JPS6227589B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to phase-holding loops, and more particularly to television horizontal oscillation phase-holding loops used in conjunction with videotape playback devices.

A raster for a television display is formed by one or more scanning electron beams with horizontal and vertical deflection frequencies synchronized with a synchronization signal that accompanies the video signal to be displayed. Since this video signal may contain a noise component, a controllable horizontal frequency oscillator is coupled to a phase-sensitive detector, a low-pass filter, and a feedback loop to synchronize the controllable oscillator with the horizontal synchronization pulses associated with the video signal. It is common practice to provide noise insensitivity to television displays in the form of a phase holding loop in which the phase detector generates pulses representing the phase difference of . The pulses generated by this phase detector are waved by a low-frequency wave detector and then sent to the oscillator.
is applied to the control input, which maintains the oscillator frequency equal to the average sync pulse frequency.

It is often desirable to use a television display in conjunction with a videotape recording or playback device, which generally uses a plurality of playback heads, each mechanically scanning across the tape; Typically, two heads are used to alternately scan the tape for a duration equal to the vertical field period. Scanning of the next field by the second head begins substantially at the same time as scanning by the first head ends so as to avoid missing or corrupted display information; Due to slight differences in the tension on the tape or the dimensions of the mechanical tape advance mechanism, the time spacing between horizontal sync pulses in recorded information will vary during playback, particularly during head switching.
This creates a discontinuity, or paragraph, in the phase of the horizontal sync pulse used to synchronize the horizontal oscillator and control the raster, and this paragraph occurs approximately five horizontal scan lines before the end of the vertical scan period. be.

This step change in phase causes the phase-holding loop to control the horizontal oscillator to change its oscillation phase to match the changed phase of the synchronization signal, but normally the controlled oscillator is at the end of the vertical retrace period. Distortion can occur in the displayed image because the gain characteristics of the phase holding loop's low pass filter prevent it from changing as quickly as possible to readjust itself.

U.S. Pat. No. 3,740,489 to D. Willis shows an external switch that allows the user to change the characteristics of the low frequency filter of the phase hold loop when using a tape recording device. This changes the loop gain characteristics of the phase-holding loop, allowing the oscillator to change its phase or response more quickly, but the user may forget to operate this switch, allowing the image distortion described above to occur. Or, when receiving an incoming signal, the receiver may forget to return the switch to its normal position, making the horizontal synchronization of the receiver susceptible to noise.

It is also known from U.S. Pat. If a phase discontinuity occurs before the synchronization signal, the displayed image can be distorted during the last few video scan lines, and the phase hold loop is activated by the horizontal oscillator at the end of the vertical retrace period and before the beginning of the video display. There may be insufficient time to complete the response. Although the response speed can be increased by increasing the loop gain, this may result in fanning of the vertical line near the top of the vertical scan due to excessive phase holding loop gain.

A horizontal oscillation frequency control device according to a preferred embodiment of the present invention is for synchronizing a horizontal oscillator with a synchronizing pulse source capable of causing a phase change in the vertical deflection frequency, and for controlling the vertical deflection frequency supplied to the vertical deflection means. It includes a source of synchronization signals and a controllable horizontal oscillator that generates horizontal frequency oscillations whose frequency and phase can be controlled. A horizontal oscillation means is coupled to this horizontal oscillator, and generates a deflection current in synchronization with the oscillation. Phase comparator means is coupled to the horizontal deflection means and the horizontal synchronization pulse source and generates a phase control signal in response to the deflection current and the horizontal deflection pulse to represent the difference in frequency and phase between the deflection current and the horizontal deflection pulse. Controllable wave means is coupled to the phase comparison means and the horizontal oscillator to generate an averaging signal for controlling the oscillator. This wave means has variable frequency amplitude characteristics.
Control means responsive to a vertical synchronization signal source are coupled to the controllable wave means for repeatedly varying the characteristics of the wave means at vertical frequency. Further, a delay means is coupled to the control means and the vertical synchronization signal source to delay the operation of the control circuit after the appearance of the vertical synchronization signal until shortly before the appearance of the next synchronization signal.

