SU1553914A1 - Digital frequency meter - Google Patents

Abstract

The invention relates to a technique of electrical radio measurements and can be used to measure the frequency of periodic signals in the presence of broadband noise. The digital frequency counter contains a shaping unit 1, a coincidence element 4, a pulse counter 6, a pulse generator 7, a master time unit 8. The introduction of a delay unit 2, an EXCLUSIVE OR 3 element and a frequency divider 5 reduced the impact of broadband noise on the frequency measurement accuracy and improving robustness . 2 hp f-ly, 4 ill.

Description

(Ls

Start

SL

cl

with so

Phie.1

The invention relates to a technique of electrical radio measurements and can be used to measure the frequency of periodic signals in the presence of broadband noise.

The purpose of the invention is to improve the accuracy and noise immunity.

FIG. 1 shows a block diagram of a digital frequency meter} in FIG. 2 and 3 are diagrams of forming and time of master blocks, respectively, in FIG. 4 - timing diagrams of the digital frequency meter.

The digital frequency meter contains serially connected forming unit (FB) 1, delay unit 2 (B3 element EXCLUSIVE OR 3, coincidence element 4 (ES), frequency divider 5 (PM) and pulse counter 6 (CI), as well as series-connected pulse generator 7 , (GI) and the time master unit (TSZ) 8, the output of which is connected to the second input of the ES 4. The output of the GI 7 is combined with the clock inputs of the KB 2, the third input of the ES 4 and FB 1, the output of which is connected to the second input of the EXCLUSIVE element OR 3. Additional inputs of DCh 5, SI 6 and VZB 8 combined with the input of Pu ck digital frequency meter.

The digital clock forming unit 1 of the totomer contains an amplifier-limiter 9, the input of which is the input of the forming unit 1 and a D-flip-flop 10, the D-input of which is connected to the output of the amplifier-limiter 9. The synchronous input of the D-flip-flop 10 is a sync input the forming unit 1, and the output - the output of the unit 1.

The time driver unit 8 contains a match element 11, the first input of which is the time input of the driver unit 8, the time driver divider 12, the input of which is connected to the output of the match element 11, the RS flip-flop 13, the R input of which is connected to the output time driver divider 12, the S-input is an additional time input of the master unit 8 connected to the Start input of the frequency meter, and the output is connected to the second input of the matching element 11 and is the time output of the master unit 8.

Digital frequency meter works as follows.

The input of the forming unit 1 receives a harmonic signal, which with the help of the amplifier-limiter 9

ten

15

(25

539144

is converted into square-wave pulses with a duty cycle of approximately two (square-wave pulses). These pulses are associated with a D-flip-flop 10 on the front and slice to a sequence of quantizing pulses received from the generator of 7 pulses on the D-flip-flop 10. The pulses generated in PB 1 are delayed by a block 2 of delays per n clocks of the quantizing sequence. Block 2 delay can be performed on D-triggers or shift register. The pulses at the outputs of the forming unit 1 and the delay unit 2 are shown in FIG. 4a1 „61. These pulses are

fall on the EXCLUSIVE OR 3 element, at the output of which the pulses are formed, shown in fig. 4 v1. The duration f of the generated pulses is equal to the delay time.

 n-t

about

(one)

where n is the number of delay ticks;

t0 is the period of following quantizing pulses.

Then, these pulses arrive at the coincidence element 4, the third input of which receives quantizing pulses, and the pulse with duration Tiel comes to the second input, the time of the master unit 8 from the output. The pulses from the output of coincidence element 4 arrive at the frequency divider 5. During a time equal to one period of the input signal with a frequency F, 2p pulses are output to the output of the frequency divider 5. When choosing the division factor of divider 5 equal to n, during the measurement time T, counter 6 fixes

eem

N

2F-T

(2)

pulses. The pulses corresponding to the specified measurement time are generated by the driver unit 8. At its output, the pulse duration

eem

 N,

(3)

where NQ is the time division divider factor 12 frequency.

As can be seen from the formula (2), the number N of pulses recorded by the counter 6 (the counter is connected to the indicator) corresponds to the measured frequency. With

5155

work with signaling, in which there are no broadband noises, the frequency limit of the digital frequency meter is the same as the error of the known frequency meter. In the presence of broadband noise, the error of a classical digital frequency meter increases dramatically, resulting in false transitions of the measured signal through the zero level (Fig. 4-2). In the proposed device, this error is significantly reduced, since the average duration of Ј positive pulses from the output of the element EXCLUSIVE OR 3

O 7-0 12 -i (, 3

These pulses are shown in FIG. 4v2.

The digital frequency meter provides high measurement accuracy in the presence of broadband noise. As a result, the dynamic range of the measured signals is expanded. The paths (forming unit 1) of digital frequency meters are wideband, therefore wideband noises are in the paths. False zero level transitions occur when

m PG / RSh 3, (5)

where rc is the rms frequency

noise

q is the signal-to-noise ratio. As can be seen from (5), to ensure high measurement accuracy, it is necessary that the signal-to-noise ratio satisfy the condition

H 3FW / F. (6)

For example, at F W 50 MHz, F 1 KHz, it is necessary that q 15 –103 With a noise level of 10 µV, the stable operation of the frequency meter is observed at a measured signal level of more than 0.15 V.

Thus, a digital frequency meter, in comparison with the known one, allows to increase the accuracy and noise immunity.

. Q) 5

20 25

thirty

40

50,146

frequency measurement in the presence of broadband noise.

Claims (3)

1. A digital frequency meter containing a shaping unit whose input is a frequency counter input, a coincidence element, a pulse counter and serially connected pulse generator and a time master unit, the outputs of which are connected to the first and second inputs of the coincidence element, respectively, are different. so that, in order to increase accuracy and noise immunity, a frequency divider and a series-connected delay block and an EXCLUSIVE OR element are inputted into it, the output of which is connected to the third input of the coincidence element the output of the pulse generator is connected to the clock inputs of the delay unit and the forming unit whose output is connected to the second input of the element. SELECTIVE OR and the input of the delay unit, the input of the frequency divider is connected to the output of the coincidence element, the output to the pulse counter , the frequency divider and the time of the master unit are connected to the Start input of the frequency meter. 2.Photometer pop. 1, characterized in that the forming unit comprises successively connected amplifying fir-bounded spruce and flip-flop, the synchronous input of which is the synchronizing input of the shaping unit, and the output - the output of the shaping unit. 3. Frequency meter according to claim 1, characterized in that the time of the forward block contains a consistently connected coincidence element, the time setting divider and the RS flip-flop, the 5-pass of which is an additional input of the time of the master unit: the second input of the match element is the output of the time of the master block. al smil ii IT