DE2460264A1 - CIRCUIT ARRANGEMENT FOR PROCESSING AN AMPLITUDE-MODULATED SIGNAL - Google Patents

Description

TLA: RCA 65,134 7743-74 Dr.v.B / S

US Serial Ho. 429,673
Filed: December 28, 1973

EOA Corporation, Hew York . NY, V.St.A.

Circuit arrangement for processing an amplitude-modulated Signals

The present invention relates to a circuit arrangement for processing an amplitude-modulated signal with an amplitude demodulator whose input circuit is connected to a Source for a carrier wave amplitude-modulated with an information signal, which may be accompanied by interference pulses, is coupled and whose output circuit is responsive to the glitches and provides an output signal that is a demodulated Information signal and interference pulses which have a first and a second polarity with respect to the information signal contains and with a circuit arrangement ("consumer") for utilizing the demodulated information signal.

In particular, the invention relates to video amplifiers for television sets that use a synchronous demodulator as a video demodulator and in particular circuitry for eliminating "whiter-than-white signals" caused by the television signal accompanying glitches can be caused and otherwise components appearing in the reproduced image Output signal of the demodulator would occur »

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It is known that synchronous demodulators with excessive Carrier or product demodulation work, a greater demodulation linearity compared to envelope curve demodulators, Have freedom from cross-modulation and insensitivity to interference? they are therefore often called in television receivers Video demodulators used for amplitude-modulated picture carriers. By using a synchronous demodulator as a Video demodulator will also reduce the risk of picture interference Beatings between the tone and color carrier (e.g. at 920 kHz in the case of the NTSC Uorm) and due to herringbone-like interference patterns creating beats between the audio and video signals can be reduced. When using a synchronous demodulator the IF filters with regard to avoiding the tone-color beats The requirements are lower and a better phase response can be achieved in the video IF amplifier section will. This in turn results in a better transient response in the color demodulator and amplifier part of a color television receiver.

In certain television systems which operate with an amplitude-modulated picture carrier, the behavior of a synchronous video demodulator is when receiving interference pulses, not as cheap as that of an envelope demodulator. An envelope The video demodulator rectifies the peaks of the interference pulses, so that when a negative image modulation is used Interfering signals running in the black direction arise, which are generally not considered to be so annoying for a viewer be considered. On the other hand, a synchronous video demodulator does not rectify interference pulses, but rather the Interference pulses are demodulated as a disruptive component in the middle of the band, which is concentrated in the area around 2 MHz, for example and contains signal parts running alternately in the black direction and in the white direction. The one in the white direction However, running parts of the interference signal component are considered to be significantly more disruptive to a viewer than those in the black direction running parts. In addition, with synchronous demodulation of glitches, signal peaks occur that

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go into the whiter-than-white area and possibly a defocusing effect of the electron beam ("blooming"), thus, the size of the whiter-than-white spots in the picture still gets bigger and these spots become even more annoying.

It is already known in synchronous video demodulator circuits To take measures to eliminate the glitches running in the white direction. With one from the TJS-PS 2,861,180, the whiter-than-white video signals appearing at the output of a synchronous video demodulator perceived and the whiter-than-white parts of the video signal are cut off.

Also the measure to identify whiter-than-white disorders and to reverse them in black that used in British television technology It is common to work with positive modulation and with envelope curve video demadulators whiter-than-white-

Glitches occur, can be used with synchronous video demodulators modify.

The present invention is based on the object of a simple, reliable and effective circuit arrangement to remove interference pulses running in white direction from the output signal of an amplitude demodulator. · '

The invention is based on a circuit arrangement which contains a demodulator for carrier oscillations with a Message or an information signal are amplitude-modulated and accompanied by interference pulses and can be disturbed. The amplitude demodulator has an input circuit coupled to a source for the carrier oscillations and an output circuit, at which the recovered message or the demodulated information signal is available. The demodulator responds to interference pulses in such a way that the message recovered in the output circuit or the demodulated information signal Contains interference pulses of a first and a second polarity with respect to the message or the information signal.

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According to the invention, the recovered message or the demodulated information signal that the interference pulses contains different polarities, processed in a common signal processing circuit, which has an even-numbered Including number of signal versions of the recovered message or of the demodulated information signal the glitches of the one (first) polarity and an un even number of signal inversions of the glitches causes another (second) polarity.

