56/80 Gb/s PCB transmission lines. and. 56 Gb/s End-launch GPPO connector

Transcription

1 White paper: WP /8 b/s PCB transmission lines and 56 b/s End-launch PPO connector Electrical Interconnection basic technology development Takada RF Labs, Inc. 214/1/2 Tel:

2 1. Back ground 1) The inter connection applications are categorized as follows in OIF next generation inter connection flame work 1) ; (Category -a) Die to Die Interconnect Within A Package (Example) Inter connection within multi-chip module, etc. (Category -b) Die to Optical Engine Within A Package (Example) Inter connection within OE/EO conversion module, etc. (Category -c) Chip to Nearby Optical Engine (Example) Inter connection within CFP2/CFP4 transceiver module, etc. 2) 56 b/s rate are set as a target speed at the above categories for realizing next generation 4 (= 5 x 8 ) b/s optical communication systems in OIF Q2 212 meeting. Reference: 1) OIF-FD-Client-4/1T-1. 2) CEI-56-VR Project start proposal, 26 April 212, Chris Cole, Finisar Corp 3) Technical info, Common Electrical Interface - 56-Ultra hort Reach 2) 3) 2. Development Results by Takada RF Labs, Inc. Development 1 High performance transmission line for 56 b/s signal 2 kinds of transmission lines were investigated using 4-layer PCB. One is a transmission line with fine pattern (FPTL). Its main application is interconnection between bare dies. The other is a relatively larger pattern transmission line with low transmission loss (LLTL). Its main application is an interconnection between packages. a) Fine Pattern transmission line, FPTL Application: Category -a and Category -b Device assembly method: wire-bonding or flip chip Feature: Fine transmission line pattern FPTL is designed for interconnection between bare dies. In case of 2-signal lane, inter connection with down to 1 um pad pitch is available as shown in Fig.1. For dies with larger than 15 um pad pitch, no limited number of multi-lane interconnection between bare dies is available as shown in Fig.2. White paper: WP /8 b/s PCB transmission lines and 56 b/s end-launch PPO 1

3 1 um pitch 4-layer RF board FPTL Fig.1 2-lane interconnection for 1 um pad pitch bare dies (Category -a and -b) 15 um pitch 4-layer RF board FPTL Fig.2 Multi-lane interconnection for 15 um pad pitch bare dies (Category -a and -b) Frequency dependency of transmission loss per unit length of FPTL is shown in Fig.3, which is measured using high frequency probe and Agilent PNA series vector network analyzer. Frequency (Hz) Transmission Loss (db/mm) db 56 Hz.28 db/mm Hz (Fundamental of 56 b/s).43 db 56 Hz 84 Hz (2nd harmonics of 56 b/s) (3rd harmonics of 56 b/s) Fig.3 Transmission loss per 1mm length FPTL (Experimental data) White paper: WP /8 b/s PCB transmission lines and 56 b/s end-launch PPO 2

4 In an ultra-short reach interface in OIF Common Electrical Interface (CEI) (Category -a), 1 mm of maximum transmission length is defined. o, we investigated on how long NRZ PRB signal can transmit on FPTL keeping enough eye opening at 56 b/s speed as follows. There is no way to measure an eye diagram because such a high speed pulse pattern generator (PP) is not currently commercially available. Thus, instead of experimental direct measurement using PP and oscilloscope, we used Agilent software PLT (Physical Layer Test ystem) and obtained the PRB eye diagram after over 1 mm on FPTL transmission at 56 b/s. In PLT, eye diagram is calculated by time domain conversion from experimental frequency domain -parameter data. This method is very useful because PLT equivalently acts as an ideal (no bit rate limitation) PP and ideal (no band-width limitation) oscilloscope. In addition, we can easily set an input signal with various pattern sequence and arbitral rise /fall time and amplitude to DUT. Figure 4 shows the eye diagram for 56 b/s PRB 2^7-1 NRZ output signal after transmitting 18 mm length FPTL when 1. ps Tr/Tf (2-8%) PRB NRZ signal is applied to FPTL as an input signal. Tr/Tf (2-8%)= 6.3 ps (2-8)% is applied to the line.) Fig b/s PRB 2^7-1 NRZ signal after transmitting 18 mm length FPTL. Fig.4-a 56 b/s PRB 2^7-1 NRZ signal after transmitting 18 mm length FPTL. From Fig.4-a, we can see that eye opening is good enough even after transmitting 18 mm length of FPTL at 56 b/s. o, it is concluded that we could attained the target of over 1 mm length multi-lane interconnection which is defined in OIF Category -a and b applications at 56 b/s speed. When FPTL transmission line length is decreased to 9mm, it can transmit 64 b/s with good eye opening as shown in Fig.4-b. White paper: WP /8 b/s PCB transmission lines and 56 b/s end-launch PPO 3

