JP2008072537A - Delay filter - Google Patents

Abstract

The flatness of the group delay time characteristic in the passband can be improved with a simple configuration, the passband can be widened by suppressing the deterioration of the insertion loss, and the size is reduced and the yield is improved. To promote.
A delay filter 10 includes an input terminal 12, an output terminal 14, and a plurality of λ / 4 resonators (first resonator 16A to first resonator 16) electrically connected between the input terminal 12 and the output terminal 14. And a band-pass filter 18 having a first resonator 16A to a fourth resonator 16D that are capacitively coupled to each other. Further, the first circuit 20 including the fifth capacitor C5 that capacitively couples the first resonator 16A adjacent to the input terminal 12 and the fourth resonator 16D adjacent to the output terminal 14; Among the four resonators 16D, the second circuit 22 includes a fourth resonator 16D adjacent to the output terminal 14 and a sixth capacitor C6 that capacitively couples the input terminal 12.
[Selection] Figure 1

Description

  The present invention relates to a delay filter including a plurality of resonators between an input terminal and an output terminal, and a bandpass filter in which the plurality of resonators are capacitively coupled.

  Recently, in a distortion compensation amplifier for reducing distortion of a base station used in a base station radio apparatus such as a mobile communication system, a delay filter is used for the purpose of distortion detection and distortion suppression.

  As shown in FIG. 13, for example, the delay filter 200 includes a band pass filter 208 having an input terminal 202, an output terminal 204, and a plurality of resonators 206A to 206I. The input terminal 202 and the first-stage resonator 206A are coupled by a capacitor C1, the output terminal 204 and the last-stage resonator 206I are coupled by a capacitor C2, and the resonators 206A to 206I are respectively coupled by capacitors C3 to C10. Are combined.

  Further, conventionally, as shown in FIG. 14, in a delay filter 210 similar to the delay filter 200 shown in FIG. 13, a plurality of coupling capacitors C3 to C8 between adjacent resonators 206A to 206G are connected in parallel, and An example in which an interlace circuit 212 having a plurality of coupling capacitors C9 to C19 is connected (see, for example, Patent Document 1) is known.

  In the example of FIG. 14, the flatness of the group delay time in the pass band in the bandpass filter 208 can be ensured without increasing the number of resonator stages, and the group delay time deviation can be reduced.

JP 2001-257505 A

  Incidentally, the delay filter 210 shown in FIG. 14 can ensure the flatness of the group delay time in the passband and increase the group delay time deviation without increasing the number of resonator stages. Since the number of circuit elements constituting 212 is increased, there is a problem that as a result, the size is increased, the insertion loss is degraded, and the yield is decreased. Further, there is a problem that the delay amount is hardly changed and the pass band is hardly changed as compared with the delay filter 200 shown in FIG. 13 in which the interlace circuit 212 is not provided.

  The present invention has been made in consideration of such problems. With a simple configuration, the flatness of the group delay time characteristic in the passband can be improved, and the passband can be widened by suppressing deterioration of insertion loss. It is another object of the present invention to provide a delay filter that can reduce the size and improve the yield.

  The delay filter according to the present invention includes a bandpass filter having a plurality of resonators between an input terminal and an output terminal, wherein the plurality of resonators are capacitively coupled. A circuit that capacitively couples any one of the output terminals and at least one of the plurality of resonators is provided.

  As a result, the flatness of the group delay time characteristics in the passband can be improved with a simple configuration, and the passband can be widened by suppressing the deterioration of the insertion loss, and further, the miniaturization and the improvement of the yield are promoted. Can be made.

  Here, the flatness of the group delay time characteristic in the pass band indicates a band that falls within a predetermined group delay time deviation (for example, 0.5 ns) in the pass band in the frequency-group delay time characteristic. The pass band indicates a band that falls within a predetermined insertion loss deviation (for example, 0.2 dB) in the frequency-attenuation characteristic.

