Oscillators – Automatic frequency stabilization using a phase or frequency... – Particular frequency control means
Reexamination Certificate
2000-06-16
2002-02-05
Mis, David (Department: 2817)
Oscillators
Automatic frequency stabilization using a phase or frequency...
Particular frequency control means
C331S10800D, C331S135000, C331S17700V, C360S051000
Reexamination Certificate
active
06344778
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-173014, filed Jun. 18, 1999; and No. 2000-160191, filed May 30, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a voltage-controlled oscillator capable of changing an oscillation frequency according to a control voltage or a control current, and a phase synchronization circuit and a signal processing circuit using the voltage-controlled oscillator. The invention relates to a voltage-controlled oscillator, a phase synchronization circuit and a signal processing circuit that are used, for example, in an information processing field such as a communication device, a hard disk driving unit, and an information storage device like an optical disk.
In a communication device or an information storage device, a phase synchronization circuit (or a phase-locked loop; PLL) has been used for extracting a clock signal to discriminate received data or reproduced data. As one of basic construction blocks of this PLL, there has been used a voltage-controlled oscillator (VCO) that has a function of changing an oscillation frequency according to a control voltage or a control current. It is general that a PLL including a VCO is constructed on the same LSI chip by combining the PLL with other functional block like an equalizer.
As a conventional VCO that is used in an information storage device, a multi-vibrator type circuit utilizing a charge and discharge to and from a capacitor has been used. The oscillation frequency of the multi-vibrator type VCO depends on three parameters including a capacity of the capacitor, charge and discharge currents of the capacitor, and a voltage between both terminals of the capacitor. Usually, in many cases, the oscillation frequency is controlled based on either the voltage between both terminals of the capacitor or the charge and discharge currents, with the capacity of the capacitor set constant.
According to the conventional multi-vibrator type VCO, the oscillation frequency of the VCO is controlled based on the voltage. Circuit noise attributable to voltage can be easily mixed into a control input voltage. Therefore, the oscillation frequency is easily affected by the noise due to voltage. As a result, there has been a problem that the oscillation frequency of the VCO is unstable against crosstalk noise, and it is difficult to achieve a stable oscillation. Further, there has been a problem that the oscillation frequency is also easily affected by crosstalk from other circuit blocks constructed within the same LSI chip, which makes the oscillation frequency unstable.
The above problems lead to an extreme aggravation of the performance of the device using a PLL including the conventional multi-vibrator type VCO. For example, an error rate is worsened in the information storage device.
On the other hand, as shown in
FIG. 1
, there has been an analog VCO consisting of a filter
301
and an automatic gain control (AGC) circuit
302
. The AGC circuit
302
provides a positive feedback of an output signal of the filter
301
to an input side of the filter by controlling the output signal at a constant level. This VCO is disclosed, for example, in Japanese Patent Application Laid-open Publication No. 9-326636. The analog-type VCO using the filter has characteristics that the VCO is not easily affected by noise due to voltage, and is not easily affected by crosstalk noise from other circuit blocks.
However, the analog-type VCO using the filter has a problem in that the AGC circuit
302
has a complex construction. Further, the operation frequency area is limited to a low level based on the construction of the filter
301
and a amplitude detector
303
for detecting an output level of the AGC circuit
302
. For example, an envelope-detection type amplitude detector as disclosed in Japanese Patent Application Laid-open Publication No. 9-326636 cannot accurately detect a signal in a high-frequency area, particularly, a signal exceeding a few hundred MHz. Therefore, a VCO using this amplitude detector cannot stably oscillate a signal exceeding a few hundred MHz. The data transfer speed of a device using a VCO has been increasing in recent years, and it is difficult to meet future demand for such high transfer-speed based on the conventional VCO.
As explained above, the analog-type VCO using the filter has the problems that the AGC circuit has a complex construction, and that the operation frequency area is limited to a low level by the construction of the filter and the amplitude detector of the AGC circuit.
In recent years, it is general that a waveform equalization filter is constructed on the same integrated circuit chip as that of a preamplifier and a PLL. When a filter is constructed on the integrated circuit chip, the characteristics of the chip are determined by the capacity of the capacitor constructed on the integrated circuit chip and the volume of a current flown through the capacitor.
In this case, the capacity of the capacitor constructed on the integrated circuit chip has a variance of plus minus 15%, which leads to a fluctuation in the frequency characteristics of the waveform equalization filter. As a result, equalization errors occur. Therefore, it has been desired to realize a filter having a frequency characteristic compensation function with high precision of frequency characteristics.
Consider a case where an active filter used for equalizing a reproduction signal and a PLL are structured together on the same LSI chip in a signal regenerating unit such as, for example, a hard disk driving unit, an optical disk driving unit, a data tape driving unit, etc.
When a signal reproduction speed of a signal generator has changed, it is usually necessary to optimize the cutoff frequency of the active filter according to this change. Further, it is also necessary to change the oscillation frequency and response characteristics of the PLL according to the change in the signal reproduction speed.
As described above, when the conventional PLL and the active filter for equalizing a reproduction signal are structured together on the same LSI chip, the active filter and the PLL are adjusted independent of each other. Therefore, these adjustments have had a problem of extremely lowering the productivity in the manufacturing process.
BRIEF SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a voltage-controlled oscillator that can be easily realized in an integrated circuit in a simple construction without an AGC circuit, and that makes it possible to supply a low-cost product. This object is to be achieved by arranging such that a delay-time variable filter controls a delay time according to a control signal input, and an output signal of the delay-time variable filter is changed into a binary pulse signal, and this signal is positively fed back to the input side of the delay-time variable filter at a desired level.
It is another object of the present invention to provide a voltage-controlled oscillator that can stably oscillate a signal in excess of a few hundred MHz, that can be easily realized in an integrated circuit, and that makes it possible to supply a low-cost product by inventive constructions of a filter and an amplitude detector of an AGC circuit. This object is to be achieved by a system in which a delay-time variable filter controls a delay time according to a control signal input, and an output signal of the delay-time variable filter is controlled at a constant level by an AGC circuit and is positively fed back to the input side of the delay-time variable filter.
It is still another object of the present invention to provide a phase synchronization circuit capable of generating a clock signal of high quality in a stable operation.
It is still another object of the present invention to provide a signal processing circuit capable of canceling aggravation in the characteristics
Goto Nobuyasu
Hashimoto Masaru
Nakamura Norio
Omi Katsuyuki
Shiramatsu Toshio
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