WO2016060978A1

WO2016060978A1 - Data transmission system with minimized crosstalk

Info

Publication number: WO2016060978A1
Application number: PCT/US2015/055084
Authority: WO
Inventors: Ulrich Keil; Chenhui JIANG; Lars Bretschneider; Holger Gaul
Original assignee: Fci Asia Pte. Ltd; Fci Americas Technology Llc
Priority date: 2014-10-13
Filing date: 2015-10-12
Publication date: 2016-04-21
Also published as: CN205883197U

Abstract

The present invention relates to an opto-electrical communication system, comprising an opto-electrical transmitter module. Said module in turn comprises an integrated circuit and an opto-electrical converter, each featuring at least a pair of contacts provided thereon. The integrated circuit is connected to the opto-electrical converter by means of two bonding wires.

Description

Data Transmission System

with Minimized Crosstalk

BACKGROUND

Field of the invention The present invention relates to a digital data communication system, and in particular to interconnections of circuits provided on different modules in an opto-electrical

communication system.

Technical background

Modern multi-channel digital communication systems comprise several single microchips, or integrated circuits (ICs), communicating with each other. Accordingly, such systems include transmitter and receiver modules, which typically allow for optical fiber-based communication between the ICs. On the transmitter side an electrical signal has to be converted into an optical signal, while on the receiver side a received optical signal has to be converted into an electrical signal for subsequent processing. Fig. i exemplarily shows a prior art configuration of an IC 11 and a corresponding optical converter (OC) 10, wherein the OC 10 may function as an opto-electrical receiver device or as an opto-electrical transmitter device. Accordingly, the shown configuration may be utilized in a transmitter module and/or a receiver module of a communication system.

The IC 11 and OC 10 of Fig. l each feature a pair of electrical contacts 20a, 20b and 2ia, 21b, respectively, whereby the IC 11 and OC 10 are electrically coupled to one another by means of bonding wires 30a, 30b. Bonding wire 30a couples contact 20a provided on OC 10 with contact 21a provided on IC 11, while bonding wire 30b couples contact 21b provided on IC 11 with contact 20b provided on OC 10. Typically, bonding wiring is generally considered to be a cost-effective and flexible interconnect technology. Generally, two bonding wires are needed in order to connect a pair of contacts provided on the IC with a pair of contacts provided on the OC. Such a group of two connected pairs of contacts will be denoted as a "channel" in the following. The exemplary prior art configuration illustrated in Fig.1 comprises two channels 12, 13.

In order to prevent contact between the bonding wires 30a, 30b, which may lead to an electrically short circuit, the design is commonly chosen such that the bonding wires are not physically intersecting each other. Accordingly, as can be seen in Fig. 1, the bonding wires are typically aligned parallel to each other.

The prior art parallel bonding design has several drawbacks. First of all, the parallel bonding technique does not allow for an optimal size, i.e. a minimal size, since the bonding wires have to be kept at a distance in order to prevent electrical short circuit. Further on, a crosstalk problem arises when applying the parallel bonding technique. As known in the art, crosstalk is a signal interference which occurs between bonding wires which are arranged in close physical proximity to each other. Crosstalk is usually caused by undesired capacitive, inductive, or conductive coupling from one circuit or wire to another. Accordingly, signals from one channel, e.g. channel 12 of Fig. 1, can couple into an otherwise isolated channel, e.g. channel 13 of Fig.1. In addition, crosstalk can also occur within one channel, e.g. within channel 12 of Fig. 1. The broken lines illustrated in the prior art configuration of Fig. 1 schematically represent the corresponding inductive coupling 40 causing crosstalk as it is undesirably occurring with the parallel bonding design.

Crosstalk can in particular be a problem in transmitter modules where relatively high voltages, which are frequently changing, are applied for creating distinct and defined optical signals. Moreover, crosstalk also limits the performance of an opto-electrical communication system on the receiver side, where faint optical signals are to be detected, converted to electrical signals, and transferred to the IC via the bonding wires for subsequent

amplification and processing. The undesired crosstalk and respective noise thereby limits the signal reception accuracy of the receiver module.

It is hence an object of the present invention to provide a data communication system exhibiting minimized crosstalk. It is in particular an object of the present invention to provide an improved wire-bonding technology to overcome above-mentioned drawbacks. It is a further object of the present invention to provide a data communication system including on-board transceivers allowing for high speed multi-channel digital data communication exhibiting better cross-talk performance.

