Fish & Richardson P.C.
Current mode I/O for digital circuits
 A digital input/output interface for use with two digital circuits connected by a transmission line having a characteristic impedance Z.sub.0 includes a current driver in one of the digital circuits and a current receiver in the other digital circuit. The current driver is configured to generate a current in the transmission line when a digital signal is applied to the current driver. The current receiver includes a current conversion element connected to the transmission line at an input node through an input impedance Z.sub.in and adapted to convert the current in the transmission line into an output voltage, and an active termination element configured to actively adjust the input impedance Z.sub.in to match the characteristic impedance Z.sub.0 of the transmission line. An impedance transforming receiver for use with a transmission line having a small characteristic impedance Z.sub.0 and carrying a relatively small current mode signal includes the following: an input element connected to the transmission line and configured to receive the small current mode signal, the input element having a small input impedance Z.sub.in that substantially matches the characteristic impedance of the transmission line; and a high impedance output element adapted to convert the small current mode signal into an output binary voltage having a noise margin large enough for digital communication. 
The Regents of the University of California
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Stephen I. Qi
Long Zhang