GB2197156A

GB2197156A - Method and circuit for adjusting the phase position of a colour subcarrier phase information signal of a pal-coded colour television signal

Info

Publication number: GB2197156A
Application number: GB08725643A
Authority: GB
Inventors: Jurgen Heitmann
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1986-11-07
Filing date: 1987-11-02
Publication date: 1988-05-11
Anticipated expiration: 2007-11-02
Also published as: DE3637935A1; DE3637935C2; GB2197156B; GB8725643D0

Abstract

A circuit for adjusting the phase position of a colour sync signal comprises two banking states 2,3 for subdividing a PAL-CCVS signal into a CCV signal and an S (line sync) signal, a delay device 7 with a fixed delay time to which the CCV signal is supplied and a second delay device 8 with a controllable delay to which the S signal is supplied, and a control stage 11 for adjusting the delay time of the second delay device 8 as a function of a phase comparison of the line sync signal and the colour sync signal at the outputs of the delay devices. <IMAGE>

Description

SPECIFICATION Method and circuit for adjusting the phase position of a colour subcarrier phase information signal of a PAL-coded colour television signal The invention relates to a method and circuit for adjusting the phase position of a colour subcarrier phase information signal of-a PALcoded colour television signal when changing signal sources.

German Patent 2921 969 discloses a method for measuring the phase position of a colour subcarrier phase information signal of a PAL-coded colour television signal in which, using the horizontal (line) sync signal, the colour subcarrier phase information signal and the PAL switching signal, in time intervals of four television lines phase-dependent on the PAL switching signal previously established time coincidences between the leading edges of the horizontal sync signal and- zero crossings of the colour subcarrier phase information signal are selected and indicated with respect to their position within the television raster.

In the introduction to the aforementioned patent specification, to which express reference is hereby made, the special features occurring in connection with the electronic cutting of PAL-coded television signals are described in detail in conjunction with the exact phase position of the colour subcarrier (8Vsequence), which only recurrs after every 8 fields.

The object of the invention is therefore to reduce the limitations occurring on cutting succeeding pictures with scarcely varying picture content.

Accordingly, the present invention provides a method for adjusting the phase position of a colour subcarrier phase information signal of PAL-coded colour television signal for obtaining a PAL-correct colour subcarrier phase position when changing signal sources, wherein a phase comparison of the line sync signal with the colour subcarrier phase information signal is performed, and one or both signals thus compared are so time-displaced in dependence upon such comparison as to produce a desired time relationship between them.

In technical statement D 23-1979 published by the European Broadcasting Union, there is a desired defined phase relationship between the colour subcarrier and the line sync signal.

Thus, the time difference, expressed in radians, of the phase of the U-component of the colour phase information signal (colour burst), extrapolated to half the amplitude value of the leading edge of the line sync signal of the first line of the first field of a PAL 8V-sequence, is precisely 0".

The invention has the advantage that the PAL-specific 8V-sequence is precisely respected at the time of e.g. recording, and the picture content coming from changing signal sources need not have this defined phase relationship.

An embodiment of the invention is shown in the single figure of the drawing and explained in greater detail hereinafter. The single figure shows a circuit for adjusting the phase position of the colour subcarrier information signal with respect to the leading edge of the line sync signal for obtaining a continuous sequence, which is repeated every 8 fields, even in the case of closely following electronic cutting processes in recording on a magnetic medium.

A CCVS signal arriving at circuit input 1 is supplied to two parallel blanking stages 2, 3, as well as to a sync signal separating stage 4.

Fron the sync signal present at the output of the sync signal separating stage 4, a blanking pulse is shaped in the blanking pulse shaping stage 5 and is supplied in non-inverted form to the control input of blanking stage 2 and through the inverting stage 6 to the control input of blanking stage 3. Therefore, from the CCVS signal at the inputs of blanking stages 2, 3, a CCV signal is produced in blanking stage 2 and a line sync signal S is produced in blanking stage 3.

The CCV signal at the output of the blanking stage 2 is supplied to a delay device 7 having a basic delay of half the oscillation time of the colour subcarrier phase information signal (colour sync signal) of a PAL colour television signal, namely 112 ns. The S signal from the output of the blanking stage 3 passes through a further delay device 8 having a variable delay between 0 and 225 ns, the delay being a function of the magnitude of a control signal present at a control input.

To derive this control signal the sync signal separated in the sync signal separating stage 4 is supplied to one input of an 8V recognition circuit 9, to whose second input there is supplied across a gate 10 the colour sync signal from the output of the delay device 7.

A phase comparator 11, controlled by the output of the circuit 9, is connected downstream of the 8V recognition circuit 9 and obtains from a phase comparison between the line sync signal from the output of the delay device 8 and the colour sync signal from the output of the gate 10 a control signal for adjusting the delay time of the variable delay device 8.