Next, the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 shows a portion of a television receiver adapted to receive both transmitted or broadcast signals and signals from an external video signal source, such as a tape recording device. In FIG. 1, an antenna 10 is adapted to receive a television signal transmitted by a carrier wave, and a circuit 12 including a tuner, an intermediate frequency amplifier, and a video detector is coupled to the antenna 10 to detect the received signal. It is now possible to reproduce video modulation signals from. This video signal is obtained at one terminal 14a of the selection switch 14. The other terminal 14b of the switch 14 is connected to a jack 16 for an external video signal source. Selected with switch 14〓〓〓〓〓
The video signal obtained is supplied to the input terminal of a sync signal separator 18, and a horizontal sync pulse, separated from the composite video signal and shown by waveform 19, is applied to the base of transistor 22. This transistor has a total of 20
Forms one input of the phase comparator shown by . The phase comparator 20 includes two transistors 24, 26 whose emitters are both connected to the collector of a transistor 22 via a resistor 28, and whose bases are connected between the B ⁺ power supply and ground. A bias voltage is applied from a resistive voltage divider 29 consisting of resistors 30 and 32 connected to. The bases of these transistors 24 and 26 are coupled to the taps of voltage divider 29 via resistors 34 and 36, respectively. A current mirror circuit 38, whose input and output are connected to the collectors of transistors 24 and 26, respectively, is used as a differential-to-single-ended converter to form a high impedance output terminal of phase comparator 20.

The output of comparator 20 is supplied to the input terminal of wave generator 40. This wave generator 40 includes a resistor 41 and a high frequency roll-off capacitor 42 connected between the input terminal and the ground point via a connection point 43, and a connection point 4 between the connection point 43 and the ground point.
5 and a low frequency averaging capacitor 44 and a resistor 46 connected in series through connection point 4.
3 and the low impedance input terminal of the horizontal oscillator 50.
Contains 8.

The horizontal oscillator 50 has a frequency and a phase equal to that of the wave generator 4.
It is controlled by an input from 0 and generates horizontal frequency pulses. This pulse is applied to a horizontal deflection circuit 52 to control the deflection current in a horizontal deflection winding 54 associated with a picture tube (not shown). Deflection winding 54
A deflection voltage based on the deflection current of is applied to an integrator 56 coupled to winding 54. The integrator 56 forms a horizontal frequency sawtooth voltage shown by a waveform 57 from this pulsed deflection voltage, and connects it to the transistor 26 of the phase comparator 20 via a coupling capacitor 58.
applied to the base of. This sawtooth voltage 57 is compared with the horizontal synchronization pulse in the phase comparator 20,
A current pulse is formed representing the frequency and phase difference between the sawtooth wave 57 and the horizontal synchronization pulse 19.

Sync signal separator 18 also separates vertical sync signal 62 from the composite video signal selected by switch 14. This vertical synchronization signal is applied to the vertical frequency oscillator 60 to generate a ramp voltage signal synchronized therewith. The vertical frequency ramp voltage signal from the oscillator 60 is applied to one input of a vertical deflection amplifier 64, whose output (waveform 200 in FIG. 2a) drives the vertical deflection winding 66 of the picture tube. A current sensing resistor 68 is provided in series with this winding 66 to apply a feedback voltage to the second input of the amplifier 64 in negative feedback.

The deflection voltage 200 at the output terminal A of the amplifier 64 shown in FIG. 2a is applied to the monostable multivibrator 70 via a differential coupling circuit 80. Differential coupling circuit 80 includes a differentiator made up of a capacitor 82 and a resistor 84, and this differentiator and the trigger input of multivibrator 70 are coupled via a resistor 86 and a diode 88.

The anode of this diode 88 is coupled to the base of transistor 72 of multivibrator 70;
The base of transistor 72 is coupled through resistor 75 to the B ⁺ power supply, the emitter to ground, and the collector through resistor 76 to the B ⁺ power supply. A voltage divider consisting of resistors 77 and 78 is connected in parallel to the collector-emitter circuit of the transistor 72, and the base-emitter junction of the transistor 71 is connected in parallel to the resistor 78. 73 to the B ⁺ power supply and to the base of transistor 72 via a timing capacitor 74.

