This invention relates to a filtering-type high frequency switching circuit. This invention is particularly useful for a filtering-type high frequency switching circuit having one input terminal and two output terminals.
As relatively small band-pass filters made up of 2-port high frequency circuits, for example a ‘Tri-Plate Strip Line Filter’ (MWE2000 Microwave Workshop Digest, pp. 461-468 (2000)) and a ‘Microwave Satellite Communications Filter Using Multi-Layer Printed Circuit Board’ (NEC Technology Vol. 51 No. 4/1998, pp. 119-123) are generally known.
In the case of the ‘Tri-Plate Strip Line Filter,’ because it uses an LTCC (Low Temperature Co-Fired Ceramic), it must be mounted to another circuit board. Thus, its application to an organic substrate with a low dielectric constant is difficult. In particular, instability of quality due to variations in the thickness of the organic substrate becomes a problem. In the case of the ‘Microwave Satellite Communications Filter Using Multi-Layer Printed Circuit Board’ multiple quarter-wavelength lines are necessary, and the filter circuit necessarily becomes large. Also, when a switch is turned off by a diode being rendered conductive, because a current flows in the forward direction, a considerable amount of power is consumed. It is required to enlarge the range over which the input-output power characteristic is linear after the reverse bias is made a low potential, when a switch is turned on by a diode being turned off.
In this connection, the present inventors have invented and filed patent applications (Japanese Patent Application No. 2001-315243, Japanese Patent Application No. 2002-1910, Japanese Patent Application No. 2002-22689) for a filtering-type high frequency switching circuit having the construction shown in
a) and
Now, the transmission characteristic from the terminal Portm to the terminal Portn in the circuit of
Here, a characteristic matrix S of which row m column n is Smn is considered. It is desirable to have the characteristic vector (1, 1) as an even excitation and the characteristic vector (1, −1) as an odd excitation. The characteristic value of the matrix S with respect to the even excitation characteristic vector (1, 1) will be represented by λ1 and the characteristic value of the matrix S with respect to the odd excitation characteristic vector (1, −1) will be represented by λ2. First, a matrix P made by writing the characteristic vector (1, 1) and the characteristic vector (1, −1) as vertical vectors can be expressed as shown in the following Exp. (1).
Clearly, the matrix S can be developed as the following Exp. (2).
S11=S22=0, |S12|=|S21|=1 holds when the phases of the even excitation characteristic value λ1 and the odd excitation characteristic value λ2 are 180° apart. For example, S11=S22=0, |S12|=|S21|=1 holds when λ1=−λ2=±±1. However, λ1=−λ2=1 is the case of open in odd excitation and shorted in odd excitation, and shows a transmitting line, not a filter circuit. λ1=−λ2=−1 is the case of shorted in even excitation, open in odd excitation, and corresponds to a half-wave line and not, again, a filter circuit. Accordingly, for example λ1=−λ2=±j becomes the design condition (phase condition) for a filter circuit. For λ1=±1, ±j, a correspondence on a Smith chart is shown in
When a pair of coupled lines (line A and line B) is added as shown in
On the other hand, the time a symmetrical circuit transmits a signal efficiently is when conjugate matching (impedance matching) has been carried out at the plane of symmetry. Because the high frequency circuit being studied is left-right symmetrical, this condition means the reflection coefficient Sa being a real number. That is, the characteristic impedances seen to the right and the left from the point a in
The marker m3 (at the bottom) in
It is an object of the present invention to add new characteristics and improve the characteristics of a filtering function of a filtering-type high frequency switching circuit. It is another object of the invention to provide a filtering-type high frequency switching circuit having a switch that does not consume power when turned off. It is another object to provide a filtering-type high frequency switching circuit which makes it possible to enlarge the range of linearity of the input-output power characteristic at a low potential when a switch is turned on. A filtering-type high frequency switching circuit according to the invention can be ideally realized as a 1-input, 2-output (SPDT) filtering-type high frequency switching circuit having two switch circuits.