These and other objects, which become apparent by reading the following description, are achieved by the present invention according to the subject matter of independent claim l and a PCB in accordance with claim 23.

Summary of the invention

According to the present invention there is provided an opto-electrical communication system which comprises an opto-electrical transmitter module. Said opto-electrical transmitter module in turn comprises two chips, at least one pair of contacts provided on each chip, and respective first and second bonding wires which are adapted to connect said contacts, i.e. to interconnect the two chips. Preferably, one contact of each pair of contacts is an N-contact, while the other one is a P-contact. The connection of the contacts with the bonding wires is realized such that the first bonding wire crosses over the second bonding wire, i.e. the first and second bonding wires are not parallel to each other, but are crossing over each other instead. Preferably, the first bonding wire crosses only once over the second bonding wire. This cross-bonding scheme limits and reduces the mutual inductance between channels and also the inductive coupling within each channel. Accordingly, the disclosed cross-bonding interconnection concept allows for minimizing the crosstalk of multi-channel systems. The two chips provided on the transmitter module are not limiting the disclosure to any particular kind of chips, but may be any chip or substrate suitable to be applied in optoelectronic communications systems, thereby being adapted to include the contacts.

Preferably, one of the chips is an integrated circuit (IC) which may function as a signal processing chip. The skilled person thereby understands that the IC can be adapted to prepare electrical signals which are to be transferred to another IC. Furthermore, the IC can also be adapted to possibly amplify signals received from another IC, and to process said signals. In a further preferred embodiment, the IC is a flip-chipped IC. The other chip provided on the transmitter module is preferably an opto-electrical converter (OC) which is preferably an opto-electronic transmitter chip, adapted to convert electrical signals to optical signals and to transmit said optical signals. In a preferred embodiment, the first and second bonding wires cross over each other such that a portion midway of the first bonding wire crosses over a portion midway of the second bonding wire. Preferably, the bonding wires are having approximately the same length. In a another preferred embodiment, the internal angle which is defined between the first and second bonding wire is between 30 and 90 degrees, preferably between 45 and 90 degrees, more preferably between 60 and 90 degrees, and most preferably between 75 and 90 degrees. Thereby crosstalk is even further minimized.

In another preferred embodiment, the opto-electrical communication system further comprises an opto-electrical receiver module. This receiver module also comprises two chips, at least a pair of contacts provided on each chip of said receiver module, and respective first and second bonding wires which are adapted to connect the contacts of the pair of contacts which are provided on the chips of the receiver module. As for the transmitter module, the first bonding wire thereby crosses over the second bonding wire to interconnect the two chips of the receiver module, thereby reducing crosstalk. The skilled person understands that the opto-electrical transmitter module and opto-electrical receiver module may also be present in a transceiver module. Accordingly, the opto-electrical communication system can comprise several transceiver modules allowing for optical fiber-based communication between them, wherein the transceivers feature the improved interconnect design as defined in the appended claims. Preferably, the cross bonding design applied for the transmitter module is also applied to interconnect the chips of the receiver module. Thereby, the crosstalk performance of the entire opto-electrical communication system is improved.

The chips of the transmitter module are preferably arranged on the same printed circuit board. Similarly, also the respective chips of the receiver module are preferably arranged on the same printed circuit board. More preferably, also the transmitter module and the receiver module are also arranged on the same printed circuit board, but can also be arranged on different printed circuit boards.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention is described exemplarily with reference to the enclosed figures. Fig. 1 ii a schematic illustration of an interconnection scheme according to the prior art.

Fig.2 is a schematic illustration of an interconnection scheme according to the present invention.

Fig.3 shows schematically a simulation setup of an interconnection scheme according to the prior art.

Fig.4 shows schematically a simulation setup of an interconnection scheme according to the present invention.

Figs.5 and 6 show plots of parameters extracted from simulations.

DETAILED DESCRIPTION OF EMBODIMENTS Figs.2 shows an interconnection configuration according to the present invention. This configuration is used to interconnect two chips, one of which is an integrated circuit (1C) n, while the other one is an optical converter (OC) 10. The chips are arranged on a printed circuit board (PCB) 50, which is only schematically sketched in the figure. The illustrated configuration can be used to interconnect respective chips of an opto-electric transmitter module and/or of an opto-electrical receiver module, wherein both modules can be included in an opto-electrical communication system.

When utilized in an opto-electrical transmitter module, the OC 10 preferably comprises at least one laser diode coupled with each pair of contacts provided on the OC, i.e. linked to each channel. Tn a preferred embodiment, the laser diode is a vertical-cavity surface-emitting laser (VCSEL).

