Programmable logic and driver circuits.

摘要

An output driver circuit is described which can be programmed by the user into tri-state or open-collector configurations, depending on the needs of the user. The driver circuit comprises a pair of a first pull-up (24) and a pull-down (26) FET transistor. The source of the pull-up transistor (24) and drain of the pull-down transistor (26) are both connected to the output of the driver. The gates of the pair of transistors are controlled by an input signal and its complement. The driver further includes a second pull-up FET (76) whose source is conntected to the output of the driver. The channel width to channel length ratio of the second pull-up transistor is at least about an order of magnitude greater than that of the first pull-up transistor. The driver further includes a control means (74) responsive to the input signal for applying a second signal to the gate of the second pull-up transistor for programming the driver into tri-state or open-collector modes. The driver circuit may be controlled by the output of an OR gate in an AND-OR array in a FPLA or PAL device. The driver is programmable by programming the AND gate or OR gate array and applying selected input signals to the AND gate array; the driver can also be programmed permanently into the tri-state or open-collector mode. <IMAGE>