JPS6247033B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video converter that converts a video signal and an audio signal into a high frequency television signal modulated wave. The purpose is to make it easier and more compact, and to reduce the number of adjustment points.

FIG. 1 is a block diagram of a conventionally used video converter device. In FIG. 1, 1 is a video carrier wave oscillator section and a multiplier section, and X1 is a crystal oscillator. This resonator X1 normally oscillates in the 30MHz band, and this basic oscillation frequency is
Alternatively, a video carrier wave is generated by multiplying the signal by three times. 2 is a 4.5MHz oscillator and frequency modulator section. D1 is a variable capacitance diode, and performs variable reactance frequency modulation by applying the audio signal applied to the terminal 3 to the variable capacitance diode D1. Reference numeral 4 denotes a balanced modulator which performs balanced modulation of the video carrier wave applied from the oscillation/multiplying section 1 using the video signal applied to the terminal 5. This circuit is intended to realize an amplitude modulated wave with a deep modulation degree required for television signals, and consists of a semi-fixed resistor R1.
By adding a video carrier wave at an appropriate ratio to the balanced modulated wave (by adjusting the balance of the balanced modulator), an amplitude modulated wave with a deep modulation degree is generated. 6 is a frequency modulator, which is the oscillation/FM modulation section 2
A sum signal (audio carrier wave) of the FM modulated wave (4.5 MHz) applied from the FM modulated wave and the video carrier wave applied from the oscillation/multiplying section 1 via the trimmer capacitor C1 is generated. Reference numeral 7 denotes a band pass filter provided to block difference signals generated simultaneously at this time. Reference numeral 8 denotes a signal synthesis filter, which is used to mix the video amplitude modulated wave and the audio frequency modulated wave. Terminal 9 is a high frequency television signal output terminal, and the video carrier output to audio carrier output ratio (hereinafter abbreviated as PS ratio) required for the television signal is determined by adjusting the trimmer capacitor C1.

The configuration shown in Figure 1 has the advantage that there is no need to use a crystal oscillator in the oscillation/FM modulation section 2, since it is not necessary to directly generate the audio carrier wave and only need to generate 4.5MHz with the necessary precision. However, on the other hand,
There are many parts that require adjustment, including the 4.5MHz fine tuning of the oscillation/FM modulation section 2, and the bandpass characteristics of the bandpass filter 7 (steep selectivity is required).
This method has the disadvantage of requiring additional fine-tuning operations.

Furthermore, since each part shown in FIG. 1 is an independent component and has large differences in characteristics and precision, the semi-fixed resistor R1 for adjusting the video signal modulation degree and the trimmer capacitor C1 for adjusting the PS ratio are The drawback was that it required readjustment after complete assembly.

Another drawback is that the synthesis filter shown at 8 and its surroundings become complex in order to realize the residual sideband characteristics required for television signal waves.

The present invention utilizes the features of surface acoustic wave filters to eliminate the above-mentioned drawbacks, and FIG. 2 shows an embodiment of the basic configuration thereof. In FIG. 2, a portion 10 surrounded by a dotted line is a surface acoustic wave element portion. This part is constructed on a piezoelectric substrate or an elastic substrate with a piezoelectric thin film, and the thickness is about 0.5 to 1 mm, and the overall size is usually 10 mm.
It is less than mm square. Terminals 3, 5, and 9 each have the same function as in FIG. 1, and therefore use the same signals. 11 and 12 are broadband amplifiers, and 13 is a balanced modulator.

In FIG. 2, hatched lines T1 to T8 indicate the positions of piezoelectric transducers forming a surface acoustic wave signal delay element or a surface acoustic wave filter. The piezoelectric transducers T1 to T8 all have a comb-shaped electrode structure, and their electrode fingers are all aligned in the same direction (vertical direction in FIG. 2). Therefore, a signal converted from an electric signal to a surface acoustic wave by the piezoelectric transducer propagates in a direction perpendicular to the direction of the electrode fingers (left-right direction in FIG. 2). The propagation directions of signal waves are shown in FIG. 2 by arrows only those necessary for explanation. The surface acoustic wave is generated by the width of the piezoelectric transducer, and is transmitted to the opposing piezoelectric transducer without changing its beam width. An elastic surface delay element is formed by such a surface acoustic wave generating piezoelectric transducer, a receiving transducer, and a surface acoustic wave propagation section between these two piezoelectric transducers.

Next, the operation of the circuit shown in FIG. 2 will be explained.