  And in this invention, it is preferable to have a circuit which carries out the capacitive coupling between two resonators so that at least 1 resonator may be straddled among the several resonators. In this case, the flatness of the group delay time characteristic in the passband can be further improved.

  In the present invention, a circuit that capacitively couples two resonators so as to straddle at least one of the plurality of resonators is adjacent to the resonator adjacent to the input terminal and the output terminal. The resonator to be coupled may be capacitively coupled.

  In the present invention, a circuit that capacitively couples one of the input terminal and the output terminal and at least one of the plurality of resonators includes the input terminal, Among the plurality of resonators, the resonator adjacent to the output terminal may be capacitively coupled, or the output terminal and the resonator adjacent to the input terminal among the plurality of resonators. May be capacitively coupled.

  The resonator may be a λ / 4 resonator, a λ / 2 resonator, or an LC resonance circuit.

  As described above, according to the delay filter of the present invention, the flatness of the group delay time characteristic in the passband can be improved with a simple configuration, and the passband can be widened by suppressing the deterioration of the insertion loss. In addition, downsizing and improvement in yield can be promoted.

  Hereinafter, embodiments of the delay filter according to the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the delay filter 10 according to the present embodiment includes an input terminal 12, an output terminal 14, and a plurality of λ / 4 resonances electrically connected between the input terminal 12 and the output terminal 14. And a band-pass filter 18 having a first resonator 16A to a fourth resonator 16D and capacitively coupled between the first resonator 16A and the fourth resonator 16D.

  Specifically, in the band-pass filter 18, the input terminal 12 and the first resonator 16A adjacent to the input terminal 12 are coupled by a capacitor C0, and the first resonator 16A and the first resonator 16A are adjacent to each other. The second resonator 16B is coupled by the first capacitor C1, the second resonator 16B and the third resonator 16C adjacent to the second resonator 16B are coupled by the second capacitor C2, and the third resonator 16C. And the fourth resonator 16D adjacent to the third resonator 16C are coupled by the third capacitor C3, and the fourth resonator 16D and the output terminal 14 adjacent to the fourth resonator 16D are coupled by the fourth capacitor C4. Composed and configured.

  Further, the delay filter 10 includes a first circuit 20 having a fifth capacitor C5 that capacitively couples the first resonator 16A adjacent to the input terminal 12 and the fourth resonator 16D adjacent to the output terminal 14, and Among the first resonator 16A to the fourth resonator 16D, the second resonator 22 includes a fourth resonator 16D adjacent to the output terminal 14 and a sixth capacitor C6 that capacitively couples the input terminal 12.

  That is, the delay filter 10 includes a first delay filter 100A in which the first circuit 20 is connected to the bandpass filter 18 as shown in FIG. 2, and a second circuit 22 in the bandpass filter 18 as shown in FIG. And a second delay filter 100B connected to each other has a composite circuit configuration.

  Here, after describing the frequency-attenuation characteristic and the frequency-group delay time characteristic of the first delay filter 100A and the second delay filter 100B, the frequency-attenuation characteristic and frequency of the delay filter 10 according to the present embodiment. -Explain the group delay time characteristics.

  First, FIG. 4 shows frequency-attenuation characteristics of the first delay filter 100A shown in FIG. 2, and FIG. 5 shows frequency-group delay time characteristics. 4 and 5, the broken line A indicates the characteristic when the value of the fifth capacitor C5 is 0 pF, and the two-dot chain line B indicates the characteristic when the value of the fifth capacitor C5 is 0.1 pF. The alternate long and short dash line C indicates the characteristics when the value of the fifth capacitor C5 is 0.2 pF, and the solid line D indicates the characteristics when the value of the fifth capacitor C5 is 0.3 pF.

  As can be seen from FIG. 4, as the value of the fifth capacitor C5 is increased, the passband is expanded. Further, as can be seen from FIG. 5, when the fifth capacitor C5 is 0 pF, the characteristic curve (see the broken line A) in which the group delay time becomes a minimum value at the substantially center frequency of the passband is shown. As it increases, the group delay time corresponding to the center frequency gradually increases, and the characteristics on the lower frequency side than the center frequency are increased so as to be larger than the group delay time corresponding to the center frequency. .

