At-speed I/O Test for Fast Vref Optimization in High Speed Single-ended Memory Systems

Single-ended memory interfaces have gone through a remarkable increase in data rates over the last decade increasing the challenges faced by system designers and OEMs. One of the major challenges in single-ended system design is optimizing the reference voltage level (Vref) in the receiver. The traditional method to choose Vref is to sweep the reference voltage level while performing a link Bit Error Rate (BER) test. This existing method has serious disadvantages like additional circuitry, system overhead and a very long time to completion. In this paper, a fast technique to obtain optimum value of Vref is proposed. It uses a simple density test at the receiver to perform the operation. This technique has been demonstrated in a POD (Pseudo Open-Drain) signaling based single-ended transceiver designed in TSMC 40nm process. System level measurements in the lab at 6 Gb/s data rate prove that this technique is as accurate as the traditional technique in choosing Vref while being several thousand times faster.