1. Field of the Invention
The present invention relates to an impedance conversion device, and in particular to an impedance conversion device that can be inserted into a stacked pair line.
2. Description of the Related Art
An example of a conventional impedance conversion device that can be inserted in a transmission line is given in Japanese Patent Application Publication No. 10-224123. The disclosed device is designed for insertion into a microstrip line, however, and is too wide in the direction orthogonal to the line for insertion into a stacked pair line.
An object of the present invention is to provide an impedance conversion device that is narrow enough for insertion into a stacked pair line.
The invented impedance conversion device comprises first, second, third, and fourth conductors, each having a first end and a second end. The conductors are arranged so that the first and second conductors form a first transmission line having a first characteristic impedance, the first and third conductors form a second transmission line having a second characteristic impedance different from the first characteristic impedance, the second and fourth conductors form a third transmission line having the second characteristic impedance, and the third and fourth conductors form a fourth transmission line having the first characteristic impedance.
A first resistor having a resistance equal to the first characteristic impedance is connected between the second ends of the second and fourth conductors, which are mutually proximate. A second resistor having a resistance equal to the second characteristic impedance is connected between the first ends of the third and fourth conductors, which are mutually proximate.
The four conductors transmit a signal that is input at the first ends of the first and second conductors and output at the second ends of the first and third conductors. The fourth conductor preferably has a length not exceeding one-fourth of the fundamental wavelength of the transmitted signal.
The impedance of the transmitted signal is converted efficiently, and the dimensions of the impedance conversion device in the directions orthogonal to the longitudinal direction of the conductors are comparatively small, permitting the impedance converting device to be formed in a confined space and in particular to be inserted into a stacked pair line. Use of this impedance conversion device can contribute to a reduction in the size of microelectronic parts.
In the attached drawings:
An impedance conversion device embodying the invention will now be described with reference to the attached drawings, in which like elements are indicated by like reference characters.
As shown in
The dielectric sheet 17 has a first surface or upper surface 17a (uppermost in FIGS. 1 and 4-7) and a second surface or lower surface 17b. The first and third conductors 11, 13 are disposed side by side on the upper surface 17a of the dielectric sheet 17, spaced apart from each other in a direction orthogonal to their lengths and parallel to the upper surface 17a and lower surface 17b of the dielectric sheet 17. The second and fourth conductors 12, 14 are similarly disposed side by side on the lower surface 17b of the dielectric sheet 17.
The first conductor 11 and the second conductor 12 are disposed on opposite sides of the dielectric sheet 17, facing each other in a direction orthogonal to the upper surface 17a and lower surface 17b of the dielectric sheet 17. The third conductor 13 and the fourth conductor 14 are similarly disposed on opposite sides of the dielectric sheet 17, facing each other.
As shown in
The first conductor 11 extends across the input region 1a, the central region 1b, and the output region 1c of the impedance conversion device 1; the first conductor 11 has an input part 11a, a central part 11b, and an output part 11c disposed in the input region 1a, the central region 1b, and the output region 1c, respectively.
The second conductor 12 extends across the input region 1a and the central region 1b of the impedance conversion device 1, and has an input part 12a and a central part 12b disposed in the input region 1a and the central region 1b, respectively.
The third conductor 13 extends across the central region 1b and the output region 1c of the impedance conversion device 1, and has a central part 13b and an output part 13c disposed in the central region 1b and the output region 1c, respectively.
The fourth conductor 14 extends only across the central region 1b, and has a central part 14b disposed in the central region 1b.
The first conductor 11 and second conductor 12 form a transmission line having a first characteristic impedance z1.
The second conductor 12 and fourth conductor 14 form a transmission line having a second characteristic impedance z2 different from the first characteristic impedance z1.
The first conductor 11 and the third conductor 13 form a transmission line having the second characteristic impedance z2.
The third conductor 13 and the fourth conductor 14 form a transmission line having the first characteristic impedance z1.
The first conductor 11 is disposed so that one end (the input end) 11d is at the input end 1d of the impedance conversion device 1, and the other end (the output end) 11e is at the output end of the impedance conversion device 1.
