JPH0252410A - Elimination of crosstalk in rotary transformer - Google Patents

Abstract

PURPOSE:To eliminate noise by mixing a crosstalk signal due to a rotary transformer with a crosstalk signal having the same level and opposite phase so that they cancel each other. CONSTITUTION:Regenerative signals output from heads 12, 22 of a first and a second channels 10, 20 are in-phase each other and input to input terminals 18, 28 of a switching circuit 5 via rotary transformers 13, 23 and preamplifiers 16, 26, but crosstalk signals induced in stator coils 25, 15 by rotor coils 14, 24 are in opposite phase and output from preamplifiers 26, 16. The signals from the channels 10, 20 are mixed each other at a level determined by a resistor 7. When the resistance value R of the resistor 7 is selected to be a definite value according to the output impedance (r) of the preamplifier and the crosstalk factor alpha, the crosstalk can always be eliminated by cancelling even if the level of the regenerative signals input to the rotary transformers 13, 23 is varied from 0 to the maximum value irrespective of the amplification factor A of the preamplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a two-channel signal transmission system using a rotary transformer.

[Summary of the invention]

In a two-channel signal transmission system that transmits signals via rotary transformers, the present invention inverts the phases of crosstalk signals generated by the rotary transformers of both channels, and mixes a portion of the signals of both channels with each other. This is to eliminate crosstalk.

[Conventional technology]

Devices with two-channel signal transmission systems that transmit signals via rotary transformers include, for example, various types of video tape recorders (VTRs) and digital audio tape recorders (DATs) that record and play back signals in a helical scan format. be.

The signal recorded and reproduced using the helical scan format is DAT.
(PCM digital audio signal) and early home V
One type of TR (FM modulated video signal), a professional VTR that requires high performance (divides the video signal into a luminance signal and a color signal), or an economical high-density recording. A home VTR that processes multiple signals that are each individually FM modulated, such as a home VTR (standard recording and triple recording, separate signal systems for high-speed/slow/still playback, or two or more audio recording VH3 systems) There is.

In each of these VTRs and DATs, channels consisting of multiple heads, rotary transformers, signal processing circuits, etc. are assigned to one signal, and they are arranged at equal central angles (for example, 180 degrees) on a rotating drum. A plurality of (two) heads record time-divided signals at a constant cycle, each as one track diagonally in the running direction of the tape.
Further, the signals reproduced from each track are sequentially switched and reproduced as continuous signals.

FIG. 9 is a circuit diagram showing a conventional example of a two-channel audio signal transmission system during reproduction.

This signal transmission system has the first and second channels 10.20
, switching circuit 5, stereo audio circuit glue, R
Bandpass filter (BPF) 5 for each channel
The first and second channels 10.20 each include a head 12.22 and a rotary transformer 13, 2.
3. It consists of a preamplifier 16.28.

In addition, in the rotary transformer 15.23, a rotor coil 14.24 provided on the rotating drum 1 side and a stator coil 15.25 provided on the fixed drum on the 1 body side face each other, and are concentric with each other around the rotation axis. It is structured as follows.

The time-divided signals are sent from each track to the head 1.
2. Regenerated alternately by 22, rotary transformer 15
．． 23 and amplified by the preamplifiers 16 and 28, the signals are alternately switched by the switching circuit 5 synchronized with the rotation of the rotary drum 1 to become a continuous reproduction signal, and the B
It is output to PF6L, 5R and subsequent circuits following them.

[Problem to be solved by the invention]

However, the rotary transformer 13 shown in FIG.
23, as shown in FIG. 6 and described later, due to its structure, crosstalk from other channels is quite large.

Therefore, there is no problem when the reproduction output of one head is O, but during the overlap period when signals are simultaneously reproduced from the two heads before and after the switching circuit 5 operates,
Signals output from the switching circuit 5 to the circuits after the BPF 6L and SR overlap each other with playback signals from other heads due to crosstalk, which is the main cause of noise in the audio signal.

The purpose of this invention is to provide a method of canceling out crosstalk signals from other channels due to this rotary transformer cross 1-1 and removing noise at a small cost by adding a simple circuit. do.

[Means to solve the problem]

In order to achieve the above object, the present invention has a two-channel signal transmission system that transmits signals via rotary transformers, and inverts the phases of crosstalk signals generated by the rotary transformers between the two channels. A signal corresponding to the level of the crosstalk signal is mixed with each signal using an impedance element.

[For production]

According to the present invention, by doing as described above, the crosstalk signal generated by the rotary transformer is mixed with the crosstalk signal having the same level and inverted phase, and the crosstalk signals cancel each other out, thereby making it possible to remove noise.

