Flip-flop with input and output select and output masking that enables low power scan for retention

Abstract

A flip-flop including a scan enable input for receiving a scan enable signal, a clock input for receiving a clock signal, input select circuitry that is configured to select between a data input and a scan input based on a state of the scan enable signal for providing a selected input, latching circuitry that is configured to latch the selected input to a preliminary output node in response to transitions of the clock signal, and output select circuitry that is configured to provide a state of the preliminary output node to a selected one of a scan output and a data output based on a state of the scan enable signal. The flip-flop may be implemented using fast yet leaky transistors. The data output may be disabled to prevent toggling other circuitry when scanning into or out of a memory for data retention.