FI61982B - ANORDNING FOER BEHANDLING AV AMPLITUDMODULERADE SIGNALER - Google Patents

Description

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Jgari LBJ <”) utlAggnincsskrift 6 I ytii c (45) Patent granted 11 10 1982 Patent meddelat ^ v (51) Kv.lk?/lnt.CI.3 H 04 N 5/21 (21) Patent application - Patantansttkning 3712/7 ^ (22) Hakamlspllvl - Antttknlngsdag 20.12.7 ^ * (FI) (23) Alkuptlvi — Glltlghatsdag 20.12.7 ^ (41) Tullut lulklsakal - Bllvlt offantllg 29.06.75

Patent and Registration Office (44) Nihaviks, date of issue, date of issue. -

Patent and Registration Office of the United States of America and the Public Administration of Publications 30.06.82 (32) (33) (31) Requested «« lolkeu * —Begird priorltet 28.12.73 USA (US) U29673 (71) RCA Corporation, 30 Rockefeller Plaza , New York, NY 10022, USA (72) John Barrett George, Indianapolis, Indiana, USA (7M Oy Kolster Ab (5 * 0 Device for processing amplitude modulated signals - Anordning för behandling av amplitudmodulerade signaler

The present invention relates to video amplifier circuits for use in connection with synchronous detector devices used as a video detector for a television receiver, and in particular to a device for removing harmful "whiter" counterparts from impulse noise associated with television signals.

Synchronous detectors using either a highlighted carrier or an input detector are known per se, providing improved detection of linearity, freedom from cross-modulation and noise immunity compared to envelope detectors, and have therefore been proposed for video detectors in television receivers designed to process amplifiers. Problems in producing image oscillation frequency components between audio and color value carriers (e.g., at 920 kHz when using the NTSC standard) and the "herringbone pattern" oscillation frequency component between audio and image information can be reduced using a synchronous video detector. When using a synchronous detector, 2,61982 allowed a less accurate intermediate frequency filter requirement to still avoid sound and color value jitter in the better phase detection-response video 1-f amplifier circuit. This in turn allows for a better transient response in the color value detector and amplifier portion in the color television receiver.

In certain types of systems that use image transmission amplitude modulation, the operation of a synchronous video detector during pulse noise reception is less desirable than what a curtain curve detector would have. An envelope-type video detector rectifies the peaks of the impulse noise so that if negative image modulation is used, random signals moving in the black direction are developed, which the viewer generally considers to be less harmful. The synchronous video detector does not rectify impulse noise. Instead, impulse noise is observed as a random intermediate frequency component focused, for example, at 2 megahertz, which forms an alternating part moving in the black direction and in the white direction. The white-shifting components of this random noise component are generally considered to be substantially much more annoying to the viewer than the black-shifting components. Also, whiter peaks of the mark may cause, due to the synchronous expression of impulse noise, "bursting" in which the electron beam defocuses, which increases the size of the whiter dots on the image surface and thus makes them even more disturbing.

U.S. Patent 2,861,180 describes a principle used to eliminate impulse noise moving in the white direction in previously synchronous video detector structures. An off-white video mark that develops at the output of the synchronous video detector is detected and the video mark is changed to remove this off-white component. In said patent, the character of the video is changed by cutting off its whiter portions.

Methods for detecting and inverting whiter noise than white used in British television practice, which uses positive modulation and generates impulse noise whiter than white in envelope video detectors, are also applicable to use in synchronous video detectors.

The present invention relates to an apparatus for processing amplitude-modulated signals, the apparatus comprising a carrier source (101) in which information is encoded in amplitude modulation of the carriers, said carriers being likely to be associated with and "contaminated" by pulse noise, an amplitude modulation detector (6191982). 109) having an input circuit and an output circuit coupled to said carrier source for providing the recovered information, said output circuit being operable depending on said pulse noise, said recovered information obtained from the output circuit including pulse noise having a first (56) and a second (57) polarity of said information the means for accessing the retrieved information (121).