In FIG. 2, piezoelectric transducer T1,
T2 constitutes the input and output parts of the surface acoustic wave delay element, and together with the broadband amplifier 11 constitutes a delay line type surface acoustic wave oscillator, which directly generates an image carrier wave on the elastic substrate. In this kind of oscillator,
The stability of the oscillation frequency is governed by the signal delay time, that is, the distance between the piezoelectric transducers, and if the necessary delay time is secured, the stability of the oscillation frequency is determined by the piezoelectric substrate or piezoelectric thin film. It depends on the stability of the velocity of the sound wave propagating on the surface of the elastic substrate. The temperature coefficient of sound velocity can be reduced to 10ppm/℃ by selecting the substrate or thin film material.
It can be as follows. This guarantees practically sufficient frequency stability. In addition, the oscillation frequency accuracy mainly depends on the variation in the distance between piezoelectric transducers, but this variation can be corrected by increasing the precision during manufacturing or, in the case of piezoelectric thin films, by known means such as fine adjustment of the film thickness. It can be made small enough.

The piezoelectric transducers T4, T5, T6 and the broadband amplifier are connected to the audio carrier (video carrier frequency +
4.5MHz), and also constitutes a circuit that frequency-modulates the audio carrier wave using the audio input signal applied to the terminal 3. FIG. 3 is a diagram showing the specific configuration of only this part.

In FIG. 3, transistors Q1, Q2, Q
3 constitutes a differential amplifier. R3, R4, R
5 and R6 are bias resistors, terminal 3 is an audio input terminal, and low resistor R7 is inserted for high frequency blocking. Capacitors C2, C3, C4, and C5 are all coupling capacitors. The signal extraction directions of the piezoelectric transducers T5 and T6 are opposite to each other, and they are connected to the differential amplifier input. When the wavelength is λ, the position of piezoelectric transducers T5 and T6 is λ/4
Since they are different, the oscillation condition of the audio carrier frequency should be set so that it is satisfied at a bias point where the outputs from the piezoelectric transducers T5 and T6 are added equally across both ends of the load resistor R2 of the transistor Q1. , when the base voltage of transistor Q2 changes due to the audio signal input, the gain for the two signals having different phases changes, and the phase of the composite output voltage obtained at both ends of _R2 changes accordingly. Oscillation in this system occurs at a frequency where the sum of the phase changes in the differential amplifier section and the surface acoustic wave delay element section is an integer multiple of 2π, so if the base voltage changes, the frequency that satisfies the oscillation phase condition changes. It is possible to generate a frequency modulated wave by doing this.
FIG. 4 shows an example in which the configuration of the piezoelectric transducer shown in FIG. 3 is simplified.
A piezoelectric transducer T9 is arranged in place of T6, and a phase modulator 15 is inserted in its place. 1
4 is a wideband amplifier.

As is clear from the above, in this embodiment, the surface acoustic wave delay element section for oscillating the video carrier wave and the surface acoustic wave delay element section for generating the audio carrier wave and for frequency modulation are formed on the same substrate. There is an advantage that the frequency difference between the video carrier wave and the audio carrier wave is always maintained correctly, and the circuit configuration is simplified because a frequency conversion means as shown in FIG. 1 is not required. In addition, along with this, 4.5MHz from the video carrier wave
Since low frequency components are no longer generated, the bandpass filter shown in FIG. 17 is also unnecessary. Furthermore, the first
Since there is no need to oscillate and multiply a low frequency using a crystal oscillator as in the example shown in the figure, harmonics can be easily suppressed, and the circuit configuration of the video carrier generation section can also be simplified.

Next, the operation of the amplitude modulator section will be explained.
In FIG. 2, reference numeral 13 denotes a balanced modulator, a specific circuit example of which is shown in FIG. In Figure 5, C6, C
7, C8, and C9 are coupling capacitors, C10 is a bypass capacitor, R8, R9, R10, and R13 are bias resistors, and semi-fixed resistor R11 provides an appropriate bias to diodes D2 and D3 to maintain the linearity of the modulation signal. (This can be replaced with a fixed resistor if the variation in diode characteristics is small.) Semi-fixed resistor R12
is for balancing D2 and D3, and in the example shown in Figure 1, it is inserted at the position corresponding to R1, but the difference from Figure 1 is that R1 shifts the balance and changes the amplitude modulation degree. It is for adjusting the
Although it cannot be omitted, in the example shown in Fig. 5, the diode D is simply used to balance the diode characteristics.
2. If the characteristics of D3 are the same, it can be replaced with a fixed resistor.

In FIG. 5, the balanced modulator is used in a state in which the balance is maintained correctly, so even if adjustment of this part is necessary, there is an advantage that the adjustment can be made by the balanced modulation circuit unit alone. In FIG. 5, when a video signal with a DC component superimposed is applied to terminal 5, the video carrier taken from piezoelectric transducer T3 is balanced-modulated with the video signal.

