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1. (WO1997019563) COMB FILTER MODULE WITH BOTH COMPOSITE AND Y/C-SEPARATED INPUTS
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DESCRIPTION

COMB FILTER MODULE WITH BOTH COMPOSITE AND Y/C-SEPARATED INPUTS

The present invention relates to a comb filter module comprising an input for a composite video signal, a comb filter circuit for separating a composite video signal supplied to the input into separate luminance and chrominance signals and first and second outputs to which respectively the luminance and chrominance signals from the comb filter circuit are supplied. The invention relates also to a television apparatus including such a comb filter module.

An example of a comb filter module of the above kind is the CFM 102 module available from Philips Components Ltd. Another example of such a comb filter module is described in US-A-4734662. These modules comprise a package containing a glass delay line connected electrically to an associated hybrid circuit on a substrate carried alongside the glass delay line within the package which together constitute a comb filter circuit. The package is provided with connection pins projecting through a base wall which enable the package to be mounted on a pcb with the pins electrically connected to tracks of the pcb, and through which the video signal input, the separate component outputs and a power supply to the comb filter circuit are provided. Such a comb filter module has a number of advantages over comb filter circuits of the kind in which a packaged glass delay line and the associated circuitry are provided as separate components and mounted independently on a pcb. Because it is usually necessary to adjust components of the associated circuit to match the delay line such adjustments must, when the delay line is supplied as a separate component, be performed by the equipment, e.g. TV receiver, manufacturer when assembling the components on a pcb and this requirement can be time consuming and hinder production. With a comb filter module, however, such adjustments are made by the module manufacturer so that the need for adjustment by the equipment manufacturer is eliminated. Moreover, the size of the package used for the module can be approximately the same as that used for a glass delay line alone so that with a comb filter module space savings can be achieved.
Television apparatus, which term is used herein to include video equipment such as multimedia PCs as well as conventional TV sets, that are capable of displaying pictures from more than one video signal source, for example from an auxiliary source such as a VCR or camcorder as well as from a received TV broadcast signal, are known. The other input video signals can be of the separate component type, i.e. separate luminance and chrominance signals, rather than of the composite type. For example, a composite video signal is obtained from an NTSC or PAL demodulator and separate, Y-C, components are obtained from a camcorder, digital satellite receiver or VCR using the S-VHS or Hi-8 standards. In such apparatus means are provided to select between the different video signals. An example of television apparatus including a switching circuit for selecting input video signals including composite and non-composite type video signals in this manner is described in EP-A-0645934.

It is an object of the present invention to provide an improved comb filter module suitable for use in such apparatus.

According to one aspect of the present invention, there is provided a comb filter module of the kind descĪ€bed in the opening paragraph which is characterised in that the module includes two further inputs for the separate luminance and chrominance component signals of a second video signal and switching means for selectively supplying the separate luminance and chrominance signals from either the comb filter circuit or the two further inputs to the first and second outputs. Thus, the switching means required for selecting between different video inputs, one being a composite signal and one being a separate component signal, is provided by, and contained in, the module and the need to provide a separate switching circuit elsewhere is removed. This has considerable benefit to the TV apparatus manufacturer since the requirement for comb filtering and signal switching are satisfied by just one component. The number of components needed to be used by the manufacturer is significantly reduced and production of the TV apparatus, and in particular the pcb carrying the TV circuitry, is greatly simplified. Furthermore, it is possible for the additional inputs required for the second video signal and the switching means to be accommodated in the same size of package as a known comb filter module. Consequently, a further beneficial space saving is obtained from the apparatus manufacturer as the switching means does not need to be Iocated independently. The invention provides, therefore, a very simple and cost effective solution to the problem of switching between two input video signals.
The module preferably comprises, as with the known modules, a housing having connection pins projecting from a wall of the housing, and electrically connected to the comb filter circuit, for use in mounting the module on a pcb, respective pins serving as terminals and constituting the aforementioned video signal inputs and outputs. With the comb filter circuit comprising a glass delay line electrically connected to an associated circuit, comprising electronic components, carried on a substrate then advantageously the switching means may also be carried on that substrate. In this way, the switching means is accommodated within the module housing conveniently and, apart from the substrate, can use the same components, such as the delay line and housing, as those used in the known modules.
The operation of the switching means to select between the luminance and chrominance signals obtained from the comb filter circuit or from the second video signal is preferably arranged to be controlled by a control signal applied to one of the said inputs of the comb filter module, and preferably the input for the composite video signal. Thus the need to provide an extra, dedicated, input i.e. an additional terminal pin, for the control signal is avoided.

