Differential controlled delay elements and skew correcting detector for delay-locked loops and the like
AssigneeAT&T Bell Laboratories
InventorJeffrey L. Sonntag
Life of this patent
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Abstract
A fully differential variable delay element for providing precision delays for use in digital phase-locked loops or the like. The delay in each stage is controlled by changing bias currents and the coupling of a capacitance load thereto, therby reducing the sensitivity of the delay element to electrical noise at low bias current levels (long delay times). Included is a circuit which substantially removes any skew in the differentially delayed signals from the delay element.
Claims12
A variable delay element with an input and an output, formed in an integrated circuit, for delaying signals, the delay varying in response to a control signal, having:
- a first capacitive means;
- and
- a first variable coupling means, having an output coupling to the output of the variable delay element, for variably coupling the output of the variable delay element to the first capacitive means in response to the control signal;
- wherein the delay element is characterized by:
- the first capacitive means having first and second capacitors and the first variable coupling means having first and second transistors of opposite conductivity types, connected between corresponding first and second capacitors and the output of the first variable coupling means;
- wherein the delay of the variable delay element is dependent on the control signal and the amount of coupling by the first variable coupling means, such that the amount of coupling varies proportionally with the desired delay of the variable delay element.
A skew corrector for substantially removing skew in differential digital signals, characterized by:
- a flip-flop stage having first and second power terminals and having first and second inputs;
- a driver stage having first and second power terminals and having outputs coupling to the first and second inputs of the flip-flop stage;
- a first pair of resistors coupling between corresponding first and second power sources and corresponding first and second power terminals of the flip-flop stage;
- and,
- a second pair of resistors coupling between the corresponding first and second power sources and corresponding first and second power terminals of the driver stage;
- wherein the resistances of the resistors of each pair are substantially the same.
Dependencies are inferred from the claim text.