JPS62147366A - Frequency measuring circuit - Google Patents

Abstract

PURPOSE:To measure at high accuracy frequency with a pseudo-specimen signal, by dividing the specimen signal, when a frequency of the specimen signal is not small enough as compared with the reference clock. CONSTITUTION:A divider 1 divides a specimen signal fx into proper frequencies and one of them is output from a selector for synchronization with the reference clock fref with a FF circuit 3. A n-bit counter 4 making the signal fx as a clock allows the frequency to be counted 6 only when a carrier output is issued once in n times and a 2-bit counter 5, using the signal fx as the clock, determines time from starting of the counter 6 up to the end of it by the output of the counter 5 and by counting 6 and frequencies of the clock fref in the mean time for latching 7 the values. A ROM8 using the output of the latch 7 as an address outputs a frequency value corresponding to the input counter value and a selector 2 is controlled by its i bit and when a counter value is small, a dividing ratio of output signal of the selector 2 is increased for reducing the signal fx as compared with the clock fref for improvement of accuracy of the measurement.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a frequency measurement circuit.

[Conventional technology]

In FIG. 2 showing a conventional example, 3 is a flip-flop circuit, 4 is an n-bit counter, 5 is a 2-bit counter, and 6 is a flip-flop circuit.
is a frequency counter, 7 is a latch, and 8 is a read-only memory. The signal under test is synchronized by the flip-flop circuit 1 using a reference clock. The n-bi-so I-counter 4, which uses the signal under test as a clock, sets 1 to n bits.
The frequency counter 6 operates only when the carry signal is output. Furthermore, the 2-bit counter 5 which uses the output of the flip-flop circuit 3 as a clock input,
A carry output is output once every 2 bits, and the frequency counter 6 counts how many times the reference clock is input during the carry output, and the value is latched in the latch circuit 7.
The read-only memory 8, which uses the output as an address, converts it into a frequency value and measures it. This method is effective when the frequency fX of the signal under test is sufficiently smaller than the reference clock frer.

[Problem that the invention seeks to solve]

However, the above-mentioned conventional circuit has the disadvantage that when the frequency fx of the signal under test is not sufficiently smaller than the reference tally clock frequency frer, the accuracy deteriorates and the usage rate of the frequency measurement counter 6 is low. .

[Means for solving problems]

According to the present invention, when the frequency of the signal under test is not sufficiently small compared to the reference clock, the signal under test is frequency-divided until the usage rate of the frequency measurement counter becomes high, a pseudo signal under test is created, and the signal is used as the reference clock. This method creates a signal that is sufficiently small compared to the conventional one, and as a result measures the frequency of the signal under test.

〔Example〕 Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows an embodiment of the invention. In Figure 1, 1
2 is a frequency divider, 2 is a selector, 3. is a 71717071 circuit, 4 is an n-pitch 1~counter, 5 is a 2-bit counter, 6
is a frequency counter, 7 is a latch, and 8 is a read-only memory. A frequency divider 1 divides the signal under test into frequency signals of the same type, one of the signals is outputted by a selector 2, and synchronized by a flip-flop circuit 3 with a reference tarlock. n where the signal under test is tarokku
The bit counter 4 determines the frequency measurement interval and measures the frequency once every n times.
The frequency counter 6 operates only when that output is produced by the carry output. In addition, the 2-bit counter 5 uses the signal under test as a tarock, and the carry output of the 2-bit counter 5 indicates one clock of the signal under test. The time to reach the whelk is determined. The frequency counter 6 counts how many times the reference clock has cycled 1 during that time, and the latch 7 latches this value. The read-only memory 8 whose address is the output of the latch 7 outputs a frequency value corresponding to the input counter value. At this time, the i bit of the output controls the selector 2, and when the counter value is small, the frequency division ratio of the output signal of the selector 2 is increased, and the value of the measured signal frequency fX is set to the reference tally clock frequency f ref. It is made sufficiently small compared to the actual size and measured in the same way to achieve highly accurate measurements.

[Effects of the Invention] The present invention has the advantage that the frequency to be measured can be appropriately divided and the frequency can be measured with high accuracy.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional example. 1... Frequency divider, 2... Selector, 3... Fritz Aflo knob circuit, 4... n-bit counter, 5...
・2-bit counter, 6... Frequency counter, 7...
・U...lchi, 8...Read-only memory,

Claims (1)

[Claims] a frequency divider that divides the frequency to be measured by several types of frequency division ratios; a selector that selects one of the outputs of the frequency divider; a flip-flop circuit that synchronizes the output of the selector with a reference clock; The output of the flip-flop circuit is used as a counter clock input to determine the time between one measurement and the next measurement, and the output of the flip-flop circuit is used as the counter clock input to start and stop frequency measurement. a 2-bit counter for determining a frequency, a clear input being controlled by a carry output of the n-bit counter, an enable input being controlled by a carry output of the 2-bit counter, and a frequency measuring counter having a counter clock controlled by a reference clock; Consists of a latch circuit that latches the output of the counter, and a read-only memory that uses the output of the latch circuit as an address, outputs a signal that controls the selector based on the counter value, and converts the counter output into a frequency value. A frequency measurement circuit characterized by: