JPH0363968A - Cosine equalizer - Google Patents

Abstract

PURPOSE:To applicably execute amplitude correction corresponding to the frequency of a signal component included in an input signal by controlling the length of delay time while responding to the FM modulated input signal. CONSTITUTION:A signal S1 is outputted from a head amplifier 20 while responding to an FM signal from a video head and signals S2 and S3, which are delayed rather than the signal S1, are outputted by two variable time delay elements 2. The delay time is changed corresponding to a clock pulse to be outputted from a PLL circuit 10, and added by an adder 3 to obtain a signal S4. The signal S4 is amplified by an amplifier 4 and afterwards, it is inverted by a phase inverter 5. Then, the inverted signal and the signal S2 are added by an adder 6 to constitute a cosine equalizer. The FM signal, for which the amplitude correction is executed in an FM video band by the cosine equalizer 1, is inputted through a spurious removing equalizer 30 to an FM detector 40. Thus, the amplitude correction is applicably executed to the amplitude correcting frequency while responding to the frequency of the FM signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention generally relates to a cosine equalizer, and in particular,
The present invention relates to a cosine equalizer that can adaptively perform amplitude correction in response to an FM modulated input signal.

[Prior Art] FIG. 4 is a block diagram showing an FM demodulation circuit including a conventional cosine equalizer used in an FM playback device such as a VTR. Referring to FIG. 3, this FM demodulation circuit is as follows:
A head amplifier 20 for outputting an FM signal, a cosine equalizer 50 for performing amplitude correction of the FM signal output from the head amplifier 20, and a second harmonic of the FM signal whose amplitude has been corrected by the cosine equalizer 50. A spurious removal equalizer 30 for removing extra components, and an FM detector 4 for detecting the FM signal from which extra components have been removed by the spurious removal equalizer 30.
Including 0.

The cosine equalizer 50 includes two delay elements 7 for setting amplitude correction frequencies, and an adder for adding the FM signals output from the two delay elements 7 and the FM signal output from the head amplifier 20. 3, an amplifier 4 for amplifying the FM signal added by the adder 3, a phase inverter 5 for inverting the phase of the FM signal amplified by the amplifier 4, and the first of the two delay elements 7. and an adder 6 for adding the FM signal output from one of the phase inverters and the FM signal output from the phase inverter 5.

FIG. 5 is a characteristic diagram of the cosine equalizer 50. Referring to FIG. 5, the horizontal axis indicates the frequency of the FM signal, and the vertical axis indicates the gain. K represents the amplification factor amplified by the amplifier 4, and τ represents the delay time set by the delay element 7. Note that the amplitude correction frequency f whose amplitude is corrected by the cosine equalizer 50 is fixed to f-1/2τ by the delay element 7. Further, as shown by the phase line in FIG. 4, in the cosine equalizer 50, the phase does not change even if the amplitude of the FM signal is corrected. As described above, since the conventional cosine equalizer is capable of amplitude correction without phase distortion, it is used in an FMI adjustment path for amplitude correction of high-frequency loss in an electromagnetic conversion system. For example, in 5-VH8, amplitude correction is performed at an amplitude correction frequency of f-6, 5 to 8.0 MHz by setting the delay element of the cosine equalizer to τ-70 to 801 seconds.

On the other hand, the frequency of the FM signal changes depending on the level of the video signal. FIG. 6A shows the low frequency F from the head amplifier 20.
FIG. 6 is a characteristic diagram when an M signal is output. FIG. 6B is a characteristic diagram when a high frequency FM signal is output from the head amplifier 20. FIGS. 7A and 7B are characteristic diagrams when the FM signals shown in FIGS. 6A and 6B are amplitude-corrected by the conventional cosine equalizer 50, respectively.

Amplitude correction of a low frequency FM signal will be described with reference to FIGS. 6A and 7A. As is clear from arrow A, the gain of the FM signal output from the head amplifier decreases as the frequency increases due to loss in the electromagnetic conversion system. When this FM signal is amplitude corrected by the cosine equalizer 50, it becomes as shown by arrow A'.

