JPH07106913A - SAW filter device - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] SA that can meet the demand for miniaturization of circuits such as mobile communication equipment and reduce the number of large components such as capacitors mounted.
Provide a W filter. [Structure] SAW filter 1 and S
An input buffer circuit 2 for generating a signal to be input to the AW filter 1 and an output buffer circuit 3 for receiving a predetermined output signal of the SAW filter 1 and outputting the output signal to the outside are provided. The output buffer circuit 3 is configured such that the potential difference from the signal potential of the input signal of the output buffer circuit 3 is within the range of the voltage allowed between the input and output of the SAW filter 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SAW (surface acoustic wave) filter device. More specifically, the present invention can be used in place of a conventional SAW filter for timing reproduction in data communication equipment and frequency selection in mobile communication equipment, and is a novel S that is easy to handle.
The present invention relates to the configuration of an AW filter device.

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing a general structure of a SAW filter.

As shown in the figure, the SAW filter 1 is
Stem the piezoelectric material substrate 12 loaded with two pairs of comb-shaped electrodes 13.
After being mounted on 11, the upper surface of the stem 11 is sealed by a case 16. Lead pin 17 on stem 11
Is attached to each comb-shaped electrode 13 and bonding wire.
Connected by 14. Further, a sound absorbing material 15 is attached to an end portion of the piezoelectric material substrate 12.

It is known that the SAW filter as described above has a low electric breakdown voltage between terminals, especially when the operating frequency becomes high. Therefore, when connecting the SAW filter to another electronic circuit, it is common to use so-called AC coupling using a coupling capacitor for the purpose of preventing an excessive voltage from being applied between the terminals. .

[0005]

By the way, due to various technological advances, SAW filters are becoming very small in size today. Also, ordinary electronic circuits have been miniaturized to the utmost by integration. However, it is difficult to integrate an element whose physical size influences the function, such as a capacitor, and the size of a module using a SAW filter is inevitably large because a coupling capacitor is used. There wasn't.

Further, as shown in FIG. 5 (a), the SAW filter is currently generally used in a so-called single connection. If this is differentially connected as shown in FIG. 5 (b), more capacitors must be used, which is substantially another limitation when using a SAW filter.

Particularly in mobile communication equipment and the like, miniaturization of the circuit is a very important issue, and in this respect, the use of the SAW filter in which the capacitor is inevitably mounted is incompatible with the miniaturization of the circuit. Has become. Therefore, an object of the present invention is to provide a novel SAW filter device that solves the above-mentioned problems of the prior art and does not require a capacitor for connection.

[0008]

According to the present invention, a SAW
A filter, an input buffer circuit that generates a signal to be supplied to the SAW filter, and an output buffer circuit that receives the output signal of the SAW filter. The signal potential of the output signal of the input buffer circuit and the output buffer circuit There is provided a SAW filter device characterized in that a potential difference from a signal potential of an input signal is configured to fall within a withstand voltage range allowed between input and output of the SAW filter.

[0009]

The SAW filter device according to the present invention includes the input buffer circuit and the output buffer circuit configured so that the potential difference between the input and output of the SAW filter does not exceed the withstand voltage of the SAW filter itself. It is configured so that it can be connected to other electronic circuits without being used.

That is, the conventional SAW filter has a structure in which the comb electrodes, which are easily destroyed by an excessive voltage, are directly connected to the outside. Therefore, when the SAW filter is used, it is inevitable to use the coupling capacitor, which is disadvantageous in terms of space factor, and the differential connection in which the number of capacitors used is increased is substantially limited.

On the other hand, the SAW filter device according to the present invention includes the input buffer circuit and the output buffer circuit, and the potential difference between the output voltage of the input buffer circuit and the input voltage of the output buffer circuit is the SAW filter. It is configured not to exceed the withstand voltage of. Since the input of the input buffer circuit and the output of the output buffer circuit can be directly connected to other circuits, as in a normal electronic circuit,
When mounting this SAW filter device, it is not necessary to use a coupling capacitor which is an obstacle to downsizing.

The potential difference between the output voltage of the input buffer circuit and the input voltage of the output buffer circuit as described above can be achieved by appropriately unifying the specifications of the input buffer circuit and the output buffer circuit. Feedback control may be performed so that the signal potential difference between the two is minimized. Also,
Each buffer circuit that can be configured by an amplifier is S
It may be incorporated in the package of the AW filter, or may be connected outside the SAW filter package as will be specifically described later. Furthermore, each buffer circuit may also be used as an output circuit or an input circuit at the front stage or the rear stage of the SAW filter.

As described above, in the SAW filter device according to the present invention, it is not necessary to use the capacitor, which is an element having a bad space factor, so that miniaturization by integration can be efficiently promoted.

If the signal potentials of the input signal and the output signal to the SAW filter device according to the present invention are unified to, for example, the signal potentials of the semiconductor circuits connected before and after the SAW filter device, for example, the ECL level. It is convenient to handle.

Hereinafter, the present invention will be described in more detail with reference to examples, but the following disclosure is merely an example of the present invention and does not limit the technical scope of the present invention.

[0016]

1 is a diagram showing another example of the structure of a SAW filter device according to the present invention.

The SAW filter device shown in FIG. 1 (a) includes an input buffer circuit 2 which receives a signal from the outside to generate an input signal to the SAW filter 1 and a signal which receives the output of the SAW filter 1 and outputs the signal to the outside. And an output buffer circuit 3 for generating. These input buffer circuit 1 and output buffer circuit 2 are basically amplifiers,
The output voltage of the input buffer circuit 2 is designed to match the input voltage of the output buffer circuit 3. The input from the input buffer circuit 2 to the SAW filter 1 is non-differential connection. Therefore, the vacant terminal of the SAW filter 1 is connected to ground via the capacitor C ₀ . This is to prevent an excessive DC voltage from being applied to the SAW filter 1 due to the DC potential difference between the signal potential and the ground level.