The present invention may be better understood with reference to the accompanying drawing, in which: Figure 1 is a circuit diagram in the form of a block diagram of a television receiver incorporating the present invention.

Figure 2 is a schematic circuit diagram of a common processing apparatus according to the present invention.

Figures 3a, b and c are timing diagrams for the television waveforms shown in Figure 1.

Figure 4 is a schematic circuit diagram of a video detector system incorporating the present invention.

Referring now to Figure 1, the television receiver 100 has an antenna 101 for receiving transmitted television signals, which is then processed in a radio frequency (rf) amplifier 103, a frequency converter 105 typically consisting of a mixer and a local oscillator in combination, and an intermediate frequency (if) amplifier 107 to provide the combination. video signal carriers detected by the synchronous video detector 109. The combined video signal detected by the detector 109 is input to the synchronization separator 111 through the video amplifier and the white detector 127. The synchronization separator 111 operates by supplying the separated horizontal and vertical synchronization pulses to the horizontal sweep generator 113 and the vertical sweep generator 115, respectively, timing their sweep waveforms so that they are timed correctly with respect to the received television signals. The sweep waveforms are applied to the horizontal and vertical deflection windings 117 associated with the picture tube 119. The synchronization separator 111 also supplies the separated synchronization to an automatic power control (AGC) circuit 120 which adjusts the gains of the amplifiers 103 and 107 to maintain the sensitivity of the detector 109 . The comparison generator 129 is coupled to the synchronous detector 109 to generate a demodulation reference quantity, e.g., a 45.75 megahertz continuous reference wave 107 for synchronous detection of the i-f signal of the incoming modulated video from the video amplifier i-f. The phase detector 110 is connected between the reference generator 129 and the frequency converter 105 to maintain the output band of the i-f amplifier centered at 45.75 megahertz by adjusting the frequency converter 105 in a known manner. The output circuit of the video amplifier 127 is connected to the input circuit of the video processing circuit 121, which precedes the picture tube 119. The video processing circuit 121 typically includes light channel amplifiers, and in color receivers it also includes a chrominance detector and an amplifier circuit. The illustrated receiver 100 also includes a voice recorder circuit 131 and a loudspeaker 133 for reproducing accompanying audio information.

Part of a particularly suitable structure for use in a video amplifier and white detector 127 is shown schematically in the form of a circuit diagram in Figure 2. Referring to Figure 2, an input switch terminal 212 from a video amplifier 127 is connected to an input transistor 201 having base, collector and emitter electrodes. The collector of the input transistor 201 is connected to the voltage + V supply source by means of a resistor 202. The connection point of the collector of the transistor 201 and the resistor 202 is connected to the base of the second transistor 204. The emitter of transistor 201 is connected to the collector of third transistor 205, which acts as a power source for input stage 201. The collector of transistor 204 is connected to the supply voltage + V supply source via resistor 203. The connection point of the collector of the transistor 204 and the resistor 203 is connected to the output switch terminal 213, where the output signal as a result of the input signal is available. The emitter of transistor 204 is connected to a reference voltage point (ground) so as to supplement the operating transistor amplifier stage 204. Resistors 206, 207 and 208, which are associated with transistor 205, provide the relevant bias voltages and produce the desired current.

In use of the apparatus shown in Figures 1 and 2, an intermittent carrier amplitude modulated with the desired video information and harmful noise pulses are applied to the synchronous video detector 109.

Figure 3a shows a typical horizontal line time slot from the modulated video carrier i-f input to the detector 109 by the video amplifier 107. The envelope of this modulated carrier is indicated by an outline and the actual variations in the carrier are omitted because they occur at too high a rate to be clearly represented on the illustrated time scale. Noise pulse 50 occurs between time points tQ and tf. The time scale of these waveforms has been stretched for the noise pulse to illustrate the description.

