A channel-emulating high-speed transmitter with pseudo-logarithmic and low-bandwidth amplifiers

Abstract

This paper describes a transmitter that can emulate a wide variety of frequency-dependent loss characteristics of high-speed dynamic random-access memory (DRAM) channels, with an aim to facilitate an automated test procedure for a DRAM interface, which does not require physical reconfiguration of channels. Specifically, the proposed transmitter can generate the waveform of an NRZ data stream that has experienced adjustable amounts of skin-effect loss and dielectric loss in electrical channels. To save the hardware cost of implementing a high-speed, high-resolution digital-to-analog converter, the transmitter constructs the waveform using a set of logarithmic and exponential basis functions, each of which is implemented using a pseudo-logarithmic amplifier and low-bandwidth amplifier with adjustable gain and bandwidth, respectively. The prototype chip, fabricated in a 65-nm CMOS process, occupies an area of 5200 µm² and operates over 1.4–7 Gbps while dissipating 38 mW at 7 Gbps. It is demonstrated that the implemented transmitter can emulate 10–40”-long microstrip lines on an FR4 grade material with a peak error less than 12.5% in the pulse response.