A case where a high frequency FM signal is amplitude corrected will be described with reference to FIGS. 6B and 7B.

When the frequency of the FM signal output from the head amplifier 20 is low, as shown by arrow B, the gain does not decrease.

When this FM signal is amplitude corrected by the cosine equalizer 50, the C/N (carrier power noise) is degraded and the upper side band is raised as shown by arrow A'.

[Problem WU to be Solved by the Invention] As described above, in the conventional cosine equalizer, the amplitude correction frequency is fixedly set to a high frequency by the delay element 7. As a result, when the FM signal includes signal components with low frequencies, when the FM signal is amplitude corrected, the C/N
As the upper side band deteriorates, the upper side band becomes lifted. When demodulating this, there were problems such as deterioration of S/N and inversion phenomenon (white breakage).

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to provide a cosine equalizer that can adaptively perform amplitude correction according to the frequency of a signal component included in an input component. do.

[Means for Solving the Problems] A cosine equalizer according to the present invention includes a first delay means that can control the delay time length of an input signal, and a delay time length of an output signal of the first delay means. a second delay means capable of controlling the output signal; a first addition means for adding the input signal and an output signal of the second delay means; and an inversion means for inverting the signal output from the first addition means. and the first
a second adding means for adding the output signal from the delay means and the output signal from the inverting means;
and control means for controlling the delay time length by the second delay means.

[Operation] In the cosine equalizer according to the present invention, the delay time length is controlled by the control means in response to the FM-modulated input signal, so that the amplitude correction frequency is set according to the frequency component of the input signal.

[Embodiment of the invention] FIG. 1 is a block diagram of an FM demodulation circuit including a cosine equalizer showing an embodiment of the present invention. Referring to FIG. 1, this FM demodulation circuit includes a head amplifier 20 for outputting an FM signal, a cosine equalizer 1 for performing amplitude correction of the FM signal output from the head amplifier 20, and a cosine equalizer 1 for performing amplitude correction of the FM signal output from the head amplifier 20. F with amplitude correction by
It includes a spurious removal equalizer 30 for removing extra components such as the second harmonic of the M signal, and an FM detector 40 for detecting the FM signal from which the extra components have been removed by the spurious removal equalizer 30.

The cosine equalizer 1 includes a PLL circuit (Phase 1 locked) for outputting clock pulses synchronized with the frequency of the FM signal output from the head amplifier 20.
1oop) 10, two time variable delay elements 2 for changing the frequency for amplitude correction based on the clock pulse output from the PLL circuit 10, and the FM signal output from the two delay elements 2 and the head. An adder 3 for adding the FM signal output from the amplifier 20, an amplifier 4 for amplifying the FM signal added by the adder 3, and an inverting phase of the FM signal amplified by the amplifier 4. and an adder 6 for adding the FM signal output from the first one of the two delay elements 2 and the FM signal output from the phase inverter 5.

The time variable delay element 2 is composed of a CCD or the like whose delay time changes in response to the frequency of the clock pulse.

The PLL circuit 10 includes a phase comparator (PD) 11 for comparing the phases of FM signals, and a low-pass filter (LP) connected to receive a signal output from the phase comparator 11.
F) 12 and a voltage controlled oscillator (VC0) 13 for generating clock pulses in response to the voltage output from the low-pass filter 12.

The relationship between the PLL circuit 10 and the time variable delay element 2 will be explained. A voltage controlled oscillator (VC) responds to the frequency of the FM signal.
The frequency of the clock pulse output from O) changes. As the frequency of the clock pulse increases, the transfer rate of the time variable delay element 2 increases.
delay time becomes shorter. In this way, the time variable delay element 2 whose delay time changes depending on the frequency of the FM signal can be realized.

