JPH0153815B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an intermediate frequency block, and more particularly to a control section for correcting temperature drift of an acoustic wavefront Nyquist filter connected to a tuner section.

[Technical background of the invention and its problems]

Normally, television video signals require a frequency band of 4.5MHz. This is DSB (Double Side
If the data is sent using the Bond method, the occupied bandwidth will be 9MHz, which is too large. Therefore, SSB (Single Side Band)
Although it is being considered to send television video signals using this method, it would require complicated equipment to receive them. Therefore, as shown in Figure 1, VSB (Vestigial Side Band) removes part of the lower side band and transmits it.
In other words, the vestigial sideband method is adopted.

However, when receiving the waveform shown in Figure 1, the receiving side is affected by the fact that part of the lower sideband is not sent, so the characteristics of the demodulator are changed in order to obtain the characteristics shown in Figure 2. , an acoustic wavefront Nyquist filter (hereinafter referred to as a Nyquist filter) in which weighting electrodes and regular electrodes are formed on a piezoelectric substrate is used to prevent distortion during demodulation.

Next, a conventional example of an intermediate frequency block using a Nyquist filter will be explained with reference to FIGS. 3 and 4.

In FIG. 3, the intermediate frequency block includes a tuner, a detection section, a vestigial sideband type Nyquist filter placed between the tuner section and the detection section, and a thermostatic chamber in which the Nyquist filter is placed. It consists of 11. In order to prevent temperature drift in the frequency amplitude characteristics due to changes in the ambient temperature of the Nyquist filter, that is, to suppress the amount of change in the frequency characteristics due to changes in temperature, the temperature of the Nyquist filter is kept constant using a constant temperature bath 11. I was doing it. However, thermostatic chambers are expensive and large, which poses a problem.

Therefore, in FIG. 4, a system has been considered in which the intermediate frequency block shown in FIG. 3 has a control section in the local oscillation section and a temperature sensor 20 is disposed in this control section near the Nyquist filter. In this method,
This method uses a temperature sensor 20 to detect a temperature drift in the frequency amplitude characteristic due to the influence of the ambient temperature of the Nyquist filter, and cancels it by changing the oscillation frequency of the local oscillator. However, there is a drawback that the temperature sensor 20 and the control circuit are complicated and expensive. Moreover, maintenance to constantly sharpen the sensor function of the temperature sensor 20 has been difficult.

[Purpose of the invention]

The present invention has been made in view of the above points, and it is an object of the present invention to provide an intermediate frequency block that is easy to handle and has a simple structure.

[Summary of the invention]

In order to achieve this object, the present invention uses a surface acoustic wave resonator that also serves as a local oscillation section in the control section, and uses the surface acoustic wave resonator in the local oscillation circuit to increase the ambient temperature of the acoustic wave front Nyquist filter. This change causes the local oscillation frequency of the surface acoustic wave resonator to follow the temperature drift of the Nyquist filter frequency of the elastic wave front, thereby canceling the temperature drift.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

In FIG. 5, the intermediate frequency block of the present invention is arranged in a surface acoustic wave device 25 consisting of a surface acoustic wave resonator 251 and a Nyquist filter 252 between a tuner section and a detection section. In the intermediate frequency block shown in FIG. 5, if the transmission frequency 21 is 91.25MHz, the first local oscillator 2
The local oscillation frequency 24 of the local oscillation circuit consisting of the second local oscillation section 251 and the second local oscillation section 251 is 130.15MHz. That is, since the resonant frequency of the surface acoustic wave resonator 251 constituting the second local oscillation section is 38.85MHz, L
Taking into consideration the increase of 0.05 MHz due to the oscillation with the component, the oscillation frequency 26 becomes 38.9 MHz. That is, the local frequency of the local oscillation circuit 23 is
If fixed at 91.25MHz, the local oscillation frequency 24 will be
It becomes 130.15MHz. However, in the surface acoustic wave device 25 of the present invention, the Nyquist filter 2
52 and uses the surface acoustic wave resonator 251 in the second local oscillation section, when the ambient temperature of the surface acoustic wave device 25 rises, the Nyquist filter 252 has a lower amplitude characteristic, for example. (38.9MHz−Δ). That is, if the normal demodulation frequency of the Nyquist filter 252 is v, then (v-Δ) is obtained. At this time, since there is a surface acoustic wave resonator 251 constituting the second local oscillation section on the same plane as the Nyquist filter 252, if the normal resonance characteristic of the surface acoustic wave resonator 251 is r, the resonant frequency is ( r−Δ). Therefore
Since v and r are equal, the oscillation frequency of the surface acoustic wave resonator is (38.9MHz−Δ).

The local oscillation frequency 91.25MHz and the oscillation frequency (38.9MHz-Δ) obtained by the surface acoustic wave resonator are mixed, and the local oscillation frequency 24 is (130.15MHz-Δ).
become.

