JPH0267806A - Modulator for television high frequency signal - Google Patents

Abstract

PURPOSE:To stabilize the carrier frequency by always comparing the phase of the oscillation signal of a voltage controlled oscillator VCO and that of a reference signal with each other by a PLL circuit and varying the voltage applied to the VCO in accordance with the phase difference. CONSTITUTION:A frequency division ratio of a programmable divider 15 for a desired channel frequency is inputted from a frequency division ratio input terminal 18. The oscillation frequency picked up by a VCO 12 is divided by a frequency divider 14 and is divided by the frequency division ratio inputted to the programmable divider 15 and has the phase compared with the phase of the reference frequency from a reference frequency generator 19 by a phase comparator 19. When a phase difference is detected, this difference is applied as the control voltage to a varicap diode 13 through an error amplifying circuit 16 and an LPF 20. This operation is repeated to determine the carrier frequency so that the phase difference in the phase comparator 17 is eliminated. Thus, the degree of stability of the carrier frequency is improved.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is directed to home automation (hereinafter referred to as HM).
The present invention relates to a television high frequency signal modulation device used in the field of video equipment such as systems.

BACKGROUND OF THE INVENTION In recent years, due to the amazing progress in semiconductor technology, various systems that integrate computers and communication technology are entering the home, and one of the representative systems is the HM system. Furthermore, it is expected that televisions using frequency synthesizers will become popular in the future.

Against this background, there is a strong demand for highly stable carrier wave frequencies in television high frequency signal modulation devices used in video equipment.

A conventional television high frequency signal modulation device has a circuit configuration as shown in FIG. 3, and its operation will be explained below.

The carrier wave signal is modulated by the video signal and audio signal input from the input terminals 1 and 2 in FIG. 3, and converted into a television high frequency signal that can be received by a general television. It is output from the output terminal 11 of. Among them, the carrier oscillation circuit 4 in FIG. 3 is a circuit that generates something equivalent to a carrier wave of a television broadcast wave.
A variable capacitance element 6 such as a variable capacitor shown in the figure adjusts the carrier oscillation frequency and the carrier wave frequency to a desired channel frequency.

Note that 3 is a power supply terminal, 6 is Ro, 8 circuits, 7 is a pre-emphasis circuit, a is IO, 9 is an s IF filter circuit, and 10 is a single balanced mixer circuit.

Problems to be Solved by the Invention In such a conventional configuration, when setting the carrier frequency,
As mentioned above, since adjustment is made by rotating the adjustment part of the variable capacitance element 6 shown in Fig. 3 with an adjustment rod such as a screwdriver, the adjustment accuracy may be affected by the stray capacitance caused by the adjustment part and the adjustment rod and considering mass production. There was a limit.

Further, since fluctuations due to environmental changes, such as the distributed capacitance between the oscillation circuit elements that determine the carrier wave frequency and the patterns of the printed circuit board forming the oscillation circuit, are unavoidable, the carrier wave frequency also changes accordingly. As described above, with the conventional circuit configuration, it is extremely difficult to achieve high stability of the carrier frequency.

The present invention solves this problem, and aims to provide a television high-frequency signal modulation device that has excellent carrier frequency setting accuracy and carrier frequency stability against environmental changes. .

Means for Solving the Problems In order to achieve such objects, the present invention provides a voltage controlled oscillator (hereinafter referred to as V, C) whose oscillation frequency can be varied by voltage control.
, O) and the video/audio signal into a television signal high frequency signal;
.

Effect: With this configuration, the control voltages applied to V, a, and O are:
The V, C, O oscillation signals and the reference signal are constantly compared in phase by a PLL circuit and varied according to the phase difference. Therefore, there is no need for the conventional adjustment of the carrier wave frequency, and furthermore, the carrier wave frequency does not fluctuate due to environmental changes.
It depends only on the variation of the reference frequency of the PLL circuit.

