JPS61236290A - Comb-shaped filter circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a comb filter circuit of the type defined in the preamble of claim 1.

[Conventional technology]

In order to achieve long-term recording and playback, the tracks of commercially available recording media, especially in video tapes, are very narrow and very close together.

Thus, when reading a video track to reproduce the video information contained in the track, the reading device also picks up information from adjacent tracks. This introduces crosstalk from adjacent tracks to the track being read. In recent years, this crosstalk has been eliminated by comb filter circuits. In order to be able to eliminate crosstalk, each line between adjacent tracks must be recorded on the recording medium in a predetermined phase pattern. During playback, each line read from a track is phase shifted in the playback channel so that each line within that track is in phase. Crosstalk signals from adjacent tracks on both sides are thus opposite in phase. With proper alignment, the overlap between information on a read line and information on an adjacent line on the same track results in an average superposition of useful information on the two read lines and the removal of crosstalk signals from adjacent tracks. results in

The magazine Funkschau, Vol. 15, 1984, pages 42-45 describes a comb filter circuit used in the color reproduction section of a video recording device to remove crosstalk signal components. This known comb filter circuit has a first non-delayed signal path and a second signal path with a delay line providing a delay equal to two horizontal scan line periods. Both signal paths terminate in a summing circuit stage in which the amplitudes of the useful signals are summed and the crosstalk signals are subtracted. To eliminate crosstalk, this difference must be zero. To achieve this condition, a very finely tuned delay line must be used in the comb filter, since even the slightest deviation from the nominal delay can cause significant loss and interference. This is because However, delay lines used in video equipment fall far short of the accuracy required for crosstalk signal cancellation.

[Problem that the invention seeks to solve]

It is an object of the present invention to design a comb filter circuit such that commercially available inexpensive video delay lines can be used.

[Means for solving problems, their actions and effects]

According to the invention, this object is achieved by the technical features described in the features of claim 1. One advantage of the comb filter circuit according to the present invention is that it can not only use inexpensive commercially available video delay lines that have been used in video equipment for a long time, but also that the two signal paths are completely isolated.

Further advantages of the invention are set out in the dependent claims. Claim 2 describes a very simple phase shifter which requires only a few additional circuits and is capable of eliminating large deviations in the delay of the delay line from the nominal delay amount. The embodiment of the comb filter circuit according to claim 3 provides good isolation between the outputs of both signal paths and is characterized by perfect alignment of the comb filter circuit due to the symmetry of the described adder circuit. In another embodiment of the comb filter circuit according to claim 4, no comb filter circuit can be used, in particular SECAM 11
Effective turn-off and bridging of the comb filter circuit is ensured for operation. This bridging connection requires very little additional circuitry. Furthermore, the gain, particularly that of the transistor stages of the summing circuit, can be adjusted such that the total gain of the comb filter circuit is unity. In this case, the operational change from PAL to SECAM 9 could be made in the comb filter circuit without the need for additional gain compensation circuitry.

Comb filter circuits are known in which an inductance is connected in parallel to the output of a delay line. This inductance, together with the output capacitance of the delay line, forms a resonant circuit tuned to the frequency of the color carrier, which is designed to increase the amplitude of the color carrier frequency. The delay line used in this known comb filter circuit is a high precision delay line that does not require any other compensation means. Due to the absence of isolation, the frequency alignment I and amplitude alignment of this kind of comb filter circuit has to be repeated several times with increasingly smaller alignment stages. In the comb filter circuit of the present invention, this is not necessary.

〔Example〕

A preferred embodiment of the invention will now be described in more detail with reference to the accompanying drawing, which is a block diagram of the color reproduction portion of a video recording device. The illustrated color reproduction section includes a color signal processing circuit 1 for processing video information read from a video track 3 of a video tape 4 by a video head 2 into a color signal F'. By means of a comb filter circuit 6 connected to the output 5 of the chrominance signal processing circuit, the coherent crosstalk signals from the tracks 7 and 8 adjacent to the track 3 being read are removed from the chrominance signal which cannot be obtained from the video information of the track 3. F' is filtered out. After removing the crosstalk signal, the color signal F' is transferred from the output 9 of the comb filter circuit to the composite color signal line 11 via the switching diode 10.
is applied to

After the output 12 of the input stage 16 on the flexible side, the comb filter circuit 6 has a first delay signal path 13 and a second signal path 14 with a delay line 15 .

An inductance 18 is connected to the output 17 of the delay line 15, which together with the output capacitance 15 of the delay line 15 forms a damped resonant circuit. This resonant circuit consists of a delay line 15
The phase shifter 20 at the output of the inductance 18 can be detuned by a predetermined amount within the frequency range of the color carrier transmitted by the delay line 15 by means of an adjustment device 21 of the inductance 18.