As described above, the carrier frequency 27 of the tuner output is (130.15MHz - Δ) - 91.25MHz = 38.9M
Hz−Δ. That is, when the ambient temperature of the surface acoustic wave device 25 rises, the Nyquist filter 251
The carrier frequency 27 of the tuner output follows the carrier frequency (v−Δ) of the Nyquist filter 252.
temperature drift can be canceled.

Next, a surface acoustic wave device used in the intermediate frequency block of the present invention will be explained with reference to FIG.
In Figure 6, 50 mm x 50 mm made of metal such as iron
Epoxy adhesive (not shown) on stem 31 of mm
30mm made of LiTaO ₃ etc. with thickness 0.48mm through
A Nyquist filter 33 is placed on a ×30mm piezoelectric substrate.
and a surface acoustic wave resonator 34 are arranged. Also, this stem 31 has a lead pin 336,
338,345 are planted. The Nyquist filter 33 includes a regular electrode 331 at one end of a piezoelectric substrate 31, and a weighting electrode 331 at the other end.
33 are configured. Between the regular type electrode 331 and the weighting electrode 333, the regular type electrode 33
A shield electrode 332 for preventing electromagnetic induction is configured from 1 to the weighting electrode 333. This regular type electrode 331 and weighting electrode 333
A sound absorbing material 334 is provided at the end of the piezoelectric substrate, respectively.
335 is applied. And regular type electrode 33
1 is electrically connected to a lead pin 336 via a bonding wire 337. Similarly, the weighting electrode 333 is also electrically connected to the lead pin 339 via a bonding wire 339.

On the other hand, in the surface acoustic wave resonator 34, reflective electrodes 342, 343 are provided at both ends of the piezoelectric substrate 32.
is formed. These reflective electrodes 342, 343
A regular electrode 341 is formed between the two.
Further, the regular electrode 341 is electrically connected to a lead pin 345 via a bonding wire 344. The stem 31 and the shell 35 are hermetically sealed, for example, laser sealed, and constitute a surface acoustic wave device. Further, the stem 31 and the shell 35 constitute an envelope.

By the way, the intermediate frequency block shown in FIG. 5 using this surface acoustic wave device 30 does not use a constant temperature oven, so the manufacturing cost is low, and the ambient temperature of the Nyquist filter is reduced because no heat is emitted from the constant temperature oven. will no longer reach high temperatures. Furthermore, since no temperature sensor is used, the cost is reduced and there is no need for a complicated structure. Furthermore, since this surface acoustic wave device 30 has a Nyquist filter and a surface acoustic wave resonator configured on the same piezoelectric substrate, the carrier frequency and the resonant frequency match, and temperature drift can be easily canceled by changing the local oscillation value. can do.

Next, referring to FIG. 7, the oscillation frequency of the surface acoustic wave device of the present invention, the ambient temperature of the Nyquist filter,
The relationship between the electrodes of the Nyquist filter and the electrodes of the surface acoustic wave resonator 135 (see FIG. 6) will be explained. Here, the electrodes of the Nyquist filter refer to a regular electrode, a shield electrode, and a weighting electrode, and the electrodes of a surface acoustic wave resonator refer to a reflector and a regular electrode. In this case, a resonance frequency of 38.85MHz was used.

In FIG. 7, a characteristic curve 51 is a characteristic curve showing the demodulation frequency of a Nyquist filter, a characteristic curve 52 is a characteristic curve showing the resonant frequency of a surface acoustic wave resonator with a minimum distance 135 of 1 mm, and a characteristic curve 53 is a characteristic curve showing the resonant frequency of a surface acoustic wave resonator with a minimum distance 135 of 1 mm. The characteristic curve 54 is a characteristic curve showing the resonant frequency of a surface acoustic wave resonator with a shortest distance 135 of 10 mm, and the characteristic curve 54 is a characteristic curve showing the resonant frequency of a surface acoustic wave resonator with a shortest distance 135 of 20 mm. Shortest distance 1
If 35 is less than 1 mm, there is a risk that dielectric development will occur between the electrodes of the Nyquist filter and the electrodes of the surface acoustic wave resonator. Also, the shortest distance 135 is
If the distance is within 10 mm, the resonant frequency of the surface acoustic wave resonator substantially matches the demodulation frequency of the Nyquist filter, so that the temperature drift of the Nyquist filter can be effectively canceled. Moreover, if the shortest distance 135 is 1 mm to 10 mm, the error range of the measuring device is approximately 5% even under adverse conditions.
can be accommodated in the standard.