5 Tr/Tf (2-8%)= 5.1 ps (2-8)% is applied to the line.) Fig.4-b 64 b/s PRB 2^7-1 NRZ signal after transmitting 9 mm length FPTL. b) Low loss transmission line, LLTL Application: Category -c (multi-lane) or Category -a and -b (single lane) Assembly: Reflow or manual soldering Feature: Low transmission loss LLTL was designed for interconnection between packages rather than bare dies. Using LLTL, multi-lane (no limited number) interconnection between over 3 um Lead pitch package is available as shown in Fig.5. Although LLTL is designed for interconnection between packages, it is also applicable for bare die (15 um pad pitch) interconnection for the case of single signal lane as shown in Fig.6. 3 um pitch PK LLTL PK Fig.5 Multi-lane interconnection for >3 um lead pitch packages (Category -c) White paper: WP /8 b/s PCB transmission lines and 56 b/s end-launch PPO 4

6 15 um pitch LLTL Fig.6 ingle lane interconnection for 15 um pad pitch bare dies (Category -a and -b) Frequency dependency of transmission line of unit length LLTL is shown in Fig.7, which is obtained from two different length LLTL -parameter measurement results using adaptor removal method by PLT software. The transmission loss of LLTL is.17 db/mm at 56 Hz that is 4% lower in db than FPTL. Frequency (Hz) Insertion Loss (db/mm).75 db.17db 28 Hz (Fundamental of 56 b/s) 56 Hz (2nd harmonics of 56 b/s) 84 Hz Fig.7 Transmission loss per 1mm length LLTL (Experimental data) White paper: WP /8 b/s PCB transmission lines and 56 b/s end-launch PPO 5

7 We have measured transmission loss of LLTL with 18 mm length by assembling 1mm-coax end-launch connector at both end. The result is shown by red line in Fig.8. Frequency (Hz) Insertion 2 Loss (db) Improved End-launch PPO connector 3 db 1mm-coax end-launch connector 1 Fig. 8 Transmission loss for 18 mm LLTL with 1mm-coax end-launch connector at both end in red and one for 18 mm LLTL with improved version end-launch PPO at both end in blue From this frequency domain measurement data, we obtained the eye diagram after transmitting 18mm LLTL with 1mm-coax end-launch connector at both end using PLT software. The result for 56 b/s NRZ PRB signal is shown in Fig.9. Input signal Tr/Tf is set to 1 ps (2-8%). Tr/Tf (2-8%) = 5.9 ps (2-8%) is applied to the line.) Fig.9 56 b/s PRB 2^7-1 NRZ signal after transmitting 18 mm length LLTL with 1mm-coaxial end-launch connectors at both end. We can see that the eye opening of eye diagram in Fig.9 is much better than Fig.4-a. This is because transmission loss of LLTL is lower than FPTL. The eye diagram in case that LLTL length is reduced to 9mm from 18 mm and 1mm-coax end-launch connector is assembled at only one end is simulated by PLT as well. In this case, much higher bit rate of 8 b/s signal can be transmitted with keeping good eye opening as shown in Fig.1. White paper: WP /8 b/s PCB transmission lines and 56 b/s end-launch PPO 6