In FIG. 5, piezoelectric transducer T8 is an output transducer for taking out the video/audio synthesis output. The piezoelectric transducers T3 and T7 have, for example, a regular comb-shaped electrode structure as shown in FIG. 7, while the piezoelectric transducer T8 has a comb-shaped electrode structure (not shown) with appropriate weighting. It has a frequency selection characteristic as shown in FIG. The characteristics shown in FIG. 6 can be realized by a known electrode design method. Various surface acoustic wave signals arrive at the piezoelectric transducer T8 as indicated by arrows in FIG. A balanced modulation signal output is transmitted from piezoelectric transducer T7 and received by piezoelectric transducer T8, while at the same time
Since both T2 and T3 partially face each other, the video carrier wave also arrives and the amplitude modulated wave is synthesized. At this time, the position of the piezoelectric transducer T2 is determined so that the phases of the video carrier waves are correctly matched. The degree of amplitude modulation can be set by the length l of the opposing portions of the piezoelectric transducers T2, T3 and T8. The audio frequency modulation signal frequency sent out from the piezoelectric transducer T4 passes through the opposing piezoelectric transducer T7 and reaches T8. At this time, the PS ratio can be set by the ratio of the length n of the opposing portions of the piezoelectric transducers T4 and T8 to the length m of the opposing portions of the piezoelectric transducers T7 and T8.

Therefore, the image modulation degree and PS ratio are determined by the electrode arrangement of the surface acoustic wave element, and adjustment is not necessary.

FIG. 8 shows that the arrangement of the piezoelectric transducers in FIG. 2 is changed, and between the piezoelectric transducers T1 and T2 in the delay element part for video and audio carrier wave oscillation,
In this example, the distance between T4, T5, and T6 is made as long as possible, and the piezoelectric transducer T
3, T7 and T8 are different from FIG. 2 in that they are inserted in the middle. This arrangement has the advantage of further improving the stability of the oscillation frequency.

The piezoelectric transducer T3 in FIG. 2 is used to wave the harmonics generated by the broadband amplifier 11 when a video carrier wave is generated, and to reduce the influence of the video modulation circuit on the video carrier wave generation section, but is omitted. You can also. FIG. 9 shows an example of the configuration, and parts having the same functions as those in FIG. 2 are indicated using the same symbols. The difference from FIG. 2 is that the output side of the wideband amplifier 11 is a balanced type and the piezoelectric transducer T3 is omitted, and the piezoelectric transducer T1, T2, T7 related to the video signal and the transducer related to the audio signal are The reason for this is that T4, T5, and T6 are arranged separately to reduce mutual influence, and that a viscoelastic material 16 is applied between T2 and T7. However, this viscoelastic body 1
6 is applied slightly shorter than the electrode finger length of T2 so that a part of the signal from T2 can reach T8. In this case, it is necessary to accurately determine the coating length.

As described above, according to the present invention, the configuration of the video converter device is simplified, unnecessary radiation signals are reduced, and ultra-miniaturization is possible, especially by combining a surface acoustic wave oscillator and a surface acoustic wave filter. Because of this, inductance and resonant capacitance are unnecessary, and circuit parts other than surface acoustic wave elements can be used.
It is easy to integrate into an IC, there is no need to adjust the amplitude modulation degree and PS ratio, and the video converter output signal is obtained through a surface acoustic wave filter with good phase and amplitude characteristics, resulting in high standards and high quality. It has many advantages such as the ability to easily obtain an output signal, and its effects are extremely large.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional video converter device, Fig. 2 is a block diagram showing an embodiment of the video converter device of the present invention, and Figs. 3, 4, and 5 are details of the present embodiment. 6 is an output filter characteristic diagram, FIG. 7 is a top view showing the shape of the comb-shaped electrode, FIG. 8 is a main part configuration diagram showing the second embodiment of the present invention, and FIG. 9 FIG. 2 is a configuration diagram showing a third embodiment of the present invention. 3...Terminal for audio signal input, 5...Terminal for video signal input, 9...Terminal for output, 10...
Surface acoustic wave element section, 11, 12... broadband amplifier, 13... balanced modulator, _T1 , _T2 to _T9 ... piezoelectric transducer.

Claims (1)

[Claims] 1. A first surface acoustic wave signal delay element formed by an input piezoelectric transducer, a surface acoustic wave propagation path, and an output piezoelectric transducer and whose signal passband includes an image carrier frequency on the same elastic substrate. and a second surface acoustic wave signal delay element including the audio carrier frequency of the channel corresponding to the video carrier frequency, and a wideband amplifier is installed between the input and output of these surface acoustic wave signal delay elements to adjust the carrier frequency. A video converter device characterized by having an oscillator section.