In the circuit configured as described above, the output signal potential of the input buffer circuit 2 and the output buffer circuit 4
With respect to the input signal potential of, the potential difference that exceeds the withstand voltage of the SAW filter 1 does not occur. That is,
For example, by designing the output signal voltage of the input buffer circuit according to the input voltage of the output buffer circuit, the potential difference between the two is prevented from increasing.

The device shown in FIG. 1 (a) uses a capacitor C ₀ , but since this capacitor C ₀ is connected to the ground, it is connected to the outside of the electronic circuit including the SAW filter device. You can put it on. Therefore, the use of this capacitor C ₀ is not a significant obstacle to miniaturization.

The SAW filter device shown in FIG. 1 (b) has the same configuration as the above device in that it has an input buffer circuit 2, a SAW filter 1 and an output buffer circuit 3 which are connected in sequence, but the input buffer circuit 2 From the SAW filter 1 is a differential connection, and the output from the SAW filter 1 to the output buffer circuit 3 is a non-differential connection. Therefore, the vacant terminal of the SAW filter 1 is connected to the ground via the capacitor C ₀ and the resistor R ₀ . This is to prevent an excessive DC voltage from being applied to the SAW filter 1 due to the DC potential difference between the signal potential and the ground level. Note that the resistor R ₀ is not always necessary, and in some cases, the capacitor C
_In some cases, one end of ₀ is directly connected to ground. The other functions are the same as those of the apparatus shown in FIG. 1 (a), and detailed description thereof is omitted.

FIG. 2 is a diagram showing another configuration example of the SAW filter according to the present invention.

As shown in FIG. 3, the basic structure of this SAW filter device is that the input buffer circuit 2, the SAW filter 1 and the output buffer circuit 3 are connected in order from the input side. It is similar to the conventional circuit shown. However, as can be seen from the figure, in the SAW filter device according to the present invention, between the input buffer circuit 2 and the SAW filter 1, and between the SAW filter 1 and the output buffer circuit 2.
And are directly connected by differential connection.

In the SAW filter device as described above, unlike the SAW filter device shown in FIG. 1, there is no need to use a capacitor when using the SAW filter device. this is,
This is because the signal potentials of the respective constituent elements are unified and there is no fear that a large DC voltage will be applied to the SAW filter 1.

As a method of unifying the signal potentials on the input side and the output side of the SAW filter 1 in the above SAW filter devices, the input voltage of the output buffer circuit 3 matches the output voltage of the input buffer circuit 2. The most basic method is to design and manufacture the output buffer circuit 3 as described above. Further, a method may be considered in which the input buffer circuit 2 is feedback-controlled based on the input voltage of the output buffer circuit 3 to automatically match the two voltages, but such a circuit is generally known to those skilled in the art. Can be realized by a general circuit design method.

Further, FIG. 3 is a diagram showing another configuration example of the SAW filter according to the present invention.

As shown in the figure, in this device, an input buffer circuit 2 and an output buffer circuit 3 are integrated together with other electronic circuits, and a single SAW filter 1 is connected to this integrated circuit. Has become.

That is, when the specifications of the SAW filter to be used are known in advance, the input buffer circuit 2 and the output buffer circuit 3 can be integrated together with the electronic circuit used by connecting to the SAW filter. . SA
Since the W filter 1 itself is formed on the piezoelectric material substrate, its manufacturing process is different from that of the semiconductor integrated circuit, and it is difficult to integrate it with other semiconductor circuits. Therefore, by forming only the SAW filter having a different manufacturing process as a separate body and configuring the other circuits as an integrated circuit including the input buffer circuit and the output buffer circuit, the overall productivity can be improved. .

[0028]

As described above in detail, since the SAW filter device according to the present invention can be connected to another electronic circuit without using a capacitor which is an obstacle to downsizing, it can be connected to another electronic circuit. It is possible to efficiently carry out miniaturization by integration. The SAW filter device according to the present invention as described above can be advantageously applied to mobile communication devices and the like in which demands for downsizing are extremely severe.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of a SAW filter device according to the present invention.

FIG. 2 is a diagram showing another configuration example of the SAW filter device according to the present invention.

FIG. 3 is a diagram showing one practical configuration example of a SAW filter according to the present invention.

FIG. 4 is a diagram showing a general configuration of a SAW filter.

FIG. 5 is a diagram showing a general connection method when a SAW filter is used.

[Explanation of symbols]

1 ... SAW filter, 2 ... Input buffer circuit, 3 ... Output buffer circuit, 11 ... Stem, 12 ... Piezoelectric material substrate, 13 ... Comb-shaped electrode, 14 ... Bonding wire, 15 ... sound absorbing material, 16 ... case, 17 ... lead pins, C ... coupling capacitor, C ₀ · · capacitor, R ... resistance

Claims (3)

[Claims] 1. A SAW filter, an input buffer circuit for receiving a signal from the outside to generate a signal to be input to the SAW filter, and an output buffer circuit for receiving a predetermined output signal of the SAW filter and outputting the output signal to the outside. The input buffer circuit is configured such that the potential difference between the signal potential of the output signal of the input buffer circuit and the signal potential of the input signal of the output buffer circuit falls within the range of the voltage allowed between the input and output of the SAW filter. SAW filter device. 2. The SAW filter device according to claim 1, wherein at least one of the input buffer circuit and the output buffer circuit and the SAW filter are differentially connected. 3. The SA according to claim 1 or 2.
In the W filter device, the input signal potential of the input buffer circuit and the output signal potential of the output buffer circuit are signal potentials of the ECL circuit.