First bit data eye compensation for open drain output driver

摘要

An open-drain output circuit for a semiconductor device is provided with a mechanism for compensating for variations in the length of time that the driver circuit presents valid data at an output terminal of a semiconductor device. In one embodiment, the valid data “data eye” for the driver circuit is reduced for the first bit following extended turn-off of the driver circuit as compared with the valid data eye for subsequent bits, a “first bit data eye phenomenon.” To compensate for the first bit data eye phenomenon, circuitry is provided for causing the driver circuit to turn on earlier when the driver circuit has previously been off for relative to when the driver circuit has not been off for. In one embodiment, the compensation circuitry comprises circuitry for assessing the voltage level present on a specified node in the driver circuit, where that voltage level is indicative of the length of time that the driver circuit has been turned off. The voltage level is fed back to a pre-driver circuit which provides a pre-driver output signal to the output circuit in response to data read input signals. In one embodiment, the pre-driver circuit asserts its output after a delay interval following assertion of the data read input signal, and the length of that delay interval is determined by the voltage level on the specified node in the driver circuit.