Current-Mode Receivers

Abstract

The main function of a serial link receiver consists of : (i) Impedance matching - provide a broadband matching impedance to the channel to minimize the reflection at the far end of the channel. Receiver-end impedance matching is more critical than transmitter-end impedance matching because perfect receiver-end impedance matching will reduce the time interval between two adjacent symbols to one delay time of the channel. (ii) Pre-amplification - the received signal is usually amplified prior to signal processing. Because the transmitted signals are broadband, an amplifier with large bandwidth, a low noise figure, and a sufficient gain is required. Pre-amplification is particularly critical for optical communications where the current from photo-diodes is small. For serial and parallel data communications, pre-amplification is usually replaced with samplers whose regenerative amplification stage provides the needed gain. (iii) Clock and data recovery - timing information of the incoming data is recovered from the transition of the received data. Once the edges of a data eye is allocated, the data eye is sampled at its center to recover data. The operation of clock and data recovery is controlled by a multi-phase clock generated using either a DLL or a PLL.