This simplifies the construction of the module and eliminates the need for the user of the module to provide an additional connection on the printed circuit board onto which the module is mounted. In a preferred embodiment, the switching means comprises a diode circuit in which the luminance and chrominance signals from the comb filter circuit and the luminance and chrominance signals from the two further inputs are supplied to the first and second outputs via respective diodes. The diode circuit is preferably arranged such that the luminance and chrominance signals from the comb filter circuit render their associated diodes conducting and the diodes associated with the luminance and chrominance signals from the two further inputs non-conducting, thereby allowing the luminance and chrominance signals from the comb filter circuit to pass to the first and second outputs. Thus, when the comb filter circuit is operating, the luminance and chrominance signals produced are supplied to the outputs and any signals at the further two inputs are blocked by the associated diodes. When luminance and chrominance signals are not being supplied by the comb filter circuit, the associated diodes become nonconducting and the diodes associated with the luminance and chrominance signals from the two further inputs become conducting, thereby allowing these signals to pass to the outputs. The switching operation of the switching means is thus controlled by operation of the comb filter circuit and switching between the first and second video signals is accomplished merely by turning the comb filter circuit on and off. Besides simplifying the control of signal switching this manner of operation has a power saving advantage in that whenever the second video signal is required from the module, the comb filter circuit does not consume power unnecessarily. Moreover, the required on/off control of the comb filter circuit, and hence switching between the two video signal inputs, can be achieved in a simple and convenient manner by means of a control signal applied to the input of the comb filter circuit, i.e. the composite video signal input.
The use of a diode circuit for the switching means is particularly attractive as the diodes can be provided as surface mount devices and, because such components occupy little space, can readily be accommodated on the same substrate as the comb filter circuit elements.
According to another aspect of the present invention, there is provided a television apparatus including means for selecting between first and second video signals from different sources, the first video signal comprising a composite video signal and the second video signal being in separate luminance and chrominance signal form, which is characterised in that the selecting means comprises a comb filter module in accordance with the one aspect of the present invention. The television apparatus can be, for example, a television set, a multimedia PC or the like for displaying the input video signals or other equipment such as a VCR for recording the input video signals.

An embodiment of a comb filter module in accordance with the invention and a television apparatus employing such will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 shows schematically components of the comb filter module in side view with its cover removed;
Figure 2 is a schematic block diagram of the comb filter module illustrating its general operation;
Figure 3 is a circuit diagram of the module; and
Figure 4 is a simple schematic block diagram of a television apparatus using the comb filter module.

