Voltage reference and current source for video DAC

摘要

There is disclosed a circuit and method for providing a reference voltage to a matrix array of video DAC cells. The circuit is located substantially within a center of the matrix array in order to minimize any effects upon the delivered reference voltage that process variations within the integrated circuit supporting the video DAC may produce. The center location minimizes the average distance between the voltage reference circuit and each of the DAC cells within the matrix array. In a preferred embodiment, the circuit is divided so that a reference voltage supplied by one portion of the circuit is unaffected by inherent capacitances within the MOSFET devices utilized within the circuit coupling that voltage reference to the other reference voltages supplied by the second portion of the circuit. In another preferred embodiment, the circuit is supplied with a current from an external current source, the external current produced by an external voltage and an external precision resistor whereby the external current is regulated by comparing the external voltage to a second reference voltage produced by the external current, wherein the regulation of the external circuit is accomplished with a circuit utilizing an N-channel device in order to reference the external current to ground and not to a noisy voltage supply.