A filtering-type high frequency switching circuit provided by the invention has one input terminal, one output terminal, and a switch circuit between the input terminal and the output terminal. By the potential of at least one location in the switch circuit being made controllable, a high frequency of a desired bandwidth is passed or cut off. The switch circuit is made up of a first line having one end electrically connected to the input terminal and the other end connected to a first potential via a first capacitor, a second line forming a pair of coupled lines by being at least partly disposed substantially parallel to the first line and having one end connected to one end of a first diode having its other end connected to a second potential, a third line having one end connected to the other end of the second line and the other end connected to one end of a second diode having as its other end the same pole as the first diode connected to the second potential, a fourth line forming a pair of coupled lines by being at least partly disposed substantially parallel to the third line and having one end electrically connected to the output terminal and the other end connected to a third potential via a second capacitor, and a fifth line having one end connected to the connection point between the second line and the third line and the other end connected to a fourth potential. The first and second capacitors, the first and fourth lines, the second and third lines and the first and second diodes respectively have the same device characteristics. The switch circuit is symmetrical about the connection point between the second line, the third line and the fifth line, and at least one or the other of the second potential and the third potential is made the above-described controllable potential.
A diode can be made to operate as a capacitor if a current does not flow through it. Therefore, lines (the first and fourth lines) are connected to the input terminal and the output terminal, and two lines (the second and third lines) respectively coupled with these are connected in series. The same poles of two diodes are connected to the ends of the series connection of these latter two lines. The potential difference between the other poles (kept at the same potential) of the two diodes and the two lines between the two diodes is made controllable. That is, the potential of at least one or the other of the point of connection between the two lines and the poles of the diodes opposite from the sides thereof connected to the lines is made controllable. When the potential of only one of these is made controllable, the potential of the other is fixed. By this means, in the case of a reverse bias, under which no current flows through the diodes, or a forward bias such that the potential difference is small, the two diodes act as capacitors, and high frequency can be outputted to the output terminal from the input terminal through the first line, the second line coupled with the first line, the third line connected to the second line, and the fourth line coupled with the third line. At this time, by design of the first and second capacitors connected to the first and fourth lines, the switch circuit can be made to function as a band-pass filter from the input terminal to the output terminal. Its band can be set easily by suitable design of the lines, the capacitors and the diodes.
By combining two filtering-type high frequency switching circuits constructed as above, it is possible to make a 1-input, 2-output filtering-type high frequency switching circuit. That is, a 1-input, 2-output filtering-type high frequency switching circuit has one input terminal, two output terminals, and switch circuits each of the same construction between the input terminal and the two output terminals, and by the potential of at least one location in the switch circuit being made controllable in each of the two switch circuits, at least one of the switch circuits passes a high frequency of a desired bandwidth. Accordingly, when two switch circuits are provided like this, it is possible to make a filtering-type high frequency switching circuit function as a 1-input, 2-output band-pass filter.
Of the above two switch circuits, in one switch circuit the potential difference between the second potential and the third potential may be made 0 or a reverse bias while in the other the potential difference between the second potential and the third potential is made a forward potential difference in a range such that no current flows through the first and second diodes. When no current flows through the first and second diodes, changes in that potential difference become changes in capacitors formed by the diodes. By making the potential differences different in the two switch circuits, it is possible to make them function as band-pass filters having different bands.
Of the above two switch circuits, in one of the switch circuits the potential difference between the second potential and the third potential may be made a reverse bias and larger than the voltage amplitude of the high frequency wave inputted through the input terminal while in the other switch circuit the potential difference between the second potential and the third potential is made a forward potential difference in a range such that a current flows to the first and second diodes and made larger than the voltage amplitude of the high frequency wave inputted through the input terminal. By applying an ample reverse bias voltage to the diodes, it is possible to make distortion low even with respect to large high frequency inputs and to make large the dynamic range over which linearity can be maintained.
An open stub or a capacitor for shorting a second harmonic wave of the high frequency that is the center frequency of the band being passed and an open stub or a capacitor for similarly shorting a second harmonic wave may be provided at the point of connection of the second line, the third line and the fifth line. If open stubs or capacitors are connected so as to short out a second harmonic wave and a second harmonic wave, it is also possible to make large the dynamic range over which linearity can be maintained because distortion caused by the harmonic waves can be removed.
An inductor may be provided instead of the fifth line. The line between the voltage control point and the coupled lines can be replaced with an inductor, and both can easily be designed to have the same action.
