JP2665375B2 - Inversion prevention device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inversion prevention device for preventing an inversion phenomenon in a narrow band FM signal.

[Conventional technology]

FIG. 5 is a block diagram of a conventional reversal prevention device disclosed in, for example, Japanese Patent Application Laid-Open No. 62-219372. In the figure, reference numeral 601 denotes an input terminal of a reproduced FM signal, and 602 denotes an input FM signal. HPF (High Pass Filter) that passes the carrier wave component and attenuates the lower band component greatly, 603 is a limiter that eliminates the amplitude difference of the input signal and obtains a sine wave output signal with constant amplitude,
604, a phase corrector for correcting the phase; 605, an LPF (Low Pass Filter) for sufficiently attenuating the carrier component of the input FM signal;
6 is a combiner that combines the outputs of the phase corrector 604 and the LPF 605,
Reference numeral 607 denotes a limiter for keeping the amplitude constant so that the subsequent FM demodulator does not cause distortion in the demodulation output due to the AM component. Reference numeral 608 denotes an FM signal output terminal.

In the conventional inversion prevention device configured as described above, in a portion where the carrier component of the input FM signal is small and easily inverted, the carrier component is amplified by the limiter 603 until the amplitude becomes a predetermined amplitude (where S / N is Therefore, an FM signal in which only the carrier wave component is amplified and difficult to invert is obtained at the output of the combiner 606. In a portion where the carrier wave component of the input FM signal does not significantly invert, the carrier wave component has a predetermined amplitude without being amplified by the limiter 603 (therefore, the S / N does not deteriorate).
An FM signal approximately equal to the signal is obtained. Therefore, an FM signal that does not always cause inversion is output.

By the way, performing signal processing by digital technology has advantages such as downsizing, non-adjustment, and high accuracy of the circuit, and it is necessary to consider a method for realizing the conventional analog part with a digital circuit in an inversion prevention device. There is. FIG. 6 is a block diagram for realizing the inversion prevention device disclosed in Japanese Patent Application Laid-Open No. Sho 62-219372 by a digital processing circuit as it is.

This device uses digital FM signals, which are sampled and quantized FM signals, as input / output signals. In FIG.
701 is digital FM signal input terminal, 702 is HPF, 703 is HP
Limiter that keeps the output amplitude of F702 constant, 704 is HPF702
Amplitude detector that obtains an amplitude signal that is the amplitude of the output signal of
5 is a divider for dividing the output signal of the HPF702 by the amplitude signal from the amplitude detector 704 to obtain a carrier component having a constant amplitude, and 706 is an LP.
F and 707 are the output of the limiter 703, that is, the output of the divider 705.
A synthesizer that combines the output of the LPF706 and a digital FM 708
This is a signal output terminal. Since the HPF702 and LPF706 can easily have linear phase characteristics, a phase corrector is not required, and the limiter 607 in FIG. 5 is omitted because it is a circuit not directly related to the prevention of inversion.

The basic operation of the conventional digital inversion prevention device configured as described above is the same as that in the case of FIG. 5, and the description thereof will be omitted.

[Problems to be solved by the invention]

However, such a configuration requires a divider having a larger circuit scale than a multiplier. Moreover, while the output signal of the LPF706 is a sideband component with a small amplitude,
Since the output signal of F702 is a carrier component having a large amplitude, it is necessary to increase the data word length. Therefore the divider 70
5. There is a problem that the circuit size of the amplitude detector 704 becomes larger, and it is difficult to realize a digital inversion prevention device.

SUMMARY OF THE INVENTION In view of the foregoing, an object of the present invention is to provide an inversion prevention device which has a small circuit scale, is inexpensive and easy to realize.

[Means for solving the problem]

An inversion prevention apparatus according to the present invention has a quantized digital FM signal as an input, a sideband suppression filter for suppressing upper and lower sidebands or a lower sideband, and an output of the digital FM signal and an output of the sideband suppression filter. A discriminator for discriminating whether or not the codes match; a detector for detecting a peak of the digital FM signal; the digital FM signal or the sideband suppression filter according to an output result of the discriminator and the detector; And a selector for selecting and outputting one of the outputs.

