JPH0213485B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a frequency conversion device that can be used for frequency conversion of color signals in, for example, a video tape recorder (hereinafter referred to as VTR).

[Technical background of the invention]

For example, when recording and playing back standard color television signals on a VTR, the 3.58MHz color signal is frequency-converted to a reduced frequency (688kHz) and recorded, and during playback, it is inversely frequency-converted back to the original frequency band. It's becoming like that.

Regarding reproduction, conventionally, as shown in Fig. 3, the reproduced color signal (frequency ₁ = 688 kHz) input from terminal 11 is frequency-controlled using the carrier signal (frequency ₂ = 4.27 MHz) input from terminal 12. The frequency is converted by the converter 13. As a result, the frequency conversion output of the frequency ( ₂ ± ₁ ) is obtained at the terminal 14, of which the required frequency is ₂ − ₁ (3.58MHz).
The conversion output of is a band pass filter (BPF) 15
is taken out to the terminal 16 by.

Incidentally, in addition to the frequency conversion output ( ₂ ± ₁ ), two input signals ₁ and ₂ actually leak into the output of the frequency converter 13. Among these, since it is difficult to remove the leakage of the carrier signal ₂ by the bandpass filter 15, the frequency converter 1
By adjusting the input level of reproduced color signal ₁ relative to color signal 3 (hereinafter, this adjustment will be referred to as carrier balance adjustment), leakage of carrier signal ₂ is suppressed. For this adjustment, a constant voltage source V _B , a variable voltage source V _C , a voltage dividing resistor R _X ,
The reproduced color signal _{1 whose} direct current is cut off by the capacitor C1 is set at a direct current level according to the amount of _adjustment of the variable voltage source _Vc .

[Technical background of the invention]

However, in the above configuration, it is necessary to adjust the carrier balance while monitoring with a spectrum analyzer (simply called a synchroscope) during the VTR manufacturing process.
This increases the number of man-hours and time required to manufacture VTRs.

[Purpose of the invention]

The present invention was made in order to cope with the above-mentioned circumstances, and an object of the present invention is to provide a frequency conversion device that can automatically perform carrier balance adjustment.

[Summary of the invention]

This invention detects the leakage of the carrier signal by multiplying the output of the frequency conversion means and the carrier signal for frequency conversion, and transfers the DC component of this detection output to the signal path of the input signal of the frequency conversion means. By returning the signal to the carrier signal, leakage of the carrier signal is suppressed.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention. In FIG. 1, the same parts as in FIG. 3 are given the same reference numerals.

For example, the frequency converter 1 constituted by a multiplier
The output of 3 is a band pass filter 15 as before.
In addition, in this invention,
For example, a synchronous detector 21 composed of a multiplier
is input. The output of this synchronous detector 21 is passed through a low pass filter (LPF) to cut out high frequencies.
22, and the DC component is taken out. This DC component is given to the adder 23, and the capacitor
The DC component is cut off by C ₁ and resistor R ₁ and added to the reproduced color signal ₁ set at a predetermined DC level by constant voltage source V _B.

The synchronous detector 21 detects leakage of the carrier signal ₂ by frequency converting the output of the frequency converter 13 using the carrier signal ₂ , and obtains a DC component and an AC component of frequency ₂₂ .

Here, in order to be able to accurately detect the carrier signal ₂ , the synchronous detector 21 is designed to work during a period where there is no color signal or during a period when the color signal is at a very low level. For example, a horizontal synchronizing pulse period is selected as the period in which there is no color signal or a minute level period, and the synchronous detector 21 is provided with a gate circuit so as to be turned on by the horizontal synchronizing pulse HD applied to the terminal 24. ing.

The output of the synchronous detector 23 is passed through the low pass filter 22
A DC component is extracted here, and this DC component is added to the reproduced color signal in an adder 23. Therefore, the DC level of the reproduced color signal changes depending on the level of the leakage component of the carrier signal ₂ . In this case, the adder 23 adds the DC component from the low-pass filter 22 to the reproduced color signal with a characteristic that suppresses leakage of the carrier signal ₂ .