It is possible to eliminate the fifth line, by connecting the third potential and one end of a capacitor to the point of connection between the second line and the third line and grounding the other end of the capacitor. In this way it is also possible to construct a filtering-type high frequency switching circuit performing the same function.
a) is a frequency characteristic chart of when one output of the filtering-type high frequency switching circuit 100 is turned on and the other output is turned off, and
a) is an output characteristic chart of the filtering-type high frequency switching circuit 200, and
a) is an output characteristic chart of the filtering-type high frequency switching circuit 300, and
a) through 9(c) are circuit diagrams illustrating a basic construction of the invention.
a) through 10(c) are Smith charts illustrating simulation results relating to reflection characteristics of the circuits of
a) is a circuit diagram showing circuit elements effective during even excitation, and
a) is a graph showing the transmittance characteristic of the circuit of
A number of embodiments of the invention will now be described with reference to specific circuit diagrams. The invention is not limited to these embodiments.
Two lines A10 and A20 are connected to the input terminal In, and these have switch circuits 11 and 12 and the output terminals Out-1 and Out-2. The two switch circuits 11 and 12 each constitute a 1-input, 1-output switch with a filter function. They have exactly the same construction. The lines A10 and A20 are provided for characteristic adjustment, and in the first embodiment they are not essential constituent parts.
The construction of the switch circuit 1i between the line Ai0 and the output terminal Out-i (i=1 or 2) is as follows. On the opposite side of the line Ai0 from the input terminal In, a line Ai1 and a capacitor Ci1 are connected in series to ground. Although as the capacitor Ci1 a pair of coupled lines is shown in
The device characteristics of the capacitor Ci1 and the capacitor Ci2, the line Ai1 and the line Ai2, the line Bi1 and the line Bi2 and the diode Di1 and the diode Di2 are respectively the same. The switch circuit 1i is a construction symmetrical on its input and output sides about the connection point of the line Bi1 and the line Bi2. The switch circuits 11 and 12 have exactly the same construction except that voltages can be applied independently to the voltage control terminals VCTL1 and VCTL2.
When the voltage control terminal VCTLi of the switch circuit 1i is grounded, no current flows through the diodes Di1 and Di2 and the diodes Di1 and Di2 both assume the same capacitor. The switch circuit 1i is designed as described above so that at this time it becomes a desired band-pass filter. That is, when the voltage control terminal VCTLi is grounded, a high frequency of a required band is outputted to the output terminal Out-i. When a positive voltage of a level such that a current flows through the diodes Di1 and Di2 is applied to the voltage control terminal VCTLi, a high frequency is not supplied from the line Ai1 to the line Bi1, and a high frequency is not outputted to the output terminal Out-i. That is, when a sufficient positive voltage is applied to the voltage control terminal VCTLi, no high frequency is outputted to the output terminal Out-i.
A simulation carried out in relation to this is shown in
(Variation)
In the filtering-type high frequency switching circuit 100 of
b) shows the relationship between the frequency of the high frequency inputted to the input terminal In and the outputs of the output terminals Out-1 and Out-2. As shown in
At the center frequency of 4.8 GHz, conversely at the output terminal Out-1 the attenuation was extremely large and high frequencies were cut off well, and at the output terminal Out-2 the attenuation was extremely small and high frequencies were outputted well.
From the first embodiment and the variation thereof described above, the following can be easily deduced. That is, in the filtering-type high frequency switching circuit 100 of
The filtering-type high frequency switching circuit 200 of
A filtering-type high frequency switching circuit provided by the invention has one input terminal, one output terminal, and a switch circuit between the input terminal and the output terminal. By the potential of at least one location in the switch circuit being made controllable, a high frequency of a desired bandwidth is passed or cut off. The switch circuit is made up of a first line having one end electrically connected to the input terminal and the other end connected to a first potential via a first capacitor, a second line forming a pair of coupled lines by being at least partly disposed substantially parallel to the first line and having one end connected to one end of a first diode having its other end connected to a second potential, a third line having one end connected to the other end of the second line and the other end connected to one end of a second diode having as its other end the same pole as the first diode connected to the second potential, a fourth line forming a pair of coupled lines by being at least partly disposed substantially parallel to the third line and having one end electrically connected to the output terminal and the other end connected to a third potential via a second capacitor, and a fifth line having one end connected to the connection point between the second line and the third line and the other end connected to a fourth potential. The first and second capacitors, the first and fourth lines, the second and third lines and the first and second diodes respectively have the same device characteristics. The switch circuit is symmetrical about the connection point between the second line, the third line and the fifth line, and at least one or the other of the second potential and the fourth potential is made the above-described controllable potential.