Preferably, when utilized in an opto-electrical receiver module, the OC of the receiver module comprises at least one photo-sensor coupled with each pair of contacts provided on the OC, i.e. linked to each channel. Preferably, the photo-sensor is a PIN diode.

Similar to the configuration shown in Fig. 1, the IC 11 and OC 10 of Fig.2 each comprises two pairs of contacts. Accordingly, Fig.2 shows a configuration with two channels 12, 13. It will be appreciated that the transmitter and/or receiver module can have any number of channels.

As shown in Pig.2 and generally preferred, the IC 11 and OC 10 are aligned parallel to each other and the chips are preferably positioned such that the distance between them, in particular the distance between the respective pairs of contacts (i.e. the distance between 20a and 2ib or the distance between 20b and 21a) provided on the IC and OC, is less than 30 mm, more preferably less than 20 mm and most preferably less than 10 mm.

As can be seen from Fig.2, the contacts 20a, 20b of the OC 10 are connected with the contacts 21a, 20b of the IC 11 by means of bonding wires 31a, 31b. Bonding wire 31a thereby connects contact 20a provided on OC 10 with contact 21a provided on IC 11, while bonding wire 31b connects contact 21b provided on IC 11 with contact 20b provided on OC 10. Thus, the two bonding wires 31a, 31b cross over each other once. Although not clearly visible in Fig. 2, the bonding wires are however not in direct contact with each other, so as to prevent any undesired short circuiting. The bonding wires 31a, 31b have approximately the same length, and a midway portion of bonding wire 31a crosses over a midway portion of bonding wire 31b without touching the same. Accordingly, the bonding wires 31a, 31b cross over each other preferably such that both angles a and β, which are the internal angles defined between the first and second bonding wire, each facing a pair of contacts provided on the IC or OC, respectively, are the same. The bonding wires illustrated in Fig. 2 cross over each other such that said internal angles a and β are approximately 60 degrees each. The skilled person understands that both internal angles do not have to be the same. Preferably, the internal angles are close to 90 degrees.

The contacts illustrated in Pig.2 are provided with an equal distance along each chip.

Preferably, the contacts 20a, 20b of channel 12 provided on the OC 10 and also the contacts 21a, 21b of channel 12 provided on the IC 11 are spaced less than 5 mm from each other. It will be appreciated, that the configuration of channel 12 can also be adopted for the other channels, such as e.g. channel 13 of Fig.2.

The interconnection scheme according to the present invention allows for reduced mutual inductance between adjacent channels and reduced inductive coupling within each channel. The broken line illustrated in Fig.2 schematically represent the corresponding inductive coupling 41, causing less crosstalk compared to the crosstalk occurring with the prior art parallel bonding design as illustrated in Fig. 1. In order to undergird the positive effect, an electromagnetic simulation study will be outlined in the following.

Fig.3 shows a conceptual arrangement created for the electromagnetic simulation study, featuring bonding wires 30a', 30b' which are connecting the contacts 20a', 20b' provided on chip 10' with the contacts 21a', 21b' provided on chip 11', respectively. The bonding wires 30a', 30b' do not cross over each other, but are rather aligned parallel to each other. This arrangement corresponds to the prior art wire bonding technology, as also illustrated in Fig. 1.

Fig.4 shows a similar conceptual arrangement utilized for the electromagnetic simulation study. Compared to the arrangement of Fig.3, the bonding wires 31a', 31b' are crossing over each other according to the present invention. The skilled person understands, that due to the crossing, the polarity of the pairs of contacts provided on chip 10' or chip 11' has to be different compared to the arrangement of Fig.3. The skilled person thus understands that for example the polarity of the optical components (PIN or VCSEL) of the receiver module and transmitter module does not match the polarity of the respective flip-chipped IC.