  On the other hand, the group delay time is gradually shortened in the characteristics on the higher frequency side than the center frequency. In particular, the group delay time at a frequency higher by about 25 MHz from the center frequency takes a specific value. That is, as the value of the fifth capacitor C5 increases, the characteristic decreases as a whole and rises upward.

  In the first delay filter 100A shown in FIG. 2, when the fifth capacitor C5 is set to 0 pF, as shown in FIG. 6, the delay filter 100C having almost the same configuration as the circuit according to the conventional example of FIG. Become.

  Next, the characteristics of the second delay filter 100B shown in FIG. 3 will be described. FIG. 7 shows frequency-attenuation characteristics of the second delay filter 100B, and FIG. 8 shows frequency-group delay time characteristics. 7 and 8, the broken line E indicates the characteristic when the value of the sixth capacitor C6 is 0 pF, and the two-dot chain line F indicates the characteristic when the value of the sixth capacitor C6 is 0.1 pF. The alternate long and short dash line G indicates the characteristics when the value of the sixth capacitor C6 is 0.2 pF, and the solid line H indicates the characteristics when the value of the sixth capacitor C6 is 0.3 pF.

  As can be seen from FIG. 7, as the value of the sixth capacitor C6 increases, the passband does not change much, but the base of the characteristic expands. Further, as can be seen from FIG. 8, when the sixth capacitor C6 is 0 pF, the characteristic curve (see the broken line E) at which the group delay time becomes a minimum value at almost the center frequency of the passband is shown. As it increases, the group delay time corresponding to the center frequency gradually increases, and the characteristics on the higher frequency side than the center frequency are increased so as to be larger than the group delay time corresponding to the center frequency. .

  On the other hand, the increase rate on the lower frequency side than the center frequency is smaller than the increase rate on the higher frequency side. In particular, the group delay time at a frequency lower by about 25 MHz from the center frequency takes a specific value. That is, as the value of the sixth capacitor C6 increases, the overall characteristic increases to the right and rises upward.

  The delay filter 10 according to the present embodiment has a combination of the characteristics of the first delay filter 100A and the characteristics of the second delay filter 100B. That is, by appropriately selecting the value of the fifth capacitor C5 of the first circuit 20 and the value of the sixth capacitor C6 of the second circuit 22, as shown by the solid line I in FIG. As shown by the solid line K in FIG. 10, the range (band) in which the group delay time takes a substantially constant value within the pass band is shown in the conventional case (broken line). (See M)).

  As described above, the delay filter 10 according to the present embodiment can improve the flatness of the group delay time characteristic in the pass band with a simple configuration, and can suppress the deterioration of the insertion loss and widen the pass band. In addition, downsizing and improvement in yield can be promoted.

  In the above example, the fourth resonator 16D adjacent to the output terminal 14 of the first resonator 16A to the fourth resonator 16D and the input terminal 12 are capacitively coupled by the sixth capacitor C6 of the second circuit 22. In addition, as shown in the delay filter 10a according to the modified example of FIG. 11, the input terminal 12 of the first resonator 16A to the fourth resonator 16D is the sixth capacitor C6 of the second circuit 22. The first resonator 16A adjacent to the output terminal 14 may be capacitively coupled.

  In the above example, the λ / 4 resonator is used as the first resonator 16A to the fourth resonator 16D. However, a λ / 2 resonator or an LC resonance circuit may be used. it can.

  Next, the characteristics of the delay filter 100C (Comparative Example 1) shown in FIG. 6 (see the broken line A in FIGS. 4 and 5) and the fifth capacitor C5 in the first delay filter 100A shown in FIG. 2 are set to 0.1 pF. The characteristic of the case (Comparative Example 2) (see the two-dot chain line B in FIGS. 4 and 5) and the characteristic of the delay filter 10 (Example) according to the present embodiment shown in FIG. FIG. 12 shows the result of comparison with 10 (see the solid line K). The characteristic here refers to the flatness of the passband and the delay time characteristic within the passband.

