JPS645399Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides a method for using a so-called surface wave filter made of an acoustic wave device or a band filter belonging thereto in a converter section of an SHF satellite broadcasting receiver, for example, in this band. The present invention relates to an output circuit for a bandpass filter that effectively matches the high frequency amplification stage disposed next to the filter and makes full use of the performance of the bandpass filter.

[Background technology of the invention]

SHF satellite broadcasting is being put into practical use as a means of eliminating urban reception interference caused by high-rise buildings. In the general system of SHF satellite broadcasting, broadcast radio waves are transmitted from the ground to a satellite, where the satellite converts the frequency to, for example, a 12 [GHz] band and sends it back to the ground. These returned radio waves can be received individually in each home on the ground, or as signals for cable television broadcasts. The reception system for this purpose, the so-called SHF satellite broadcast receiver, is far away from the satellite and the frequency is high, so the incoming radio wave strength is very weak, so the outdoor antenna itself has a circuit with frequency conversion and amplification functions. The system incorporates an outdoor unit consisting of a UHF band, and this outdoor unit converts the received signal to a UHF band frequency before sending the received signal to the indoor unit. In other words, such a configuration is a double
It is equivalent to a super-heterodyne receiving system, in which the outdoor unit corresponds to a first frequency converter, and the indoor unit corresponds to a second frequency converter called a converter device of a so-called SHF satellite broadcast receiver. There is.

FIG. 1 is a circuit diagram showing the conventional configuration of this second frequency converter. In FIG. 1, an input terminal 1 is a terminal into which a signal sent from the first frequency converter is input, and is connected to a mixer 3 via a high frequency amplifier 2 having a predetermined bandwidth. ing. The input signal is, for example, an FM signal, and is a first intermediate frequency signal (hereinafter referred to as the first IF signal) output by a first frequency converter (not shown).
It is. The carrier wave of this first IF signal is, for example, 305 [M
Hz] to 485[MHz] UHF band frequency.
Therefore, this band defines the receiving band range of the first frequency converter.

Next, the first IF signal is led to a second frequency converter 5 consisting of the mixer 3 and local oscillator 4. In this second frequency converter 5, the oscillation frequency of the local oscillator 4 is tuned to the frequency of the first IF signal.
Convert to 2IF signal frequency. Its output is led out to an output terminal 7 via a bandpass filter 6. This bandpass filter 6 passes the FM signal whose frequency of the second IF signal is, for example, 130 [MHz] and whose band is 27 [MHz]. Thereby, the second IF signal band-amplified for each center frequency of the first IF signal can be received by the UHF or VHF tuner of a general television receiver.

However, as mentioned above, this device has a narrow reception band range of 305 [MHz] to 485 [MHz].
It is designed to receive SHF radio waves, and if the broadcast frequency range becomes wider than this, it will no longer work effectively against image interference. That is, in the above circuit, the local oscillator 4 that outputs the second IF signal of 130 [MHz] has an image frequency of 260 [MHz] in the case of upper heterodyne for the receiving band range of 180 [MHz].
Since there is no risk of tuning to a signal with a frequency higher than 100 Hz, it was possible to receive the signal without any interference by simply providing a bandpass filter 6 after the mixer 3. However, when the reception band range is expanded, problems such as image interference and cross modulation occur.

Therefore, a circuit has been proposed in which a second frequency converter (hereinafter referred to as a converter device) of a receiver that receives broadcasts in the SHF band is provided with a preselector function to widen the reception band. This is shown in FIG. The configuration shown in FIG. 2 differs from the configuration shown in FIG. For example, a surface wave filter 9, which is better than a general LC filter, is used. Furthermore, a high frequency amplifier 10 is connected to both ends of the surface wave filter 9.
11 is provided so that a desired signal can be selected without deteriorating the characteristics of the surface wave filter 9. This makes it possible to make the image signal resistant to interference, eliminate the need for band adjustment of the frequency-converted output signal, and furthermore reduce the number of parts.

