Method for period counting using a tunable oscillator

#The invention generally relates to the use of digital electronics to accurately produce and measure the period or frequency of an electrical signal. More specifically, the invention relates to a method and system for period counting using a tunable oscillator without an additional reference oscillator.

#Electronic circuits may sometimes require the use of a very stable and accurate electronic oscillator in order to measure the period or frequency. Period counting (or, equivalently, frequency measurement) is necessary for providing very accurate timing or phase locking in a feedback loop. Oscillators are used for other applications, such as for transmitting and receiving an electronic signal or for producing an accurate waveform, but these applications do not always require a high degree of stability and accuracy.

#Typically, an electronic circuit designed for an application that requires a stable and accurate oscillator will use a Quartz crystal oscillator as a reference oscillator. In its crystalline form, Quartz exhibits the special property of piezoelectricity: when pressure is applied to a Quartz crystal, there will be a change in an electrical voltage that is measured at the surface of the Quartz crystal. Conversely, an applied electric voltage may cause the Quartz crystal to physically deform. When a Quartz crystal is cut and polished, it will vibrate at a single specific frequency as an electric field is applied through electrical contacts plated onto its surface.

#The foregoing and other objects, advantages, and features of the present invention will be apparent from the following detailed description and the accompanying drawings, in which:

#FIG. 1 is a block diagram showing prior art in period counting, and the use of a Quartz crystal as reference oscillator; and

#FIG. 2 is a block diagram of the electronic components of the improved system for period counting, in accordance with an embodiment of the present invention.

#While the present invention is susceptible to various modifications and alternative forms, certain preferred embodiments are shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the description is not intended to limit the invention to the particular forms described; to the contrary, the description is intended to cover all modifications, alternatives, and equivalents falling within the spirit and scope of the invention defined by the appended claims.

#As mentioned above, it is known to those of ordinary skill in the art that the accuracy and speed of low frequency measurements may be improved by counting the period of the signal rather than its frequency. It is easy to find the frequency of a signal once its period is known: the frequency is simply the inverse of the period (period=1/frequency). For the following discussion of the related art, it may be helpful to refer to the following text: Horowitz, P. The Art of Electronics, N.Y., Cambridge University Press, 2001, p. 1019-1022.

#Referring to FIG. 1, there is shown a block diagram of the prior art in period counting with a Quartz crystal reference oscillator. The input signal to be measured is shown in FIG. 1 and FIG. 2 as originating with a device under test (or “DUT”). An N-divider 10, which might be constructed from one or more flip-flops or from programmable digital logic, is used to increase the length of the period of the input signal by a factor N. In an embodiment, the factor N might be selected by a user, for example, with a switch. With the reference frequency for the period counter fixed, increasing the factor N increases the length of the measurement time and increases the resolution of the measurement; decreasing the factor N decreases the length of the measurement time and decreases the resolution of the measurement. In this manner, a user of this system may balance the desired accuracy for his or her measurement with the amount of time necessary for the measurement to be completed.