JPH03187527A - Uhf-rf converter - Google Patents

Abstract

PURPOSE:To improve accuracy for setting a frequency and to enlarge a range for varying the frequency by automatically setting the oscillating frequency of an RF oscillator with a PLL circuit composed of the RF oscillator, frequency divider, error voltage generating means, control voltage oscillating means and frequency dividing ratio setting means. CONSTITUTION:An FM modulator 1, amplitude modulator 2, RF oscillator 3, frequency divider 4, error voltage generating means 5, microcomputer 6 and integration circuit 7 are provided. The PLL circuit is composed of the RF oscillator 3, frequency divider 4, error voltage generating means 5, frequency dividing ratio setting means 11 and control voltage generating means 13 and the oscillating frequency of the RF oscillator 3 is automatically changed corresponding to the frequency dividing ratio of the frequency divider 4. Thus, the accuracy is improved for setting the frequency and the range is enlarged for varying the frequency.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to UHF, which is applied to output circuits of European specification video tape recorders, satellite broadcast receivers, etc.
-Relates to RF converter.

[Conventional technology]

For example, as shown in FIG. 2, a UHF-RF converter that converts a video signal and an audio signal into a UHF RF signal includes an FM modulator 11, an amplitude modulator 12, and an R
F oscillator 13. The RF oscillator 13 includes transistors Tr,..., coil Lll, and capacitor C0.
The oscillation frequency is adjusted by an air variable capacitor C1! connected in parallel to the capacitor C□. This is done by changing the capacity of the

In such a UHF-RF converter, an input audio signal is subjected to FM modulation by the FM modulator 11 and output to the amplitude modulator 12 . And amplitude modulator 12
As a result, the FM-modulated audio signal is mixed with the video signal, and the amplitude of the RF multiplied signal output from the RF oscillator 13 is modulated with this mixed signal, thereby obtaining an RF modulated output. Also, the RF modulation output is the air variable capacitor CI! By adjusting the oscillation frequency of the RF oscillator 13, it can be matched to the frequency of the designated broadcast channel.

[Problem to be solved by the invention]

However, in the conventional U)IF-RF converter mentioned above,
The RF oscillator 13 is equipped with an air variable capacitor CI that mechanically changes the capacitance! As a result, the frequency stability with respect to temperature and humidity is low, and the initial setting rate with respect to the regular broadcast channel frequency is low. For this reason, it has become impossible to widen the frequency variable range of the RF modulated output, leading to interference with existing broadcast channel frequencies. In addition, if a European-spec video tape recorder is equipped with the above UHF-RF converter, the European-made television connected to it will have A
FT (＾automatic Fine Tuning
) have a narrow frequency pull-in range, so if the frequency stability and initial setting are low as described above, normal image reproduction may become difficult.

[Means to solve the problem]

In order to solve the above-mentioned problems, the UHF-RF converter according to the present invention includes an FM modulator that performs FM modulation on an audio signal, an RF oscillator that outputs an RF multiplied signal, and a video signal and an FM-modulated audio signal. In a UHF-RF converter equipped with an amplitude modulator that performs amplitude modulation of the RF multiplied signal using the mixed signal, the following measures are taken.

In other words, the UHF-RF converter is configured such that the oscillation frequency of the RF oscillator is made variable by a control voltage, and includes a frequency divider that divides the RF multiplied signal from the RF oscillator at a set frequency division ratio, and a frequency divider that divides the frequency at a set frequency division ratio. Error voltage generation means for comparing the frequency and phase of the RF multiplied signal with a constant frequency reference signal and generating an error voltage according to the difference; The control voltage ordering means generates a control voltage to be applied to the RF oscillator based on the error voltage, and the frequency division ratio setting means sets the frequency division ratio of the frequency divider according to the set oscillation frequency of the RF oscillator.

