JP6754334B2 - Termination circuit and wiring board that composes the termination circuit - Google Patents

Description

The present invention relates to a termination circuit, and more specifically, constitutes a termination circuit and a termination circuit for supplying a high-frequency signal to a high-frequency element such as a semiconductor optical integrated element in which a semiconductor laser and a modulator are monolithically integrated. Regarding the wiring board to be used.

In recent years, the required communication capacity has been rapidly increasing due to the expansion of the use of the Internet, IP phones, video downloads, etc., and the demand for optical transmitters installed in optical fibers and optical communication equipment is increasing. .. Optical transmitters or the components that make them up are called pluggables, and modularization by specifications is rapidly progressing so that they can be easily mounted and replaced. XFP (10 Gigabit Small Form Factor Pluggable) is one of the industry standards for 10 Gigabit Ethernet (10GbE) detachable modules, and the light sources mounted on optical transmitter modules are also being modularized according to this standard. .. This is called TOSA (Transmitter Optical Sub-Assembly), and as a typical module form, there is a box-shaped TOSA module (see, for example, Non-Patent Document 1).

FIG. 1 shows the appearance of a conventional TOSA module. The housing of the TOSA module 100 is formed by a ceramic portion 103 made of sintered ceramic and a metal portion 104 in accordance with XFP. A terrace portion 101 is provided so as to penetrate the housing, and a wiring terminal 102 penetrating toward the inside of the housing is formed. The wiring terminal 102 is used for high-frequency signals supplied to the modulator and DC power supply for supplying the semiconductor laser.

FIG. 2 shows a part of the internal configuration of the conventional TOSA module. On the bottom surface of the housing 200, a small metal plate called a carrier 206 is mounted via a thermo-electric cooling element (TEC: Thermo-Electric Cooler) 207. The TEC 207 absorbs the heat generated by the element on the carrier 206 and exhausts the heat from the lower part of the housing. From the viewpoint of power saving and reduction of the number of parts, TOSA without TEC207 is also being developed.

The carrier 206 is equipped with a thin plate 201 called a subcarrier. A wiring pattern is formed on the subcarrier 201 by plating or depositing a metal on a dielectric material. Further, the subcarrier 201 is equipped with elements necessary for an optical transmitter, such as a semiconductor laser 202, an optical modulator 203, a terminating resistor 204, and a capacitor 205. The wiring terminal 208 provided on the terrace portion 212 penetrates from the outside to the inside of the housing, and the wiring terminal 208 and the high-frequency wiring 211 of the subcarrier 201 are connected by a wire-shaped gold wire 209 and a ribbon-shaped gold wire 210. ing.

The operating frequency of the XFP-compliant TOSA module extends to 10 GHz, and the electric signal behaves strongly as a wave (microwave). That is, at a discontinuity point (reflection point) where impedance matching is not performed, a reflected wave is generated starting from that point, and the reflected wave travels toward the drive driver of the semiconductor laser. Under these circumstances, it has been conventionally important to eliminate discontinuities (reflection points) in the transmission line between the wiring terminal 208 and the terminating resistor 204.

FIG. 3 shows a subcarrier equipped with a conventional semiconductor optical integrated device (see, for example, Non-Patent Document 2). The subcarrier 400 is a coplanar line in which ground (GND) patterns are arranged facing each other on both sides of the signal line S at a predetermined distance, and a high frequency wiring 401 designed at 50 ohms is formed. The high-frequency wiring 401 is connected to the electrode pad 411 of the EA modulator of the EA modulator integrated DFB laser (EML) 402 by wire-shaped gold wires 403a and 403b. Further, a wire-shaped gold wire 403c connects the electrode pad 411 and the 50 ohm terminating resistor 404. The DFB laser electrode 412 is connected to the electrode pad 405 by a wire-shaped gold wire 403d.