According to those simulation setups, parameters for near-end crosstalk (NEXT) and insertion loss were extracted, which are illustrated in Figs.5 and 6, respectively. Fig.5 shows the S-parameters P₅, 6 andX₅,6 for NEXT occurring between pins 5 and 6 of the setups of Figs.3 and 4, respectively. Accordingly, P₅,6 is characteristic for the NEXT of the prior art parallel interconnection design, while Χ₅ ,6 is characteristic for the NEXT of the design according to the present invention. In addition, Fig.5 also shows the S-parameters P₈,6 and XB, 6 for NEXT occurring between pins 8 and 6 of the setups of Figs.3 and 4, respectively. As can clearly be seen, the cross-bonding configuration of Fig.4 according to the present invention exhibits better crosstalk performance than the prior art parallel bonding configuration of Fig.3. At a frequency of 25 GHz, the respective values are as follows: P₅,6= -30,2 dB,

X₅,6= -34,3 dB,

P₈,6 -44,8 dB, and

X₈,6 -57, 3 dB. The values of X_5,6 Χ_8,6 in comparison to P_5,6 P₈, 6 are highlighting the advantageous effect of the disclosed bonding technique to be applied preferably in both an opto-electrical transmitter module and opto-electrical receiver module, and more preferably in on-board transceivers of an opto-electrical communication system. Fig.6 shows the extracted values P18, 6 and Χ18, 6, characteristic for the insertion loss with respect to pins 18 and 6 of the setups of Figs.3 and Fig.4, respectively. At a frequency of 25 GHz, the extracted values are as follows:

P18.6 = -o.15 dB,

X18,6 = -o.13 dB. As can be seen, the corresponding configuration according to the present invention not only exhibits better crosstalk performance, but also similar insertion loss compared to the parallel bonding configuration.

Although the presented values and data were extracted from simulation studies, the skilled person understands that the presented data does not have to correspond to actual data, but rather allows for a comparison of the inventive bonding scheme with the prior art bonding scheme.

The present invention provides better performances, in particular since the crosstalk of opto- electrical transmitter modules is reduced. Since the applied voltages at said modules are relatively high, the effect of crosstalk can be quite severe. Due to the inventive design, the overall performance of the opto-electrical communication system is improved.

Generally preferred, both the transmitter module and receiver module of an opto-electrical communication system are provided with the inventive bonding scheme. These systems feature minimal crosstalk, allowing for high speed communication with minimal noise.

Referencege,chart

10 Optical converter, OC

11 Integrated circuit, IC

12, 13 Channels 20a, 20b, 21a, 21b, 20a', 2ob', 21a', 21b' Contacts

30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b' Bonding wires 40,41 Inductive coupling 50 PCB

Claims

Claims What is claimed is:

1. Opto-electrical communication system, comprising:

an opto-electrical transmitter module, comprising:

two chips;

at least a pair of contacts (20a, 20b, 21a, 21b, 20a', 20b', 21a', 21V) provided on each chip; and

first and second bonding wires (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31V) adapted to connect the contacts (20a, 20b, 21a, 21b, 20a', 20b', 2ia', 21b¹) of the pair of contacts (20a, 20b, 21a, 21b, 20a', 2ob', 2ia', 21b') provided on a first one of the chips with the contacts (20a, 20b, 21a, 21b, 20a\ 20b', 21a', 21b") of the pair of contacts (20a, 20b, 21a, 21b, 2oa\ 20b', 21a', 21V) provided on a second one of the chips;

characterized in that the first bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b^*) crosses over the second bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31V).

2. The system of claim 1, wherein one of the two chips is an integrated circuit, IC (11), preferably a flip chip IC, and the other one is an opto-electrical converter, OC (10).

3. The system of claim 2, wherein the OC (10) comprises at least one laser diode coupled with the pair of contacts (20a, 20b, 20a', 20b') provided on the OC (10), in particular wherein the laser diode is a vertical-cavity surface-emitting laser, VCSEL.

4. The system of any one of the preceding claims, wherein a portion midway of the first bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31V) crosses over a portion midway of the second bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b").

5. The system of any one of the preceding claims, wherein the two chips are positioned adjacent to each other in a distance of less than 30 mm, preferably less than 20 mm and most preferably less than 10 mm.

6. The system of any one of the preceding claims, wherein the contacts (20a, 20b, 21a, 21b, 20a', 20b', 21a', 21b') of the pair of contacts (20a, 20b, 21a, 21b, 20a', 2ob\ 21a', 21b') provided on the first one of the chips is spaced less than 5 mm from each other and/or wherein the contacts (20a, 20b, 21a, 21b, 20a ', 20b', 21a', 21b') of the pair of contacts (20a, 20b, 21a. 21b, 20a', 20b', 21a', 21b ') provided on the second one of the chips is spaced less than 5 mm from each other,

7. The system of any one of the preceding claims, wherein the first bonding wire (30a,

30b, 31a, 31b, 30a', 30b', 31a', 31b') crosses over the second bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b') and wherein the internal angle defined between said first and second wire facing one pair of contacts (20a, 20b, 2ia, 21b, 20a^', 20b', 21a', 21b') is between 30 and 90 degree, preferably between 45 and 90 degree, more preferably between 60 and 90 degree, and most preferably between 75 and 90 degree.