  In this embodiment, the flatness of the group delay time characteristic in the pass band indicates a band within the group delay time deviation of 0.5 ns in the pass band in the frequency-group delay time characteristic. The pass band indicates a band in which the insertion loss deviation falls within 0.2 dB in the frequency-attenuation characteristic.

  As can be seen from FIG. 12, the pass band of the example is 100 MHz, which is significantly wider than the pass band (80 MHz) of Comparative Example 1 and the pass band (88 MHz) of Comparative Example 2. Further, the flatness of the group delay time is 96 MHz in the example, which is extended from the flatness of the group delay time of Comparative Example 1 (44 MHz) and the flatness of the group delay time of Comparative Example 2 (56 MHz). The flatness of the group delay time has been greatly improved.

  It should be noted that the delay filter according to the present invention is not limited to the above-described embodiment, and various configurations can be adopted without departing from the gist of the present invention.

It is a circuit diagram which shows the delay filter which concerns on this Embodiment. It is a circuit diagram which shows a 1st delay filter. It is a circuit diagram which shows a 2nd delay filter. It is a characteristic view which shows the frequency-attenuation amount characteristic of a 1st delay filter. It is a characteristic view which shows the frequency-group delay time characteristic of a 1st delay filter. It is a circuit diagram which shows the delay filter which has the same circuit structure as a prior art example. It is a characteristic view which shows the frequency-attenuation amount characteristic of a 2nd delay filter. It is a characteristic view which shows the frequency-group delay time characteristic of a 2nd delay filter. It is a characteristic view which shows the frequency-attenuation amount characteristic of the delay filter which concerns on this Embodiment. It is a characteristic view which shows the frequency-group delay time characteristic of the delay filter which concerns on this Embodiment. It is a circuit diagram which shows the modification of the delay filter which concerns on this Embodiment. It is a table | surface figure which shows the result of the flatness of the pass band and group delay time of the comparative example 1, the comparative example 2, and an Example. It is a circuit diagram which shows the delay filter which concerns on a prior art example. It is a circuit diagram which shows the delay filter concerning another prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 10a ... Delay filter 12 ... Input terminal 14 ... Output terminal 16A-16D ... Resonator 18 ... Band pass filter 20 ... 1st circuit 22 ... 2nd circuit C0-C6 ... Capacitance

Claims (6)

In the delay filter having a plurality of resonators between the input terminal and the output terminal, and including a bandpass filter in which the plurality of resonators are capacitively coupled,
A delay filter comprising a circuit that capacitively couples one of the input terminal and the output terminal and at least one of the plurality of resonators. The delay filter of claim 1, wherein
A delay filter comprising a circuit that capacitively couples two resonators so as to straddle at least one of the plurality of resonators. The delay filter according to claim 2, wherein
A circuit that capacitively couples two resonators so as to straddle at least one of the plurality of resonators,
A delay filter, wherein a resonator adjacent to the input terminal and a resonator adjacent to the output terminal are capacitively coupled. The delay filter according to any one of claims 1 to 3,
A circuit that capacitively couples any one of the input terminal and the output terminal and at least one of the plurality of resonators,
A delay filter, wherein the input terminal and a resonator adjacent to the output terminal among the plurality of resonators are capacitively coupled. The delay filter according to any one of claims 1 to 3,
A circuit that capacitively couples any one of the input terminal and the output terminal and at least one of the plurality of resonators,
A delay filter, wherein the output terminal and a resonator adjacent to the input terminal among the plurality of resonators are capacitively coupled. The delay filter according to any one of claims 1 to 5,
The delay filter is a λ / 4 resonator, a λ / 2 resonator, or an LC resonance circuit.

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