U.S. Philips Corporation

Nxp B.v.

Koninklijke Philips Corporation N.V.

Joachim C Brilka

Wolfgang Weltersbach

Axel Kattner

Thomas Hafemeister

Ernst-Peter Ragosche

An arrangement is described for demodulating a vestigial sideband signal component contained in an amplitude-modulated frequency signal, and preferably in a vision intermediate-frequency signal derived from a television signal. What distinguishes the invention is that there are provided two parallel, preferably identical, mixing stages () that operate at a phase shift of substantially, and preferably exactly, 90&#xb0;, of which mixing stages a first one () produces from the frequency signal a first output signal and a second one () produces from the frequency signal a second output signal that is phase shifted by substantially, and preferably exactly, 90&#xb0; relative to the first output signal, a downstream phase-shifter () that causes a phase shift between the first and second output signals from the mixing stages () of substantially, and preferably exactly, a further 90&#xb0;, an adder () that adds together the output signals from the phase shifter (), which output signals have been phase shifted relative to one another by substantially, and preferably exactly, 180&#xb0;, a local oscillator () that drives the mixing stages with a phase shift of substantially, and preferably exactly, 90&#xb0;, and a setting device for setting the frequency and phase of the local oscillator (), the setting device setting the frequency and phase of the local oscillator () substantially, and preferably exactly, to the frequency and phase of the frequency signal.

Arrangement for demodulating a vestigal sideband signal

The invention relates to a compensation circuit for filters of a video signal receiver. To compensate a non-linear amplification of a small signal in dependence upon the control of a large signal which is superimposed on the small signal, the invention proposes to detect the control of the large signal and to vary the working point of the filter in dependence upon the control of the large signal. Since the filter amplifies the small signal differently in dependence upon the position of the working point, the non-linearity of the filter can thereby be compensated.

Compensation circuit for frequency filters

In order to improve a circuit arrangement () and a method of controlling at least one transistor (), especially of controlling the resistance value of at least one MOS transistor with vanishing DC modulation in such a way that a compensation of resistance variations without control deviation is also possible for the case where the transistor () is operated with a vanishing DC voltage, i.e. with a zero DC voltage and indeed without the aid of a reference frequency, it is suggested that in addition to at least a first reference element (), which has at least a first reference transistor () with a first offset from the operating point, at least a second reference element () is provided which has at least a second reference transistor () with a second offset from the operating point equal in value but opposed in sign to the first buffer storage, wherein an in particular arithmetic average can be formed from the first offset and the second offset for approximating and achieving an optimum operating point.

Circuit arrangement and transistor control method

A down-converter for processing frequency signals, preferably received, particularly digital, television signals, comprising two, preferably identical mixer stages () for down-converting the signal, a local oscillator () controlling the mixer stages by a 90&#xb0; phase shift, a complex filter () which couples the output signals of the mixer stages () by means of a complex filtering method in such a way that the signal components outside a predetermined useful band are substantially suppressed, an adjusting device () for adjusting the frequency of the local oscillator () and a subsequent low-pass filter.

Down-converter

A circuit arrangement for demodulating an intermediate-frequency video signal, comprising a video demodulator ( ) and a phase-locked loop ( ) formed as a Costas loop, in which an output signal of a controllable oscillator ( ) arranged in the Costas loop and the intermediate frequency video signal are coupled to the video demodulator ( ), should always supply a demodulated video signal of a predetermined polarity, independent of overmodulation occurring in the intermediate-frequency video signal. To this end, this circuit arrangement is characterized in that a polarity inverter ( ) is provided, which is preceded by the video demodulator and by means of which the polarity of the demodulated video signal is invertable in dependence upon a control signal supplied by a polarity detector ( ), and in that the polarity detector ( ) determines the polarity of the output signal of the video demodulator ( ) or of the polarity inverter ( ) and, in dependence upon the determined polarity, controls the polarity inverter ( ) by means of the control signal in such a way that the demodulated video signal at the output of the polarity inverter ( ) has a predetermined polarity.