The second conductor 12 is disposed so that one end (the input end) 12d is at the input end 1d of the impedance conversion device 1, and the other end (the output end) 12e is at the boundary 1g between the central region 1b and the output region 1c of the impedance conversion device 1.
The third conductor 13 is disposed so that one end (the input end) 13d is at the boundary 1f between the input region 1a and the central region 1b of the impedance conversion device 1, and the other end (the output end) 13e is at the output end 1e of the impedance conversion device 1.
The fourth conductor 14 is disposed so that one end (the input end) 14d is at the boundary 1f between the input region 1a and the central region 1b of the impedance conversion device 1, and the other end (the output end) is at the boundary 1g between the central region 1b and the output region 1c of the impedance conversion device 1.
The output end 12e of the second conductor 12 and the output end 14e of the fourth conductor 14 are both disposed on the lower surface 17b of the dielectric sheet 17 and are mutually proximate. The input end 13d of the third conductor 13 and the input end 14d of the fourth conductor 14 are disposed on the lower surface 17b and the upper surface 17a of the dielectric sheet 17, respectively, and are mutually proximate.
A first resistor 15 is mounted on the lower surface 17b of the dielectric sheet 17. The first resistor 15 interconnects the output end 12e of the second conductor 12 and the output end 14e of the fourth conductor 14, and has a resistance R1 equal to the first characteristic impedance z1.
A second resistor 16 is formed so that it extends through the dielectric sheet 17. The second resistor 16 interconnects the input end 13d of the third conductor 13 and the input end 14d of the fourth conductor 14, and has a resistance R2 equal to the second characteristic impedance z2.
The value (the absolute value) of the first characteristic impedance z1 is, for example, fifty ohms (50Ω), and the value (the absolute value) of the second characteristic impedance z2 is, for example, 82Ω.
The first to fourth conductors 11 to 14 have identical cross-sectional configurations, for example, a thickness (the vertical dimension in
The dielectric sheet 17 has a thickness of 170 micrometers; the distance between the first conductor 11 and the second conductor 12 and the distance between the third conductor 13 and the fourth conductor 14 are equal to the thickness of the dielectric sheet 17.
The distance between the first conductor 11 and the third conductor 13 and the distance between the second conductor 12 and the fourth conductor 14 are identically 100 micrometers (0.1 millimeters).
The first to fourth conductors parallel each other in the central region 1b, which therefore may be referred to as the ‘quadri-parallel’ part below. In contrast, the input region 1a and the output region 1c may be referred to as ‘duo-parallel’ parts, as only the first and second conductors 11 and 12 are parallel in the input region 1a, and only the first and third conductors 11 and 13 are parallel in the output region 1c.
The length of the central region 1b of the impedance conversion device, that is, the length of conductor 14 (the length in the longitudinal direction in which conductors 11 to 14 extend) preferably does not exceed one-fourth of the fundamental wavelength of the signal that is transmitted, and is preferably at least ten times as long as the larger of the two distances that separate the first conductor 11 from the second conductor 12 and the first conductor 11 from the third conductor 13. More specifically, the length is preferably longer than 1/64 of the fundamental wavelength of the transmitted signal.
When the impedance conversion device 1 is configured as above, its input impedance Zin is equal to the first characteristic impedance z1 (50Ω) and its output impedance Zout is equal to the second characteristic impedance z2 (82Ω). Impedance conversion therefore takes place. This was confirmed by using TDR (time domain reflectometry) to measure the impedance of the transmission lines.
TDR is carried out by transmitting a pulsed signal and observing the reflection of the pulse from the circuit under test; TDR detects changes in impedance along the transmission path of the signal.
