Poly-phase VCO with rail to rail output voltage swing and duty cycle control across tuning range

An even number phase ring oscillator having at least eight equally-spaced phases, comprising:

• at least eight stages, defining at least four pairs of stages, with each pair including a first stage and an associated second stage, each stage having a primary input and an output, such that when eight stages are provided, the output of the first stage of the first pair defines the primary input of the first stage of the second pair, and the output of the first stage of the second pair defines the primary input of the first stage of third pair, and the output of the first stage of the third pair defines the primary input of the first stage of the fourth pair, the output of the first stage of the fourth pair defines the primary input of the second stage of the first pair, the output of the second stage of the first pair defines the primary input of the second stage of the second pair and the output of the second stage of the second pair defines the primary input of the second stage of the third pair and the output of the second stage of the third pair defines the primary input of the second stage of the fourth pair, with the output of the second stage of the fourth pair crossing over the output of the first stage of the fourth pair and defines the primary input of the first stage of the first pair, thereby defining a closed loop,
• a first cross connection between an output of each first stage of each pair and an input of each associated second stage, and a second cross connection between an input of each first stage of each pair and an output of each associated second stage, thereby ensuring that the oscillator provides an odd number inversions around the loop, and
• a feed forward connection between and input of each (n) stage and an output of each (n+2) stage, with (n) being any one of the stages, so as to provide a feed forward input to each stage to increase a speed at which an output of each stage switches,
• wherein two bias inputs are provided to control a strength of N pull-down and P pull-up of each stage.

A method of providing an even number phase ring oscillator having at least eight, equally-spaced phases, the method including:

• providing at least eight stages constructed and arranged to define a primary oscillation closed loop, and to ensure that an odd number inversions is provided around the closed loop although one inversion occurs in each stage,
• providing a feed forward connection between an input of each (n) stage and an output of each (n+2) stage, with (n) being any one of the stages,
• feeding an input to each stage via each feed forward connection to increase a speed at which an output of each stage switches, and
• providing two bias inputs to control a strength of N pull-down and P pull-up of each stage.