In the following, exemplary embodiments of the invention are explained in more detail with reference to the drawing:

FIG. 1 shows a block diagram of a television receiver with a circuit arrangement according to the invention;

FIG. 2 shows a circuit diagram of an embodiment of a common signal processing circuit according to an embodiment of the invention;

Figure 3a, b and c graphical representations of the time course of signals in the television receiver according to Figure 1 occur and

FIG. 4 is a circuit diagram of a video demodulator according to an embodiment of the invention.

The television receiver 100 shown in simplified form in FIG has an antenna 101 for receiving television broadcast signals, which are transmitted by an RF amplifier 103 »a frequency converter 105, which usually contains a mixer and oscillator circuit, and an IF amplifier 107 which sends an IF signal for demodulation to a synchronous video demodulator 109 supplies. The demodulated video signal generated by the video demodulator 109 is transmitted via a circuit arrangement 127i which contains a video amplifier and a "white stage", a sync pulse separator stage 111 and a video section fed. The separation stage 111 supplies separated line and image synchronizing pulses to a line deflection part 113 or

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Image deflection part 115 around the generated by these deflection parts Synchronize signals with the received television signal. The deflection parts supply deflection voltages to a deflection coil set 117 for a picture tube 119. The Abtennstufe 111 supplies the separated synchronization pulses also to an AGC circuit 120, the gain of the amplifier 103, 107 such controls that the video demodulator 109 is a relatively constant Input signal received. A reference generator 129 is also coupled to the synchronous video demodulator 109, which is a Demodulation reference signal supplies, e.g. a continuous oscillation of 45.75 MHz, which is used for synchronous demodulation of the modulated video IF signal from the video IF amplifier 107 is used. A phase detector 110 is connected between the reference generator 129 and the frequency converter 105 in order to measure the frequency band to keep the output signal of the video IF amplifier centered at 45.75 MHz that the frequency converter 105 is readjusted in the usual way. The one coupled to the output circuit of the video amplifier in circuit arrangement 127 Video part 121 typically contains luminance channel amplifiers and in a color television receiver also a color demodulator and amplifier circuit. The illustrated amplifier 100 also includes a sound section 131 and a loudspeaker 133 for reproducing the sound information.

Part of a particularly suitable circuit for use in the one containing the video amplifier and the white level Circuit arrangement 127 is shown in FIG. These Circuit has a video amplifier input terminal 212, which is coupled to an input transistor 201, the base of which, The collector and emitter are labeled B, ö and E, respectively. The collector 0 of the input transistor 201 is through a resistor 202 coupled to a source of voltage + V. The connection between the collector O dee transistor 201 and resistor 202 is to base B of a second transistor 204 coupled. The emitter E of transistor 201 is connected to the collector of a # s third transistor 205, the

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serves as a current source for the input transistor 201. Of the The collector of the second transistor 204 is coupled to the source for the operating voltage + V via a resistor 203. The connection between the collector of the transistor 204 and the resistor 203 is connected to an output terminal 213, at which an output signal dependent on the input signal is available. The emitter of transistor 204 is connected to a coupled to ground and another reference potential, the circuit point containing the transistor 204 To complete the operational amplifier stage. The transistor is used to bias and set a desired current 205 associated with resistors 206, 207 and 208, which are connected in the manner shown in FIG.

When operating the television receiver shown in Figure 1 and the circuit shown in Figure 2, the synchronous video demodulator 109 an IF signal is supplied, which is a between Frequent carrier oscillation with the desired video information is amplitude modulated, and contains unwanted glitches.

FIG. 3a shows a typical line interval of the modulated video IF carrier wave as it is supplied from the video IF amplifier 107 to the synchronous video demodulator 109. In the drawing, only the envelope curve of the modulated carrier oscillation is shown, while the course of the carrier oscillation itself is not shown because this is not possible due to the high frequency on the time scale used. An interference pulse 50 is shown between the times t _Q and t _f. For the sake of clarity, the time scale in FIG. 3 is stretched during the duration of the interference pulses.

Figure 3b shows a typical response of the synchronous video demodulator 109 modulated to the one shown in FIG. 3a Video IF carrier wave. The glitch 50 lets in so-called doublet 55 arise, one in the black direction running part 56 (hereinafter referred to as relatively negative should be designated) and one running in the white direction

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Part 57 (which will be referred to as relatively positive in the following) contains. Longer duration glitches became several Cause spurious oscillations in the output signal of the video demodulator 109. The whiter-than-white that goes beyond the white value 58 Part 57, if not eliminated, results in conspicuous disturbances, which appear as white spots in that of the picture tube 119 displayed image appear.