〔Example〕

The present invention will be described below with reference to an example of a two-channel signal transmission system that records and reproduces FM-modulated audio signals in a helical scan format.

For example, in a VH3 home Hi Hi-VTR, two carrier waves with different frequencies (for example, 1.3M
Hz and 1.7 MHz) are respectively applied as stereo audio signals, and after FM modulation with the R signal, the synthesized FM audio signals are recorded deep into the tape, and video signals with different modulation frequency bands are superimposed on top of the FM audio signals. It is recorded in the shallow layer.

As shown in FIG. 4, two recording/reproducing heads 12 and 22 (hereinafter only heads related to audio) are installed at positions 180° apart and symmetrical about the rotational axis of the rotary drum 1 rotating in the direction of arrow B. (the head related to the image is omitted), the rotating drum 1 is helically wound for more than half a turn and the head related to the image is omitted.
An FM audio signal is recorded on a tape 2 running in the direction.

FIG. 5 is a developed view visually showing the signals recorded on the tape 2 when viewed from the base surface of the tape.

In the figure, reference numeral 3 indicates a control track for correctly tracking the recorded track by the head 12.22.

The FM audio signal is divided into signals corresponding to one field of the video signal (1/60 seconds in NTSC), and each signal is divided into signals corresponding to one field of the video signal (1/60 second in NTSC), and each signal is divided into signals corresponding to the FM audio track 11 diagonally with respect to the running direction of the tape 2 (arrow A) by heads 12 and 22. .21, but the adjacent FM audio tracks 11.21 are recorded so that the end a of the preceding track overlaps the leading end a of the succeeding track by about 5%. .

The two heads 12.22 are tilted at an azimuth angle of, for example, ±6° (azimuth recording) in opposite directions from a position perpendicular to the direction of trunk movement (arrow C) with their herad gaps (not shown). Signals from tracks with different azimuth angles are not reproduced.

That is, the FM audio track 11 recorded by the head 12
The signal is reproduced by the head 12, but not by the head 22. Conversely, the signal of the FM audio track 21 is not reproduced by the head 12, but is reproduced by the head 22.

Therefore, during reproduction, the signal of the control track 3 is detected, and the heads 12.22 are controlled so as to correctly track the FM audio tracks 11.21 and reproduce the signals.

The FM audio signal reproduced by the head 12°22 rotating together with the rotating drum 1 is transferred to the VT by a rotary transformer.
The signal is transmitted to a circuit provided on the fixed side of the R main body.

FIG. 6 is an explanatory diagram showing an example of the structure of the rotary transformer lance, and FIG. (b) is a schematic cross-sectional view of the rotary transformer.

4 channel rotary transformer 15,25°33.4
are rotor coils 14, 24, 34, 44 provided on the lower end surface of the rotating drum 1, and stator coils 15, 25, 5 provided on the upper end surface of the fixed tram 4 on the main body side, respectively.
5.45.

For example, the rotor coil 14 and stator coil 15 of the rotary transformer 13, which have the same radius, are arranged concentrically with the rotating shaft 1a of the rotating drum 1 with a small gap in the axial direction. Approximately 0.1M to input
~l OM I (The signal with the high frequency of z is output from the other coil regardless of whether the rotating drum 1 is stationary or rotating.

The same applies to the other rotary transformers 23.3:5 and 4.

Among these, the rotary transformer 13.22i is used for the audio signal transmission system, and the rotary transformers 3"S and 43; are used for the video signal transmission system, but the frequency of the signal transmitted by each rotary transformer is high as described above. Therefore, crosstalk between adjacent rotary transformers can be, for example, about 10 dB.

Figure 7 shows the FM audio track 11.21 shown in Figure 5.
FIG. 2 is an explanatory diagram schematically showing a state in which one of the cables is taken out and a video signal is recorded on top of it.

The FM audio track 11 and the video track 9 on which the video signal is recorded are shown shifted at right angles to the direction of travel of the head indicated by the arrow for the sake of clarity, but in reality, the FM audio track 11 and the video track 9 on which the video signal is recorded are shown shifted at right angles to the running direction of the head indicated by the arrow. .

Since the video signal is recorded on top of the tape in the shallower layer, the shallower layer of the FM audio signal is erased and recorded in the deeper layer of the tape.

