Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By frequency
Reexamination Certificate
2001-12-21
2003-07-22
Ton, My-Trang Nu (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By frequency
Reexamination Certificate
active
06597205
ABSTRACT:
TECHNICAL FIELD
The present invention is generally related to frequency measurement methods and systems. The present is also related to pulse signal measurement methods and systems. The present invention is additionally related to timer clock and crystal controlled oscillator devices. The present invention is additionally related to frequency measurement circuits.
BACKGROUND OF THE INVENTION
The frequency measurement of a periodic pulse signal can be defined as the average number of pulses evaluated over a time period. In a typical micro controller, a crystal-controlled oscillator can generate a timer clock, which is utilized as a reference for the measurement. The accuracy of the timer clock is very accurate. The actual measurement of the pulse signal, however, can introduce unacceptable accuracy. For some measurement techniques that are accurate at high frequencies, the low frequency measurements are inaccurate. Other methods that are inaccurate at low frequencies can be prone to be inaccurate at high frequencies.
FIG. 1
depicts a prior art timing diagram
10
illustrating a pulse count over a fixed period. One technique for calculation involves counting the number of pulses that occurred over a fixed period of time. In such a technique, as illustrated in
FIG. 1
, a timer and a counter can be initiated simultaneously. The timer is set to expire after a predetermined amount of time. The counter can count the number of pulses that occur while the timer is enabled. When the timer terminates, the counter will stop. The number of counts that occurs at the end of the period is divided by the time period to determine frequency. As indicated in timing diagram
10
of
FIG. 1
, a pulse input signal
12
indicates the number of pulses that occur a fixed measurement period
16
, while a timer clock
14
(i.e., timer) runs over the fixed measurement period
16
. In general, the percent accuracy of this measurement technique can be determined by the following formulation of equation (1):
Percent
Accuracy
=
100
%
×
2
Number
Pulse
Counted
(
M
)
(
1
)
Additionally, frequency can be determined according to the formulation indicated in equation (2):
Frequency=Number of Pulses/Time Period (2)
The approach illustrated in
FIG. 1
is limited because the first and last pulses that are counted are not synchronized to the measurement timer clock
14
. This can result in an error of up to two pulse times. At high frequencies, this may be insignificant because at a high frequency, the number of pulses counted over a measurement period is very large and an error of two pulses is relatively small. At lower frequencies, the number of pulses counted becomes proportionally smaller. As a result, the accuracy of the measurement decreases as the frequency decreases. At frequencies close to the sample period, accuracy can exceed 100%.
FIG. 2
illustrates a prior art timing diagram
20
illustrating pulse time measurement for a fixed number of pulses. In the approach illustrated by timing diagram
20
of
FIG. 2
, the time between one or more pulses is measured. Timing diagram
20
depicts a timer clock
26
and a pulse input signal
24
. A time period
22
extends over a range of pulses generated by pulse input signal
24
. The technique illustrated in
FIG. 2
can solve the low frequency inaccuracy inherent with the method discussed above with reference to FIG.
1
. In the method illustrated in
FIG. 2
, however, a timer (i.e., timer clock
26
) is initiated by an enable signal that is triggered at the rising edge of an input pulse. A counter can then be used to count a particular number of pulses. After a predetermined number of pulses have been counted, a trigger generated by the rising edge of the next input signal disables the timer. In general, timing diagram indicates that the timing measurement takes place for a fixed number of pulses. Percent accuracy can be calculated according to the formulation of equation (3):
Percent
Accuracy
=
100
%
×
Input
Frequency
Timer
Frequency
(
3
)
The measurement method illustrated in
FIG. 2
permits the pulse input frequency to be determined by dividing the number of pulses (which is a constant) by the measurement time period. Frequency can be determined according to the following formulation of equation (4):
Frequency
=
(
Sample
Clock
Rate
)
×
Number
of
Pulses
(
M
)
Measured
Time
Period
(
N
)
(
4
)
where
M=Set Number of Pulses (Constant)
N=Number of Clock Pulses that Elapse
The method illustrated in
FIG. 2
provides good accuracy at lower frequencies where the pulse count is small compared to the timer clock frequency. In order to make low frequency measurements in a reasonable amount of time, the number of pulses that are counted is relatively small. For example, in order to measure a 10 Hz signal at least once every 200 milliseconds, a pulse count of 2 can be used. This is fine for low frequencies; however, at a higher frequency this small number of pulses can result in inaccuracy caused by the resolution of the timer/counter. For example, at 100 kHz, 2 pulses will occur in 20 microseconds. The resolution of a 1 megahertz timer counter is 1 microsecond. This results in an error of 1 part in 20 or 5%.
Besides the error being dependent on the input frequency, so is the acquisition period. The amount of time is inversely proportional to the input frequency. This makes it inconvenient to apply to measurement processes that require a predictable amount of time to perform input acquisition.
Based on the foregoing, the present inventors have concluded that a need exists for a method and system for determining the frequency of a pulse input signal over a wide frequency range. Such a method and system, if implemented properly, should additionally result in highly accurate measurement results over a wide frequency range. A need also exists for an improved method and system for measuring pulse frequency, unlike previous techniques, which focus on the measurement of power of a signal with regard to a reference signal.
BRIEF SUMMARY OF THE INVENTION
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is therefore one aspect of the present invention to provide an improved method and system for measuring frequency.
It is another aspect of the present invention to provide a method and system for reliably measuring the frequency of an input periodic pulse signal over a wide frequency range.
It is still another aspect of the present invention to provide a frequency measurement method and system whose measurement accuracy is dependent only upon a reference timer clock.
It is yet another aspect of the present invention to provide a frequency measurement method and system whose measurement accuracy is constant over an entire specified frequency range.
It is yet another aspect of the present invention to provide a measurement method and system, which provides a measurement acquisition time that is predictable regardless of the frequency of the measured signal.
The above and other aspects can be achieved as is now described. A method and system for determining the frequency of a pulse input signal is disclosed herein. A pulse count and a timer count can be captured at a start and end of a predetermined measurement interval to thereby obtain a start pulse count and an end pulse count and a start pulse time and an end pulse time thereof. A pulse frequency can then be determined, wherein the pulse frequency comprises the end pulse count minus the start pulse count divided by
DiGiulian Anthony F.
Komatsu Toru
Powell Robert W.
Abeyta Andrew A.
Honeywell International , Inc.
Nu Ton My-Trang
Ortiz & Lopez PLLC
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