8 It can be concluded that LLTL is useful not only for 56 b/s transmission for over 18 mm length but also available to be used up to 8 b/s NRZ signal transmission if transmission length is less than 9mm. Tr/Tf (2-8%) = 4.8 ps (2-8%) is applied to the line.) Fig.1 8 b/s PRB 2^7-1 NRZ signal after transmitting 9 mm length LLTL with 1mm-coaxial end-launch connector at one end. Development 2 High performance PPO connector for maximum 56 b/s signal As described above, we have successfully developed the transmission lines at the speed of over 56 b/s for FPTL and over 8 b/s for LLTL. However, maximum signal speed is determined by not only transmission line performance but also connector performance, actually. Although we confirmed over 8 b/s transmission as above described, this result was obtained using 1mm-coaxial end-launch connector having over 11 Hz band width that was developed for ultra-high frequency measurement purpose such as E/V band wireless communication application. ince size of the 1mm-coaxial end-launch connector is too big as shown in Fig.11 to apply to multi-channel devices and its cost is very expensive, it may not able to be widely used in actual optical communication applications except special cases such as measurement instrument applications. 1 mm Female 1mm-Connector Male 1mm-Connector Fig.11 1mm-coaxial end-launch connector mounted on the 4 layer RF PCB White paper: WP /8 b/s PCB transmission lines and 56 b/s end-launch PPO 7

9 On the other hand, PPO connector is very small and is inexpensive. o, it is commonly used in high speed optical communication devices currently. Although higher coaxial mode cut off frequency of PPO is theoretically over 65 Hz, 3-dB band width of commercially available end-launch type PPO connector is limited to about 4 Hz due to the mismatch between RF substrate transmission line and connector itself. The 4 Hz band width is too low to apply to over 56 b/s transmission purpose. o, we have tried to improve the RF performance of PPO type connector by changing connector physical structure and assembling way to have good impedance matching. Finally, we have attained over 65 Hz of 3 db down band-width as shown in Fig.12. Frequency (Hz) /-.2 db at < 56 Hz Insertion Loss (db) Fig.12 Measured transmission loss of improved version PPO connector The blue color curve in Fig.8 is transmission loss measurement data when improved version end-launch PPOs are assembled on 18 mm length LLTL at both end. We can see that transmission band width is entirely determined by PPO performance. Fig.13 shows 56 b/s NRZ eye diagram after transmitting 18 mm length LLTL with two end-launch PPO connectors at both end. We can see that eye quality is much worse in comparison with the case using 1mm-coaxial end-launch connector (Fig.9), which may not be enough eye opening for high quality transmission. Fig.14 shows a simulated 56 b/s NRZ eye diagram after transmitting half-length (9 mm) LLTL with one end-launch PPO connectors at one end. In this case, eye quality becomes acceptable range. Tr/Tf (2-8%)= 8.6 ps (2-8%) is applied to the line.) Fig b/s PRB 2^7-1 NRZ signal after transmitting 18 mm length LLTL with end-launch PPO connectors at both end. White paper: WP /8 b/s PCB transmission lines and 56 b/s end-launch PPO 8

10 Tr/Tf (2-8%) = 7.8 ps (2-8%) is applied to the line.) Fig b/s PRB 2^7-1 NRZ signal after transmitting 9 mm length LLTL with one end-launch PPO connecter 3. ummary For the purpose of developing over 56 b/s lane speed various devices such as optical transceiver module for next generation 4 b/s optical transmission systems, two kind of transmission lines on 4-layer PCB and improved version end-launch PPO connector has been successfully developed. 1) Transmission lines (FPTL and LLTL) FPTL can be used for multi-signal lane transmission between bare dies with minimum 15 um pad pitch and for 2-signal lane transmission with down to 1 um pad pitch. 18 mm length transmission is available on FPTL transmission line at 56 b/s, and 64 b/s is possible for less than 9mm transmission length. LLTL can be used for multi-signal lane transmission between packages with minimum 3 um lead-pitch, and also used for single-signal lane transmission between bare dies with 15 um pad pitch. LLTL can be available for 56 b/s transmission for over 18 mm length with good eye opening and also available for transmission at up to 8 b/s for less than 9mm transmission length. 2) Improved version end-launch PPO connector 3-dB down band width of improved version of PPO is over 65 Hz band-width. Using the improved version of PPO, good eye opening was confirmed for 9 mm length LLTL transmission at 56 b/s. White paper: WP /8 b/s PCB transmission lines and 56 b/s end-launch PPO 9