Strip-like leads 121 to 124 formed of the same material as the conductors are mounted at the ends 111h to 114h of the first to fourth conductors 111 to 114 (the left ends in
Measurements were made of the impedance of each of the transmission lines formed by conductor 111 and conductor 112, conductor 112 and conductor 114, conductor 113 and conductor 114, and conductor 111 and conductor 113. As shown in
Specifically, to measure the impedance of the transmission line formed by conductor 111 and conductor 112, connecting pads 131 and 132 of conductor 111 and conductor 112 were contacted by probes 53a and 53b; to measure the impedance of the transmission line formed by conductor 113 and conductor 114, connecting pads 133 and 134 of conductor 113 and conductor 114 were contacted by probes 53a and 53b. To measure the impedance of the transmission line formed by conductor 111 and conductor 113, the other ends 111i and 113i of conductor 111 and conductor 113 were contacted by probes 53a and 53b; and to measure the impedance of the transmission line formed by conductor 112 and conductor 114, the other ends 112i and 114i of conductor 112 and conductor 114 were contacted by probes 53a and 53b.
Exemplary waveforms that appeared on the display of the TDR apparatus 51 are shown in
The leftmost regions RXa to RXd of these curves indicate the impedance of the coaxial cable 52 (50Ω); the regions adjacent to regions RXa to RXd on the right correspond to the sections in which probes 53a and 53b make contact with connecting pads 131 to 134 or the ends 111i to 114i of conductors 111 to 114; the central regions RPa to RPd indicate the impedance of conductors 111 to 114 (the impedance of the transmission line comprising conductors 111 and 112, the transmission line comprising conductors 113 and 114, the transmission line comprising conductors 111 and 113, and the transmission line comprising conductors 112 and 114); and the rightmost regions ROa to ROd indicate the impedance at the electrically open ends. Regions RLa and RLb of curves B5a and B5b, which are between the central regions RPa and RPb and the regions RCa to RCd corresponding to the contact sections of probes 53a and 53b, indicate the impedance of the leads 121 to 124; regions RLc and RLd of curves B5c and B5d, which are between the central regions RPc and RPd and the regions ROc and ROd corresponding to the electrically open ends, indicate the impedance of the leads 121 to 124.
The values shown in Table 1 can be read from the measured waveforms as the impedance of each pair of conductors.
The impedance conversion efficiency and waveform distortion of the novel impedance conversion device 1 were studied under various conditions.
In the first case studied, a load resistor 18 with a value equal to the second characteristic impedance z2 (82Ω) was connected between the output ends of the impedance conversion device 1, that is, between the output ends 11e and 13e of conductors 11 and 13, as shown in
When a direct current voltage Vin is supplied from a direct current source 60 to the input end of the impedance conversion device 1 in
Vout=Vin×{R2/(2×R2+R1+Rin)}
where Rin is the internal resistance of the direct current source 60.
The internal resistance Rin is generally made equal to the input impedance R1; when Rin=R1, the above equation becomes:
Vout=Vin×{R2/(2×R2+2×R1)} (1)
If R1=50Ω and R2=82Ω, then:
If the value of Vin is five hundred millivolts (500 mV), then:
Vout=500×82/264=155 mV (3)
Next, the voltage that appeared at the output end when a voltage pulse train was applied from a pulse generator 61 to the input end of the impedance conversion device 1 in
The experimental impedance conversion device 1 shown in
Measurements were made by connecting resistors 15 and 16 as shown in
A pulse generator 61 having an internal resistance Rin equal to the first impedance z1 (50Ω) and was used. The probes 63a and 63b of the pulse generator 61 were placed in contact with the connecting pads 131 and 132 on the input side. An oscilloscope 65 having high-impedance differential probes 66a and 66b was used. The measured waveforms are shown in
In
The wave height values and rise times (the time required for the voltage level to increase from 20 percent to 80 percent of the wave height) determined from the measured waveforms are shown in Table 2.
The difference between the wave height values obtained experimentally and the value obtained from equation (3) (the value of the output voltage when direct current is applied) is due to electromagnetic coupling in the transmission line.
For example, when the frequency is 500 MHz, the measured wave height was 255.1 mV. The difference between this value and the value obtained from equation (3) (255.1 mV−155 mV=100.1 mV) represents a voltage component induced by electromagnetic coupling, and indicates that impedance conversion has been carried out effectively.