Since the FM audio signal and the video signal are recorded using different heads, and the recording start times of the tracks are shifted, the track lengths of the FM audio track 11 and the video track 9 do not necessarily match, and the lengths of the FM audio track 11 and the video track 9 do not necessarily correspond to Since there is a slight deviation in the perpendicular direction, there are parts at both ends of the FM audio track 11 that do not overlap with the video track 9.

In this non-overlapping area, the audio recording remains on all layers of the tape, so the playback level will be high when played back with the audio head.

Figure 8 shows an example of each reproduced signal waveform near the signal overlap period on the oscilloscope screen (vertically symmetrical waveform).
It is a schematic diagram showing the negative side cut away, and the switching point is shown with a dashed line.

Figures 8(a) and (b) show the reproduced signal at a height of 12°22.
Each trailing part of the waveform seen at the output terminal of.

The beginning part is shown, and the level at both the ending part and the beginning part is rising.

FIGS. 8(C), (d), and (e) show the waveforms of the reproduced signal at the input terminal 18, 28 and the output terminal of the switching circuit 5, respectively. The dashed lines indicate the cases where there is.

As shown in (Q) and (d) of the same figure, when there is no crosstalk, the waveforms are the same as those shown in (a) and (b) of the same figure, but when there is crosstalk, the waveforms are reproduced on that channel. It does not become 0 even when there is no signal, and the waveform is deformed during the overlap period.

As shown in FIG. 5(e), the continuous reproduction signal switched by the switching circuit 5 is flat when there is no crosstalk, but when there is crosstalk, the signal is flat at both ends of the overlap period.

The effect of leveling up the terminal section appears.

Figure 8(f) shows the waveform of the continuous reproduced signal shown in Figure 8(e) when viewed at the output side of BPF8L (or SR).It is flat when there is no crosstalk, but when there is no crosstalk, it is flat. In some cases, severe level ups or downs often appear at both ends of the overlap period.

Although it is difficult to understand just by looking at the waveform at the level shown in FIG. Since a phase difference occurs between the two channels, a phase difference also occurs between the reproduction signal and the crosstalk signal of both channels.

Therefore, on the output side of BPF13L (or 8R), when they are in phase, a level up (upper limit) appears as the sum of the amplitudes of the reproduced signal and crosstalk signal, and when they are in opposite phase, a level down (lower limit) appears as the difference between them. , an intermediate level appears when the phase is not reversed.

Generally, after the BPF, the signal is input to the FM detection circuit via an amplitude limiter, so most level fluctuations are absorbed and do not appear in the audio signal (detected output). 60Hz signal
Pulse noise that tends to cause discomfort appears as a so-called buzz.

Figure 1 shows how this invention is applied to a VH8 system HiFi-VTR.
FIG. 2 is a circuit diagram showing a first embodiment applied to a two-channel audio reproduction signal transmission system, and FIG. 2 is an equivalent circuit diagram thereof.

In the embodiment shown in FIG. 1, parts that are the same as those in the conventional example shown in FIG. The winding directions of the two coils 14.15 and 24.25 of the rotary transformer 13.2'5 of the first and second channels 10.20 are opposite to each other.

(2) The first and second channels 10.20 are each bridged to each other by an impedance element resistor 7 with a resistance value R on the output side of the preamplifier 16.26.

(3) A load resistor 17 whose one end is grounded and whose resistance value is RL is connected between the bridge portion of each of the first and second channels 10.20 and the input terminal 18°28 of the switching circuit 5.
．． The above three points are that 27 was connected.

According to (1) above, the first and second channels are 10°20
The reproduced signals outputted from the heads 12.22 are in phase with each other and are input to the input terminals 18.
However, the crosstalk signals induced from the rotor coils 14 and 24 to the stator coils 25 and 28 are outputted from the preamplifiers 28 and 18 with opposite phases.

According to (2) above, the first and second channels 10.20
signals are mixed together at a level determined by resistor 7, as described below.

Theoretically, this resistor 7 may be bridged on the input side of the preamplifier 16゜26, but noise from other sources is likely to be mixed in, and the impedance before and after the bridge will exceed the inductance of the stator coil, etc. Since it is desirable that the resistance be close to pure resistance, in the embodiment, it is bridged on the output side.

Although the load resistors 17.27 mentioned in (3) above may be omitted, the load resistors 17.27 have a relatively high resistance value RL so as not to be affected by variations in the input impedance of the switching circuit 5. 27 was installed to improve safety.

In the equivalent circuit shown in FIG. 2, when the signal output induced from the rotor coil 14.24 to the stator coil 15.
Let α (0<α<1) be the crosstalk signal output, that is, the crosstalk rate induced by α, the amplification factor of the preamplifier 18.28 be A, and the output impedance be r.