Circuit arrangement for demodulating an intermediate-frequency video signal

For an optimal adjustment of the filter frequency of a signal filter, independently of external influences, process spreads and temperature fluctuations, a filter circuit for filtering at least one sound carrier in a composite video signal by at least one signal filter ( ) having at least one filter frequency which is adjustable in dependence upon a control signal, is characterized in that the filter circuit ( ) includes a reference filter ( ) whose filter frequency is adjustable in dependence upon the control signal and which shifts the phase of a reference signal applied thereto by a defined value when tuning the filter frequency to the frequency of said reference signal, in that a phase comparator ( ) is provided which receives the output signal of the reference filter ( ) and the reference signal, in that the control signal is derived from the output signal of the phase comparator ( ) in such a way that the reference filter ( ) is tuned to the frequency of the reference signal, and in that an output signal of a controlled oscillator ( ) of a phase-locked loop ( ) is used as a reference signal which serves for demodulating a sound signal modulated on the sound carrier and whose controlled oscillator ( ) supplies an output signal at the frequency of the sound carrier in the locked state of the phase-locked loop ( ).

Filter circuit

An IF demodulator circuit with IF gain control at a variable time constant, which receives an IF carrier including synchronizing pulses, a black porch and picture information with a positively modulated picture signal, in which the IF picture signal is amplified to a nominal amplitude value by the gain control, and which includes an IF demodulator (3) which demodulates the IF picture signal and supplies a picture signal from the output, while, for a gain control which is independent of DC offsets that may occur in the picture signal, the demodulator circuit is constructed in such a way that a black level detector (8) for generating a black level signal used as a threshold value signal in conformity with the amplitude value of the black porch of the picture signal supplied by the amplitude demodulator (3) is provided, that a DC offset circuit (4) is provided, which raises the DC component of the picture signal and/or lowers the DC component of the threshold value signal in such a way that both signals are offset by a predetermined value relative to each other, that a comparator circuit (7) is provided which receives the two signals which are offset relative to each other, in which signals the comparator circuit compares the voltage value of the synchronizing pulses occurring in the picture signal with the voltage value of the threshold value signal, and that the comparator circuit (7) supplies a comparison signal in dependence upon this comparison, in dependence upon which comparison signal the time constant of the gain control is changed.

IF demodulator circuit with variable IF gain control

An oscillator (1) includes first frequency-determining elements (13-16) for providing a first oscillation frequency, at least second frequency-determining elements (23, 24) connectable to the first frequency-determining elements (13-16) via at least a switching diode (25, 26) for adjusting the oscillator (1) to a second oscillation frequency, the oscillator further having a supply circuit (27-44, 54) which includes at least a controllable current source (27-30), the supply circuit being coupled to the switching diode (25, 26) for optionally switching the switching diode between a conducting state and a blocked state, and having a current source (4) feeding the oscillator (1). In this oscillator, an improved operating behavior is achieved in that the current source (4) feeding the oscillator (1) is switchable by the supply circuit (27-44, 54), jointly with the connection of the controllable current source (27-30) to a supply current which is dimensioned with respect to a current available from the controllable current source (27-30) in such a way that influences exercised on the operating point and the oscillation amplitude of the oscillator (1) are at least substantially compensated by the connection of at least one of the second frequency-determining elements.

Oscillator

Circuit arrangement for demodulating a video signal (IF signal) which is frequency-modulated on an intermediate-frequency carrier oscillation, including a first demodulation stage (a frequency or phase demodulator) for multiplicatively combining the IF signal with a carrier oscillation of a controllable oscillator and for supplying a first output signal, a second demodulation stage (a frequency or phase demodulator) for multiplicatively combining the IF signal with the carrier oscillation phase-shifted by a quarter period of the intermediate-frequency carrier oscillation, and for supplying a second output signal, a first filter stage for low-pass filtering the first output signal and for supplying a third output signal, a multiplier stage for multiplicatively combining the second output signal and the third output signal to form a fourth output signal, a superposition stage for forming a seventh output signal by additively combining a fifth output signal and a sixth output signal derived from the second output signal and the fourth output signal, and a second filter stage for deriving a control signal from the seventh output signal for controlling the frequency and/or phase of the controllable oscillator. To ensure a reliable operation, also upon overmodulation, this circuit includes a first coefficient member for deriving the fifth output signal from the second output signal, and a second coefficient member for deriving the sixth output signal from the fourth output signal, the signal applied to each coefficient member being multiplied by a predeterminable coefficient (k1, k2) for forming the signal derived therefrom, wherein the coefficient (k1) of the first coefficient member being chosen is larger than the coefficient (k2) of the second coefficient member.