The same reference numerals are used throughout the Figures to indicate the same or similar parts.
Referring to Figure 1 , the comb filter module 10 comprises a housing containing circuit components. The housing includes a base 1 1 of plastics insulating material which supports an ultrasonic glass delay line 12 and an associated hybrid IC 13 consisting of a substrate 14 carrying circuit elements comprising surface mounted and thick film components together with electrical interconnections in the form of printed conductive tracks. The substrate 14 extends alongside, and spaced from, the delay line 12 vertically from the base 11. Connection between the delay line 12 and the circuit on the substrate 14 is provided by way of soldered wires, for example as shown at 15. The housing includes a plastics cover 17, shown in dashed outline, which is secured to the base 11 to enclose and protect the components 12 and 13. Extending through the base 11 are electrical terminal pins 16 which at their one ends electrically connect with respective contact pads of the conductive tracks on the substrate 14. Their other ends project away from the base 11 and, in use of the module, are intended to pass through respective, and appropriately spaced, apertures in a printed circuit board (pcb), forming part of, for example, the circuit in a television receiver, and to be fixed therein by means of solder so as to mount the module on the pcb with the terminal pins being electrically connected to a respective conductive tracks of the pcb.
The terminal pins 16 provide input, output, and power supply terminals for the comb filter module. In operation, with the module mounted on a suitable pcb in a TV receiver or the like, two pins are connected to ground and a predetermined voltage source respectively. Another pin is supplied with a composite video signal, for example an NTSC TV video signal, comprising a basement luminance component and a quadrature modulated chrominance component which is separated by operation of the comb filter circuit within the module 10 into a chrominance (colour) signal, C, and a luminance (brightness) signal, Y. The separate chrominance and luminance signals are then fed back to the pcb via respective outputs of the module constituted by two further pins 16.
Such a module is convenient to use as all adjustments necessary in the hybrid IC circuit can be made by the module manufacturer prior to supply to, for example, a TV receiver manufacturer and the need for the latter to perform any adjustments to the comb filter circuit during assembly of the equipment is removed.
The kind of comb filter module described thus far is similar in many respects to known comb filter modules such as the modules designated by the product codes CFM 101 , CFM 102, CFM 202 and CFM 204 manufactured by Philips Components Limited at Blackburn, England, or the module described in US-A-4734662, to which reference is invited for further information. The glass delay line 12 may be of the kind described in GB-A-1230036.
In addition to providing a comb filter function for a composite video signal, the module 10 also has an integrated second video signal switching capability. In this respect, the module 10 further includes an additional two inputs, each provided by a respective terminal pin 16, to which a second video signal of separate chrominance and luminance signal component type is intended to be supplied, and a switching arrangement that is operable selectively to connect to the respective two, Y and C, output terminal pins either the separated Y and C components according to the first, composite, video signal obtained from the comb filter circuit or separate Y and C components according to the second video signal as required. The second video signal may be an SVHS signal or a Hi-8 video signal and can be provided by a supplementary video source such as a VCR, a camcorder or an external receiver such as a digital satellite receiver. Figure 2 shows the module diagrammatically in block form to illustrate its operation in this respect. The module 10 has seven terminal pins 16 which are designated 16(1 ) to 16(7). In use, pins 16(1) and 16(5) are connected to a power supply (VCC), e.g. a 9v supply line, and ground respectively. The composite video signal, Vd1 , is supplied to the input pin 16(2) from where it is fed to the comb filter circuit 20, comprising the glass delay line 12 and associated circuitry on the substrate 14, where it is separated into its component parts, here designated Y1 and v which are provided on respective output lines of the circuit 20. The separate Y and C signals of the second video signal, Vd2, here designated Y2 and C2, are supplied to two further inputs of the module, provided by the terminal pins 16(3) and 16(4). The pins 16(7) and 16(6) provide Y and C outputs from the module. A switching arrangement 25 is included which is operable selectively to switch either the Y1 ( C signals from the comb filter circuit 20 or the Y2, C2 signals from inputs 16(3) and 16(4) to the Y and C outputs 16(7) and 16(6).