Next, similar measurements were made with the output ends of the impedance conversion device 1, more specifically the output ends 11e and 13e of conductors 11 and 13, left electrically open. The measurement conditions were the same as described above, except that to leave output ends 11e and 13e electrically open, the load resistor 18 was omitted. The measured waveforms are shown in
As shown in
When the output ends 11e and 13e of the impedance conversion device 1 are connected to a CMOS circuit gate, they are in nearly the same state as when left electrically open, so presumably the results will be nearly the same as shown in
Though the resistor 16 (R2=50Ω) connected between conductors 13 and 14 causes mismatch reflection, and reflection this has a frequency dependence, if there were no mismatch, the waveforms should be smooth. The reason for the mismatch will be explained later with reference to
In the above examples (
As described above, the characteristic impedance of the duo-parallel parts 1a and 1c and the characteristic impedance of the quadri-parallel part 1b are slightly different. Multiple reflections therefore occur. In order to avoid multiple reflection resonance, the quadri-parallel part should have a length not exceeding one-fourth of the fundamental wavelength of the signal that is transmitted. If the specific inductive capacity of the transmission line is four, then the electromagnetic wave speed is 1.5×108 m/s, and if the frequency of the pulse train supplied from the pulse generator 61 is 3 GHz, it follows that the wavelength is 50 millimeters, one-fourth of which is 12.5 millimeters.
The length of the quadri-parallel part 1b need only be sufficient for electromagnetic waves to reshape the electromagnetic space between the parallel conductors. Interference between the conductors is caused by the spreading of the electromagnetic waves in a direction orthogonal to their direction of propagation, and the spreading speed is the same as the speed with which the electromagnetic waves propagate along the transmission line. Reshaping of the electromagnetic space is possible if an electromagnetic wave can travel back and forth between the conductors about five times; the length corresponding to the delay time is a length ten times as long as the larger of the two distances separating the conductors (the larger of the distance (170 micrometers) between the first conductor 11 and the second conductor 12 and the distance (100 micrometers or 0.1 millimeter) between the first conductor 11 and the third conductor 13). Thus, if the larger of the two distances between the conductors is 170 micrometers, ten times that length is 1.7 millimeters; the quadri-parallel structure is effective if its length is equal to or greater than this value.
The characteristic impedance of the quadri-parallel part 1b and the characteristic impedance of the duo-parallel part 1a and 1c were confirmed to be different using time-domain reflectometry.
In
The impedance of the quadri-parallel part (length LD) shown in
In the region RPa2 corresponding to the duo-parallel part, the characteristic impedance changes gradually in the region RPa21 adjacent to the region RPa1 corresponding to the quadri-parallel part. This part corresponds to 125 picoseconds of time, which is the sum of the slump due to the rise time of the step waveform of the TDR apparatus 51 (35 picoseconds, the same as the slump at the contact section RCa and the electrically open end ROa) and the time taken to detect the change; these factors cannot be separated accurately, but the physical phenomena that operate during detection are similar to the reshaping of the electromagnetic space described above.
Next, electromagnetic coupling between the conductors, in other words, crosstalk, will be described with reference to
As shown in
Though the conductors are disposed on the upper surface and lower surface of the dielectric sheet in
In the above embodiment, the first to third conductors 11 to 13 have input parts 11a and 12a and output parts 11c and 13c as well as central parts 11b, 12b, and 13b, but the impedance conversion device may comprise only the central parts; the input parts 11a and 12a and output parts 11c and 13c may be omitted.
Although the first to fourth conductors 11 to 14 extend in straight lines in the above embodiment, they may be curved. The cross-sectional shapes and dimensions of the first to fourth conductors 11 to 14 need not all be the same; some may differ from the others.
Those skilled in the art will recognize that further variations are possible within the scope of the invention, which is defined in the appended claims.
Number | Date | Country | Kind |
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2006-020479 | Jan 2006 | JP | national |
Number | Name | Date | Kind |
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4383227 | de Ronde | May 1983 | A |
5523622 | Harada et al. | Jun 1996 | A |
5812034 | Yoshida | Sep 1998 | A |
6023209 | Faulkner et al. | Feb 2000 | A |
Number | Date | Country |
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10-224123 | Aug 1998 | JP |
Number | Date | Country | |
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20070176708 A1 | Aug 2007 | US |