Fig. 3b shows a typical response in a synchronous detector 109 to a modulated video carrier i-f, as shown in Fig. 3a. The noise impulse 50 develops a phenomenon represented by the dual 55 where there is a black shifting portion (which will be termed relatively negative) and a white direction shifting portion 57 (which will be termed a relatively positive portion). Longer duration noise pulses cause multiple flicker in response to detector 109. The whiter white portion 57, which rises above the white level 58, produces harmful noise if not removed, as this appears as white spots in the image produced on the picture tube 119.

The signal waveform shown in Fig. 3b is amplified and normally inverted by the transistor amplifier 201. The transistor amplifier 204 then develops further gain and performs a second inversion of the input waveform.

Figure 3c shows the output of the video amplifier and the white detector 127. The black shift portion 56 remains black but the whiter white portion 57 is inverted only once as seen from portion 57 '. In order to understand how the positive direction pulse is inverted only once while the remaining portion of the waveform in Figure 3b including the negative direction noise pulse 56 is inverted twice, it is necessary to consider the input transistor stage 201 under the influence of a large negative and positive input, representing identified as 56 and 57 in waveform 3b. When a negative waveform component such as a noise pulse 56 is applied to the input transistor 201, it is amplified and inverted according to the gain and limiting characteristics of this transistor stage 201. This amplifier 201 normally receives a bias voltage for substantially linear gain over the full range of video characters between the sync peaks and the white level. When a positive waveform component such as a noise pulse 57 is applied to the input of transistor stage 201, an increasing positive voltage causes saturation of transistor 201 and transistor 201 receives a forward voltage in the downstream direction to the collector connection. The forward voltage generation at the junction of the base and the collector in the transistor 201 develops the equivalent 6 61982

Darlington switching of transistors 201 and 204. It is to say that the saturated transistor 201 passes through a strongly positive part of the input signal without inversion. The total circuit thus becomes only a one-time inverting phase for the duration of the positive noise pulse, which occurs as a negative or black-shifting component 57 'of the output waveform (compare Figure 3c).

Thus, when the impulse noise is associated with a carrier provided by the intermediate frequency amplifier 107 to the detector 109, it operates in accordance with the detected video signal, which involves noise components as they oscillate from whiter to whiter. In the absence of any corrective hardware, the output of a whiter to whiter detector would result in white spots on the image surface of the picture tube 119.

The video amplifier and the white detector 127 act as a common signal processor, providing a video detector output gain for efficient operation of this video processing circuit 121 while inverting the white and white noise pulse response from the detector output to black, thus preventing white dots from forming on the image tube 119 surface.

Fig. 4 shows a practical embodiment of the present invention including a synchronous video detector 109 coupled to a video amplifier and a white detector 127. The switch terminals identified by reference numerals 210, 211, 212 and 213 in Fig. 4 correspond to the correspondingly identified switch terminals in Figs. 1 and 2. It is convenient to use an integrated circuit. 25 implementations of the desired video amplifier 127. A commercially available part of an integrated circuit suitable for use in the present invention as shown in the schematic diagram of Figure 2 is a CA 3031/702 integrated circuit amplifier manufactured by RCA Corporation, Somerville, New Jersey, USA. The switch terminals shown in the amplifier 25 in Figure 4 correspond to the corresponding terminals of the CA 3031/702 device.

In order to ensure the correct operation of the amplifier 25, so that only a simple inversion of the pulses moving in the white direction must be carried out, care must be taken with respect to the bias voltage, operating voltages and external impedances when using a commercially available integrated circuit such as CA 3031/702. As shown in Figure 4, the amplifier 25 is connected and phase compensated according to the manufacturer's recommendations.

