An Analysis of Data Bus Inversion: Examining Its Impact on Supply Voltage and Single-Ended Signals

The DBI function is applied to DDR4 and LPDDR4 to reduce I/O power in system memory. In addition to power savings, this feature also directly improves the power -supply noise by constraining the number of bits simultaneously drawing dc current. A comparison of PDN noise, with and without DBI enabled for VDDQ, VDDQ/2, and VSS termination schemes, shows measurable power noise improvement to the system, with some dependence on the particular termination scheme. Measurements were performed to validate the effectiveness of the DBI function in reducing the droop voltage, phase noise, and jitter for a test system driven by an FPGA device. A DDR4 system with DBI functionality was employed to demonstrate and quantify the performance improvement. Through this process, the application of DBI was shown to be an effective method to enhance multiple key aspects of the signaling and a key enabler of the ongoing success of these single -ended memory interfaces.