Therefore, when only the head 12 of the first channel 10 outputs the reproduction signal to the rotor coil 14 of the rotary transformer 13, if the reproduction signal V is induced in the stator coil 15, the output signal of the preamplifier 16 is AV, Since the crosstalk signal -αV is induced in the stator coil 25 of the second channel 20, the output signal of the second preamplifier is -αAV.

Here, if the ratio of the output impedance r of the preamplifier to the load resistance RL is P, then P=r/RL.

Now, assuming that the output signal of the preamplifier 1B is El6 and the output signal of the preamplifier 26 is O, calculating the values of the input signals E1s and E2g of the input terminals 18 and 28 of the switching circuit 5, (r + (1 + P) R) El, 6 AV E 16 .

Also, if the output signal of the preamplifier 1st is 0, the preamplifier 26
Similarly, when the output signal of is Ez6, E26 may be substituted for El6 in the above equation, and the coefficients of Ets and E28 may be exchanged.

Therefore, as described above, the input signal of the input terminal 18.28 when the output signal of the preamplifier 16.26 is AV and -αAV, respectively, is calculated as V zs + V za .

Here, the input signal VZII is a rotary transformer 13°2
This is caused by the crosstalk of the 3-way switch and the mixing of signals due to the bridging of the resistor 7, so if this value becomes 0, it means that the crosstalk has been canceled.

The condition for Vzt”:O is that the numerator of the above formula V2,9 is 0, so [r+(1+P)R)αAV=rAV α(1+P)R=r−rα r αAV (1+P)( 2r +(1+P)R)(1+P)
L2r+(1+PJLl) However, in general, the output impedance r of the preamplifier
is low, and the load resistance RL is much higher than that, so
r<<RL Therefore, P<<1, and if P is ignored for 1, the following approximate expression may be used.

1- α R= r (approximate formula) In other words, the resistance value R of the resistor 7 is the output impedance r of the preamplifier
If the value determined by the above formula is determined by the crosstalk rate α (and P), the level of the reproduced signal input to the rotary transformers 13i and 23 will increase from O to the maximum value, regardless of the preamplifier increase rate A. Even if it fluctuates, crosstalk can always be canceled out and removed.

Furthermore, since the constants of the elements constituting the first and second channels are the same, it is possible to remove the cross 1-1 from the rotary transformer of either channel in the same way.

Note that the level of the input signal V18, that is, the reproduction signal at this time, is 1. °°゛°° (Table (Heron 2), crosstalk rate α = 0.25 (= 12d
When calculating the value of the approximate formula as B), R=3 r, V1
s=0.6AV.

As explained above, by bridging the first and second channels with the resistor 7 with the resistance value R=(1-α)r/α, the crosstalk between the rotary transformers 13 and 23 is canceled and eliminated. and audio tracks 11 and 21 respectively.
The FM audio signals reproduced by the heads 12 and 22 are amplified by the preamplifier 16.2 and input to the input terminals 18 and 28 of the switching circuit 5.

The switching circuit 5 is turned on near the center of the overlap period by a head position signal output from a head position detector (not shown) provided on the shaft 1a of the rotating tram 1 (FIGS. 4 and 6). The live channel that was previously was switched to the follow channel that newly started outputting the playback signal.

Therefore, disturbances in the playback signal level at both ends of each FMM voice track are cut out, and the switching circuit 5
flat continuous FM with no crosstalk.
An M voice reproduction signal is output.

BP16L, 5R are, for example, rotary transformers 2;, 5
F of video signals mixed due to crosstalk between 3
In addition to blocking noise outside the MM voice signal band, it also uses two carrier waves with different frequencies (1.3M and 1.7MI (z
), BPF13L has a center frequency of 1 and 3 M.
Only the FM audio signal of I(z), BPF 5R outputs only the FM sound multiple signal with a center frequency of 1.7M7.

After level fluctuations are removed by an amplitude limiter (not shown), the output is 1.3 MI (z, 1.7
An FM demodulation circuit (not shown) adjusted to MHz demodulates the signal into a noise-free R stereo audio signal, which is output to a subsequent audio circuit.

FIG. 3 is a circuit diagram showing a second embodiment in which the present invention is similarly applied to a two-channel audio reproduction signal transmission system.

This second embodiment differs from the first embodiment (FIG. 1) in that: (A) two coils 14.15 and 24 of the rotary transformer +3.23 of the first and second channels 10.20, respectively; (B) The polarities of the input terminals of the preamplifier +E3.26 of the first and second channels 10.20 are reversed.