[Problems with background technology]

The use of this surface wave filter 9 before the amplification stage has been conventionally used in television receivers as a means of adjusting the video intermediate frequency signal to the required band. are connected to obtain a balanced output. FIG. 3 shows an output circuit of a surface wave filter for explaining this configuration. In FIG. 3, the surface wave filter is designated by the same reference numeral 9 as in FIG.
The other end is connected to a grounded unbalanced input, and the output electrode side is configured to provide a balanced output. That is, the output electrodes are configured to obtain a balanced output, and each terminal of the balanced output line is connected to a video intermediate amplifier circuit having differential input terminals via a matching circuit consisting of a coil L ₁ and a resistor R ₁ . 13, the video intermediate frequency signal is derived.

However, when the surface wave filter 9 is used in a place where UHF band signals are handled, that is, when it is mounted on the above-mentioned converter device, the method for taking out the output electrode is the same as the input electrode side. must be taken out as. Further, the circuit using the surface wave filter in such a place is itself a new attempt, and a means for stabilizing its operation has not been established.

The following problems arose as unstable factors. That is, when the high frequency amplifier circuit 11 is connected to the surface wave filter 9 in FIG.
1 causes abnormalities such as oscillation. The reason for this is that since the surface wave filter 9 is a high impedance element, if the input impedance of the high frequency amplifier circuit 11 is increased, the oscillation conditions in the high frequency amplifier circuit 11 will be satisfied due to the relationship with the load of the high frequency amplifier circuit 11. .

In addition, as a second problem, the high frequency amplifier circuit 1
1 input impedance (device impedance)
If the value is high, the amplification operation becomes unstable due to the properties of the amplification semiconductor element used, making it impossible to sufficiently transmit the characteristics of the surface acoustic wave filter 9. For this reason, even if an attempt is made to reduce and stabilize the input impedance of the high frequency amplifier circuit 11 by providing a matching resonant circuit that reduces fluctuations in the input impedance of the surface wave filter 9 in the passband of the surface wave filter 9, if the input impedance is made too small, the amplification performance will deteriorate. Because of this, we have not yet been able to obtain sufficient characteristics.

[Purpose of invention]

This idea was made in view of the above circumstances.
A bandpass filter that matches the bandpass filter used in the converter device of the SHF satellite broadcasting receiver and the high-frequency amplifier circuit installed in the next stage to prevent abnormal oscillations and to fully utilize the characteristics of the bandpass filter. The purpose is to provide an output circuit.

[Summary of the idea]

For the above purpose, the present invention is novel in that a matching resistor is provided between the bandpass filter and the high-frequency amplification circuit, and this resistor is located near the bandpass filter due to the layout configuration, thereby achieving high-frequency amplification. The impedance of the bandpass filter viewed from the input end of the circuit is lowered, and the input impedance of the high frequency amplifier circuit is lowered to achieve matching between the two circuits.

[Example of idea]

The present invention will be explained below based on FIGS. 4 and 5. Here, FIG. 4 is a circuit diagram of an embodiment of the circuit of the present invention, and FIG. 5 is a circuit layout diagram thereof.
These will be explained in order. First, in Figure 4,
The bandpass filter uses a surface wave filter 21, which is composed of an acoustic wave device having opposing input and output electrodes formed on the surface of a piezoelectric substrate. One of the input electrodes _P1 of the surface wave filter 21 is connected to the input terminal 22, and the other input electrode _P2 is grounded, so that an input signal in a predetermined band is applied as an unbalanced input. There is. Further, one of the output electrodes _P3 is connected to the base of a high frequency amplification semiconductor (hereinafter referred to as a transistor) T constituting the high frequency amplification circuit 23 via a capacitor _C1 , and the other output electrode _P4 is grounded. The base of this transistor T is connected to one end of the inductance _L1 , and the other end of the inductance _L1 is connected to the power supply terminal 24 side. That is,
The other end of the inductance _L1 is connected to the power supply terminal 24 via a resistor _R2 , and the connection point with this resistor _R2 is grounded via a bypass capacitor _C2 .