Collector terminal B of transistor 72 forms the output of multivibrator 70. This terminal B is coupled through a resistor 94 to the base of a transistor 92 of a control circuit 90. The emitter of this transistor 92 is grounded, and the collector is connected to the connection point 45 via a resistor 47. The collector-emitter circuit of this transistor 92 is a controllable circuit that connects the resistor 47 in parallel to the resistor 46 and changes the characteristic that the wave generator 40 exhibits with respect to the control signal of the phase comparator so as not to disturb the wave voltage. form.

In operation, during the main portion of the vertical scan period, the reverse base-emitter bias generated by capacitor 74 causes transistor 72 to be cut off but transistor 71 to be conductive, so that the multi-bar
Ibrator 70 is in an unstable state. Since the charge on capacitor 74 varies with the current flowing through resistor 75, the reverse bias at the base of transistor 72 gradually decreases. Since point B is at B ⁺ potential, transistor 92 becomes conductive and resistors 46 and 47
are in parallel. The phase comparator 20 compares the sawtooth wave 57 and the horizontal synchronizing signal 19 and generates a current pulse depending on the degree of phase matching. Current from the output terminals of comparator 20 flows through resistors 41 and 48 to generate voltage pulses that are averaged across capacitors 42 and 44 to form a control voltage that controls horizontal oscillator 50. The voltage pulse is attenuated according to its frequency spectral distribution by an amount that depends on the value of the resistor in series with capacitor 44. When the transistor 92 is conductive and the resistors 46 and 47 are connected in parallel, the attenuation of the wave generator 40 becomes relatively large within a certain frequency range, so that the phase holding loop gain within that range is low and noise insensitivity is obtained. .

Several scan lines before the end of the vertical scan period, just before a step change in phase is expected to appear in the horizontal sync pulse from the videotape machine, the charge on capacitor 74 is transferred to the base-emitter junction of transistor 72. It will be discharged until it becomes biased. Transistor 72 begins to conduct, and when the voltage at point B drops to the saturation voltage of transistor 72, transistor 71 is cut off. This is the stable state of the multivibrator 70. When the voltage at point B decreases, the base-emitter bias of transistor 92 is removed and it becomes non-conducting, thereby removing resistor 47 from wave circuit 40 and reducing the attenuation of the wave circuit. The signal becomes controlled. The decrease in the attenuation of wave generator 40 increases the loop gain of the phase holding loop.

When operated with a broadcast signal instead of a playback signal from a tape, there is no substantial change in phase in the next period and an increase in the loop gain of the loop does not cause any change in the operation of the horizontal oscillator 50. do not have. When the input is from tape playback, a change in phase may occur a short time after multivibrator 70 has reached its stable state. This change in phase is detected by phase comparator 20, and the control signal generated by comparator 20 causes horizontal oscillator 50 to shift more quickly in its low gain state. Oscillator 50 begins to shift toward a new phase just before the vertical blanking interval, and this occurs for substantially the entire vertical blanking interval. Near the end of the vertical blanking period, the vertical blanking period ends at time _T1 . At this time, the differential coupling circuit 80
The multivibrator 70 is reset by applying a negative signal to the base of the multivibrator 70, and is brought into an unstable state. As shown in FIG. 2b, at the beginning of the vertical scan, the voltage at point B rises toward B ⁺ , which causes transistor 92 to conduct again and resistors 46 and 4 to
7 are in parallel to reduce the gain of the transducer and enhance noise insensitivity during the vertical scan period.

With the arrangement of the present invention, the television receiver receives from the videotape recording device a synchronization signal that shows a gradual phase change prior to the vertical blanking period, and at the same time, during substantially the entire vertical scanning period, the television receiver receives The use of phase-holding loops adapted for reception allows the noise insensitivity normally obtained to be maintained. Since the operation is continuously controlled during the reception of these two types of signals, there is no need for a switch to be operated by the user, and noise components in the video signal from the tape recording device that appear during the vertical scanning period are suppressed. .

FIG. 3 shows another embodiment of the invention, similar in part to FIG. Components used in the embodiment of FIG. 3 and serving a similar purpose as similar components of FIG. 1 are provided with the same reference numerals. The tuner, IF amplifier, video detector complex 12, synchronizing signal separator 18, phase comparator 20, wave generator 40, horizontal oscillator 50, vertical oscillator 60, and vertical deflection amplifier 64 of FIG. 3 are all shown in FIG. Since it has the same effect as those of , I will not explain it repeatedly.

