Oscillators – Automatic frequency stabilization using a phase or frequency... – Plural a.f.s. for a single oscillator
Reexamination Certificate
2000-02-29
2001-08-14
Grimm, Siegfried H. (Department: 2817)
Oscillators
Automatic frequency stabilization using a phase or frequency...
Plural a.f.s. for a single oscillator
C331S017000, C331S025000
Reexamination Certificate
active
06275115
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of The Invention
The present invention relates generally to a PLL circuit.
2. Description of The Prior Art
Typically, a PLL circuit comprises: a phase comparator for comparing the phase of a reference input clock signal F
ref
, which is supplied from the outside, with the phase of an internal clock signal F
vco
to output a phase difference signal; a loop filter for receiving the phase difference signal to output a control voltage V
cnt
; and a voltage control oscillator for outputting the internal clock signal synchronized with the reference input clock signal in accordance with the control voltage V
cnt
.
In such a conventional PLL circuit, the output (oscillating frequency) F
vco
of a voltage control oscillator varies in accordance with the control voltage V
cnt
outputted from the loop filter. In order to remedy the irregularity in process for the PLL circuit to enhance the product yield, the variable range (operating frequency range) of the oscillating frequency F
vco
, of the voltage control oscillator is desired to be wider. In order to increase the variable range of the oscillating frequency F
cnt
, it is required to enhance the gain of the voltage control oscillator. In this case, the variation in the oscillating frequency F
vco
to the unit variation in the control voltage V
cnt
increases, so that there is a problem in that the frequency variation due to noises increases.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a PLL circuit capable of extending the operating frequency range and of controlling the frequency variation due to noises.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, a PLL circuit comprises: a phase comparator for comparing the phase of an input signal with the phase of a reference input signal to output a signal according to the phase difference therebetween; a low pass filter for outputting a low frequency control voltage on the basis of the output of the phase comparator; a voltage control oscillator for controlling ani oscillating frequency on the basis of the control voltage; and a characteristic control part for controlling the characteristic of oscillating frequency to control voltage of the voltage control oscillator on the basis of n+
1
ranges of first through n+
1
-th ranges obtained by dividing a variable range of the control voltage by first through n-th (n≧
2
) thresholds which are different from each other.
The characteristic control part preferably comprises: a voltage comparator for determining which range of the first through n+
1
-th ranges the control voltage belongs to, by comparing the control voltage with the first through n-th thresholds; and an additional current generating part for generating an additional current on the basis of the output of the voltage comparator, wherein the characteristic of the voltage control oscillator is controlled on the basis of the additional current.
The voltage control oscillator preferably comprises: a voltage-to-current converter for converting the control to a current; and a current control oscillator for controlling the oscillating frequency on the basis of the sum of the output of the voltage-to-current converter and the additional current.
The number n of the thresholds may be 2, the first threshold may be lower than the second threshold, and the voltage comparator may perform the analog-to-digital conversion of the output of the low pass filter, the voltage comparator outputting a signal having a value of “−1” when the AD converted control voltage is lower than the first threshold and belongs to the first range, a signal having a value of “0” when the AD converted control voltage is not lower than the first threshold and lower than the second threshold and belongs to the second range, and a signal having a value of “1” when the AD converted control voltage is higher than the second threshold and belongs to the third range.
The additional current generating part may have a memory for adding the output of the voltage comparator to a value stored therein, to update the added result to output the updated value as a code, the additional current generating part generating the additional current on the basis of the code outputted from the memory.
REFERENCES:
patent: 5382922 (1995-01-01), Gersbach et al.
patent: 5384502 (1995-01-01), Volk
patent: 5459653 (1995-10-01), Seto et al.
patent: 5504459 (1996-04-01), Gersbach et al.
patent: 3-206726 (1991-09-01), None
Grimm Siegfried H.
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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