U.S. Philips Corporation

Hendrik G Van Veenendaal

Engel Roza

Yanling Sun

An oscillator is formed by a resonator (RES) coupled to an amplifier (AMP) via a coupling path (COP). In order to counter unwanted oscillations due to parasitic resonances in the coupling path (COP), the coupling path (COP) includes a series resistance (RS). This allows better performance in terms of noise for countering unwanted oscillations, despite the fact that the series resistance is in itself a source of noise. An even better noise-performance is obtained if the coupling path (COP) also includes a series capacitance. Such a series capacitance will also effectively widen a frequency range over which the oscillator can be tuned.

Oscillator having a resonator coupled to an amplifier by a series

A frequency-drift (.DELTA.F) of an oscillator (OSC) is compensated (.apprxeq.-.DELTA.F) by varying various different biassing parameters (V,I) in the oscillator. The biassing parameters (V,I) which are varied may include, for example, voltages (V) or currents (I), either exclusively or in combination, which are supplied to transistors forming part of the oscillator (OSC). The biassing parameters (V,I) may be varied as a function of temperature by one or more elements with suitably chosen temperature coefficients and/or by one or more biassing circuits which provide biassing voltages or currents which vary as a function of temperature, or both.

Oscillator frequency drift compensated by varying different biassing

An oscillator which inhibits unwanted oscillations and requires a comparatively small power supply voltage is described. The oscillator includes an amplifier transistor 110 (220), an output current of which flows into the emitter of a load transistor 120 (220) via a load signal path. The amplifier stage acquires a bandpass characteristic by a passive capacitive bootstrap signal transfer from this signal path to the base of the load transistor. The oscillator thus preferably oscillates within the passband of the amplifier stage. The amplifier stage has a comparatively large gain within the passband even without a load resistor in the load signal path. Such a load resistor would cause a voltage drop and, hence, increase the required power supply voltage.

Oscillator

A tunable oscillator circuit provided with a pair of oscillator transistors whose bases are crosscoupled to the opposite collectors, and provided with a capacitance which is arranged between the emitters of the oscillator transistors, each emitter being AC-connected via an emitter current source to a reference voltage is disclosed. In order to considerably increase the tuning range without being limited in the choice of the output amplitude, a pair of buffer transistors in common base configuration is added whose two collectors are connected via a pair of collector resistors to a supply voltage and constitute an output of the tunable oscillator circuit, said pair of buffer transistors arranged in a cascode configuration with the pair of oscillator transistors by being coupled to the collectors of the oscillator transistors.

Tunable astable multivibrator with buffer transistors

A head-end for a signal distribution system with selection facility, includes a matrix (8) and a multiplexer (12) connected thereto for forming a multiplex signal. The head-end further comprises A/D converters (4-1 to .DELTA.-N) for converting the wide-band input signals into digital signals prior to supply to the matrix. The multiplexer comprises two amplitude modulators (13, 14) for the mutual quadrature amplitude modulation of a carrier (17) by two digital signals, and a summing means (18) for adding a digital signal in the base band to the modulated signal. A signal receiver for one of the modulated signals comprises a synchronous amplitude demodulator (21) connected to a synchronized carrier source (20) and also comprises means for digital-to-analog conversion (24).

Signal distribution system

Head-end and receiver for a signal distribution system for signals having a wide frequency band and for accompanying signals having a narrow frequency band, such as the video signal and the sound signal of a television signal, respectively, digital signals being used for the distribution. The head-end comprises a first (4) and a second (5) A/D-converter for the signal having the wide frequency band and the signal having the narrow frequency band, respectively. The receiver comprises corresponding D/A-converters (13, 14). In order to avoid a specific frame structure and corresponding frame synchronization, the digital output signal of the second A/D-converter is modulated in a modulator (7) in the head-end on a subcarrier from a source (6) and thereafter added to the signal having the wide frequency band, and the combined signal is applied to the first A/D-converter (4) which is provided by a one-bit modulator. In the receiver the received digital signal is applied to a demodulator (17) via a bandpass filter (15), the demodulator output signal being applied to the second.

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Eindhoven, Netherlands

Hendrik G Van Veenendaal