Further, the capacitor C ₁ and the inductance L ₁ resonate in the band of the signal derived from one of the output electrodes of the surface wave filter 21, and lower the input impedance of the high frequency amplifier circuit 23 seen from the surface wave filter 21 in this band. ing. A resistor R ₃ is interposed between the signal line 25 from which signals in this band are derived and the ground line. That is, this signal line 25 is a connection line between one of the output electrodes of the surface wave filter 21 and the base of the transistor T, and the resistor R ₃ is connected to this signal line 25.
From the capacitor C ₁ above, the circuit is transistor T.
It is connected to the base side of the The resistor R ₃ is designed to further lower the input impedance of the high frequency amplifier circuit 23 seen from the surface wave filter ₂₁ by multiplying its own resistance value than the input impedance of the transistor T due to the circuit composed of the capacitor C ₁ and the inductance L 1. This is to match the surface wave filter 21 and the high frequency amplification circuit 23 mainly composed of the transistor T. In this embodiment, the resistance value of the matching resistor R ₃ is, for example, 3 [KΩ].
It is set before and after. As a result, the input impedance of the high frequency amplifier circuit 23 as seen from the surface wave filter 21 became approximately 50 [Ω] in the band of the signal.

In addition, the emitter side of the high frequency amplifier circuit 23 is a resistor.
It is bypassed via R ₄ and capacitor C ₃ in parallel, and a resonant circuit consisting of inductance L ₂ and capacitor C ₄ is provided on the collector side to match the input impedance. An output terminal 26 is provided so that the output is derived from the capacitor _C4 . Further, the power supply terminal 24 has a bypass capacitor _C5 connected to the ground line.

Although the circuit of the present invention is constructed as described above, the construction in which each element is actually mounted on a printed wiring board will be explained next. FIG. 5 omits an actual printed wiring board and shows the actual circuit pattern and each element detailed in FIG. 4 in a plan view. In FIG. 5, the surface wave filter 21 is mounted at the position indicated by the circular broken line 21'. In this case, the other input electrode P ₂ and the other output electrode P ₄ are grounded, so they are fixed to the insertion holes P ₂ ', P ₄ ' on the ground pattern 27, and one input electrode P ₁ is connected to the input terminal 22. It is fixed in the insertion hole P ₁ ' of the pattern 22' corresponding to the pattern 22'. Further, the output electrode P ₃ is similarly fixed to the output side insertion hole P ₃ ′. The ground pattern 27 is connected to the substrate portion of one of the input electrodes P ₁ and one of the output electrodes P ₃ , that is,
Pattern 2 corresponding to a part of the signal line 25
5A is formed on the surface wave filter 2.
They are separated in terms of circuit operation by electrodes P ₂ and P ₄ (ground) on the diagonal line of No. 1 as a boundary. In addition, the pattern 2
5A is formed near the surface wave filter 21, and from this position a pattern 25 corresponding to the other part of the signal line ₂₅ is connected via the capacitor C1.
It is connected to B. The matching resistor R ₃ is mounted on the ground pattern 27 and the pattern 25B of the signal line 25 in the vicinity of the capacitor C ₁ . Therefore, the resistor R ₃ is the transistor T
It is arranged closer to the surface wave filter 21.
Since the following configuration is almost the same graphically as the circuit shown in FIG. 4, the reference numerals of each element are only shown in the drawing.

