On-die termination resistors with analog impedance control for standard CMOS technology

We have designed a new voltage-controlled resistor for the purpose of on-die termination in standard CMOS technology. Current-voltage (I-V) characteristics show that this on-die termination resistor has good linearity across a wide range of gate bias, and is suitable for an analog impedance control technique using a feedback loop. The analog impedance control technique has the advantage of continuous impedance adjustment without interfering with normal data transmission and receiving operations. Experimental I-V characteristics show excellent linearity and are in good agreement with simulations. Measured resistance values are within ±5% over process, temperature, and across die variations.