JPS62219372A - Digital inversion preventing device - Google Patents

Abstract

PURPOSE:To make a circuit scale small by providing a sideband wave suppressing filter, a sideband wave emphasizing filter, a carrier wave separating filter, a control signal generator, a multiplier, and a synthesizer. CONSTITUTION:A digital FM signal E of an output is obtained by synthesizing by a synthesizer 107 a signal (an output of a multiplier 106) which is obtained by multiplying a control signal (an output of a control signal generator 105) being roughly proportional to amplitude of a carrier wave component (an output of a carrier wave separating filter 104) of a digital FM signal I of an input, by both sideband wave components or the lower sideband wave component (an output of a sideband wave emphasizing filter 103) of the digital FM signal I, and the carrier wave component of the digital FM signal I, or the carrier wave component and the upper sideband wave component (an output of a sideband wave suppressing filter 102). In a part where amplitude of the carrier wave component of the digital FM signal I is not inverted large, the digital FM signals I, E are roughly equal, and in a part where the amplitude of the carrier wave component becomes large relatively by attenuating the sideband wave component. Or an unbalance of the upper sideband wave and the lower sideband wave is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applied to VTR (Video Tape Reco)
The present invention relates to an inversion prevention device that prevents an inversion phenomenon in a demodulated signal of a narrowband FM signal such as an FM signal.

When a conventional VTR performs FM recording of a video signal that rises stepwise from a black level to a white level, an inversion phenomenon may occur in which the rising portion of the white level of the demodulated signal falls to the black level. The reason for this is that when the FM signal is recorded and reproduced, the lower sideband is emphasized and the upper sideband is suppressed, and as a result, the intersection with the zero level of the FM signal disappears.

Conventionally, one of the measures to prevent reversal in the regeneration system is HPF.
There is a method of suppressing the lower sideband side using (High Pa5s Filter) etc., but it is best to suppress the lower sideband with good S and /H and emphasize the upper sideband with bad S/H.
There was a problem that the frequency characteristics deteriorated.0 Conventional methods to solve these problems include, for example, the 1977 National Conference of the Television Society, 5'-11, ``Prevention of inversion using double limiters and S/H ``About improvements''.

FIG. 6 shows a block diagram of this conventional reversal prevention device, in which 601 is an input terminal for the reproduced FM signal;
02 is an HPF (High P&ss Fi) that passes the carrier wave component of the input FM signal and greatly attenuates the lower sideband component.
603 is a limiter that eliminates the amplitude difference of the input signal and obtains a sinusoidal output signal of constant amplitude; 604
605 is a phase corrector that corrects the phase, and 605 is a LI P F (Low
Pa5s Filter), 606 is a phase corrector 60
4 and LPF 605, 607 is a limiter that keeps the amplitude constant so that the FM demodulator does not cause distortion in the demodulated output due to the M component, 608 is an FM signal output It is a terminal.

In the conventional reversal prevention device configured as described above,
In a portion where the carrier wave component of the input FM signal is small and is likely to cause inversion, the carrier wave component is amplified by the limiter 603 until it reaches a predetermined amplitude (however, the S/N deteriorates), so the carrier wave component is output from the combiner 606. FM signals that are difficult to invert are obtained. In the part where the carrier wave component of the input FM signal does not undergo significant inversion, the carrier wave component is IJ.
Since the predetermined amplitude is obtained with almost no amplification by Mitsutaro 03 (therefore, the S/N does not deteriorate), the synthesizer 6
06, an FM signal approximately equal to the input FM signal is obtained. Therefore, an FM signal that does not always undergo inversion is output.

Incidentally, as seen in digital TVs, the merits of digital signal processing are attracting attention even in consumer equipment, and it is necessary to consider methods of realizing devices that were conventionally realized with analog circuits with digital circuits.

The configuration shown in the block diagram of FIG. 7 is conceivable as an implementation of the conventional inversion prevention device using a digital signal processing circuit. This device uses a digital FM signal, which is a sampled and quantized FM signal, as an input/output signal. 7th
In the figure, 701 is a digital FM signal input terminal;
702 is an IFF, 703 is an IJ transmitter that makes the output amplitude of HP F 702 a constant value, and 704 is an HP F 7
An amplitude detector 705 obtains an amplitude signal that is the amplitude of the output signal of HPF 704;
706 is an LPF, 707 is a synthesizer that combines the output of the i-i-tsuta 703, that is, the output of the divider 705, and the output of the LPF 06; This is an output terminal for digital FM signals. Since HPF702゜L P F Toe can easily have linear phase characteristics, a phase corrector is not required.
The limiter 607 in FIG. 6 is omitted because it is a circuit not directly related to inversion prevention.

The basic operation of the conventional digital reversal prevention device constructed as described above is the same as that shown in FIG. 8, so the explanation thereof will be omitted.