In a mixing stage 12, the CCV signal from the output of the delay device 7 and the line sync signal S from the output of the variable delay device 8, and which has been appropriately adjusted in time, are combined to form the correct CCVS signal, which is available at the output 13 and can e.g. be recorded on magnetic tape.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Method and circuit for adjusting the phase position of a colour subcarrier phase information signal of a PAL-coded colour television signal The invention relates to a method and circuit for adjusting the phase position of a colour subcarrier phase information signal of-a PALcoded colour television signal when changing signal sources. German Patent 2921 969 discloses a method for measuring the phase position of a colour subcarrier phase information signal of a PAL-coded colour television signal in which, using the horizontal (line) sync signal, the colour subcarrier phase information signal and the PAL switching signal, in time intervals of four television lines phase-dependent on the PAL switching signal previously established time coincidences between the leading edges of the horizontal sync signal and- zero crossings of the colour subcarrier phase information signal are selected and indicated with respect to their position within the television raster. In the introduction to the aforementioned patent specification, to which express reference is hereby made, the special features occurring in connection with the electronic cutting of PAL-coded television signals are described in detail in conjunction with the exact phase position of the colour subcarrier (8Vsequence), which only recurrs after every 8 fields. The object of the invention is therefore to reduce the limitations occurring on cutting succeeding pictures with scarcely varying picture content. Accordingly, the present invention provides a method for adjusting the phase position of a colour subcarrier phase information signal of PAL-coded colour television signal for obtaining a PAL-correct colour subcarrier phase position when changing signal sources, wherein a phase comparison of the line sync signal with the colour subcarrier phase information signal is performed, and one or both signals thus compared are so time-displaced in dependence upon such comparison as to produce a desired time relationship between them. In technical statement D 23-1979 published by the European Broadcasting Union, there is a desired defined phase relationship between the colour subcarrier and the line sync signal. Thus, the time difference, expressed in radians, of the phase of the U-component of the colour phase information signal (colour burst), extrapolated to half the amplitude value of the leading edge of the line sync signal of the first line of the first field of a PAL 8V-sequence, is precisely 0". The invention has the advantage that the PAL-specific 8V-sequence is precisely respected at the time of e.g. recording, and the picture content coming from changing signal sources need not have this defined phase relationship. An embodiment of the invention is shown in the single figure of the drawing and explained in greater detail hereinafter. The single figure shows a circuit for adjusting the phase position of the colour subcarrier information signal with respect to the leading edge of the line sync signal for obtaining a continuous sequence, which is repeated every 8 fields, even in the case of closely following electronic cutting processes in recording on a magnetic medium. A CCVS signal arriving at circuit input 1 is supplied to two parallel blanking stages 2, 3, as well as to a sync signal separating stage 4. Fron the sync signal present at the output of the sync signal separating stage 4, a blanking pulse is shaped in the blanking pulse shaping stage 5 and is supplied in non-inverted form to the control input of blanking stage 2 and through the inverting stage 6 to the control input of blanking stage 3. Therefore, from the CCVS signal at the inputs of blanking stages 2, 3, a CCV signal is produced in blanking stage 2 and a line sync signal S is produced in blanking stage 3. The CCV signal at the output of the blanking stage 2 is supplied to a delay device 7 having a basic delay of half the oscillation time of the colour subcarrier phase information signal (colour sync signal) of a PAL colour television signal, namely 112 ns. The S signal from the output of the blanking stage 3 passes through a further delay device 8 having a variable delay between 0 and 225 ns, the delay being a function of the magnitude of a control signal present at a control input. To derive this control signal the sync signal separated in the sync signal separating stage 4 is supplied to one input of an 8V recognition circuit 9, to whose second input there is supplied across a gate 10 the colour sync signal from the output of the delay device 7. A phase comparator 11, controlled by the output of the circuit 9, is connected downstream of the 8V recognition circuit 9 and obtains from a phase comparison between the line sync signal from the output of the delay device 8 and the colour sync signal from the output of the gate 10 a control signal for adjusting the delay time of the variable delay device 8. In a mixing stage 12, the CCV signal from the output of the delay device 7 and the line sync signal S from the output of the variable delay device 8, and which has been appropriately adjusted in time, are combined to form the correct CCVS signal, which is available at the output 13 and can e.g. be recorded on magnetic tape. CLAIMS

1. A method for adjusting the phase position of a colour subcarrier phase information signal of a PAL-coded colour television signal for obtaining a PAL-correct colour subcarrier phase position when changing signal sources, wherein a phase comparison of the line sync signal with the colour subcarrier phase information signal is performed, and one or both signals thus compared are so time-displaced in dependence upon such comparison as to produce a desired time relationship between them.

2. A method according to claim 1, wherein the phase comparison of the line sync signal with the colour subcarrier phase information signal takes place as a function of the output signal of a PAL-8V sequence recognition circuit.

3. A method according to Claim 1 or 2, wherein the PAL colour signal is subdivided in two blanking stages into two components, whereof one contains the line sync signal and the other the colour sync signal, wherein the phase of the line sync signal contained in one component is compared with the phase of the colour sync signal contained in the other component as a function of the result of PAL-8V recognition, and wherein the signals are so time-adjusted by a controllable delay device that after combining the two components of the PAL colour signal in a mixing stage a continuous PAL colour video signal is obtained.

4. A circuit for performing the method according to one of the claims 1 to 3, comprising two blanking stages for subdividing a PAL-CCVS signal into a CCV signal and an S signal, a fixed delay device with a delay of half the oscillation time of the colour sync signal in the CCV signal and a further delay device with an adjustable delay time between zero and the full oscillation time of the colour sync signal, the fixed delay device being connected to the output of the first blanking stage and the further delay device being connected to the output of the second blanking stage, an 8V recognition circuit for controlling a phase comparator which compares the phase of the colour sync signal from the output of the fixed delay device with the phase of the line sync signal from the output of the further delay device and adjusts the further delay device accordingly, and a mixing stage for combining the two components of the PAL colour signal from the outputs of the two delay devices.

5. A method as claimed in Claim 1, substantially as described with reference to the accompanying drawing.