FIG. 4 shows a connection form using flip-chip bonding in a subcarrier equipped with a conventional semiconductor optical integrated element. Flip-chip bonding is one of the methods for mounting chips on a mounting substrate. When electrically connecting a chip surface and a substrate, they are arranged in an array instead of being connected by wires as in wire bonding. Connect by wire bump. Since the wiring is extremely short as compared with wire bonding, high frequency characteristics can be improved.

As shown in FIG. 4A, the EML 402 on the subcarrier 400 and the high frequency wiring 401 are connected by a wiring board 300. FIG. 4B shows the configuration of the bottom surface of the wiring board 300. The signal line S of the high-frequency wiring 401 is connected to the electrode pad 411 of the EA modulator via the bump 311, the high-frequency wiring 301, and the bump 312. The GND pattern of the high frequency wiring 401 is connected to the GND wiring 302 via bumps 313a and 313b.

Further, a 50 ohm termination circuit is also formed on the wiring board 300. The high frequency wiring 301 is further extended from the bump 312 connected to the electrode pad 411 of the EA modulator and connected to one terminal of the 50 ohm terminating resistor 303. The terminating resistor 303 may have a chip resistor soldered to the wiring board, or may be built into the wiring board. The terminating resistor 303 should be as short as possible to reduce the parasitic capacitance, and the other terminal should be directly connected to the GND wiring 302 without providing a gap so that the parasitic component is not contained. ..

With such a configuration, it is important to improve the high frequency characteristics by reducing the parasitic inductance and the parasitic capacitance.

Dongchurl Kim et.al., “Design and Fabrication of a Transmitter Optical Subassembly in 10-Gb / s Small-Form-Factor Pluggable Transceiver”, IEEE JORNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS. VOL. 12, No.4, JULY / AUGUST 2006, pp776-782 Chengzhi Xu, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 24, NO. 22, 2012

In the structure shown in FIG. 4, impedance matching can be achieved by setting the high frequency wiring 301 and the terminating resistor 303 to 50 ohms each. Further, the parasitic inductance can be reduced by shortening the terminating resistor 303. However, although the conventional termination circuit considers impedance matching between the high frequency wiring 301 and the terminating resistor 303, impedance matching including an EA modulator electrically connected to the high frequency wiring 301 is not considered.

The EA modulator absorbs the light of the DFB laser and increases the light loss to perform the modulation. As an example, the applied voltage is -3V (LOW) to -0.5V (HIGH), and the received current flows about 15mA. When the EA modulator is converted into a resistance component, it is 200 ohms, which may deviate significantly from the 50 ohm line. In addition, the equivalent circuit of the EA modulator, high-frequency wiring, and the like also include parasitic components such as capacitors that have impedance in the imaginary part. Therefore, in general, in order to perform impedance matching in a wide band up to a high frequency region exceeding 10 GHz, it is difficult to perform impedance matching in a resistor-only termination circuit having only the actual value.

Further, when a bias voltage is applied to the EA modulator together with a high-frequency signal for modulation, a current also flows through the terminating resistor, so that power consumption and heat generation are expected to increase.

An object of the present invention is to provide a termination circuit having impedance matching over a wide band and consuming less power due to a terminating resistor, and a wiring board constituting the termination circuit.

In order to achieve such an object, one embodiment of the terminating circuit includes a first conductor line having a predetermined characteristic impedance, a terminating resistor connected to the first conductor line, and the terminating resistor. The second conductor line connected to the first conductor line, the ground wiring arranged to face the first conductor line, the terminating resistor and the second conductor line at a predetermined distance, and the second conductor line are connected to each other. The first conductor line and the ground wiring are each formed so that the line width becomes narrower toward the terminating resistor side.

Further, in one embodiment of the wiring board, the first conductor line having a predetermined characteristic impedance, the second conductor line, the first conductor line, and the second conductor line face each other with a predetermined distance. A wiring board on which the ground wiring to be arranged is formed, and the first conductor line and the ground wiring are each formed so that the line width becomes narrower toward the second conductor line side. A terminating resistor is connected between the first conductor line and the second conductor line, and a capacitor is connected to the second conductor line to form a terminating circuit.