The course shown in Figure 3b is caused by the transistor 201 (Figure 2) amplified and normally inverted. The transistor 204 then effects a further amplification and renewed inversion of the input signal.

Figure 3c shows the output of the video amplifiers and White level circuit 127. The part 56 running in the black direction remains directed further into the black, the however, whiter-than-white part 57 is inverted only once

as part 57 * shows. To understand how the in positive direction impulse only once, the remainder of the oscillation shown in Figure 3b including the in negative-going interference pulse part 56 is inverted twice, it is necessary to change the behavior of the stage with the input transistor 201 under the influence of large negative and positive input signals as they go through the interference signal doublet 56, 57 are shown in the signal curve according to Figure 3 to examine. If the Elngarig transistor 201 an oscillation component running in the negative direction, such as the interference pulse part 56 is supplied, occurs Gain and inversion according to the gain and limiting behavior of the stage with the input transistor 201. Input transistor 201 is for substantially linear amplification of the full range of video signals between "sync peaks" and the white level normally biased / If a positive-directional vibration component, such as the interference pulse 57, fed to the input of the input transistor 201 becomes, the increasingly positive voltage has the consequence that the transistor 201 saturates and the transit gate 201 · am

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Base-collector junction is biased in the flow direction. The forward bias of the base-collector junction of transistor 201 creates a Darlington circuit equivalent Circuit of transistors 201 and 204. That is, the saturated transistor 201 contains the strongly positive parts of the Passes the input signal without inversion. The circuit as The whole is then for the duration of the positive disturbance pulse a step that is inverted only once and this positive pulse therefore appears in the output signal as a negative or black component 57 '(see FIG. 3o).

So if the through the IF amplifier 107 to the synchronous video demodulator 109 is accompanied by interference pulses, the synchronous video demodulator delivers 109 is a demodulated video signal that contains components reaching the whiter-than-white range. Without corrective action these portions of the demodulator output would produce white spots on the picture tube 119 screen.

The video amplifier and whitening circuit 127 (FIG. 2) operates as a common signal processing circuit, the one Amplification of the video demodulator output signal, as it is necessary for proper functioning of the video part 121, causes and at the same time the interference impulse response of the demodulator output signal extending into the whiter-than-white area inverts into black-directed signals, so that the appearance of white spots in the one on the screen the image displayed on the picture tube 119 is prevented.

Figure 4 shows a practical embodiment of the Invention, the synchronous video demodulator 109 and a video amplifier and white stage circuit coupled with this 127 contains.

Terminals 210, 211, 212 and 213 of the circuit arrangement according to Figure 4 correspond to those with the same reference numerals designated terminals in Figure 1 and 2. For the implementation

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an integrated circuit .25 is expediently used in the circuit arrangement 127. The commercially available integrated circuit OA 3031/702, which is available from ROA Corporation, Somerville, Ή, J., V.St.A. will be produced. The terminals of the amplifier 25 shown in FIG. 3 correspond to those of the circuit OA 3031/702.

In order to ensure that the amplifier 25 only inverts the white pulses only once, when using a commercially available integrated circuit, such as type OA 3031/702, the bias voltages, Control and input signal levels and external impedances are correctly measured. With the circuit arrangement according to FIG. 4, the amplifier 25 is switched and phase compensated in accordance with the manufacturer's recommendations.

In order to extend the frequency range of the amplifier above 5 MHz, a lead-Naoheil compensation in the form of a capacitor 27 is used. In order to enable a relatively large high-frequency output signal swing despite a capacitance 28 acting parallel to the output, a resistor 29 is connected between the output terminal 7 and the negative operating voltage terminal (ground). The input bias voltage and reference voltages of the amplifier are generated by means of a voltage divider with resistors 31, 32 and 33 which are connected to an operating voltage + V. The reference potential of the amplifier (terminal 1) is typically 0.3 volts more negative than the DC voltage at one of the two signal input terminals 2 and 3. The input signal is typically a video signal with an amplitude of 100 ®Nqq. In typical cases, glitches of both polarities with amplitudes on the order of several volts can occur. The output impedance of the video demodulator 109 can be 100 to 200 ohms in typical cases. Interference pulses of the amplitude mentioned are able to overdrive the amplifier 25 so that