A diode can be made to operate as a capacitor if a current does not flow through it. So, lines (the first and fourth lines) are connected to the input terminal and the output terminal, and two lines (the second and third lines) respectively coupled with these are connected in series. The same poles of two diodes are connected to the ends of the series connection of these latter two lines, and the potential difference between the other poles (kept at the same potential) of the two diodes and the two lines between the two diodes is made controllable. That is, the potential of at least one or the other of the point of connection between the two lines and the poles of the diodes opposite from the sides thereof connected to the lines is made controllable. When the potential of only one of these is made controllable, the potential of the other is fixed. By this means, in the case of a reverse bias, under which no current flows through the diodes, or a forward bias such that the potential difference is small, the two diodes act as capacitors, and high frequency can be outputted to the output terminal from the input terminal through the first line, the second line coupled with the first line, the third line connected to the second line, and the fourth line coupled with the third line. At this time, by design of the first and second capacitors connected to the first and fourth lines, the switch circuit can be made to function as a band-pass filter from the input terminal to the output terminal. Its band can be set easily by suitable design of the lines, the capacitors and the diodes.
By combining two filtering-type high frequency switching circuits constructed as described above, it is possible to make a 1-input, 2-output filtering-type high frequency switching circuit. That is, a 1-input, 2-output filtering-type high frequency switching circuit has one input terminal, two output terminals, and switch circuits each of the same construction between the input terminal and the two output terminals, and by the potential of at least one location in the switch circuit being made controllable in each of the two switch circuits, at least one of the switch circuits passes a high frequency of a desired bandwidth. Accordingly, when two switch circuits are provided like this, it is possible to make a filtering-type high frequency switching circuit function as a 1-input, 2-output band-pass filter.
Of the two switch circuits described above, in one switch circuit the potential difference between the second potential and the third potential may be made 0 or a reverse bias while in the other the potential difference between the second potential and the third potential is made a forward potential difference in a range such that no current flows through the first and second diodes. When no current flows through the first and second diodes, changes in that potential difference become changes in capacitors formed by the diodes. By making the potential differences different in the two switch circuits, it is possible to make them function as band-pass filters having different bands.
Of the above-described two switch circuits, in one of the switch circuits the potential difference between the second potential and the third potential may be made a reverse bias and larger than the voltage amplitude of the high frequency wave inputted through the input terminal while in the other switch circuit the potential difference between the second potential and the third potential is made a forward potential difference in a range such that a current flows to the first and second diodes and made larger than the voltage amplitude of the high frequency wave inputted through the input terminal. By applying an ample reverse bias voltage to the diodes, it is possible to make distortion low even with respect to large high frequency inputs and to make large the dynamic range over which linearity can be maintained.
An open stub or a capacitor for shorting a second harmonic wave of the high frequency that is the center frequency of the band being passed and an open stub or a capacitor for similarly shorting a second harmonic wave may be provided at the point of connection of the second line, the third line and the fifth line. If open stubs or capacitors are connected so as to short out a second harmonic wave and a second harmonic wave, it is possible to make large the dynamic range over which linearity can be maintained because distortion caused by higher harmonics can be removed.
Further, an inductance may be provided instead of the fifth line. The line between the voltage control point and the coupled lines can be replaced with an inductor, and both can easily be designed to have the same action.
Also, it is possible to adopt a construction wherein the fifth line is dispensed with and the third potential and one end of a capacitor are connected to the point of connection between the second line and the third line and the other end of the capacitor is grounded. In this way also it is possible to construct a filtering-type high frequency switching circuit performing the same function.
For the filtering-type high frequency switching circuit 200 of
The filtering-type high frequency switching circuit 300 of
An output characteristic chart of the filtering-type high frequency switching circuit 300 of
As shown in
A brief explanation of the operation of the open stubs OSi2 and OSi3 resonating at the second harmonic wave and second harmonic wave of the center frequency of the band-pass filter is as follows. With t as time, a Taylor development to the tertiary term of an output y(t) with respect to an input x(t) is as shown by the following Exp. (3).
y(t)=α1x(t)+α2{x(t)}2+α3{x(t)}3 (3)
The input x(t) can be defined in terms of an amplitude A and an angular frequency ω as shown in expression (4).