Next, in FIG. 3, the deflection voltage 200 at point A is applied to the input of the threshold circuit 700. The threshold circuit 700 includes a reference voltage divider 760 consisting of resistors 770 and 780 connected in series between the -400V supply and ground, with a reference voltage at the taps of the voltage divider.
Generate VR. Threshold circuit 700 also includes a comparator 710 that compares the sawtooth voltage at point A with its reference voltage and generates a control signal at output terminal D in response. This comparator 710 is the transistor 7
20 and a current limiting resistor 7 connected in series to its base.
40 and the transistor 7 of this resistor 740
The end opposite to the base of 20 is at point B', and point B' is the resistance 〓〓〓〓〓
730 to output terminals A of amplifiers 64, respectively. The anode of diode 750 is connected to the tap of voltage divider 760 and its cathode is connected to point B' to prevent point B' from dropping substantially more negative than the reference voltage. Terminal A is also coupled via diode 79 to emitter terminal C of transistor 720, which emitter terminal is grounded via a parallel circuit of resistor 800 and capacitor 81. The collector of transistor 720 is coupled to the 327V power supply through a load resistor 820 and grounded through a diode 83 to prevent its collector from dropping significantly below ground potential. The cathode of this diode 83 forms the output terminal D of the comparator 710.

Output D of comparator 710 is coupled to the base of transistor 92 via series resistor 94. The emitter of this transistor 92 is grounded, and the collector is coupled to the connection point 45 of the wave generator 40 via a resistor 47. transistor 92
And the resistors 94 and 47 include a variable section 90 for connecting the resistor 47 and the resistor 46 in parallel in the same way as in FIG. Form.

During the operation during the main part of the vertical scanning period, the deflection voltage 200 significantly exceeds the reference voltage VR, the diode 750 becomes non-conductive, and the falling voltage 200 at point A
is applied to the capacitor 81, so the diode 7
9 conducts. With diode 79 conducting and diode 750 non-conducting, the base-emitter junction of transistor 720 is reverse biased and the transistor is non-conducting. The voltage at output terminal D is B ⁺ , as shown by waveform 230 in FIG. 4d.
Since the voltage at terminal D is at a high level, transistor 92 conducts and resistor 47 is coupled in parallel with resistor 46. A phase comparator 20 compares the sawtooth wave 57 with the horizontal synchronization pulse 19 and generates a current pulse depending on the degree of phase matching. The output current of comparator 20 flows through resistors 41 and 48 to produce voltage pulses which are averaged across capacitors 42 and 44 to form a control voltage for controlling horizontal oscillator 50 as in FIG. This voltage pulse is attenuated by its frequency spectral distribution by an amount that depends on the value of the resistor in series with capacitor 44. resistor 47,
46 in parallel relatively increases the attenuation of wave generator 40 within a particular frequency range, thereby reducing the gain of the phase holding loop within that range and providing noise insensitivity.

At time T ₂ , several horizontal scan lines before the end of the vertical scan period, just before a step change is expected to appear in the horizontal sync pulse from the videotape recording device, the voltage at point A is slightly below the reference voltage VR. becomes lower. This causes diode 750 to be forward biased, resulting in a dot as shown by waveform 210 in FIG. 4b.
The voltage at B' will no longer decrease below that level. However, the voltage at point C continues to decrease with the voltage at point A, as shown by waveform 220 in FIG. 4C. As a result, the base-emitter junction of transistor 720 becomes forward biased and conductive, and its emitter current flows through resistor 8.
00 and the current from capacitor 81 begins to flow through diode 79. Due to the conduction of transistor 720 at time _T2 , the voltage at output terminal D of the comparator drops sharply, as shown in FIG. 4d. This removes its base-emitter bias from transistor 92 so that it becomes non-conducting, disconnecting resistor 47 from wave circuit 40 and attenuating the wave circuit for phase control signals within a specified frequency range. Reduce. This attenuation of wave generator 40 increases the loop gain of the phase holding loop.

The voltage at point A is at the waveform 200 in Figure 4 a.
As long as the voltage continues to decrease as shown between T ₂ and T ₃ , transistor 720 continues to conduct, and the gain of the phase holding loop maintains a high value. When operating with a broadcast signal rather than a tape playback signal, there is no substantial change in phase during this period, and the increase in loop gain does not change the operation of oscillator 50; however, if the input is tape In the case of a reproduced signal, a phase change may appear a short time after time _T2 . Phase comparator 20 detects this phase change and generates a control signal that causes horizontal oscillator 50 to shift more quickly than in the low gain state.