[For production]

According to the above fN precept, the RF oscillator, frequency divider, error voltage generation means, control voltage oscillation means, and frequency division ratio setting means
Since an LL (Phase Locked Loop) circuit is formed, the oscillation frequency of the RF multiplied signal and the RF oscillator is controlled by the control voltage output from the control voltage generation means, so that the The signal is stabilized. Therefore, it is possible to improve the frequency stability with respect to temperature and humidity and the degree of initialization with respect to the regular broadcast channel frequency. Therefore, frequency setting accuracy can be improved and the frequency variable range can be expanded.

〔Example〕

Two embodiments of the present invention will be described below with reference to FIG.

The UHF-RF converter according to this embodiment is installed in a video tape recorder of European specifications, and as shown in FIG.
It includes an oscillator 3, a frequency divider 4, an error voltage generating means 5, a microcomputer 6, and an integrating circuit 7. F
The M modulator 1 is a circuit that performs FM modulation on an audio signal. The amplitude modulator 2 mixes the video signal and the audio signal FM modulated by the FM modulator 1, uses the mixed signal to amplitude-modulate the RF multiplied signal output from the RF oscillator 3, and generates an RF modulated output. This is the circuit to obtain.

The RF oscillator 3 includes a transistor T r + and a coil L.
+ and a capacitor CI, which constitute an LC oscillation circuit, and a varactor diode VD as a variable reactance element is provided in parallel with the capacitor C1. Therefore, the oscillation frequency of the R1 oscillator 3 is variable according to the control voltage applied to the varactor diode VD, so that the frequency of the RF signal can be adjusted.

The frequency divider 4 is, for example, a circuit configured with a counter whose frequency division ratio setting can be changed, and divides the frequency of the RF signal output from the R1 oscillator 3 by the set frequency division ratio. The error voltage generating means 5 includes a phase comparator 8, a low-pass filter (LP
F) 9 and a crystal oscillator IO. The phase comparator 8 converts the RF signal frequency-divided by the frequency divider 4 into
This circuit compares the frequency and phase with a constant frequency reference signal output from the crystal oscillator 10, and outputs the difference as an error signal. The low-pass filter 9 is a circuit that removes high frequency components and the like from the error signal of the phase comparator 8 and generates an error voltage.

The microcomputer 6 has a timer function, and is, for example, a control circuit that manages the time of a clock installed in a video tape recorder and generates a reference clock used for channel settings and the like. This microcomputer 6 is equipped with a frequency division ratio setting means 11 and a pulse width modulation means 12 by utilizing a part of its functions. The frequency division ratio setting means 11 is, for example,
The load data of the counter constituting the frequency divider 4 is stored in memory according to the frequency of the RF signal to be set, and when a frequency setting instruction is input from the outside, the load data corresponding to the frequency is stored. The signal is output to the frequency divider 4. The pulse width modulation means 12 digitally performs pulse width modulation processing based on the error voltage from the phase comparator 8, thereby outputting a control pulse with a duty corresponding to the level of the error voltage. .

The integrating circuit 7 is a circuit that smoothes the control pulse from the pulse width modulating means 12 and generates a control voltage to be applied to the varactor diode VD in the R1 oscillator 3. In addition, in the UHF-RF converter according to this example,
The integration circuit 7 and the pulse width modulation means 12 of the microcomputer 6 constitute a control voltage generation means 13, and the R1 oscillator 3, the frequency divider 4, the error voltage generation means 5, the frequency division ratio A PLL circuit is formed by the setting means 11 and the control voltage generating means 13, and the oscillation frequency of the R1 oscillator 3 is automatically changed and set according to the frequency division ratio of the frequency divider 4.

In the above configuration, when the frequency division ratio corresponding to the channel frequency to be set is set in the frequency divider 4 by the load data of the frequency division ratio setting means 11 in the microcomputer 6, the RF signal is output from the R1 oscillator 3. However, divider 4
The frequency is divided by the above frequency division ratio. Error voltage generation means 5
Then, the frequency-divided RF signal is compared in frequency and phase with the reference signal of the crystal oscillator 10 by the phase comparator 8,
The error signal obtained as a result passes through the low-pass filter 9 to obtain an error voltage.

