Efficient Built-In Test and Calibration of High Speed Serial I/O Systems Using Monobit Signal Acquisition

Abstract

This paper proposes a new high-speed self-calibrating digital transmitter with the ability to deliver high quality signals at low hardware cost. The proposed self-calibrating system performs on-line monitoring of the channel by performing measurements on the time-domain reflected (TDR) waveform. Unlike complex TDR instrumentation, the proposed system has the capability to reconstruct the reflected waveform using a single bit (monobit) sampler. Using very little hardware, a specific feature of the reflected waveform (area over time or integral) is extracted and used to drive a signal pre-emphasis scheme that maximizes the opening of the signal eye diagram without any communication with the receiver. The absence of such physical loopback significantly reduces the time and complexity of feedback based transmitter calibration techniques, especially where multiple transmission channels are concerned. Further, the proposed scheme is useful in the presence of single or multiple transmission line imperfections or defects. The proposed technique is implemented via a printed circuit board (PCB) prototype and measurement results demonstrate that it is capable of detecting defects in the digital I/O channel and adapting the channel to improve the received signal eye-diagram without direct feedback from the receiver.