Problems to be Solved by the Invention However, the above configuration requires a divider with a larger circuit scale than the multiplier. Moreover, LPF70
The output signal of HPF02 is a carrier wave component with a large amplitude, whereas the output signal of HPF02 is a carrier wave component with a large amplitude, so it is necessary to increase the data word length. Therefore, the circuit scale of the divider 705 and the amplitude detector 704 is larger, making it difficult to realize a digital inversion prevention device.

In view of this, an object of the present invention is to provide a digital reversal prevention device that has a small circuit scale and is easy to implement.

Means for Solving the Problems The present invention is a digital inversion prevention device that uses digital FM signals I and E as input signals and output signals, respectively.
A sideband suppression filter that suppresses both sideband waves or lower sideband waves of digital FM signal I, a sideband emphasis filter that emphasizes both sideband waves or lower sideband wave of digital FM signal engineering, and a sideband wave enhancement filter that emphasizes both sideband waves or lower sideband waves of digital FM signal engineering; a carrier wave separation filter to be extracted; a control signal generator that detects the amplitude of the output signal of the carrier wave separation filter and outputs a control signal approximately proportional to the amplitude; and a control signal generator that detects the amplitude of the output signal of the carrier wave separation filter and outputs a control signal approximately proportional to the amplitude; The present invention is a digital inversion prevention device comprising a multiplier for multiplication, and a synthesizer for synthesizing two output signals of the sideband suppression filter and the multiplier to obtain a digital FM signal E. Depending on the configuration, a signal obtained by multiplying the sideband component of the digital FM signal by a control signal approximately proportional to the amplitude of the carrier component of the input digital FM signal and the carrier component of the digital FM signal are combined to generate an output signal. A digital FM signal E is obtained. In the part where the amplitude of the carrier wave component of the digital FM signal is large and no inversion occurs, the digital FM signal 1. E is almost equal, and in parts where the amplitude of the carrier component is small and inversion is likely to occur, attenuating the sideband component makes the carrier component relatively large or improves the imbalance between the upper and lower sidebands. A digital FM signal E without inversion can be obtained.

Embodiment FIG. 1 shows a block diagram of a digital reversal prevention device in an embodiment of the present invention. In Figure 1,
101 is an input terminal of the digital FM signal, 1o2 is a sideband suppression filter that suppresses both sideband waves or lower sideband of the digital FM signal, and 103 is a sideband that emphasizes the both sideband or lower sideband of the digital FM signal. a wave emphasizing filter; 104 is a carrier separation filter that extracts the carrier component of the digital FM signal 1; 106 is a control signal generator that detects the amplitude of the output signal of the carrier separation filter 104 and outputs a control signal that is approximately proportional to the amplitude; A multiplier 106 multiplies the output of the sideband emphasizing filter 103 by the control signal, and a multiplier 107 synthesizes the two output signals of the sideband suppression filter 102 and the multiplier 106 to generate an output signal, the digital FM signal E. It is a synthesizer that obtains.

The operation of the digital reversal prevention device of this embodiment configured as described above will be explained below.

The control signal (output of the control signal generator 106) is approximately proportional to the amplitude of the carrier component (output of the carrier separation filter 104) of the input digital FM signal. (output of sideband emphasizing filter 103)
06 output) and the carrier wave component of the digital FM signal I, or the carrier wave component and the upper sideband component (the sideband suppression filter 10
The output digital FM signal E is obtained by combining the two outputs.

In parts where the carrier wave component of the digital FM signal is large and no inversion occurs, the control signal is also large, and the output digital FM signal E is almost equal to the input digital FM signal, and the S/N is also inverted.

Frequency characteristics do not deteriorate. Also digital FM
In areas where the signal carrier component is small and is prone to inversion, the control signal is also small, so both sidebands or lower sidebands of the output digital FM signal E are attenuated, and the carrier component becomes relatively large or the upper sideband wave is attenuated. Since the unbalance of the lower sideband is improved, the output digital FM signal E does not undergo inversion. Therefore, the digital FM signal E always does not undergo inversion.

In this embodiment, the divider 705, which was required when the conventional example was digitalized (FIG. 7), is not required, and the multiplier 106 is required instead. Comparing the same data word length, the multiplier has a smaller circuit scale than the divider, and the sideband wave has a smaller amplitude than the carrier wave. Since the input signal of the divider 705 is smaller than that of the input signal of the divider 705, the circuit scale becomes smaller.

FIG. 2 shows a block diagram of an example of a control signal generator. 201 is an input terminal for the carrier wave component, 202 is a 90' phase shifter that changes the phase of the input signal and outputs two signals X and Y having a phase difference of 900, and 203 and 204 are squares that square the input and output it. 205 is an adder that adds two human forces, 206 is a square rooter that obtains the square root of the input, and 207 is a square rooter that obtains the square root of the input. ) is a signal converter that generates

The operation of this control signal generator will be explained below.

The carrier wave component at the input terminal 201 is
t (where A, w, and t are the amplitude and angular frequency of 9 hours, respectively), then the 2 output signals X of the 9d phase shifter.

