ODT calibration is a technique that involves calibrating the termination impedance in order to optimize the reduction of signal reflections. ODT calibration allows an optimal termination value to be established that compensates for variations in process and operating conditions.
A calibrated ODT value significantly reduces unwanted signal reflections while only minimally attenuating the magnitude of the signal swing due to the added resistive loading. The resulting cleaner data signal allows for higher data rates.
ODT calibration is achieved by establishing an ODT impedance that is proportional to an external precision resistor. The same external resistor can also be used for Output Driver Calibration.
The ODT calibration controller, compares the voltage drop across the ODT resistor network with a voltage drop across an external resistor represented. The controller modifies the resistor network with coarse tuning and fine tuning to achieve an impedance value that closely approximates the external, reference resistance.
ODT calibration delivers benefits at the device, subsystem and system level. By implementing ODT calibration, devices are able to achieve enhanced signal performance and higher data rates, which enables designers to achieve superior DRAM device and module performance.
In addition, placing the termination components on the DRAM devices removes these elements from the PCB. In doing so, the number of components and signal lines on the motherboard is reduced, lowering the cost and complexity while increasing reliability.
Finally, the system benefits from the superior data rates and module performance that are enabled through the improved signal integrity achieved with ODT calibration.