Next, the operation will be explained. FM from video head
In response to the signal, the head amplifier 20 outputs a signal S. Two time variable delay elements 2 (delay time τn5e
c) by the signal S. Sec delayed signal S
2 and 2τ. A signal S delayed by Sec is output. Delay time τ. Sec changes in response to the clock pulse output from the PLL circuit 10, as described above. Signal S
, and signal S are added by adder 3 to obtain signal S4. The signal S4 is amplified by an amplifier 4 set to a predetermined amplification factor (K), and then inverted by a phase inverter 5. The inverted signal and the signal S2 are added by an adder 6 to form a cosine equalizer. The FM signal whose amplitude within the video FM band has been corrected by the cosine equalizer 1 is then passed through a spurious removal equalizer 30 that removes signal components outside the video FM band, such as second harmonics.
The FM detector 40 is manually powered. The FM signal input to the FM detector 40 is sent to a video processing circuit. In this way, in the cosine equalizer of this embodiment, the head amplifier 2
The amplitude correction frequency is adaptively controlled in response to the frequency of the FM signal output from 0.

FIG. 2 is a characteristic diagram showing the amplitude correction characteristics of the cosine equalizer 1 of FIG. 1.

FIG. 3A is a characteristic diagram of the FM signal when the high frequency FM signal shown in FIG. 6A is subjected to amplitude correction. FIG. 3B is a characteristic diagram of the FM signal when the low frequency FM signal shown in FIG. 6B is subjected to amplitude correction. Figures 3A and 3B
Referring to the figure, in this embodiment, the amplitude correction frequency is controlled in response to the frequency of the FM signal, so even when the FM signal is low frequency, C/N deterioration and upper side lifting state are prevented. It never occurs. Therefore, in this embodiment, when demodulating the FM signal, the deterioration of S/N as in the conventional case,
Inconveniences such as a reversal phenomenon (white breakage) do not occur.

[Effects of the Invention] As described above, according to the present invention, the control means controls the delay time length in response to the FM modulated input signal, thereby adjusting the amplitude correction frequency according to the frequency component of the input signal. is controlled, it is possible to adaptively perform amplitude correction according to the frequency of the signal component included in the input signal.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an FM demodulation circuit including a cosine equalizer showing an embodiment of the present invention, Fig. 2 is a characteristic diagram showing amplitude correction characteristics by the cosine equalizer shown in Fig. 1, and Fig. 3A is a high frequency Figure 3B is an amplitude-frequency characteristic diagram when a low frequency FM signal is amplitude corrected, Figure 4 is an FM demodulation diagram including a conventional cosine equalizer. A block diagram showing the circuit, Fig. 5 is a characteristic diagram of the cosine equalizer shown in Fig. 4, Fig. 6A is a characteristic diagram when a low frequency FM signal is output, and Fig. 6B is a characteristic diagram when a high frequency FM signal is output. The characteristic diagram when output, Figure 7A, is the FM shown in Figure 6A.
FIG. 7B is a characteristic diagram when the amplitude of the FM signal shown in FIG. 6B is corrected. In the figure, 1 is a cosine equalizer, 2 is a time variable delay element, 3 is an adder, 4 is an amplifier, 5 is a phase inverter, and 6
is an adder, and 10 is a PLL circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent contents. Figure 11 Figure II Figure 3

Claims (1)

[Claims] A cosine equalizer for correcting distortion of an FM-modulated input signal, the cosine equalizer comprising: a first cosine equalizer connected to receive the input signal and capable of controlling the delay time length of the input signal; delay means; a second delay means connected to the output of the first delay means and capable of controlling the delay time length of the output signal of the first delay means; first adding means connected to receive the output signal from the delay means and adding the input signal and the output signal of the second delay means; an inverting means for inverting the signal output from the first adding means; and an inverting means connected to receive the output signal from the output means of the first delay means and the inverting means, and the output signal from the first delay means. and a second addition means for adding the output signal from the inversion means; and a control means for controlling the length of delay time by the first and second delay means in response to the input signal. equalizer.