a frequency located between the frequency bands of the two signals, the arrangement having an input for the stereo multiplex signal and left and right stereo signal outputs, the input being coupled both, via a pilot selection circuit, to a phase-locked loop for regenerating the sub-carrier and to a multiplier circuit for multiplying at least the modulated stereo difference signal by the regenerated sub-carrier. In order to improve the stereo channel separation, the pilot selection circuit includes a bandpass filter of the switched capacitor type, a clock input of which is coupled to an output of an voltage-controlled oscillator incorporated in the loop.

Abstract: A digital demodulator demodulates and separates the individual components of a digitized stereo multiplex signal which contains a narrowband information channel at three times the pilot signal frequency. Demodulation is accomplished by means of five digital demodulators to which respective carriers are applied from a carrier conditoning circuit. Each carrier has a frequency of the pilot signal frequency, twice the pilot signal frequency or three times the pilot signal frequency. The carriers are generated as data word sequences which contain only the values +1, -1 and 0. The sampling interval for the remaining carrier is 60.degree., beginning from 0.degree.. The signal sampling frequencies are adapted to the different sampling frequencies of the carriers by means of decimation circuits. Each of the six components is freed from interfering adjacent signals by a low-pass filter.

Abstract: A charge pump arrangement receives a digital error word representing an error signal and charges or discharges a capacitor in accordance with the sign of the error word by an amount that is proportional to the absolute value of the error word. The voltage produced in the capacitor is coupled to a frequency control terminal of a voltage controlled crystal oscillator that is used in, for example, a stereo decoder.

Abstract: A method and a circuit arrangement for receiving frequency-modulated stereo multiplex signals is disclosed in which the channel to be received is converted to the zero IF using negative feedback for reducing the frequency deviation in the IF band. The conversion takes place in a quadrature converter stage, and adjacent-channel selectivity is provided by low-pass filtering the two outputs of the quadrature converter stage, with the slopes of the selectivity characteristics of the two low-pass filters being relatively slight and lying partly in the zero IF band. The amount of the average attenuation of the frequency-modulated stereo subcarrier signal is equal to the amount of the reduction of the frequency deviation of the frequency-modulated main-channel signal. The negative-feedback signal is the demodulated main-channel signal, the amount of negative feedback being determined by an amplifier in the negative-feedback path.

Abstract: A stereo signal separation system for separating the L+R and L-R components of a BTSC stereo signal mixes the BTSC signal with a multiple of the pilot frequency. To recover the L+R component the mixer output is combined with the input BTSC signal, and to recover to L-R component the mixer output is combined with a second mixer output shifted ninety degrees. The combined output is low pass filtered to recover the desired component.

Abstract: A radio receiver most suitable for use in a car includes a pulse count demodulating circuit and a second demodulating circuit other than a pulse count detecting circuit so that a demodulation signal from selected one of the demodulating circuits is supplied according to the level of a detection signal supplied from a received electric field intensity detecting circuit.

Abstract: A stereo decoder is provided for decoding an encoded stereo signal. In one form, the encoded stereo signal is digitized and coupled to two sampling circuits. By selectively sampling the encoded signal relative to a stereo pilot signal contained in the encoded signal, both a left-hand audio signal and a right-hand audio signal may be separately recovered from the encoded signal and latched. A phase locked loop monitors the phase of the stereo pilot signal relative to the encoded signal and controls the time sampling of the encoded signal at predetermined phases of the pilot signal. The stereo decoding may also be performed by using analog circuitry to directly time sample the encoded stereo signal. In an analog approach, the time sampled output signal must be low pass filtered to provide decoded stereo output signals.

Abstract: An L+R separation system separates the L+R component of a composite stereo signal, such as a BTSC signal or an FM broadcast stereo signal, from the L-R suppressed subcarrier component by sampling the composite stereo signal at a rate which is twice the frequency of the L-R component subcarrier frequency. The sampling signal, which is derived from the composite stereo signal, is synchronized with the subcarrier frequency such that the sampling occurs at the zero crossings of the subcarrier frequency, eliminating the L-R component from the sampled output. A simple lowpass filter recovers the L+R component.

Abstract: A composite FM stereo multiplex signal is demodulated using a double-balanced switching circuit cooperating with current mirror circuits so that demodulation and separation of the multiplexed signals occurs in the current domain. The switching circuit receives a switching signal that is a sub-carrier frequency of the FM stereo multiplex carrier signal, and the switching circuit is provided with the composite stereo signal as a output current signal from a first current mirror circuit. Outputs from the switching circuit are then fed to respective left and right channel current mirror circuits where the current output signals therefrom are substracted in respective current difference circuits from the composite current output signal produced by the first current mirror circuit, thereby producing left and right channel stereo signals having predetermined separation and signal-to-noise ratio.

Abstract: A clock-controlled filtering arrangement for suppressing a number of interference frequencies related to a clock frequency, which comprises a time-discrete comb filter included in a negative feedback loop for a selective negative feedback of the said interference frequencies, which time-discrete comb filter is connected to an output of a clock generator for controlling the frequency location of the pass ranges of the comb filter. In order to avoid on the one hand the introduction of quantizing noise and the use of additional circuits, such as A/D and D/A converters, and on the other hand the occurrence of error cumulation while maintaining an adequate interference suppression, the time-discrete comb filter is of the switched capacitor N-path filter type.