In other words, if the reference frequency oscillator that emits the reference frequency of this PLL circuit is made of a crystal with excellent frequency stability, it will be possible to modulate television high-frequency signals with excellent carrier frequency setting accuracy and carrier frequency stability against environmental changes. The device will be obtained.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a television high frequency signal modulation device according to an embodiment of the present invention. FIG. 2 is a circuit layout diagram of an embodiment of the present invention. In Figures 1 and 2, 1 is a video signal input terminal, 2 is an audio signal input terminal, 3 is a power supply terminal, and 6
is R, IC, 8 circuit, 7 is pre-emphasis circuit, 8 is IC, 9 is SIF filter circuit, 10 is single node (lance mixer circuit, 11 is RF output terminal, 12 is V, C, 0113 is Paris Cap diode, 14 is a frequency divider, 16 is a programmable divider, 16 is an error amplifier, 17 is a phase comparator, 18 is a frequency division ratio input terminal, 19
is a reference frequency generator, 20 beams, P, F, 21 are housings,
22 is a PLL circuit arrangement part, 23 is an RF modulation circuit and V
, is the C1O arrangement part. The components 1 to 13 above constitute the RF modulation circuit, and the components 14 to 20 constitute the PL
It constitutes an L circuit.

The operation of the television high frequency signal modulation device configured as described above will be described below.

The basic operation is to modulate the signal of V, 0.012 in FIG. This is the same as the conventional television high frequency signal modulation device shown in FIG.

However, in this operation, the setting of the carrier wave frequency is different. In the conventional television high frequency signal modulation device, the carrier wave frequency is adjusted by rotating the adjustment section of the variable capacitance element 6 shown in FIG. 3 with an adjustment rod such as a screwdriver, whereas the present invention The frequency division ratio of the programmable divider 15 for the desired channel frequency is input from the frequency ratio input terminal 18 . The oscillation frequency picked up from "/" and JO 12 in FIG. 1 is divided by the frequency divider 14 in FIG.
The frequency is divided by the frequency division ratio input to the phase comparator 1 in FIG.
At step 7, the phase is compared with the reference frequency from the reference frequency generator 19 of FIG. If a phase difference occurs here, the difference is applied as a differential voltage to the varicap diode 13 in FIG. 1 via the error amplification circuit 16 in FIG. By repeating this operation, the first
The carrier frequency is determined so as to eliminate the phase difference in the phase comparator 17 shown in the figure.

Therefore, the carrier frequency of the television high frequency signal modulation device of the present invention does not require adjustment if the programmable divider 160 frequency division ratio according to the desired channel frequency is input.

In addition, in response to environmental changes, the conventional television high frequency signal modulation device has the carrier oscillation circuit 4 shown in FIG. 3 and the lumped capacitance of the capacitance variable element 6 shown in FIG. Changes occur due to variations in distributed capacitance between patterns. On the other hand, in the television high frequency signal modulation device of the present invention, as in the prior art, when the carrier frequency fluctuates, a phase difference occurs in the phase comparator 17 in FIG. The control voltage applied to the diode 13 is varied to operate to eliminate the phase difference.

In other words, the setting accuracy of the carrier wave frequency and the stability of the carrier wave frequency against environmental changes all depend on the stability of the reference frequency of the reference frequency generator 190 shown in Figure 1. If the reference frequency generator uses oscillation, high stability will be achieved.

Now, let us express numerically the difference in carrier frequency stability between the conventional television high frequency signal modulation device and the present invention.

Now set the conditions , (A) Desired carrier frequency is 591.25M) 4Z.

(B) The reference frequency is the reference oscillator divided by 1024.

(C) The reference oscillator is 4Ml-1Z0 (D) The accuracy of the reference oscillator is ±30ppHl.