This detuning also shifts the phase of phase shifter 20 within a predetermined range in a positive or negative direction. The effect of phase shifting is to decrease or increase the delay of the delay line. That is, by adjusting the adjustment device 21 of the inductance 18, deviations of the delay line from the nominal delay amount are compensated within relatively wide limits.

Signal paths 13 and 14 are the adder circuit 2 of the comb filter circuit.
It is connected to the signal input terminals 22 and 23 of 4. Two transistor stages 25 of equivalent design to these signal inputs 1
and 26 input circuits. The collectors of both transistors are connected to each other, and the connection point forms the output end 9 of the comb filter circuit. At the common load resistor 27 of both transistor stages, the color signals transmitted in the two signal paths 13 and 14 are added together and the difference between the crosstalk signals is formed.

In the non-delayed signal path 13, the lost signal amplitude required for crosstalk signal cancellation is provided by an adjustment device 28 of the load resistor 29 of the input stage 16.

For PAL-SECAM switching, a switching diode 31 in FIG. 2 is connected between the emitter circuit 30 of the input stage 16 of the comb filter circuit 6 and the composite color signal line 11, and connected between the output terminal 9 of the comb filter circuit 6 and ground. A switch 31 between allows short-circuiting of the output 9 of the comb filter circuit. In the off position of the switch 32, this is e.g.
Although it is in the L mode position, the switching diode 10 connected to the output 9 of the comb filter circuit is turned on.
Switching diode 3 connected to input stage 16
1 turns off. That is, after removing the crosstalk signal, the color signal F' from the output terminal 5 of the color signal processing circuit 1 is applied to the composite color signal line 11 via the comb filter circuit 6.

In the on position of switch 32, this is e.g.
In the CAM mode position, the switching diode 10 is turned off and the switching diode at the output of the input stage 16 of the comb filter circuit 6 is turned on, so that the color signal F' from the output terminal 5 of the color signal processing circuit 1 is as follows. At this time, the signal is applied from the output of the input stage 16 of the comb filter circuit 6 to the composite color signal line 11 via the switching diode 31. In order to equalize the color signal levels on the composite color signal line 11 at the reposition of the switch 32, the gains of the transistor stages 25 and 26 in the summing circuit are equal to the output of the emitter circuit 30 of the input stage 16 of the comb filter circuit. be selected so that the amplitude at the output stage 9 of the comb filter circuit is equal to that at the output stage 9 of the comb filter circuit. Therefore, even if the mode switch 32 is placed in another position, there is no need to perform another switching to adopt the output level of the composite color signal line 11.

[Brief explanation of drawings]

The figure is a block diagram of a comb filter circuit according to the present invention. In the figure, 3, 7, 8 are tracks, 4 is a recording medium, 6 is a comb filter circuit, 9 is an adder circuit output, 10°30 is a diode switch, 11 is a common second output, 13 is a first signal path, 14 is a parallel second signal path, 15 is a delay line, 18 is a variable inductance, 19 is a delay line output capacitance,
20 is a phase shifter, 22 and 23 are signal input terminals, 24 is an adder circuit, and 32 is a PAL-SEC M selection switch. Agent Patent Attorney Masatoshi Sato BAS

Claims (1)

[Claims] 1. A non-delayed first signal path having a device for adjusting signal amplitude and a predetermined delay in order to eliminate crosstalk between adjacent tracks when reproducing video information from a recording medium. a comb-shaped filter circuit comprising a parallel second signal path having a delay line giving (21
) is connected to a phase shifter (20) having an adjustable transmission delay amount (Δτ), and the adder circuit (24) is connected to each signal path (13, 14).
The adder circuit has signal input terminals (22, 23) for the addition circuit, and is characterized in that both signal inputs are isolated from each other and are symmetrical in phase with respect to the output terminal (9) of the adder circuit. comb filter circuit. 2. The phase shifter (20) is a damped resonant circuit formed by an output capacitance (19) of a delay line (15) and a variable inductance (18) connected in parallel to the output end (17) of the delay line. 2. A comb filter circuit according to claim 1, wherein the resonant circuit is detunable by a predetermined amount within the frequency range of the color carrier. 3. The adder circuit (24) is connected between collectors.
A comb filter circuit according to claim 1, characterized in that it consists of two equivalent transistor stages, the connection point between the collectors forming the output (9). 4. The input and output (9) of the comb filter circuit are each 1
Each of the two outputs (11) is connected to the common second output (11) via a diode switch (31, 10), and a switch (32) that short-circuits the output of the comb filter circuit connects the two outputs (11).
, 9), and the comb filter circuit has a gain of 1.