Abstract: A demodulator circuit for demodulating a signal which varies substantially sinusoidally with time, such as a stereo signal having a carrier frequency, comprises a mixer circuit having a first input with a linear transfer characteristic which receives the stereo multiplex signal u.sub.m to be demodulated and having a second input with a substantially hyperbolic tangent transfer characteristic, the second input receiving a signal u.sub.d. The signal u.sub.d is a voltage having a triangular wave shape superimposed with the triangular wave shape having the carrier frequency. A stereo output signal L and R is produced having minimal third and fifth harmonics of the carrier frequency is produced from a matrix circuit as a result of the triangular shape and amplitude of the signal u.sub.d.

Abstract: An FM stereo demodulating circuit comprising a pulse counter detector 1 for generating a pulse train signal including the frequency spectrum of the FM signal, DC biasing means for current biasing the detector output about a midpoint, a subcarrier signal generator 2 and current drivers 8, 10 for generating dual polarity biased subcarrier currents, first and second transistor pairs 3, 4, the emitters of each being connected to one of the current drivers, and the bases of the pairs being cross-connected to one of the biased detector outputs, at least one reference transistor pair whose emitters are connected to a current source 11 and whose collectors are connected to each of the biased detector outputs. The currents entering the cross-connected collectors of the first and second transistor pairs, when referenced against the currents into the emitters of the reference transistor pair, produce signals proportional to the right and left channels of the FM signal.

Abstract: Disclosed is an FM stereo demodulator in which components of the demodulated signal corresponding to odd harmonics of the subcarrier signal are eliminated.In order to prevent the production of odd harmonics, the multiplication between positive and negative sinusoidal subcarrier signals is performed with a stereo pilot signal and positive and negative pulse train signals produced by pulse detection of an FM signal.The multiplication signals are further added with each other to directly reproduce left and right stereophonic signals.

Abstract: An FM stereo demodulator having improved separation and distortion characteristics comprising a high-frequency pulse signal which is modulated by a sinusoidal subcarrier signal produced in accordance with a stereo pilot signal. The high-frequency pulse signal is multiplied with a composite signal at a multiplier so as to reproduce left and right signals without frequency components of noise. Constructed accordingly, the invention advantageously obviates the use of a low-pass filter which injects delay characteristics and reduces gain of the composite signal from an FM demodulator.

Abstract: A pulse position modulated (PPM) signal is derived from an input FM signal, and first and second switching signals are derived which are opposite in phase and correspond to alternating half cycles of the PPM signal. First and second opposite phase subcarrier signals are derived synchronized to the pilot signal in the input FM signal, and various combinations of the switching and subcarrier signals are multiplied together and the multiplication products combined to obtain left and right channel outputs.

Abstract: FM-broadcasting system comprising a FM-transmitter (1-16, 32-34) and a receiver (14-31, 35, 36) cooperating therewith, the transmission signal of which comprises a multiplex signal which is frequency-modulated on a main carrier wave, which multiplex signal comprises an audio-frequency information signal (L+R) and, in the case of a stereo transmission, a stereo information signal (L-R) modulated on a (38 kC) suppressed stereo subcarrier wave, also comprising a (19 kC) stereo pilot which is situated between the frequency spectra of the two information signals and a binary, differentially coded code signal which is phase-modulated on a (16.625 kC) code subcarrier wave which is situated outside the frequency spectra, and does not coincide with the (19 kC) stereo pilot, the receiver (14-31, 35, 36) comprising a pilot regeneration circuit (22-25) for regenerating the (19 kC) stereo pilot, the code signal having a bit repetition period which is an integral number of times the period of the (19 kC) stereo pilot.

Abstract: An FM stereophonic receiver is arranged so that a central processing unit assigned for selection of a broadcasting station is burdened, based on a clock pulse of the central processing unit, to generate sub-carriers synchronized with a pilot signal contained in a composite signal, for being used in multiplex demodulation, whereby to improve signal-to-noise ratio of the multiplex demodulated signals, and to simplify the circuit arrangement of the receiver.

Abstract: A circuit for eliminating a beat signal resulting from interference between a broadcast signal of a received station and a broadcast signal of an adjacent station during the reception of an AM broadcast. A cancel signal generating circuit for forming a cancel signal synchronized to the beat signal contained in an AM detected output signal is connected to the output of an AM detector. The cancel signal is combined with the AM detected output signal in a mixing circuit connected to the AM detector, to eliminate the beat signal. Such a beat signal cancelling circuit may be served by a pilot signal cancelling circuit in an FM receiver.

Abstract: A sampling pulse generator circuit for a stereo demodulator circuit of a sample and hold system is disclosed. The pulse generator circuit uses pilot signals of an FM stereo broadcast as an input and produces output sampling pulses, which are phase-synchronized to the stereo subcarrier but have a 180.degree. phase difference to each other. The pulse generator circuit comprises a phase lock loop circuit having a multiple number of frequency dividers arranged in cascade. Selected outputs of these frequency dividers are logically summed to produce the output sampling pulses with a predetermined and stable pulse width.

Abstract: A pulsive noise removing apparatus comprises a subtracting circuit (35) receiving one input thereto a stereo composite signal directly from a delay circuit (31). A stereo switching signal is generated as a function of a stereo pilot signal included in the stereo composite signal and a cancel signal of the same level, the same frequency and the same phase as those of the stereo pilot signal is generated as a function of the stereo switching signal. A gate (67) is interposed between the output of the cancel signal generating circuit (65) and the other input of the subtracting circuit and the gate is interrupted responsive to detection of a pulsive noise included in the composite signal. The pulsive noise is removed due to interruption of the gate and the stereo pilot signal is prevented from appearing at the output of the subtracting circuit irrespective of conduction or interruption of the gate.