Circuit arrangement for demodulating a video signal

A circuit arrangement for demodulating the sound signals in a television signal is described, which circuit arrangement ensures a simple and low-cost structure, also for operation at different transmission standards. To this end, the circuit arrangement according to the invention includes an oscillation-generating stage which derives a (first) oscillation from a television signal (IF television signal) modulated on a first intermediate-frequency carrier oscillation, whose frequency corresponds to the frequency of an intermediate-frequency picture carrier oscillation in the IF television signal and encloses a phase angle of at least substantially 90.degree. with the picture carrier oscillation, a (first) mixer stage, a first input of which can receive the (first) oscillation, and a switching device for optionally applying the IF television signal or a sound signal (IF sound signal) modulated on a second intermediate-frequency carrier oscillation to a second input of the (first) mixer stage.

Circuit arrangement for demmodulating the sound signals in a television

Oscillator having first frequency-determining elements provided for a first oscillation frequency. In order to provide an oscillator, particularly for use in video signal processing, which can be switched and tuned to at least two oscillation frequencies, at least a second frequency-determining element is provided which can be connected to the first frequency-determining element for adjusting the oscillator to a second oscillation frequency.

Oscillator with switchable varactor diodes

In order to minimize signal influences on the reference potential in a rail-to-rail amplifier arrangement this arrangement comprises a first differential amplifier which comprises a first and a second transistor whose emitters are coupled to a reference potential via a common first resistor, the collector of the first transistor forming the output node of the amplifier arrangement, a second differential amplifier to whose input side the input signal of the amplifier arrangement is applied, whose output side is coupled to the base of the first transistor of the first differential amplifier, and having an inverting input coupled to the output node of the amplifier arrangement, a first current mirror circuit having an input transistor to which a reference current is applied, having an output transistor which is formed by the second transistor of the first differential amplifier, and having the emitter side of both transistors coupled to a reference potential, and a second current mirror circuit to whose input side the output signal of the first current mirror circuit is applied and whose output side is coupled to the output node of the amplifier arrangement, which second current mirror circuit has two transistors coupled to a supply potential at the emitter side, which transistors are scaled in such a manner that the current supplied by the amplifier arrangement at its output side is twice as large as the input current applied to the arrangement.

Amplifier arrangement having a relatively stable reference potential

In a circuit arrangement for amplifying a television signal, having, arranged between an input (2, 3) and an output (6) , a differential amplifier (1) comprising two emitter-coupled transistors (101, 102), high linearity and stability is obtained in spite of a low supply voltage, a high drive and manufacture in a method which produces transistors with a comparatively low 'Early-voltage', by a combination of at least one ohmic resistor (103, 104; 202) arranged in the emitter branch of the transistors (101, 102) and a resistive feedback network (7) for feeding back a signal from the output (6) to the input (2, 3).

Circuit arrangement for amplifying a television signal

In a synchronous demodulator for demodulating a carrier signal modulated with a useful signal, the demodulator including a filter circuit (2) for selecting the carrier signal, a limiter (3) for generating an amplitude-limited reference signal from the carrier signal, a phase shifter (4) for shifting the phase of the reference signal through a phase angle of essentially 90.degree. with respect to the carrier signal, and a multiplier (5) for multiplicatively combining the modulated carrier signal with the phase shifted reference signal, a simple arrangement effectively suppresses interference phase modulations, in that a dc mixing product is supplied (via 8) by the multiplier (5) as a measure of the frequency deviation of the carrier signal from the pass frequency of the filter circuit (2) as a control signal to this filter circuit for the purpose of controlling the pass frequency.

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Hamburg, Germany

Joachim C Brilka