A scannable fast domino output latch is provided. A scannable latch circuit includes a scan logic receiving a scan data input and a scan data clock. The scannable latch circuit includes a transistor stack receiving a data input and receiving a system clock. A first inverter is connected to the transistor stack. The first inverter provides a latch output. A feedback path logic is connected across the first inverter. The feedback path logic is activated responsive to both the system clock and the scan data clock. Improved performance is provided by eliminating the transfer gate and active feedback from the critical path of the scannable latch circuit. The feedback path logic is activated when both the system clock and the scan data clock are low.
A latch has a first mode in which the latch functions as a dynamic latch and a second mode in which the latch functions as a static latch. The latch has a feedback circuit that in turn has two parallel switchable loads. The first load is responsive to a data input signal of the latch in the first mode and disabled in the second mode. The second load is responsive to a clock signal in the second mode and disabled in the first mode. The switchable loads being in parallel provides for the ability to select the feedback that is better for the particular mode of operation. The first and second switchable loads can be optimized for the particular mode of operation that will use it.
A latch device having a selectable feedback path includes a retaining device and system isolation device. The retaining device retains within the feedback path a logical value to be written out. The logical value is latched during an active clock signal. The system isolation device disconnects the retaining device from the feedback path during a write operation. Then, when the logical value is written out, the system isolation device reconnects the retaining device. Thus, the feedback path of the latch device may be disconnected to allow for a change in the latch state without overdriving a feedback inverter.
