Blaupunkt-Werke Gmbh

Stefan Bartels

Lothar Vogt

Jurgen Kasser

Djahanyar Chahabadi

Detlef Schwarz

Detlev Nyenhuis

Rainer Arnold

In a demodulator for a stereo signal transmitted by amplitude and phase modulation of a carrier, a phase signal and a quantity signal are formed. By multiplication of the quantity signal with the tangent of the phase signal reduced by a value to be preset, a difference signal is formed. The value to be preset is generated in such a way as to minimize the direct portion of the difference signal.

Demodulator

An improved Phase-Locked Loop (PLL) radio receiver circuit includes a phase detector, either an active loop filter or a set of parallel, alternately selectable loop filters, and a Voltage-Controlled Oscillator (VCO) whose input is connected to the output of the loop filter. The output of the VCO is fed to frequency divider. The output of the frequency divider and a reference frequency signal form the inputs to the phase detector/comparator. Toggling among the loop filters occurs such that the loop limit frequency, defined by a loop amplification of 1, is altered by this toggling without significantly changing the gradient of the amplification to the frequency, in a frequency range which includes the limit frequency.

Switchable PLL circuit with constant amplification gradient

In a radio receiver with an input circuit which can be supplied with received signals, with a mixer for deriving an IF signal, and with an IF filter, the passband range corresponds to a usable signal range of the received signal, the received signals are amplitude-modified with an auxiliary signal for detecting intermodulation, in the course of which sidebands are generated outside of the useful signal range. The amplitudes of at least one sideband generated by modulation with the auxiliary signal and of the received carrier are compared in the IF signal. In case of deviations from a ratio based on the modulation factor during modulation with the auxiliary signal, a signal indicating the presence of intermodulation is derived.

Radio receiver with an intermodulation detector

Digital tuning of a locally generated frequency supplied to a frequency converting mixer, a mobile radio receiver is provided with great economy of components by utilizing the sampling rate oscillator for an analog-to-digital converter provided at the output of an analog intermediate frequency amplifier of the receiver as the source of the difference frequency for a phase locked loop (PLL) for control of the phase of a local oscillator for the mixer or mixers. All frequencies used to supply local oscillations to mixers, as well as the operating frequency of the phase locked loop are integer number multiples of the sampling rate pulse generator. Some division stages have fixed dividers and others have divisors selectable by a tuning processor and in some of the divisor connections it is useful to interpose a fixed or selectable-factor multiplier. A sampling rate of 42.75 MHz is recommended and an intermediate frequency amplifier frequency which is a rational number multiple of 57 kHZ, preferably 10.6875 MHz are similarly recommended.

Radio receiver for mobile reception with sampling rate oscillator

A mobile radio receiver, for example, a car radio, needs a circuit to detect and suppress adjacent-channel interference. This can be done by using bandpass filters (14) of differing bandwidth. The present invention dynamically adjusts bandwidth to an optimum value by continuously comparing (13) a first signal level, upstream of the bandpass filter, to a second signal level, downstream of the bandpass filter, to derive a difference value representative of adjacent-channel interference, then uses an electronically controlled selector switch (6) to select a particular filter (14.sub.N) whose bandwidth is sufficiently narrow to cut out the interfering broadcast signal. A table associating each magnitude range of interference with a particular filter bandwidth assures that bandwidth is broadened as interference diminishes, thereby assuring sufficient reception signal strength.

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Hildesheim, Germany

Stefan Bartels