(C) The connections between the heads 12.22 of the first and second channels 10.20 and the rotor coils 14.24 of the rotary transformer 13.23 are reversed.

In the rotary transformer 13.23 shown in (A) above, even if the phases of the crosstalk signals induced in each stator coil 15.25 match, the above (B)
As shown in , by reversing the polarity of the input terminals of preamplifier 16 and 26, the phase is reversed at the output terminal of the preamplifier, so by bridging with resistor 7, Talostalk is canceled out and removed. You can.

However, even if the phases of the reproduced signals output from the heads 12 and 13 are aligned, the output terminal of the preamplifier 18.2E3, that is, the input terminal 18.2 of the switching circuit 5
8, the reproduced signal has an opposite phase, so if it continues as it is, the signal will become discontinuous when the switching circuit 5 is switched.

Therefore, as shown in (C) above, the connections between the head 12.22 and the rotor coil 14.24 are reversed, so that the reproduced signals at the input terminals 18.28 of the switching circuit 5 are in phase. I have it all ready.

Even if connected in this way, it does not affect the removal of crosstalk, so the effect remains the same.

According to this second embodiment, the present invention can be applied with a slight modification even to a VTR 1 manufactured using a conventional rotary transformer with the same winding direction or to a VTR already in the hands of a user. You can.

In addition, in the first and second embodiments, when the mutual phase of each signal of the first and second channels is set to the opposite phase of the crosstalk signal, the reproduction signal is connected so as not to be reversed. However, if the reproduction signal is For example, in Figure 1, the second
Even if the black mark indicating the winding direction attached to the lower side of the rotor coil 24 of the rotary transformer 23 of the channel 20 is connected to the upper side of the rotor coil 24, the noise generated due to switching by the switching circuit 5 is not practical. It's small enough that it won't be a problem.

In comparison, the noise due to crosstalk is much larger, so even if the phase of the reproduced signal is out of order, the effects of the present invention are not impaired.

As described above in the first and second embodiments, according to the present invention, the tally talk of the rotary transformer can be eliminated by simply adding one resistor.

Even if the frequency characteristics of the Talostalk rate are not flat due to the characteristics of the rotary transformer, crosstalk can be uniformly removed in the required frequency band by purchasing a bridging impedance element with a combination of resistors, capacitors, inductors, etc. The cost increase caused by this is also extremely small.

Although the present invention has been described above with reference to an example in which it is applied to an audio playback signal transmission system of a HiFi-VTR, it can be similarly applied to a video playback signal transmission system or a DAT playback signal system.

〔Effect of the invention〕

As described above, the present invention provides a method of canceling out crosstalk signals from other channels due to crosstalk of a rotary transformer and removing noise at a small cost by adding a simple circuit. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the invention, FIG. 2 is an equivalent circuit diagram thereof, FIG. 3 is a circuit diagram showing a second embodiment of the invention, and FIG. 4 is a circuit diagram showing a second embodiment of the invention. FIG. 3 is a perspective view showing the relative positions of a spatula and a tape in the target device. Fig. 5 is a development diagram that visually shows the signals recorded on the tape, Fig. 6 is an explanatory diagram showing the structure of the rotary transformer, and Fig. 7 shows the audio signal recorded in Fig. 5. FIG. 8 is an explanatory diagram showing the state in which signal recording is overlapped. FIG. 8 is an explanatory diagram showing the signal level. FIG. 9 is a circuit diagram showing a conventional example of this apparatus. 1...Rotating drum 2...Tape 4...Fixed drum 5...Switching circuit 5L, 5R
... Band pass filter (BPF) 7 ... Resistor (impedance element) 10.20 ... First and second channel 11.21.
...FM audio track 12.22...Head 13.23.33,4"S...Rotary transformer 14
．． 24.34.44...Rotor coil 15.25.3
5.45...Stator coil 18.28...Preamplifier 17゜27...Load resistance 18゜28... (of switching circuit 5) Input terminal Fig. 3 Fig. 9 Fig. 1 Fig. 2 Fig. 4 Figure 2F] 2 Figure 5 Tape running direction Figure 6 (b) Figure 7

Claims (1)

[Claims] 1. In a two-channel signal transmission system that transmits signals via rotary transformers, the phases of the crosstalk signals generated by the rotary transformers between both channels are inverted, and the crosstalk signals are applied to each signal of both channels. A method for removing crosstalk from a rotary transformer, characterized in that the crosstalk signal is canceled by mixing signals according to the level of the crosstalk signal with each other using an impedance element.