Dual edge pulse width modulation system

DETAILED DESCRIPTION What is claimed is: 1.
A dual edge pulse width modulation system comprising: a ramp generator for generating a voltage ramp; an n bit digital to analog converter having a normal and an inverted output for establishing a leading edge and a trailing edge reference; comparator means, responsive to said ramp and to said leading edge and trailing edge references, respectively, for defining the leading edge and the trailing edge of a pulse; and pulse generating means for producing a pulse having the width determined by the defined leading and trailing edge.
2.
The dual edge pulse width modulation system of claim 1 further including control means for providing an operating current through said digital to analog converter to establish one of said leading and trailing edge references on one of said normal and inverted outputs and providing a bias current approximately equal to said operating current to establish the other of said leading and trailing edge references on the other of said normal and inverted outputs for enabling production of a pulse up to the full n bit width definable by said digital to analog converter without crossover of said leading edge and trailing edge references.
3.
The dual edge pulse width modulation system of claim 2 in which each of said currents is capable of establishing a voltage level at said outputs equivalent to approximately one half of the full n-bit capacity of said digital to analog converter.
4.
The dual edge pulse width modulation system of claim 2 in which said bias current is slightly greater than said operating current to prevent coincidence of said leading and trailing edge references.
5.
The dual edge pulse width modulation system of claim 2 in which said control means includes an operating current source and a bias current source.
6.
The dual edge pulse width modulation system of claim 5 in which said control means further includes switching means for connecting said bias current source in parallel with said operating current source for enabling provision of a total current up to the full n-bit capacity of said digital to analog converter