Y is A-cos(w-t+θ) and A-sin(
w−t+θ) (where θ is a constant), and the output of the square rooter 206 is rY′=A, that is, the amplitude of the carrier wave component. The signal converter 207 outputs a control signal C whose amplitude is approximately proportional to the input signal. FIG. 3 shows an example of the input/output characteristics of the signal converter. (The characteristics are not limited to these, and since it is a ROM, various characteristics can be easily realized.) The 9o0 phase shifter is a digital filter that has a frequency-amplitude characteristic within the required band. must be flat, but the required bandwidth is 2 MH
Since it is as narrow as z, it can be realized with a simple configuration.

Squarer 203, 204, squarer 206, signal converter 20
7 is a semiconductor memory ROM (Read Only Memory
Or7), and in this case, the square rooter 2o6,
The signal converter 207 can be realized with one ROM.

Furthermore, the sample frequency fs in signal processing is set to the carrier frequency of the FM signal (approximately 3.5 MHz for home VTRs).
z ~ 5.5 MHz with a frequency deviation of approximately 1 ~ 1
．． It is 2MH2. ) or slightly higher (1 sMHz in this example).

Since this frequency is an integral multiple of the line frequency of NTSC, PAL, and SECAM3 systems, it is also suitable for signal processing after FM demodulation. ) various filters o2, 103, 10 which are digital filters by setting
The configuration of the 4190Q phase shifter 202(7) can be simplified.

For example, the sideband suppression filter 02 and the sideband emphasis filter 03 are expressed as -(1+2Z +Z
), -(-1+2Z -Z ) or =(
1+2Z +Z ), j(-1+22 -Z )
,! :M can be realized even with a simple configuration (not limited to this configuration). These frequency characteristics are
As shown in Fig. 5. In each figure, a, b, and c are a sideband emphasis filter 1o3 and a sideband suppression filter 10, respectively.
2. Expresses the frequency characteristics of the entire digital reversal prevention device.

Further, part or most of the circuits of the sideband suppression filter 102, the sideband emphasis filter 103, and the carrier separation filter 104 can be shared, which further reduces the circuit scale.

An example of the configuration of a 9d phase shifter is −(1-1-sZ −
sZ −Z ). However, in this example, since the gain is not 1, it is necessary to take measures such as correcting the ROM data of the squarer in advance.

As described above, according to this embodiment, by controlling the sideband components using a multiplier with a control signal that is approximately proportional to the amplitude of the carrier component, the sampling frequency can still be increased to approximately four times the carrier frequency of the FM signal. By setting this, the circuit scale of the digital inversion prevention device can be reduced.

In addition to the method shown in Fig. 2, as an amplitude detection method for the control signal generator, there is also a method of squaring or converting the input signal into an absolute value and obtaining the amplitude value through an LPF. It can also be used as an out detection output.

However, if the input signal to the digital inversion prevention device has both sideband components or lower sideband components suppressed in advance, a configuration in which the sideband suppression filter is omitted may be considered.

As described in detail, according to the present invention, the circuit scale can be reduced, making it easy to realize a digital reversal prevention device, and its practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a digital inversion prevention device according to an embodiment of the present invention, FIG. 2 is a block diagram of a control signal generation circuit, FIG. 3 is an input/output characteristic diagram of a signal converter, and FIGS. The figure is a frequency characteristic diagram of each part, FIG. 6 is a block diagram of a conventional reversal prevention device, and FIG. 7 is a block diagram of a digital reversal prevention device in which the main parts of FIG. 6 are digitally processed. ...Sideband suppression filter, 103...
... Sideband emphasis filter, 104 ... Carrier separation filter, 105 ... Control signal generator, 1
06...Multiplier, 10A...Synthesizer. Name of agent: Patent attorney Toshio Nakao and 1 other person
R Figure 4 fs/z Figure 5 jd4 fd2 Figure 6 Figure 7 3

Claims (2)

[Claims] (1) A digital inversion prevention device that uses digital FM signals I and E, which are sampled and quantized FM signals, as input and output signals, respectively, and which uses digital FM signals I and E as input signals and output signals, respectively.
a sideband suppression filter that suppresses both sidebands or the lower sideband of the digital FM signal I, a sideband emphasis filter that emphasizes the both sidebands or the lower sideband of the digital FM signal I, and a carrier separation filter that extracts the carrier component of the digital FM signal I. a control signal generator that detects the amplitude of the output signal of the carrier separation filter and outputs a control signal substantially proportional to the amplitude; and a multiplier that multiplies the output signal of the sideband emphasizing filter by the control signal. , a synthesizer for synthesizing two output signals of the sideband suppression filter and the multiplier to obtain a digital FM signal E as an output signal. (2) The digital inversion prevention device according to claim 1, wherein the sampling frequency is approximately equal to four times the carrier frequency of the FM signal.