Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Regenerating or restoring rectangular or pulse waveform
Patent
1996-05-22
1998-07-28
Ton, My-Trang Nu
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Regenerating or restoring rectangular or pulse waveform
327170, 327176, H03K 3017
Patent
active
057867186
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and device for symmetrizing a clock signal.
2. Background
Various components such as microprocessors have strict quality requirements regarding the symmetry of the pulse ratio of the clock signal they used, especially in operating near the upper frequency limit specified for their components.
The symmetrization of a clock signal can be carried out automatically using a regulator comprising a feed-back loop. In a known (e.g. U.S. Pat. No.4,959,557) device, a clock signal is applied as AC-coupled via a low pass filter to a buffer circuit, from the output of which a symmetrized clock signal is obtained. The regulation of the pulse ratio is implemented by feeding the output signal of the buffer circuit to an integrator, from which a DC voltage proportional to the pulse ratio of the signal is obtained. This voltage is compared with the desired set value voltage of the pulse ratio in an amplifier, which produces a control voltage on the basis of the measured and the set-value voltage. This control voltage is passed as a bias voltage to the same input of the buffer circuit where the clock signal to be symmetrized has also been passed. The trigger level, which the buffer circuit detects in the incoming clock signal, is controlled by the bias voltage .
Since the leading and trailing edges of the incoming clock signal have been graded by the low pass filter, the pulse ratio of the output signal of the buffer circuit also changes as the bias voltage changes. The controller seeks to find such a trigger level from the incoming clock signal above and below which level the durations of the clock signal states are equally long.
The pulse ratio of commercially available conventional crystal oscillators is normally promised to be about 40/60. If a better pulse ratio is desired, the price of the oscillator goes up considerably. If the pulse ratio is adjusted manually, the productional testing costs of the manufactured device increase.
The disadvantages of the known device based on a feedback control loop are the following:
it restricts the pulse ratio of an incoming signal, whereby the device seeks to find such a trigger level from the incoming signal above and below which level the periods of the signal are equally long. If the pulse ratio of an incoming signal is sufficiently poor, this kind of trigger level will not be found.
the accuracy of adjustment is dependent on the pulse ratio of an incoming signal.
both edges of the clock signal produced by the device are in random phase with respect to the phases of the edges of an incoming clock signal, i.e. it is not possible to use the device in decentralized applications, in which the phase of either edge of an incoming clock signal has to be maintained.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and device for symmetrizing a clock signal without the above-mentioned restrictions and disadvantages. To achieve this, the method of the invention is characterized in that the leading or trailing edge of each pulse of the clock signal to be symmetrized is used for forming the first edge of the pulse of the corresponding symmetrized clock signal; the pulse ratio of the symmetrized clock signal is measured; and on the basis of the measured pulse ratio, the time constant circuit determining the location of the second edge of the pulse of the symmetrized clock signal is adjusted by means of a control loop in such a manner that the second edge of the pulse of the symmetrized clock signal settles in a desired position in the symmetrized clock signal.
By means of the method according to the invention, it is possible to symmetrize even a clock signal with a poor pulse ratio so as to be suitable for use in applications of critical timing. The implementation of the device of the invention is simple. The restrictions of the solution based on a known controller have been obviated by forming one edge of the symmetrized clock signal directly from the clock s
REFERENCES:
patent: 4449102 (1984-05-01), Frazer
patent: 4959557 (1990-09-01), Miller
patent: 5144645 (1992-09-01), Schiffmann
Nokia Telecommunications Oy
Nu Ton My-Trang
LandOfFree
Method and device for symmetrizing a clock signal does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for symmetrizing a clock signal, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for symmetrizing a clock signal will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-25827