# 10Gbps Length adaptive on-chip RF serial link for Network on Chips and Multiprocessor chips applications

## Summary (2 min read)

### Introduction

- The attenuation is much higher for high frequencies components and causes the pulse traveling through the channel to both decrease in amplitude and spread in time domain.
- Using both RF and Base band signaling on the same transmission line is possible [5]-[6] to achieve higher data rate than only base band signaling.
- After this introduction, the system architecture is described in Section II.

### A. Differential Transmission Line used for the Link

- On-chip interconnects offer a rather constant propagation speed at mm-waves, as shown in Figure 2, where a 50-Ω microstrip line was simulated using the highest metal layer with the ground in M9 using the 10 Metal layers stack from STMicroelectronics 28-nm FD-SOI technology.
- The phase velocity increases rapidly from few MHz up to about 10 GHz.
- The transmission line is designed in the BEOL with SiO2 substrate with a relative dielectric constant equal to 4, leading to a signal that propagates with half the speed of light, (i.e. 1.5 ∙ 10 m/s).
- Furthermore, for an appropriately matched transmission line, its delay can be linearly related to its length.
- Higher performance could be reached, but at the expense of larger footprint.

### B. Main Performance Parameters

- To simplify the use of serial links in large digital ICs, a length adaptive link is proposed to cover a large range of distances with the same transceiver without any requirement of repeater, thus limiting both power consumption and system complexity.
- For different link lengths, several parameters vary.
- For simplification reasons, let us consider a simple cascaded system of a transmitter and the transmission line (attenuation ) only.
- MODULATION NRZ modulation serial links have been proposed [4]- [5].

### A. Duobinary modulation

- Duo-binary modulation is part of the poly-binary modulations invented by Adam Lender in 1963 [7].
- It can theoretically double the data rate transmitted through a channel bandwidth BW, where ISI is introduced in a controlled matter to be removed at the reception.
- In its general form, the duo-binary modulation output bit as defined in equation(2) as the sum of the previous bit 1 and the present bit to be sent.
- Considering simple duo-binary demodulation, for 200 mV where is the received signal, the received bit is easily distinguishable since it can either take the value 200 mV for a binary “1”, 200 mV for a binary “0”, for 0V the received bit is decided by inverting the previously received bit .
- Note that the duo-binary modulation compresses the main lobe of the spectrum to half the bandwidth used by NRZ modulation.

### B. Differential pre-encoder

- It can be realized using a XOR logic gate as follows: ⊕ (5) with ⊕ the modulo-2 addition (XOR logic operation).
- Using this precoding, as shown in the simple scheme in Figure 6, the duo-binary output states becomes binary “0” for 200 mV and binary “1” for 0V.

### D. Simulation results

- The signal states through the system can be seen.
- Next, is the duo-binary preencoded data used to modulate the 60 GHz carrier, is the modulated signal before self-mixing, and is the received self-mixed signal.
- In Figure 8, the eye diagram of the system before and after the channel transmission can be seen.
- To increase the spectral efficiency of the link and relax the RF design constraints, duo-binary modulation was also implemented.

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##### References

314 citations

### "10Gbps Length adaptive on-chip RF s..." refers background or methods in this paper

...Duo-binary modulation is part of the poly-binary modulations invented by Adam Lender in 1963 [7]....

[...]

...Next, to make use of the bandwidth efficiently a preencoded duo-binary modulation [7] is proposed to compress the spectrum of the signal and thus use a two time smaller bandwidth....

[...]

...This was demonstrated in [7], with equations (3) and (4) giving the utilized spectrum for duo-binary and NRZ modulations, respectively....

[...]

52 citations

### "10Gbps Length adaptive on-chip RF s..." refers background or methods in this paper

...NRZ modulation serial links have been proposed [4][5]....

[...]

...In this work, to answer these issues, an approach inherited from [4] using a modulated RF carrier and suitable for longrange links up to several mm length is proposed....

[...]

47 citations

### "10Gbps Length adaptive on-chip RF s..." refers methods in this paper

...Otherwise, to reverse the effect of the time-varying channel an adaptive equalization is required where a known training sequence is inserted periodically, then algorithms such as least mean square are used to update the coefficients of the equalizer [3]....

[...]

7 citations

### "10Gbps Length adaptive on-chip RF s..." refers background in this paper

...Using both RF and Base band signaling on the same transmission line is possible [5]-[6] to achieve higher data rate than only base band signaling....

[...]

6 citations

### "10Gbps Length adaptive on-chip RF s..." refers methods in this paper

...Equalization was used to reduce the frequency selectivity of the channel by reversing the distortion [2]....

[...]