[Action]

In the present invention, the discriminator discriminates whether or not the sign of the output of the digital FM signal and the output of the sideband suppression filter match, and the detector detects the peak of the digital FM signal. By selecting and outputting either the input digital FM signal or the output of the sideband suppression filter according to the output result, the amplitude of the carrier wave component is higher than that of the FM signal in which the upper and lower bands are unbalanced. The digital FM signal is output as it is in the portion where no significant inversion occurs, but the sideband suppression corresponding to the fact that the carrier component is relatively large in the portion where the amplitude of the discrimination wave component is determined to be small and inversion occurs in the discriminator. A digital FM signal that has passed through a filter can be output, and a digital FM signal that does not cause inversion can be obtained.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an inversion prevention device according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an input terminal of a digital FM signal, and reference numeral 3 denotes upper and lower sidebands or lower sidebands of the digital FM signal. The sideband suppression filter 2 is darkened by a delay corrector that delays the digital signal by the same time as the delay time of the signal output from the sideband suppression filter 3, and the outputs of the delay corrector 2 and the sideband suppression filter 3 are at the same time. Can be regarded as a signal quantized to 4, 5 and 7 are delay units for delaying input data by one sample clock.
And detector 6 constitute detecting means for outputting 1 if the average of the absolute value of the difference between two adjacent points of the output of the delay compensator 2 is equal to or less than a predetermined value, and outputting 0 otherwise. An XOR gate that outputs 0 if the sign bit values of the outputs of 7 and 7 coincide with each other, 1 otherwise, 9 is an AND gate, 10 is a selector, and A is output when the output of the AND gate 9 is 1. B side at 0
Side is selected, and the digital FM signal is output to the output terminal 11.

Next, the operation of the reversal prevention device according to the present embodiment will be described. Now, the output of the delay corrector 2 x (k + 1), when the output of the sideband suppression filter 3 and x _F (k + 1), the delay unit 4,
Each 7 output _{x (k), x F (} k), and the delay unit 5
Is x (k-1). A predetermined value K is set in the detector 6 in advance, and x (k) · x _F (k) <0
And The A side of the selector 10 is selected only in the case of, and the B side is selected otherwise. Assuming that x (k) is a quantized waveform shown in the experiment of FIG. 3, x
In the vicinity shown by (n), the intersection between the FM signal and the zero level has disappeared, and if the signal is demodulated as it is, an inversion phenomenon occurs. The output obtained by passing x (k) through a band-pass filter for suppressing both upper and lower sidebands or a high-pass filter for suppressing the lower sideband is a waveform indicated by a broken line in FIG. In the vicinity of x _F (n) corresponding to x (n), the intersection with the zero level has been restored, and the waveform has no inversion phenomenon even when demodulated. However, since the lower band having a good S / N is suppressed, when demodulated, no inversion phenomenon occurs, but the S / N
The demodulation output with N is bad.

Therefore, the waveform shown by the solid line in FIG.
Only to make use of the dashed waveform in the vicinity of x _F (n) portion intersection is the disappearance of the zero level in the vicinity of the (n). In other words, if demodulation is performed using the FM signal shown in FIG. 4 (which is a diagram in which the quantized signal is smoothly connected by a solid line), the S / N ratio will not be extremely deteriorated.
Moreover, since the intersection with the zero level is restored, a demodulated waveform that does not cause the inversion phenomenon can be obtained. Use conditions to achieve that. That is, first, the part where it is determined that the intersection with the zero level has disappeared is x (k) ·
x _F (k) <0. That is, if one of x (k) and x _F (k) is on the sign bit 0 side in FIG. 3, the other is sign bit 1
Side, and notice that the sign bits do not match, which is the first condition. Next, the portion where it is determined that the intersection with the zero level has disappeared is located at the peak of the waveform. Focusing on the fact that the level difference between the peak sample point and the sample point immediately before or immediately after the sample point is relatively small, it is determined that the average of the absolute value of the difference between two adjacent points is equal to or less than a predetermined value. Condition. In FIG. 3, a, b, c, and d satisfy the first condition. When the second condition is satisfied, the sample point x within the range b is obtained.
About (l) Is a large value, but x (n) within the range c
about Is a relatively small value, a predetermined value K is set so that only the data near x (n) satisfies the first and second conditions. Then, the FM signal shown in FIG. 4 is obtained.

Thus, if it meets the first condition satisfies and second condition, where it is determined that the intersection of the zero level is lost so as to select and output the x _F (k).