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that the intended negative feedback (resistor 24) no longer compensates for the signal current at the inverting input 2 able. Negative or black-running impulses then reverse the bias of the input circuit (transistor 201 in Figure 2) and generate a positive pulse with an amplitude determined by the pulse frequency and the response time (Time constant) of the amplifier is determined. Positive or white pulses cause saturation or forward bias of the input circuit (transistor 201 in FIG. 2), which results in the desired non-inversion, i.e. inversion-free Signal transmission in the input stage, results. The amplitude of the positive impulses is also corresponding Way determined by the pulse frequency and the amplifier time constant.

The circuit arrangement according to FIG. 4 thus works in short, so that the desired useful output signal from the video demodulator 109 is passed through the amplifier 25 (which in the case of the specified type is a differential amplifier with the transistors 201 and 204 according to Figure 2) is inverted and amplified. Impulses running in negative direction in the demodulated signal are inverted and limited by the amplifier, while signals running in the positive direction are limited by the amplifier, but not inverted.

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Claims (9)

Patent-a η spriiche Circuit arrangement for processing an amplitude-modulated signal, with an amplitude demodulator, whose Input circuit with a source for a carrier wave that is amplitude-modulated with an information signal and caused by interference pulses can be accompanied, is coupled, and whose output circuit responds to the glitches and an output signal provides a demodulated information signal and glitches, which have a first and a second polarity with respect to the information signal, and with a consumer for the demodulated information signal, characterized in that that the output circuit of the amplitude demodulator (109) with the consumer (121) via a Composite signal processing circuitry (127) is coupled which provides an even number of signal inversions of the recovered Information signal including the interference pulses (56) of the first polarity and an odd number of signal inversions the interference pulses (57) of the second polarity caused. 2. Circuit arrangement according to claim 1, characterized characterized in that the signal source (107) is a Carrier wave amplitude-modulated with a video signal supplies. 3. Circuit arrangement according to claim 1 or 2, characterized in that the source (107) supplies a carrier wave with a negatively modulated video signal, which synchronizes signals that extend over extend out a black level and contain a white level which corresponds substantially to the carrier value 0 and of Accompanying interference pulses (50) running in the black direction is (ligur 3A). 509828 / 0S65 4. Circuit arrangement according to claim 1, 2 or 3, characterized in that the amplitude demodulator a synchronous demodulator (109) is, which from the carrier waves a demodulieotes information signal, whose Amplitude fluctuations with respect to a predetermined polarity of a reference value, and generated at the output interference pulses of first and second polarity (57 and 56, respectively) with respect to the reference value supplies. 5. Circuit arrangement according to claim 1, 2, 3 or 4 »characterized in that the composite signal processing circuit contains cascade-connected amplifier stages, a first of which (201) for input signals (57) a first polarity with respect to a reference value in the saturation state and, in the case of input signals (56), a second polarity Polarity works essentially linearly. 6. Circuit arrangement according to claim 5 »characterized in that the amplifier stage in Cascade circuit a bias voltage arrangement (205) for operating the first amplifier stage with input signals (57) of the first polarity in saturation mode and in the case of input signals (56) of the second polarity in substantially linear. operation contains. 7. Circuit arrangement according to claim 5 or 6, d a duroh characterized in that the cascade switched amplifier stages a first transistor (201) and a second transistor (204) each with base, emitter and collector electrode that includes the base electrode of the second transistor with the collector electrode of the first Transistor is coupled; that the first transistor is biased to have input signals fed to its base drive the transistor into saturation as the input signals have a first polarity, while input signals of a second polarity are essentially linear 509828/0565 be working; and that the second transistor (204) is connected as an inverter. 8. Circuit arrangement according to claim 4, characterized marked that. the synchronous demodulator output signal a video signal with synchronization signals on a black level and a white level represented by a reference value and that the interference output pulses (56 and 57), which correspond to an input interference pulse (50), run both in the black direction and in the white direction. 9. Circuit arrangement according to claim 5, 6 or 7, characterized in that the composite signal processing circuit (127J FIG. 2) a differential amplifier (201) which is coupled to a signal inverter stage (204) is, contains. 509828/0565 Blank page