Phase advance or delay compensation in the form of capacitance27 is used to increase the frequency range of the amplifier beyond 5 megahertz. In order to achieve a relatively high high frequency output oscillation capability in the presence of a bypass output capacitance, a resistor 29 is connected from the output switch terminal 7 to a negative supply point (Oona). The input supply voltage and amplifier reference voltages are obtained from a voltage divider that includes a supply source (+ V) and resistors 31, 32, and 33. The amplifier reference voltage (switch terminal 1) is typically selected to be 0.3 volts more negative than the DC voltage in either case. of the two signal inputs 2 and 3. The input signal may typically be 100 millivolts from peak to peak video signal. Typically, noise pulses of either polarity and amplitude of the order of several volts may be encountered. The output impedance from detector 109 may typically be in the range of 100-200 ohms. Such noise pulses are capable of controlling amplifier 25 to exceed its inherent feedback (resistor 24) ability to cancel the signal current at inverting input 2. Pulses moving in the negative or black direction then provide an opposite bias voltage to the input (transistor 201 in Fig. 2) and provide a positive pulse amplifier transition speed. Pulses moving in the positive or white direction saturate or bias the input in the wiring direction (transistor 201 in Figure 2), which provides the desired non-inversion at the input stage. The amplitude of the positive pulse is controlled by the pulse frequency and the transition speed of the amplifier, respectively.

In summary, the circuit of Fig. 4 operates by inverting the desired signal output from detector 109 and amplifying by amplifier 25 (which type of amplifier indicated has a differential amplifier that includes transistors 201 and 204 in the case of Fig. 2).

Pulses moving in the negative direction at the detected signal are inverted and limited in the amplifier while pulses moving in the positive direction are not inverted, but are limited in the amplifier.

Claims (6)

8 61982 An apparatus for processing amplitude modulated signals, the apparatus comprising a carrier source (101), wherein the information is encoded with amplitude modulation of the carriers, said carriers likely being associated with and "contaminated" by pulse noise, an amplitude modulation detector (109) having an output source coupled to said carrier source; to provide recovered information, said output circuit being operable depending on said pulse noise, wherein said recovered information obtained from the output circuit includes pulse noise having first (56) and second (57) polarity with respect to said information, and means for using the recovered information (121) , characterized in that the common signal processing devices (127) connect said output circuit to the operating means to add an even number of s to the stored information and the first polarity impulse noise contained therein. ignalant inversions and an odd number of signal inversions for impulse noise of second polarity. Apparatus for processing carriers negatively amplitude modulated by a video signal having synchronization signals extending past a black plane according to claim 1, wherein the white plane is represented by a substantially zero carrier and the subsequent noise pulses (50) are directed towards black, characterized in that the amplitude modulation indicator 109) is a synchronous detector for retrieving information from a carrier input source in the form of amplitude changes having a predetermined polarity with respect to a reference plane, said detector supplying at its output impulse noise having a first and a second polarity with respect to said reference plane. Carrier device according to claim or 2, characterized in that the common signal processing devices (127) comprise cascaded amplifier stages, wherein the first stage (201) of said amplifier stages operates in saturation mode with respect to input signals having a first (57) polarity with respect to the reference plane and in a substantially linear mode for input signals having a second polarity (56). Carrier device according to claim 3, characterized in that the cascaded amplifier stages comprise biasing means (205) under which the first amplifier operates in a saturation state with respect to the input signals having said first polarity (57) and substantially linearly with respect to the input signals, with said second polarity (56). Apparatus for processing amplitude modulated signals according to claim 3 or 4, characterized in that said cascaded amplifier stages comprise first (201) and second (204) transistors, each having a base, emitter and collector electrode, wherein the base electrode of the second transistor is connected to the collode of the first transistor and the first transistor has a bias in the direction that the signals having the first polarity at the base of the first transistor bring the first transistor into a saturation state, while the signals having the second polarity are processed substantially linearly, said second transistor being connected as an inverter. Device for processing amplitude modulated signals according to claim 3, 4 or 5, characterized in that the common signal processing devices comprise a differential amplifier (201) connected to a signal inversion stage (204). 10 61982