Differential signalling | EPFL Graph Search

Differential signalling is a method for electrically transmitting information using two complementary signals. The technique sends the same electrical signal as a differential pair of signals, each in its own conductor. The pair of conductors can be wires in a twisted-pair or ribbon cable or traces on a printed circuit board. Electrically, the two conductors carry voltage signals which are equal in magnitude, but of opposite polarity. The receiving circuit responds to the difference between the two signals, which results in a signal with a magnitude twice as large. The symmetrical signals of differential signalling may be referred to as balanced, but this term is more appropriately applied to balanced circuits and balanced lines which reject common-mode interference when fed into a differential receiver. Differential signalling does not make a line balanced, nor does noise rejection in balanced circuits require differential signalling. Differential signalling is to be contrasted

26.3 A pin- and power-efficient low-latency 8-to-12Gb/s/wire 8b8w-coded SerDes link for high-loss channels in 40nm technology

Harm Cronie, Klaas Lammert Hofstra, Kia Salimi, Mohammad Amin Shokrollahi, Anant Pratap Singh, Christoph Walter

The continuing demand for higher bandwidth in serial interconnects has pushed the symbol rate of differential lanes into the high-insertion-loss region of channels. Multi-level signaling such as differential PAM-4 [1] has been used to mitigate the loss of electrical channels by lowering the signal spectrum. Such an approach suffers from lower SNR tolerance as well as higher susceptibility to crosstalk and ISI as compared to differential signaling (DS). Coded differential approaches have been reported [2] to mitigate ISI. Our approach is a generalization of DS in which ternary values are transmitted on an 8-wire bus. The set of transmitted values belongs to a code consisting of 256 code-words called the 8b8w-code (8-bits-on-8-wires) [3]. The specific correlations in the code-words of the 8b8w-code eliminate transmit common-mode and simultaneous switching output (SSO) noise and allow for detection via self-referencing comparators (unlike PAM-4), which provides additional noise immunity. Compared to DS, the 8b8w-code offers twice the throughput at 50% of the line power. Compared to PAM-4, the code offers better SNR (3dB) at 38% of the line power with enhanced tolerance of ISI and lower crosstalk generation. The design and experimental verification of an 8b8w transceiver in 40nm CMOS is described. Transmission is achieved up to 12Gb/s per wire over 55cm of Rogers with up to 15dB loss.

2014

10.1 A pin-efficient 20.83Gb/s/wire 0.94pJ/bit forwarded clock CNRZ-5-coded SerDes up to 12mm for MCM packages in 28nm CMOS

Klaas Lammert Hofstra, Ali Hormati, Sergio Pesenti, Mohammad Amin Shokrollahi, Anant Pratap Singh, Seyed Armin Tajalli, Omid Talebi Amiri, Christoph Walter

High-speed signaling over package substrates is key to delivering the promise of 2.5D integration. Applications abound and include high-density memory interfaces, sub-division of large dies to increase yield and lower development time, sub-division of a die to achieve upward or downward scalability, or connecting to an off-chip SerDes or optics engine. Each of these in-package applications typically has high throughput and onerously low power constraints along with a low-loss channel. Several solutions have been proposed. Interposer substrates [1], or Chip-on-Substrate-on-Wafer [2] allow for very high-density wiring and low power using CMOS transceivers. Their high manufacturing and testing cost makes them prohibitive for anything but high-end applications. A different approach using high-speed ground-referenced single-ended signaling is reported in [3], which is intended for shorter channels up to 4.5mm and a BER of 1e-12. An approach using differential signaling on up to 0.75" of Megtron 6 material and a BER of 1e-9 is reported in [4]. A comparison is given in Fig. 10.1.1.

2016

A GPS/INS System for Positioning and Orientation of Airborne Sensors: Results from flight tests in Portugal

Telmo Cunha, Phillip Tomé

Efficient systems for determining the precise position and orientation of airborne sensors will have a great impact in different remote sensing activities, with consequences in their productivity and therefore substantially increasing their cost effectiveness. In the scope of national and international projects, the authors have developed and tested an airborne system built with multiple GPS receivers and a low cost inertial unit. The methodology is based on the integrated processing of raw inertial measurements and GPS data collected from two receivers on board the aircraft and one, or possibly more, reference stations. The algorithm for processing GPS and IMU (Inertial Measurement Unit) raw data was implemented in an integrated feedback loop. The position determination is based on DGPS with OTF ambiguity fixing, using on-line processed inertial data to validate and increase position reliability, especially during GPS outages and when the aircraft is far away from the nearest GPS reference station. For the attitude angles, the IMU raw data is processed using absolute GPS position/velocity updates for continuous alignment. Also, by processing L1 and L2 carrier phase measurements in differential mode between two GPS antennas on the aircraft (without resorting to ground reference station data), a partial estimate of the aircraft attitude is obtained. This is critical to align the low cost inertial platform in heading either when the aircraft is stopped or in stable flight. The inertial system also provides high rate (DGPS filtered) position and velocity estimates that can be valuable during GPS signal outages and for the robustness of the ambiguity fixing procedures. By using the proposed methodology it was possible to explore the entire potential of a low cost GPS/IMU system. The position and attitude values are obtained from all the measurements through an Extended Kalman Filter. Decimeter accuracy was achieved for the positions, while the estimated accuracy for the aircraft orientation is 0.01º for roll and pitch and 0.05º for heading (maximum values). The basic idea was to develop a low cost system that can supply position and attitude with a level of accuracy and reliability similar to more expensive systems, such us gimbaled and ring laser gyro based inertial systems. The final tests of this GPS/IMU system took place during this summer. The inclusion of a radio link between a reference station and the aircraft enabled the system to operate in real time. It proved to be successful in navigating the aircraft during all flight phases, including runway approach and landing. Furthermore, aerial photographs were taken in order to have an independent evaluation of the system accuracy. Results from the airborne campaigns and the performance of this system are presented. Its potential for different applications is discussed.

1999

A GPS/INS System for Positioning and Orientation of Airborne Sensors: Results from flight tests in Portugal

Telmo Cunha, Phillip Tomé

1999