Ganesan Thiagarajan

The effect of sampling jitter in OFDM systems

In this paper we study the effect of random jitter in the sampling circuit at the receiver in an OFDM communication system. We show that the effect of jitter can be looked at as interference between different sub-carriers and derive a lower bound for the variance of the interference in terms of the eigenvalues of the covariance matrix of the jitter process. We compare the results with simulation results. We describe the effect of oversampling on the interference, and provide an explanation for the way interference varies with sub-carrier index for different sampling rates.

25.4 A 500Mb/s 200pJ/b die-to-die bidirectional link with 24kV surge isolation and 50kV/µs CMR using resonant inductive coupling in 0.18µm CMOS

Chip based digital isolators are being developed for higher speed and higher isolation capabilities [1, 2]. These make use of various coupling mechanisms such as capacitive coupling [3] and transformer coupling [4]. A limitation of these technologies is that they need to maintain a low separation (distance through insulation DTI<30µm) through high quality insulators (oxides, polyamides) in order to achieve data rate and isolation performance [2]. These require expensive special process development and special packaging techniques to meet reinforced isolation recommended by IEC 60747-5-5 and VDE 0884-10. Other high-speed die-to-die communication techniques implemented using millimeter-wave and optical solutions are expensive and not designed for isolation. In this work, an isolation technique is proposed where two standard 180nm CMOS dies placed side by side with DTI of more than 500µm, and co-packaged using regular planar MCM flow with package mold compound being the isolation material, achieve asynchronous bidirectional link with >24kV surge isolation capability and greater than 500Mb/s at 175pJ/b. Channel gain is maximized using resonance. Gain is decoupled from channel bandwidth by resetting the channel state variables. This helps in enhancing data rate well beyond what is implied by the bandwidth.

Low complexity, low latency resampling of asynchronously sampled signals

In Signal processing, activity driven data acquisition is of interest as it offers power savings and data compression when dealing with sparse real world signals. However, such schemes naturally result in asynchronous samples which cannot be handled by traditional signal processing. Hence, there is a need for efficient resampling schemes that convert the asynchronous samples to a synchronous stream. This work proposes two novel low latency non-iterative resampling schemes that allow for pipelined hardware and real-time software implementations. The first scheme caters to low complexity applications and is a modification to the Akima algorithm [1]. The second scheme addresses high performance applications and is based on windowed sinc interpolation. Simulation results are presented to demonstrate the performance. Complexity comparison with existing methods is also provided.

Frequency domain correction of residual frequency offset in OFDM and DMT systems

OFDM and DMT systems are sensitive to carrier frequency offset between the receiver and transmitter. Most of the systems employ frequency offset estimation and correction, as a part of synchronizing the receiver to the transmitter. Depending on the availability of training data and/or the computation power, frequency offset may not be corrected exactly. Moreover, some times we may want to do the correction in the frequency domain in order to reduce the latency and complexity in the receiver. This paper discusses the frequency domain modeling of the effect of residual frequency offset as a linear transformation on the sub-carrier symbols. An interesting property is observed that the transformation matrix is Toeplitz and which simplifies the frequency correction circuit complexity. Simulation results are given to validate the algorithm.