In the control voltage generating means 13, this error voltage is converted into a control pulse with a duty according to the level by the pulse width modulating means 12, and is further smoothed by the integrating circuit 7, so that as a result, the error voltage corresponds to the level of the error voltage. is converted into a DC control voltage. When this control voltage is applied to the varactor diode VD in the R1 oscillator 3, the capacitance of the varactor diode DI changes so as to cancel out the difference in frequency and phase in the phase comparator 8, so that the oscillation of the R1 oscillator 3 Frequency changes.

By repeating the above operations, the R1 oscillator 3 locks to the set frequency and phase, and as a result, the oscillation frequency of the R1 oscillator 3 matches the designated broadcast channel frequency. On the other hand, in the amplitude modulator 2, the RF signal from the R1 oscillator 3 is amplitude-modulated with a signal that is a mixture of the video signal and the audio signal FM-modulated by the FM modulator 1, and is outputted to the outside as an RF modulated output. Ru.

In this way, the oscillation frequency of the R1 oscillator 3 is accurately and automatically set by the PLL circuit using a part of the microcomputer 6, so that the oscillation frequency stability and initial setting accuracy of the UHF-RF converter can be improved. It becomes possible to increase the

In this embodiment, a configuration in which a PLL circuit is formed by using a part of the microcomputer 6 has been described, but even in equipment that does not include the microcomputer 6, the division ratio setting means having the same function can be used. It goes without saying that similar effects can be obtained by providing the pulse width modulating means 11 and the pulse width modulating means 12.

〔Effect of the invention〕

As described above, the UHF-RF converter according to the present invention includes an RF oscillator whose oscillation frequency is variable by a control voltage, a frequency divider that divides an RF signal at a set frequency division ratio, and a frequency divider that divides an RF signal at a set frequency division ratio. An error voltage generation means that compares the output signal with a reference signal of a constant frequency in frequency and phase and generates an error voltage according to the difference, and an error voltage generation means that eliminates the frequency difference and phase difference in the error voltage generation means based on the error voltage. The present invention is configured to include a control voltage generating means for generating the above-mentioned control voltage, and a frequency dividing ratio setting means for setting the frequency dividing ratio of the frequency divider according to the oscillation frequency of the RF oscillator.

Therefore, the PL formed by the RF oscillator, frequency divider, error voltage generation means, control voltage oscillation means and frequency division ratio setting means
The L circuit allows the oscillation frequency of the RF oscillator to be set accurately. This makes it possible to improve the frequency stability with respect to temperature and humidity and the degree of initialization with respect to regular broadcast channel frequencies. As described above, the UHF-RF converter according to the present invention has the effect that by improving the frequency setting accuracy, the frequency variable range can be expanded, and the performance of the UHF-RF converter can be improved.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, in which UHF
- It is a block diagram showing the composition of an RF converter. FIG. 2 shows a conventional example, and is a block diagram showing the configuration of a UHF RF converter. 1 is an FM modulator; 4 is a frequency divider; and 1 is a frequency division ratio setting means. 2 is an amplitude modulator, 3 is an RF generator, 5 is an error voltage generation means, and 11 and 13 are control voltage generation means.

Claims (1)

[Claims] 1. FM modulator for FM modulating an audio signal, and RF
A UH comprising an RF oscillator that outputs a signal, and an amplitude modulator that mixes a video signal and an FM-modulated audio signal and amplitude modulates the RF signal with the mixed signal.
In the F-RF converter, the oscillation frequency of the RF oscillator is made variable by a control voltage. error voltage generating means that compares the RF signal with a constant frequency reference signal in frequency and phase, and generates an error voltage according to the difference;
Control voltage generation means generates a control voltage to be applied to the RF oscillator based on the error voltage, and the division ratio of the frequency divider is set to the set oscillation frequency of the RF oscillator so as to eliminate the frequency difference and phase difference in the error voltage generation means. A UHF-R characterized by comprising a dividing ratio setting means for setting a frequency division ratio according to the
F converter.