In addition, therefore, to the module performing the function of separating a supplied composite video signal into Y and C components for use subsequently in, for example, the TV receiver circuitry, the module 10 is capable of performing the further role of switching the output between that video signal and a second input video signal, thereby eliminating the need for video signal switch means for switching between the two video sources to be provided separately in the TV receiver circuitry. The manufacturer of the TV receiver needs simply only to provide on the pcb onto which the module 10 is mounted appropriate supply tracks for the Y and C components of the second video signal.
The switching arrangement 25 is conveniently carried on the substrate 14 together with the comb filter circuitry. The overall dimensions of the module can remain the same as with known modules. In this particular embodiment the switching operation of the switching arrangement 25 is controlled by a control signal, S, comprising a voltage bias signal, supplied to pin 16(2), i.e. the composite video signal input, thereby avoiding the need to provide an additional pin for this purpose.
The circuit diagram for this embodiment of module is shown in Figure 3. It will be appreciated that the particular circuit illustrated in Figure 3, and especially the comb filter circuit part, is by way of example only. The design of the comb filter circuit can be varied and is dependent on particular requirements of the TV receiver circuitry in which the module is to be used. Referring to Figure 3, the comb filter circuit 20, comprising the ultrasonic glass delay line 12 and its associated hybrid IC 13, is indicated by the box 30 shown in dashed outline. The circuitry consists of resistances R1 to R11 , inductances L1 and L2, capacitors C1 and C2, transistors TR1 to TR4, and the glass delay line 12. The operation of this circuit generally follows conventional practice and it is not considered necessary to describe this here in detail. Essentially, it operates to separate the composite video signal Vd1 supplied to the input 16(2) into its luminance and chrominance, Y, and C,, components which are obtained from the emitters of the transistors TR4 and TR3 respectively. The comb filter circuit 20 is implemented by using the same polarity of transistors, TR1 , TR2, TR3 and TR4, in order to facilitate a switching operation in the module, as will be described, as well as performing the normal filtering functions.
The switching arrangement, indicated at 25, comprises four diodes D1 to D4 and two resistances, R12 and R13, connected as shown with the diodes D1 and D2 being connected respectively between the C output pin 16(6) and the emitter of TR3 and between the Y output pin 16(7) and the emitter of TR4. The diodes D3 and D4 are connected respectively between the Y output pin 16(7) and the Y input pin 16(3) for the second video signal Vd2 and between the C output pin 16(6) and the C input pin 16(4) for the second video signal. In this example, the second video signal comprises an S-VHS signal.
The Y and C signals of the S-VHS input are supplied to the diodes D3 and D4 via an input circuit, consisting of the resistances R14 to R18 and the transistor TR5, which sets the required voltages and impedances to enable the switching arrangement 25 to operate correctly. By setting the DC levels of the S-VHS Y and C inputs, whilst maintaining the desired impedances, the action of the diodes D3 and D4 can be controlled. The operation of the switching arrangement 25 is also governed by the comb filter circuit 20. By controlling the voltage at the base of the input transistor TR1 of the comb filter circuit 20, through the control signal S (Figure 2), the comb filter can be switched on and off as desired. Switching of the comb filter circuit in this manner also controls the switching arrangement 25 so as to allow the S-VHS Y and C signals to pass to the outputs 16(7) and 16(6) when the comb filter circuit is off. When the comb filter circuit 20 is operating normally, the S-VHS Y and C inputs are blocked by the switching arrangement 25, or more precisely the diodes D3 and D4. Thus, no independent pin is necessary to effect the operation of switching between the Y1 ( C, and Y2, C2 outputs. Instead this is achieved merely by altering the bias to the base of transistor TR1 , in effect by switching the control signal S (Figure 2) to provide the required bias voltage levels, which automatically configures the switching of the required Y and C signals to the module output pins 16(6) and 16(7). A further advantage of controlling the switching operation in this manner is that since the comb filter circuit is not utilised when the S-VHS Y and C signals are allowed to pass to the outputs and is turned off, power consumption is reduced to a minimum.
As will be apparent, therefore, the diodes D1 to D4 control the Y and C output paths with the diodes D1 and D2 switching the Y1 and C1 outputs from the comb filter circuit 20 while the diodes D3 and D4 control the S-VHS paths. When the circuit 20 is operating normally diodes D1 and D2 are conducting and allow the Y1 and C, signals to pass to the outputs 16(7) and 16(6). In this condition the diodes D3 and D4 are forced into their off state blocking the S-VHS channels and preventing the Y2 and C2 signals reaching the outputs.