In FIG. 5, the surface acoustic wave device of the present invention has been described with a structure in which a Nyquist filter and a surface acoustic wave resonator are arranged on the same piezoelectric substrate. however,
The surface acoustic wave device of the present invention has a Nyquist filter and a surface acoustic wave resonator formed on separate piezoelectric substrates (however, the piezoelectric substrate of the Nyquist filter, the surface acoustic wave resonator, and the piezoelectric substrate are made of the same material. ), it goes without saying that the respective piezoelectric substrates may be placed on the same plane, for example, on the stem. Further, configuring the Nyquist filter and the surface acoustic wave resonator separately has the advantage that it is easy to check individual characteristics and that temperature drift can be easily canceled.

〔Effect of the invention〕

As described above, according to the present invention, by using a surface acoustic wave resonator that also serves as a local oscillation section in the control section, the surface acoustic wave resonator is used in the local oscillation circuit, and the surface acoustic wave Nyquist filter and surface acoustic wave Since the temperature of the resonator and the resonator is the same as the ambient temperature, it is possible to cancel the temperature drift by making the local oscillation frequency of the surface acoustic wave resonator follow the temperature drift of the frequency characteristics of the surface acoustic wave Nyquist filter due to changes in the ambient temperature. did it.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the video signal frequency band of television, Figure 2 is a characteristic diagram of a demodulator obtained by a surface acoustic wave Nyquist filter, and Figure 3 is an intermediate frequency block diagram using a thermostatic oven. Fig. 4 is a block diagram showing an intermediate frequency block using a temperature sensor, Fig. 5 is a block diagram showing an embodiment of the intermediate frequency block of the present invention, and Fig. 6 shows the elasticity used in Fig. 5. FIG. 7 is an exploded perspective view showing the surface acoustic wave device. FIG. 7 is a characteristic diagram showing the characteristics of the surface acoustic wave device shown in FIG. 32...Piezoelectric substrate, 33...Surface acoustic wave Nyquist filter, 34...Surface acoustic wave resonator, 33
1,341...Regular type electrode, 333...Weighting electrode, 342,343...Reflecting electrode.

Claims (1)

[Claims] 1. A tuner section that generates an intermediate frequency by mixing the transmission frequency input from the antenna and the oscillation frequency from the local oscillation circuit, and a tuner section that generates an intermediate frequency by mixing the transmission frequency input from the antenna and the oscillation frequency from the local oscillation circuit; The local oscillation circuit has a first local oscillation section and a second local oscillation section, and the second local oscillation section is arranged on the same plane as the elastic wave front Nyquist filter. The surface acoustic wave resonator has a surface acoustic wave resonator, and the frequencies of the first local oscillation section and the second local oscillation section are adjusted to a temperature drift of the frequency of the acoustic wave front Nyquist filter due to a change in the ambient temperature of the acoustic wave front Nyquist filter. An intermediate frequency block characterized in that the local oscillation frequency of the mixed local oscillation circuit is tracked. 2. A patent characterized in that the first piezoelectric substrate constituting the electrode of the surface acoustic wave Nyquist filter and the second piezoelectric substrate constituting the electrode of the surface acoustic wave resonator are made of substantially the same material. An intermediate frequency block according to claim 1. 3. A first piezoelectric substrate, which constitutes an electrode of the acoustic wavefront Nyquist filter, and an electrode of the surface acoustic wave resonator are constituted in the stem in an envelope constituted by a shell and a stem in which lead pins are implanted. 3. The intermediate frequency block according to claim 2, further comprising a second piezoelectric substrate mounted thereon. 4. The first piezoelectric substrate constituting the electrode of the surface acoustic wave Nyquist filter and the second piezoelectric substrate constituting the electrode of the surface acoustic wave resonator are located on the same plane on the stem surface. An intermediate frequency block according to claim 3. 5. The first piezoelectric substrate constituting the electrode of the acoustic wavefront Nyquist filter and the second piezoelectric substrate constituting the electrode of the surface acoustic wave resonator are the same piezoelectric substrate, and 3. The intermediate frequency block according to claim 2, wherein the intermediate frequency block is adjacent to the surface acoustic wave resonator. 6. The first piezoelectric substrate forming the electrode of the surface acoustic wave Nyquist filter and the second piezoelectric substrate forming the electrode of the surface acoustic wave resonator are separate piezoelectric substrates. An intermediate frequency block according to claim 2. 7. The arrangement direction of the electrode fingers of the acoustic wavefront Nyquist filter and the arrangement direction of the electrode fingers of the surface acoustic wave resonator are adjacent to each other so as to be substantially parallel, and the electrodes of the acoustic wavefront Nyquist filter and the elastic surface The narrowest distance between the wave resonator and the electrode is approximately 0.1cm.
7. An intermediate frequency block according to claim 5 or 6, characterized in that the intermediate frequency block is in the range of 1.0 cm to approximately 1.0 cm. 8. The intermediate frequency block according to claim 1, wherein the passband center frequency of the surface acoustic wave Nyquist filter and the resonance frequency of the surface acoustic wave resonator are approximately equal.