According to the present invention, a capacitor is connected to the second conductor line to suppress power consumption due to a terminating resistor, and the shape of the first conductor line, the second conductor line and the ground wiring enables highly accurate impedance matching over a wide band. Can be planned.

It is an external view which shows the conventional TOSA module. It is a perspective view which shows a part of the internal structure of the conventional TOSA module. It is a top view which shows the subcarrier which carries the conventional semiconductor optical integrated element. It is a figure which shows the connection form which used the flip chip bonding in the subcarrier which mounted the conventional semiconductor optical integrated element. It is a figure which shows the wiring board used for the subcarrier which carries the semiconductor optical integrated element which concerns on 1st Embodiment of this invention. It is a figure which shows the equivalent circuit of the wiring board which concerns on 1st Embodiment. It is a figure which shows the connection form using the flip chip bonding which concerns on the 2nd Embodiment of this invention. It is a figure which shows the wiring board used for the subcarrier which carries the semiconductor optical integrated element which concerns on 3rd Embodiment of this invention. It is a figure which shows the wiring board used for the subcarrier which carries the semiconductor optical integration element which concerns on 4th Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. According to this embodiment, in a subcarrier equipped with a semiconductor optical integrated element represented by EML, it is possible to further improve the high frequency characteristics of the terminal circuit of the wiring board used for flip chip bonding.

(First Embodiment)
FIG. 5 shows a wiring board used for a subcarrier on which the semiconductor optical integrated element according to the first embodiment of the present invention is mounted. FIG. 5A is a perspective view of the wiring board 500, together with the EML 402 connected by flip chip bonding. In the EML 402, the electrode pad 411 for the signal and the electrode 413 for the ground are both configured on the upper surface of the EML 402. The electrode pad 411 for the signal is connected to the bump connection portion 511 of the high frequency wiring 501 of the wiring board 500 by a bump, and the electrode 413 for the ground is connected to the bump connection portion 512 of the GND wiring 502.

FIG. 5B is a diagram showing a wiring pattern on the bottom surface of the wiring board 500. The high-frequency wiring 501 (first conductor line) constitutes a 50Ω line portion 521 which is a conductor line having an impedance characteristic of 50Ω together with the GND wiring 502, and is connected to one terminal of a 50 ohm terminating resistor 503. The high-frequency wiring 501 has a bent shape 513cd that bends inward at the connection portion with the terminating resistor 503. For example, it has a tapered shape in which the line width is linearly narrowed, and constitutes an impedance transition portion 522.

The GND wiring 502 also has a tapered bent shape 513ab in the impedance transition portion 522, similarly to the high frequency wiring 501. As a result, the characteristic impedance of the impedance transition unit 522 changes toward the terminating resistor 503 side so as to be larger than 50Ω.

The characteristic impedance of the portion where the terminating resistor 503 is arranged also becomes larger than 50Ω, and constitutes the first high impedance portion 523. The other terminal of the terminating resistor 503 is connected to the GND wiring 502 via the second conductor line 504. The second conductor line 504 constitutes a second high impedance line portion 524 in combination with the opposing GND wiring 502. The second high impedance line section 524 functions as a stub, whereby the peaking amount of the frequency described later is adjusted.

FIG. 6 shows an equivalent circuit of the wiring board according to the first embodiment. In the equivalent circuit, the 50Ω line section 521, the impedance transition section 522, the first high impedance line section 523, and the second high impedance line section 524 are connected in this order, and the EA modulator of the EML402 has an impedance with the 50Ω line section 521. It is connected to the transition unit 522.

A simulation is performed using this equivalent circuit, each parameter of the wiring pattern of the wiring board 500 is determined, and a terminating circuit with impedance matching is designed. Specifically, using a three-dimensional electromagnetic analysis simulator, the length l of the terminating resistor 503, the distance between the terminating resistor 503 and the GND wiring 502, and the length of the second high impedance line section 524 are changed. , Calculate the input signal strength of the EA modulator.