8. The system of any one of the preceding claims, wherein the bonding wires (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b') are not in direct contact with each other, and/ or wherein the bonding wires (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b') have approximately the same length.

9. The system of any one of the preceding claims, wherein the two chips are arranged on the same printed circuit board.

10. The system of any one of the preceding claims, wherein the first bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b') crosses only once over the second bonding wire (30a,

30b, 31a, 31b, 30a', 30b', 31a', 31b').

11. The system of any one of the preceding claims, wherein the pair of contacts (20a, 20b, 21a, 21b, 20a', 20b^", 21a', 21b') comprises an N-contaet and a P-contact.

12. The system of any of the preceding claims, further comprising:

an opto-electrical receiver module, comprising:

two chips;

at least a pair of contacts (20a, 20b, 21a, 21b, 20a', 20b', 21a', 21b') provided on each chip of the receiver module; and

first and second bonding wires (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b') adapted to connect the contacts (20a, 20b, 21a, 21b, 20a', 20b^*, 21a', 21b') of the pair of contacts (20a, 20b, 21a, 21b, 20a', 20b', 21a', 21b') provided on a first one of the chips of the receiver module with the contacts (20a, 20b, 21a, 21b, 20a', 20b', 21a', 21b') of the pair of contacts (20a, 20b, 21a, 21b, 2oa', 20b', 21a', 2ib') provided on a second one of the chips of the receiver module,

wherein the first bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b') of the receiver module crosses over the second bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b') of the receiver module.

13. The system of claim 12, wherein one of the two chips of the receiver module is an integrated circuit, 1C (11), preferably a flip chip 1C, and the other one is an opto-electrical converter, OC (10).

14. The system of claim 13, wherein the OC (10) of the receiver module comprises at least one photosensor coupled with the pair of contacts (20a, 20b, 20a', 20b') provided on the OC (io), in particular wherein the photosensor is a PIN diode.

15. The system of any one of the preceding claims 12 to 14, wherein a portion midway of the first bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b') of the receiver module crosses over a portion midway of the second bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b^*) of the receiver module.

16. The system of any one of the preceding claims 12 to 15, wherein the two chips of the receiver module are positioned adjacent to each other in a distance of less than 30 mm, preferably less than 20 mm and most preferably less than 10 mm.

17. The system of any one of the preceding claims 12 to 16, wherein the contacts (20a, 2ob_t 2ia, 21b, 20a', 20b', 21a', 21b') of the pair of contacts (20a, 20b, 21a, 21b, 20a', 20b',

21a', 21b') provided on the first one of the chips of the receiver module is spaced less than 5 mm from each other and/or wherein the contacts (20a, 20b, 21a, 21b, 20a', 20b', 21a', 21b') of the pair of contacts (20a, 20b, 21a, 21b, 20a', 20b', 21a', 21b') provided on the second one of the chips of the receiver module is spaced less than 5 mm from each other.

18. The system of any one of the preceding claims 12 to 17, wherein the first bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b¹) of the receiver module crosses over the second bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b*) of the receiver module and wherein the internal angle defined between said first and second wire facing one pair of contacts (20a, 20b, 21a, 21b, 20a', 20b', 21a', 21b') is between 30 and 90 degree, preferably between 45 and 90 degree, more preferably between 60 and 90 degree, and most preferably between 75 and 90 degree.

19. The system of any one of the preceding claims 12 to 18, wherein the bonding wires (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b') of the receiver module are not in direct contact with each other, and/or wherein the bonding wires (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b') of the receiver module have approximately the same length.

20. The system of any one of the preceding claims 12 to 19, wherein the two chips of the receiver module are arranged on the same printed circuit board.

21. The system of any one of the preceding claims 12 to 20, wherein the first bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31V) crosses of the receiver module only once over the second bonding wire (30a, 30b, 31a, 31b, 30a', 30b', 31a', 31b') of the receiver module.

22. The system of any one of the preceding claims, wherein the pair of contacts (20a, 20b, 21a, 21b, 20a', 20b', 21a', 2ib') of the receiver module comprises an N-contact and a P- contact.

23. Printed circuit board (50) comprising a system in accordance with any one of claims 1 to 22.