(E) The amount of change of the reference oscillator between O'C and 60°C is +40ppm0 (5) The frequency of the divider 14 in FIG. 1 is divided by 256 based on the 26°C standard.

shall be. First, regarding the setting accuracy, according to the conventional configuration, the actual setting accuracy is approximately ±100K14z. - According to the configuration of the power tree invention, the accuracy of the reference frequency is the condition), (C
), from (D), the frequency division ratio of the divider 14 in FIG. 1 is 256, and the frequency division ratio of the programmable divider 15 in FIG. is 591.25 if the desired carrier frequency is a conditional field)
M) IZ, so it is set to 591.25. Therefore, the setting accuracy of the carrier frequency is proportional to the accuracy of the reference frequency and the frequency division ratio in Figure 1 14.15, so it is ±0.
, 1172X258X591.25b+±17.7cm, which is clearly superior to the conventional model.

Next, regarding temperature changes, consider the ambient temperature from 0'C to 60'
According to the conventional configuration, the amount of change in C based on the 25°C standard is ±200K))z.

On the other hand, according to the configuration of the present invention, the amount of change in the reference frequency is
Conditions (B), (C), 虞) 3906, 25±
0.156±, and the frequency division ratios in FIG.
．． 25 l=1±23.6, which is clearly superior to the conventional method.

As described above, according to one embodiment of the present invention, a television high frequency signal modulation device with excellent carrier frequency stability can be obtained.

In addition, in the present invention, in order to improve stability, the reference oscillator uses a low frequency of several MH2 as described above, so R
When the F modulation circuit and the PLL circuit are housed in the same housing, the oscillation signal of this reference oscillator induces the single-/; lance mixer circuit 1o in Fig. 1, V, 0.012, etc. in Fig. 1, The first component is an unnecessary component within the video/audio carrier wave band.
The signal is output from the output terminal 12 in the figure. Therefore, in order to prevent this, an RF modulation circuit (at least V
, C6O12 and single balanced mixer circuit 1
0) and the PLL circuit (at least the reference oscillator) are mechanically shielded by a metal shielding plate 24.

Effects of the Invention As described above, according to an embodiment of the present invention, the RF modulation circuit modulates the y, c, and o signals whose oscillation frequency can be varied by voltage control, and the video/audio signal into a televised radio frequency signal. By housing the reference frequency generator and the PLL circuit, which performs the voltage control of V, C, and O using a frequency synthesizer composed of a phase-locked loop circuit, in the same body, the carrier wave frequency can be set accurately and the carrier wave frequency can be adjusted to environmental changes. A television high-frequency signal modulation device with extremely high stability can be obtained.

Further, by electrically shielding the RF modulation circuit and the PLL circuit with a metal shielding plate, the induced level of the reference oscillator can be reduced, and a television high frequency signal modulation device with fewer unnecessary components can be obtained.

Furthermore, if the television high frequency signal modulation device of the present invention is used in various video systems such as HA systems, camera systems, and video systems, v, C00
Any channel setting is possible within the variable range.

It also becomes compatible with frequency synthesizer type televisions.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a television high frequency signal modulation device according to an embodiment of the present invention, FIG. 2 is a perspective view showing the circuit arrangement within the housing, and FIG. 3 is a block diagram of a conventional television high frequency signal modulation device. It is. 1...Video signal input terminal, 2...Audio signal input terminal, 3...Power terminal, 1Q...
・Single balanced mixer circuit, 11...
・RF output terminal, 12...v, C10, 13・
...Varicap diode, 14...
Frequency divider, 15... Frogramma pull divider,
16...Error amplifier, 17. ...Phase comparator, 21...Housing. Name of agent: Patent attorney Shigetaka Awano and one other person Sunny d1 Shinte Figure 2

Claims (2)

[Claims] (1) An RF modulation circuit that modulates the signal of a voltage-controlled oscillator whose oscillation frequency can be varied by voltage control, a video signal, and an audio signal into a television high-frequency signal, and a reference frequency generator that controls the voltage of the voltage-controlled oscillator. P driven by a frequency synthesizer composed of a phase-locked loop circuit and a
A television high frequency signal modulation device characterized in that a LL circuit and an LL circuit are housed in the same metal housing. (2) The television high-frequency signal modulation device according to claim 1, wherein the phase-locked loop circuit section and the RF modulation circuit section are electrically shielded by a metal shielding plate.