The output circuit of the bandpass filter of the present invention is configured as described above. Next, its operation will be explained.
An input terminal 22 is connected to the input electrode of the surface wave filter 21.
An unbalanced signal occupying a predetermined band is applied via. This signal is excited with a spectrum determined by an internal device of the surface wave filter 21, and is output from one of the output electrodes _P3 . This signal is output at a high impedance determined by the surface wave filter 21 and is transmitted to the base of the transistor T via the capacitor _C1 . At this time, the capacitor
C ₁ and inductance L ₁ resonate and work to lower the base impedance of transistor T. Furthermore, since there is a matching resistor R ₃ acting synergistically with this, the resistance value of this resistor R ₃ acts in parallel on the base impedance to lower the base impedance, and the output of the surface wave filter 21 The input impedance of the high frequency amplifier circuit 23 seen from the electrodes is made small. Furthermore, since the matching resistor R ₃ is close to the surface wave filter 21 side, the impedance of the surface wave filter 21 seen from the input side of the high frequency amplifier circuit 23 appears to be reduced. This allows the conventional capacitor C ₁
The matching conditions are closer to ideal than when matching both circuits using only the inductance L1 and the inductance _L1 , and the input impedance of the high frequency amplifier circuit 23 can be stabilized. Furthermore, since the impedance of the surface wave filter 21 does not directly affect the input impedance of the high frequency amplifier circuit 23, the high frequency amplifier circuit 23
The input impedance does not become high, and even if the load fluctuates, it will not approach the oscillation condition.

The specific experimental data of this example is that the signal input to the input terminal 22 is an FM signal with a center frequency of 130 [MHz] and a frequency deviation of ±13.5 [MHz] for use in an SHF satellite broadcasting receiver. , a resistor 3 is connected to the surface wave filter 21 that passes this signal.
Around [KΩ] was used. At this time, the input impedance of the high frequency amplifier circuit 23 as seen from the surface wave filter 21 was approximately 50 [Ω], which could be set to an ideal value that would not affect the amplification performance. It was also confirmed that the upper limit of this resistance is around 10 [KΩ].

Further, the matching resistor R ₃ may be provided at any position on the signal line 25 as long as the effect remains, and it is also possible to provide it before the capacitor C ₁ .

[Effect of idea]

As described above, according to the present invention, a high frequency amplification circuit that extracts the output of a bandpass filter constituted by an elastic wave device as an unbalanced output is configured to have a stable matching function with respect to the bandpass filter. And, since the impedance of the band filter seen from the input side of the high frequency amplification circuit is lowered, there is a problem that matching between the high frequency amplification circuit and the band filter is incomplete as in the conventional case, and the characteristics of the band filter cannot be fully utilized. solved. This has the effect that the band of the signal that has passed through the band filter can be ideally transmitted.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the circuit configuration of the converter device to explain the outline of the SHF satellite broadcasting receiver, Fig. 2 is a block diagram showing the circuit configuration of the converter device improved from the first converter device, and Fig. 3 is a block diagram showing the circuit configuration of the converter device. FIG. 4 is a circuit diagram showing the output circuit of a surface wave filter with balanced output in a general television receiver; FIG. 4 is a circuit diagram showing the output circuit of a surface wave filter showing an embodiment of the present invention; FIG. FIG. 3 is a plan view of a circuit pattern showing an example of a case where the circuit shown in the figure is mounted on a printed wiring board. 21...Surface wave filter, 22...Input terminal,
23...High frequency amplifier circuit, 24...Power terminal, 2
5... Signal line, 26... Output terminal, 27...
Earth pattern, R ₂ ~ R ₄ ... Resistance, C ₁ ~ C ₅ ...
Capacitor, L ₁ , L ₂ ...Inductance.

Claims (1)

[Scope of utility model registration request] A band filter configured with an unbalanced elastic wave device, a high frequency amplification circuit that amplifies the signal excited and output by the band filter, and a signal line that connects the high frequency amplification circuit and the band filter, a resonance matching circuit that resonates in the passband of the bandpass filter to lower the input impedance of the high frequency amplifier circuit; and a resonance matching circuit that is provided between the signal line and a reference potential point to further lower the input impedance of the high frequency amplifier circuit and the 1. An output circuit for a bandpass filter, comprising a resistor for lowering the output impedance of the bandpass filter to achieve matching between the bandpass filter and a high frequency amplifier circuit.