FIG _{. 2} shows an example of _the specific _{configuration} shown in _FIG .
Q ₇ , Q ₈ , resistors R ₈ , R ₉ , constant current sources I ₂ , I ₃ constitute a simple level shift circuit, and transistors Q ₉ to
Q ₂₀ and constant current source I ₄ constitute a synchronous detector 23, capacitor C ₂ and resistors R ₂ and R ₃ constitute a low pass filter, and transistors Q ₁ and Q ₂ and low resistors R ₆ and R ₇ constitute a synchronous detector 23. An adder 23 is configured. The constant current source _I4 of the synchronous detector 23 is turned on only during the horizontal synchronous pulse period. Further, in the figure, V _A is a constant voltage source.

In the above configuration, suppose now that transistor Q ₁
If the base potential of is at a higher potential than the base potential of transistor Q ₂ , the difference between the collector current of transistor Q ₁ and the collector current of transistor Q ₂ will result in a common connection between the collector of transistor Q ₄ and the collector of transistor Q ₆ . At this point, a carrier signal ₂ , which is in phase with the carrier signal ₂ at terminal 12, leaks and is applied to the base of transistor _Q9 . Moreover, in the synchronous detector 21, the bases of the transistors Q ₁₁ and Q ₁₄ are given a carrier signal that is in phase with the carrier signal given from the terminal 12 to the base of the transistor Q ₉ , so that the synchronous detector 21 consists of the transistors Q ₁₅ and Q ₁₆ A charging current flows through the capacitor _C2 through the current mirror circuit. As a result, the voltage across the capacitor C ₂ increases, which is divided by the resistors R ₂ and R ₃ and applied to the base of the transistor Q ₂ , thereby increasing the base potential.

Conversely, when the base potential of the transistor Q ₁ becomes low, a signal having an opposite phase to the carrier signal ₂ at the terminal 12 appears at the common connection point between the collector of the transistor Q ₄ and the collector of the transistor Q ₆ .
Therefore, this time, the discharge current of the capacitor C ₂ flows through the current mirror circuit consisting of the transistors Q ₁₇ and Q ₁₈ and the transistors Q ₁₉ and Q ₂₀ , and the base potential of the transistor Q ₂ decreases. Therefore, the output of the frequency converter 13 is finally stabilized without any leakage of the carrier signal ₂ .

As described above, the configuration shown in FIG. 2 can suppress the leakage of the carrier signal ₂ , but in addition, in the configuration shown in FIG. 2, the adder 23 has a differential amplifier configuration. , the capacitor _C1 for cutting off the DC component of the reproduced color signal ₁ is not particularly required.

Note that the horizontal synchronization pulse period does not necessarily have to be selected as the period in which there is no reproduced color signal or the minute level, and any other period may be used. In addition, although the above explanation has been made with reference to reproduced color signals, the present invention can also be applied to frequency conversion of signals other than this, such as reproduced color signals, in which there is no signal period or minute level period. Applicable.
In this case, since the leakage detection means such as the synchronous detector 23 is driven during the existence period of the input signal, the leakage detection ability may be reduced to some extent, but even so, if the configuration of the present invention is not adopted. A much greater effect can be expected compared to

〔Effect of the invention〕

As described above, according to the present invention, carrier balance adjustment can be performed automatically, and therefore,
It is possible to provide a frequency conversion device that can obtain effects such as no adjustment deviation due to temperature drift or aging.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of the specific configuration of FIG. 1, and FIG. 3 is a circuit diagram showing a conventional frequency conversion device. . 11, 12, 14, 16, 24...Terminal, 13
... Frequency detector, 15 ... Band pass filter, 21 ... Frequency converter, 22 ... Low pass filter, 23 ... Adder.

Claims (1)

[Claims] 1. Frequency conversion means for converting the frequency of a first signal, which is an input signal, with a second signal, which is a carrier signal; leakage detection means for detecting leakage of the second signal with respect to the output of the frequency conversion means; filter means for extracting a DC component from the output of the leakage detection means; and addition of the output of the filter means to the first signal. and an addition means for suppressing leakage of the second signal.