x(t)=A cos(ωt) (4)
Substituting Exp. (4) into Exp. (3) and rearranging gives the following Exp. (5).
y(t)=α2(a)2/2+(α1A+3α3A3/4)cos(ωt)+α2(a)2 cos(2ωt)/2+α3A3 cos(3ωt)/4 (5)
The coefficient α3 in the tertiary term of Exp. (3) is a normal load, and in Exp. (5), when the amplitude A of the input x(t) becomes large, the coefficient of the second term, which is the part proportional to the input x(t), becomes small, and displays a saturation phenomenon. In addition to this, the third and fourth terms, which show the secondary and second harmonic waves, also become large. These higher harmonics increase the potential differences across the anodes and cathodes of the diodes in the on-side switch circuit, where properly the potential differences should be eliminated, and increase distortion. To avoid this, by providing two stubs to short out the secondary and second harmonic waves, it is possible to eliminate at least the third and fourth terms of Exp. (5). By this means the power characteristic is improved more than when the two stubs are not provided.
Although in the filtering-type high frequency switching circuit 300 of
In the embodiments described above, if the line parts are formed as central layers of tri-plate strip lines of a 3-layer construction having grounds as an upper layer and a lower layer of the kind shown in
The correspondences between the constituent elements of the foregoing first embodiment and variation thereof, the second embodiment and the third embodiment (hereinafter, the foregoing embodiments) and the items set forth in the scope of the claim are as follows. Using i to represent the constituent devices of either of the two switch circuits without distinguishing which, the lines Ai1, Bi1, Bi2, Ai2, and Bio in the foregoing embodiments correspond to first, second, third, fourth and fifth lines set forth in the claims. Similarly, the diodes Di1 and Di2 in the foregoing embodiments correspond to ‘two diodes,’ and the capacitors Ci1 and Ci2 in the foregoing embodiments respectively correspond to ‘first and second capacitors.’ The input terminal In and the output terminals Out-1 and Out-2 in the foregoing embodiments correspond to ‘an input terminal’ and ‘two output terminals.’ The open stubs OSi2 and OSi3 correspond to ‘open stubs or capacitors for shorting a second harmonic wave and second harmonic wave’.
Thus, the present invention is not limited to the 1-input, 2-output filtering-type high frequency switching circuit 100, and can also be applied to a 1-input, 1-output filtering-type high frequency switching circuit 400.
The essential constituent elements of the filtering-type high frequency switching circuit 400 are as follows. That is, in a filtering-type high frequency switching circuit having one input terminal In, one output terminal Out and a switch circuit between the input terminal In and the output terminal Out, for passing a high frequency of a desired bandwidth by applying a predetermined potential to a voltage control point of the switch circuit, the switch circuit is made up of a first line A1 having one end electrically connected to the input terminal In and the other end grounded via a first capacitor C1, a second line B1 forming a pair of coupled lines by being at least partly disposed substantially parallel to the first line A1 and having one end connected to the anode of a first diode D1 having its cathode grounded, a third line B2 having one end connected to the other end of the second line B1 and the other end connected to the anode of a second diode D2 having its cathode grounded, a fourth line A2 forming a pair of coupled lines by being at least partly disposed substantially parallel to the third line B2 and having one end electrically connected to the output terminal Out and the other end grounded via a second capacitor C2 and a fifth line B0 having one end connected to the connection point between the second line B1 and the third line B2 and the other end grounded via a third capacitor C0, the first and second capacitors C1, C2, the first and fourth lines A1, A2, the second and third lines B1, B2 and the first and second diodes D1, D2 each having the same device characteristics, the switch circuit being symmetrical about the connection point of the second line B1, the third line B2 and the fifth line B0, and the voltage control point being made between the fifth line B0 and the third capacitor C0 of the switch circuit.
Specifically, the filtering-type high frequency switching circuit 500 of
With this construction also, a filtering-type high frequency switching circuit that functions in the same way as the filtering-type high frequency switching circuits of the embodiments described above can be realized.
Filtering-type frequency switches of the kind shown in
Number | Date | Country | Kind |
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2003-112448 | Apr 2003 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2004/005513 | 4/16/2004 | WO | 00 | 8/11/2005 |
Publishing Document | Publishing Date | Country | Kind |
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WO2004/093237 | 10/28/2004 | WO | A |
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20060192630 A1 | Aug 2006 | US |