When the circuit 20 is turned off, by changing the bias voltage at the base of

TR1 , then D1 and D2 are switched off and D3 and D4 become conducting to allow the S-VHS Y2 and C2 signals to pass to the outputs 16(7) and 16(6).
The change over between comb filter circuit and S-VHS outputs is controlled by switching the voltage on the line carrying the video signal Vd1. The dc voltage at the input pin 16(2) controls the switching function between comb filter and S-VHS modes. The setting of this voltage may be achieved by a specified resistor to ground or an active device supplying the required bias voltage. If the bias voltage at the input pin 16(2) is set to VCC then the comb filter is tumed off and the S-VHS paths are made active so that Y2 and C2 are output. If the bias voltage is set below a required threshold voltage for the transistor TR1 (between VCC and ground) then this will enable the comb filter circuit and disable the S-VHS path so that Y, and C, are output.
It will be appreciated that, in addition to circuitry of the comb filter circuit being varied as previously mentioned, various alternative circuit arrangements could be used for the S-VHS input section and the switching arrangement 25. The use of diodes and resistances for the switching arrangement 25 is attractive as these kinds of components can be readily integrated on the substrate 14 with the resistances being provided, for example, as thick film resistive elements and the diodes being surface mount type diodes, for example of SOT23 or SOD80 kind.

Switching ICs are available which are capable of providing the required switching operation. However, the switching arrangement 25 described above has a number of advantages over such switching ICs. A suitable switching IC, for example, a 4066 quad switch, would occupy a considerably greater area of the substrate 14 and in order to accommodate this a larger substrate would be required. Problems would likely be caused with impedance matching as these kinds of ICs are designed to match high impedances rather than low as required. Moreover, the voltage requirements of the FET switches used in these ICs would necessitate additional power supply connections to the module as well as a further terminal pin for a control signal.
Although the circuitry associated with the delay line of the comb filter in the above-described embodiment comprises a hybrid IC, using surface mount and thick film technology, it will be appreciated that other forms of circuitry, for example pcb based, could be used instead if desired.
The use of the comb filter module embodiment has been described in the context of television receivers to provide an integrated switching function allowing selection between, for example, an NTSC composite video signal and, for example, an S-VHS video signal. The module can be used not only in television sets but in other types of television apparatus such as multimedia personal computers and VCRs. The second video signal, supplied to the module as separate Y and C components, can be from a variety of video sources, for example S-video sources or Hi-8 video sources such as VCRs, cameras, camcorders and external receivers such as digital satellite receivers.

In Figure 4 there is shown in simplified schematic block form an example of a television apparatus utilising the comb filter module, in this case a TV set. An input terminal 40, to which a standard RF modulated television signal from a source such as an antenna, a cable TV source, a VCR or a computer is supplied, is connected to a tuner and IF processor unit 41 which is controlled to select a desired channel. The sound component of the signal is removed in conventional manner by an audio extraction circuit (not shown) and the resultant composite video signal, comprising a baseband luminance component (Y) and a quadrature modulated chrominance component (C), is fed to the appropriate input of the comb filter module 10. Auxiliary input terminals 42 and 43 to which the separate Y and C signal components of an auxiliary non-composite, video signal, such as an S-VHS signal from for example a VCR, camcorder, or satellite receiver, are connected to the comb filter module Y and C inputs. The separate Y and C signals output from the comb filter module are supplied to a display processing circuit 44 of conventional form, and including a Y - C processing unit, whose output is supplied to a display 45, for example a CRT. Selection between the video signals from the two sources, i.e. the input terminal 40 and the auxiliary input terminals 42 and 43, is achieved by means of a control unit 46 connected to the composite video signal input of the comb filter module 10 which by means of the selective application of the bias voltage signal S, i.e. the voltage VCC or between VCC and ground, controls the operation of the comb filter circuit in the module, and thus the output from the module, as previously described.
Thus there has been described a comb filter module having an input for a composite video signal, a comb filter circuit comprising a glass delay line and an associated circuit for separating the composite video signal into a Y and C signal components, and outputs for the separate Y and C signal components, which includes further inputs for a second video signal comprising separate Y and C components, e.g. an S-VHS signal, and switching means operable selectively to supply either the Y and C signals from the comb filter circuit or from the further inputs to the module outputs. In a television apparatus the module conveniently provides in one unit both comb filtering and a video signal switching functions.
From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the design, manufacture and use of systems already known in the field of television apparatus and comb filter modules and component parts thereof and which may be used instead of or in addition to features already described herein.