US 5,036,216 A · Video dot clock generator

Abstract

A video dot clock generator includes a phase-locked loop (PLL) which includes a voltage controlled oscillator, a frequency divider, a phase comparator and a loop filter. The voltage controlled oscillator (VCO) is programmable to provide multiple frequency ranges for a given range of control voltages applied to the oscillator. The programming affects both the frequency range and the gain of the VCO. The phase comparator includes circuitry which simulates a predetermined minimum phase error which, when compensated for, substantially eliminates jitter in the dot clock signal. The frequency divider used in the PLL and a similar frequency divided used to generate the reference signals for the phase comparator are programmable via an internal memory which also holds programmable control signals for the VCO. The memory, in turn, may be programmed by the user to achieve desired frequency and loop again characteristics for a given application.

Claims15

Dependent claims

Apparatus for use in generating multiple clock signals, comprising:

a source of reference oscillatory signal;
first frequency dividing means for dividing said reference oscillatory signal in frequency by an amount determined by a first control signal;
variable oscillator means having a control input terminal and responsive to a second control signal applied thereto for generating a variable frequency oscillatory signal;
second frequency dividing means for dividing said variable frequency oscillatory signal, in frequency, by an amount determined by a third control signal;
phase comparison means for producing an output signal representing the difference in phase between the respective output signals of said first and second frequency dividing means and being responsive to a fourth control signal for producing said output signal indicating no difference in phase, irrespective of the output signals of said first and second frequency dividing means;
means coupling the output signal of said phase comparison means to the control input terminal of said variable oscillator means;
and
control means, for generating said first, third and fourth control signals to change the frequency of the signal provided by said variable oscillator means.

5 more elements

Apparatus for use in generating multiple clock signals, comprising:

a source of reference oscillatory signal;
variable oscillator means, having a control input terminal and responsive to a frequency control signal applied thereto for generating a variable frequency oscillatory signal;
phase comparison means for producing an output signal representing a variance from a predetermined phase relationship between said reference oscillatory signal and said variable oscillatory signal, said phase comparison means comprising:
phase detecting means for producing a first pulse signal having a pulse width representing the difference in time between the occurrence of corresponding predetermined transitions of said reference oscillatory signal and said variable oscillatory signal, respectively;
means, responsive to one of said reference oscillatory signal and said variable oscillatory signal for producing a second pulse signal having a substantially fixed pulse width on the occurrence of the predetermined transition of said one signal;
and
means for combining said first and second pulse signals in a manner allowing said second pulse signal to substantially cancel said first pulse signal when said reference oscillatory signal and said variable oscillatory are in said predetermined phase relationship.

4 more elements

Apparatus for use ian generating multiple-clock signals, comprising:

a source of reference oscillatory signal;
variable oscillator means, having a control input terminal and responsive to a frequency control signal applied thereto for generating a variable frequency oscillatory signal, said variable oscillator means including further means, responsive to a further control signal, for changing the range of frequencies of the variable oscillatory signal that are produced in response to a predetermined range of values of said frequency control signal;
and
phase comparison means for producing an output signal representing a variance from a predetermined phase relationship between said reference oscillatory signal and said variable oscillatory signal.

1 more element

Dependencies are inferred from the claim text.

Video dot clock generator

Life of this patent

Video dot clock generator

Life of this patent

Abstract

Claims15