Current source and threshold voltage generation method and apparatus for

Abstract

A current source and threshold voltage generation circuit generates a current, through a ratio of devices, and a corresponding threshold voltage signal, to be utilized by a timing circuit for generating a timing ramp and determining when the timing ramp crosses the threshold voltage signal. The current is generated through a current generation circuit, using a ratio of matched devices. Preferably, the matched devices are transistors. The current is then utilized by a timing circuit to charge a charge storage device to a level above the level of the threshold voltage signal. The current is also mirrored, appropriately increased and used to generate the threshold voltage signal which is compared to the charge stored on the charge storage device. Accordingly, any errors in the generation of the current are also reflected in the level of the threshold voltage signal, thereby eliminating the potential for errors in the timing ramp signal generated by the timing circuit. Preferably, the charge storage device is a capacitor and the timing circuit is an HHK video circuit. The preferred embodiment of the current source and threshold voltage generation circuit is implemented within an integrated circuit and does not require any external components.