Near the end time _T3 of the vertical scanning period, the deflection voltage 200 rapidly increases toward the positive power supply voltage. This causes diode 750 to become non-conductive, disconnecting point B' from the reference voltage, and diode 79 to become non-conductive, leaving a large negative voltage at point C, as shown by waveform 220. Since the voltage at point B' is substantially more positive than the voltage at point C, the transformer
Resistor 720 continues to conduct and transistor 92 remains non-conductive. As the voltage across capacitor 81 decreases towards zero, the voltage at point C increases after time _T3 . Near time T ₁ , the vertical retrace period ends and deflection voltage 200 drops rapidly removing the base-emitter bias of transistor 720 and causing diode 79 to conduct. Transistor 92 conducts at time T ₁ and remains conductive for substantially the entire next vertical scan period, reducing the gain of the waveform generator and enhancing noise insensitivity.

The delay mechanism relies in large part on the highly stable and controlled characteristics of the vertical deflection circuit. Comparator 70
Reliability is increased and cost is reduced by reducing the number of components and the number of active devices used.

Other embodiments of the invention will be apparent to those skilled in the art.
For example, various types of loop detectors may be employed as desired, and various types of conventional phase detectors may be used with the present invention.

In the embodiment of the invention shown in FIG. 1, the following component values have been found to give satisfactory operation.

Capacitor 42 4700pF 44 1.0μF 74 0.27μF 82 0.047μF Resistor 46 33KΩ 47 3300KΩ 48 130KΩ 73 2400Ω 75 139KΩ 76 10KΩ 77 100KΩ 78 10KΩ 84 3300Ω 86 18KΩ 94 15KΩ Also, in the example shown in Figure 3, the following component values are It was found that it gave satisfactory results.

capacitor 42 4700pF 44 1.0μF 81 0.47μF Resistor 46 33KΩ 47 3.3KΩ 48 130KΩ 73 100KΩ 74 82KΩ 77 27KΩ 78 12KΩ 80 10KΩ 82 10KΩ 94 15KΩ

[Brief explanation of the drawing]

FIG. 1 is a partial schematic circuit diagram of a part of a television receiver embodying the present invention, and FIG.
FIG. 3 is a partial block partial circuit diagram of a television receiver implementing another embodiment of the present invention; FIG. FIG. 3 is a waveform diagram of vertical frequency voltages that appear during operation of the circuit shown in the figure. 10... Antenna, 16... External video signal source jack, 18... Synchronizing signal separator, 40... Controllable wave circuit, 50... Horizontal oscillator, 52... Horizontal deflection circuit, 60... Vertical oscillator, 64 ... Vertical deflection amplifier, 70 ... Delay means (monostable multi),
90...Control circuit. 〓〓〓〓〓

Claims (1)

[Claims] 1 for synchronizing a horizontal oscillator with a synchronized pulse source capable of producing phase changes at the vertical deflection frequency, comprising: controllable horizontal oscillation means for producing horizontal frequency oscillations with controllable frequency and phase; horizontal deflection means coupled to the means for generating a deflection current synchronized with said vibration; coupled to said horizontal deflection means and a horizontal synchronization pulse source, in response to said deflection current and said horizontal synchronization pulse, said phase comparison means for generating a phase control signal representative of a difference in frequency and phase; means coupled to the phase comparison means and the horizontal oscillation means for generating an averaged signal for controlling the oscillator; controllable filtering means having a variable frequency amplitude characteristic which is in a first state during the vertical retrace period and in a second state during the main period of the vertical scan period; coupled to the vertical deflection means for synchronizing the vertical deflection frequency; a vertical synchronization signal source for generating a signal; coupled to said controllable filtering means;
control means for repeatedly switching said characteristic at a vertical deflection frequency in response to a synchronization signal at said vertical deflection frequency; said control means and said vertical synchronization signal source being coupled to said synchronization signal at said vertical deflection frequency; and a delay means for delaying the switching operation from the second state to the first state by the control means until shortly before the next synchronization signal appears.