The bandwidth is improved by changing the length l of the terminating resistor 503, the peaking frequency is determined by changing the distance between the terminating resistor 503 and the GND wiring 502, and the length of the second high impedance line section 524 is changed. The amount of peaking is determined by this. For example, when used as a 10 GbE TOSA module, highly accurate impedance matching can be realized over a wide band by setting the band and peaking according to the frequency to be used.

(Second embodiment)
FIG. 7 shows a connection mode using flip-chip bonding according to the second embodiment of the present invention. As shown in FIG. 7A, the EML 402 on the subcarrier 400 and the high frequency wiring 401 are connected by a wiring board 600. FIG. 7B shows the configuration of the bottom surface of the wiring board 600. The signal line S of the high-frequency wiring 401 is connected to the electrode pad 411 of the EA modulator via the bump 611, the high-frequency wiring 601 and the bump 612. The GND pattern of the high frequency wiring 401 is connected to the GND wiring 602a-b via bumps 613a and 613b.

Similar to the first embodiment, the wiring board 600 is formed with a 50Ω line portion, an impedance transition portion, a first high impedance line portion, and a second high impedance line portion in this order.

The difference from the first embodiment is that the second high impedance line portion, that is, the other terminal of the second conductor line 604 is not connected to the GND wiring 602ab, but is connected to the capacitor 620 via the bump 615. Connected to the top electrode. The bottom electrode of the capacitor 620 is connected to ground, thereby terminating the high frequency signal and cutting off the DC component due to the bias voltage. In this way, it is possible to suppress an increase in power consumption and heat generation in the terminating resistor.

In order to cut the DC component, the capacitor 620 has a larger capacity than that of a decap or the like. In general, as the capacitance increases, the parasitic inductance also increases. Therefore, in the above-mentioned design of the termination circuit, the length l of the terminating resistor 503 or the distance between the terminating resistor 603 and the GND wiring 602ab is adjusted to cause parasitic inductance. Cancel the inductance.

(Third Embodiment)
FIG. 8 shows a wiring board used for a subcarrier on which the semiconductor optical integrated element according to the third embodiment of the present invention is mounted. The wiring pattern on the bottom surface of the wiring board 700 is shown, and the difference from the first embodiment is in the impedance transition portion 522 and the first high impedance portion 523. The high-frequency wiring 701 (first conductor line) and the GND wiring 702 form a 50Ω line portion which is a conductor line having an impedance characteristic of 50Ω. An electrode pad 411 for a signal of an EA modulator is connected to the bump connection portion 711 of the high-frequency wiring 701, and an electrode 413 for the ground is connected to the bump connection portion 712.

In the impedance transition portion of the third embodiment, the high frequency wiring 701 and the GND wiring 702 on the side to which the EA modulator is connected have bent shapes 713c and 713b that bend inward. On the other hand, only the bent shape 713d is formed on the GND wiring 702 side to which the EA modulator is not connected. That is, in the first high impedance portion, the interval on the side to which the EA modulator is connected is wider than the interval on the side to which the EA modulator is not connected.

The capacitance component is increased by the EA modulator between the high frequency wiring 701 and the GND wiring 702 on the side to which the EA modulator is connected. Therefore, in order to cancel out this capacitance component, the capacitance between the high frequency wiring 701 and the GND wiring 702 on the side where the EA modulator is not connected is increased in the first high impedance portion. With such a configuration, the coplanar line has a structure having equivalent symmetry from the high-frequency wiring 701 to the termination circuit via the connection point with the EA modulator, and highly accurate impedance matching can be realized.

As in the second embodiment, the second high impedance line portion, that is, the other terminal of the second conductor line 704 is not connected to the GND wiring 702, but is connected to the capacitor via a bump. You can also do it.

(Fourth Embodiment)
FIG. 9 shows a wiring board used for a subcarrier on which the semiconductor optical integrated element according to the fourth embodiment of the present invention is mounted. The wiring pattern on the bottom surface of the wiring board 800 is shown, and the difference from the first embodiment is in the impedance transition portion 522. The high-frequency wiring 801 (first conductor line) and the GND wiring 802 form a 50Ω line portion which is a conductor line having an impedance characteristic of 50Ω. The electrode pad 411 for the signal of the EA modulator is connected to the bump connection portion 811 of the high frequency wiring 801 and the electrode 413 for the ground is connected to the bump connection portion 812.

In the impedance transition portion of the fourth embodiment, the bent shape 813cd that bends inward is formed by a clothoid curve instead of a tapered shape in which the line width is linearly narrowed. Even in the tapered shape, the impedance changes discontinuously at the bending point between the 50Ω line section 521 and the impedance transition section 522 and at the bending point between the impedance transition section 522 and the first high impedance section 523. Therefore, the high frequency signal is slightly reflected. Therefore, by forming the impedance transition portion with a clothoid curve, impedance matching without such a discontinuity can be realized.

As in the second embodiment, the second high impedance line portion, that is, the other terminal of the second conductor line 804 is not connected to the GND wiring 802, but is connected to the capacitor via a bump. You can also do it.

In the present embodiment, the configuration in which the EML EA modulator is connected by the wiring board has been described as an example, but it is applied to the case where a high frequency signal is supplied to the high frequency element on the subcarrier from the outside of the housing via the high frequency line. be able to.

100 TOSA module 101,212 Terrace part 102,208 Wiring terminal 103 Ceramic part 104 Metal part 200 Housing 201,400 Subcarrier 202 Semiconductor laser 203 Optical modulator 204,303,404,503,703,803 Termination resistance 205,620 Capacitor 206 Carrier 207 TEC
209,403a-d Wire-shaped gold wire 210 Ribbon-shaped gold wire 211,301,401,501,601,701,801 High-frequency wiring 300,500,600,700,800 Wiring board 302,502,602,702,802 GND Wiring 311, 312,313ab, 611, 612,613a-b, 614,615,711,712,811,812 Bump 402 EA Modulator Integrated DFB Laser (EML)
405,411 Electrode pad 412 DFB laser electrode 504,604,704,804 2nd conductor line

Claims (7)

A first conductor line having a predetermined characteristic impedance and
The terminating resistor connected to the first conductor line and
The second conductor line connected to the terminating resistor and
Ground wiring arranged to face the first conductor line, the terminating resistor, and the second conductor line at a predetermined distance.
A capacitor connected to the second conductor line is provided.
A terminating circuit characterized in that the first conductor line and the ground wiring are each formed so that the line width becomes narrower toward the terminating resistor side. The claim is characterized in that the characteristic impedance of the terminating resistor and the portion of the second conductor line is set to be higher than the characteristic impedance of the first conductor line in combination with the ground wiring. The termination circuit according to 1. A high frequency element is connected between the first conductor line and one of the ground wires arranged opposite to each other.
The distance between the terminating resistor and the second conductor line and the one ground line is set wider than the distance between the terminating resistor and the second conductor line and the other ground line arranged opposite to the second conductor line. The termination circuit according to claim 1 or 2, wherein the termination circuit is characterized by the above. The termination circuit according to claim 1, 2 or 3, wherein in the first conductor line and the ground wiring, the line width is formed narrower due to a tapered shape. The termination circuit according to claim 1, 2 or 3, wherein in the first conductor line and the ground wiring, the line width is formed narrowly by a clothoid curve. A first conductor line having a predetermined characteristic impedance and
2nd conductor line and
A wiring board in which a ground wiring arranged to face the first conductor line and the second conductor line at a predetermined distance is formed.
The first conductor line and the ground wiring are each formed so that the line width becomes narrower toward the second conductor line side.
A wiring board characterized in that a terminating resistor is connected between the first conductor line and the second conductor line, and a capacitor is connected to the second conductor line to form a terminating circuit. The wiring board according to claim 6, wherein a high-frequency element is flip-chip connected between the first conductor line and one of the ground wirings arranged opposite to each other.

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