In FIG. 1, a quantized FM signal input to an input terminal 1 is input to a sideband suppression filter 3. Also,
The FM signal is also input to the delay corrector 2 is output where the output x _F (k + 1) of the sideband suppression filter 3 and the combined delay time (x (k + 1)) . That is, x (k + 1), x
_F (k + 1) can be regarded as a signal quantized at the same time. Then x (k + 1), x F (k + 1) is 1
Sample clock delayed to be inputted to the delay unit 4 and 7 output x (k), obtaining a x _F (k). So first x
The sign bits of (k) and x _F (k) are input to the XOR gate 6, respectively. If the sign bits match, 0 is output, and if not, 1 is output. The first of the
If the condition x (k) · x _F (k) <0 is satisfied, 1 is output, and if not, 0 is output. Further, x (k) is input to the delay unit 5 and outputs x (k-1). And x (k-1), x
(K) and x (k + 1) are input to the detector 6.

The configuration of the detector 6 is, for example, as shown in FIG. X (k + 1) -x (k) is calculated and output from the subtractor 21, and | x (k + 1) -x (k) | is output from the absolute value calculator 23. Similarly, | x ( k) -x (k-
1) is output, and both are added by the adder 25 and output. Multiplied by 1/2 by the multiplier 26 (actually equivalent to shifting the data one bit lower), Is output from the subtractor 28 and then the predetermined value K
Is subtracted, And the sign bit is output from the subtractor 28. That is, the detector 6 If so, output 1; otherwise output 0. Next, the output of the detector 6 and the output of the XOR 8 are input to the AND gate 9, and the AND gate 7 outputs 1 to the selector 10 only when both inputs are 1,
In that case, the selector 10 selects the A side and outputs x to the output terminal 11.
Outputs _F (K). When the output of the AND gate 9 is 0, the selector 10 selects the B side and outputs x (K) to the output terminal 11. By the above operation, the conditions 1 and 2 shown in the above are realized.

In the above embodiment, the means for detecting the peak of the digital FM signal is constituted by the detector 6 and the delay units 4 and 5. However, this may be another constitution, for example, x (K) -x
A method may be used in which the time when the output of the differentiator for calculating (K-1) becomes 0 or a value close to 0 is detected as a peak. Here, the value of K is a value to be determined based on the frequency allocation of the FM wave determined by the VTR method or the like, the transmission characteristics of the FM transmission system, the sampling frequency, and the like.

Further, in the above-described embodiment, the ROM 27 is used for holding data. However, this need not be a ROM, but may be another digital memory or data may be held by a switch.

〔The invention's effect〕

As described above, according to the present invention, the sideband suppression filter that receives the digital FM signal and suppresses the upper and lower sidebands or the lower sideband, and the sign of the digital FM signal and the output of the sideband suppression filter are the same. A discriminator for discriminating whether or not the signals match each other, a detector for detecting the peak of the digital signal, and the digital FM signal or the output of the sideband suppression filter according to the output results of the discriminator and the detector. Since a selector for selecting and outputting one of them is provided, digital signals that do not cause inversion without using a divider are provided.
An FM signal can be obtained, and a small-scale and inexpensive reversal prevention device can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an inversion prevention device according to an embodiment of the present invention, FIG. 2 is a block diagram showing an example of the detector of the above embodiment, and FIGS. 3 and 4 are embodiments of the present invention. 5 is a waveform diagram of an FM wave for explaining the operation of the reversal prevention device according to FIG.
FIG. 1 is a block diagram showing a conventional inversion prevention device, and FIG. 6 is a block diagram showing an inversion prevention device in which a main part of the device shown in FIG. 1 is a digital FM signal input terminal, 2 is a delay compensator, 3
Is a sideband suppression filter, 4, 5, and 7 are delay units, 6 is a detector,
8 is an XOR gate, 9 is an AND gate, 10 is a selector, 11 is a digital FM signal output terminal, 21 and 22 are subtractors, 23 and 24 are absolute value calculators, 25 is an adder, 26 is a multiplier, 27 is a ROM and 28 is a subtractor. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A sideband suppression filter which receives a quantized digital FM signal as input and suppresses upper and lower sidebands or a lower sideband, and wherein the sign of the output of the digital FM signal matches the sign of the output of the sideband suppression filter. A discriminator for discriminating whether the digital FM signal or the output of the sideband suppression filter according to the output result of the discriminator and the detector. And a selector for selecting and outputting any one of them.