DE1541819C3 - Device for the frequency-selective display of a signal or several signals and their application - Google Patents

Description

η =

L - L

results and that the pulses emitted by the last isolating stage are fed to the evaluation circuit (B). r>

2. Device according to claim 1, characterized in that the amplitude discriminator (A) contains a so-called Schmitt trigger (K) , the output of which is connected to one input of an AND element (Ui) , at whose other input the control pulses of the pulse generator fly.

3. Device according to claim 1 or 2, characterized in that the comparator (V) contains an EXCLUSIVE-OR element (E) , one of which v, input is preceded by a delay element (Li) , the running time of which is equal to the reciprocal sampling frequency (h ) is.

4. Device according to one of the preceding claims, characterized in that the separating ^r > o stages (Ti to Tn) each contain an AND element (U 2 to Un) , one input of which is preceded by a delay element (L2 to Ln) whose running time is equal to the reciprocal sampling frequency (fj) . τ »

5. Use of a device according to claim 1 or one of the following claims for displaying a plurality of signals, characterized in that a sampling switch (S i to Sm) is assigned to each signal source, that the samples of the series circuit which are offset in time within a sampling period Amplitude discriminator (A), a comparator (V) and one or more separation stages (Ti to Tn) are supplied and that the output pulses of the b ^r > last separation stage via electronic switches (SB I to SB m), which are in synchronism with the corresponding sampling switches (Si to 5 m) work, on integrating Auswerteschaltungcn (B 1 to B m) are distributed (Fig. 9).

6. Use of the device according to claim 5 for receiving the communication technology characters in a plurality of channels of a carrier frequency system with out-of-band signal transmission.

7. Application of the device according to claim 5 for receiving data in a plurality of channels of a carrier frequency system, with fewer data receivers than channels, such that the integrating evaluation circuits (B 1 to B m) connect the respective occupied channels to the data receiver cause.

The invention relates to a device for displaying a signal or a plurality of certain signals Frequency according to the preamble of the main claim and its application.

A frequency display device proposed in DE-PS 12 24 834 takes a sequence of samples from the electrical vibrations to be monitored with the aid of a sampling switch, the repetition frequency of which is more than twice as large as the highest vibration frequency. The polarity of successive samples is then compared, with comparison results indicating polarity reversal and polarity preservation being obtained. The frequency f of the scanned oscillation is determined by evaluating the number of these different comparison results, in each case within a period of time which is significantly longer than the shortest

Oscillation period j is. For this purpose, the

Ratio of certain comparison results, the other time the difference between multiples of certain comparison results evaluated. In the first case, a quotient measuring mechanism is used, one input of which the comparison results indicating the polarity change and its other input all comparison results be fed; the display is proportional to the frequency sought. In the second case is a counter provided, whose adding input is w times the number of polarity changes and whose subtracting input is the / 7 times the number of polarity repetitions are supplied, which means that the counter reading is constantly around its Initial state fluctuates when the frequency of the vibration to be monitored exceeds a predetermined Reference frequency matches. The proposed frequency display devices can also be used simultaneously several separately supplied vibrations by means of cyclic sampling according to the time division multiplex method monitor.

In contrast, the invention is based on the object to provide a device that consists of a Mixture of signals of different frequencies a signal of a certain frequency increases, with this Frequency is above the frequency band that the other signals occupy, so that a signal receiver with high pass character is obtained.

According to the invention, the solution to this problem results from the characterizing features of Main claim.

It is true that from US-PS 3189 820 the The use of isolating stages in connection with a frequency display arrangement is known, the

Isolation stages contain delay elements. It is possible with this known frequency display arrangement determine at which point of a relatively wide reception frequency band the frequency of an evaluated Vibration is. For this purpose, the vibration received is fed to the two inputs of the fed to each other in parallel isolators, whereby at their outputs as a result of the with different delay times applied to the second inputs of the isolating stages due to interference caused amplitude pattern results, whose respective characteristic the frequency of the received Oscillation localized within the frequency band. With this known arrangement, however, it is in the In contrast to the frequency display device according to the invention, the presence of a Determine signal oscillation of a certain frequency if this is from within the receiving frequency band other vibrations occurring at the same time are accompanied, since then none on the specific frequency indicative characteristic amplitude pattern is obtained at the outputs of the separation stages.

In the frequency display device according to the invention, the amplitude discriminator advantageously contains a bistable multivibrator known under the name Schmitt trigger, its square-wave output oscillation which is fed to one input of an AND element, at the other input of which the Control pulses of the pulse generator are. The tasks of the comparator and the isolating stages take over one gate in each case, namely an EXCLUSIVE-OR element in the comparator, in each of the separation stages an AND element is required, with one input of these logic elements each having a delay element is connected upstream, the running time of which is equal to the reciprocal sampling frequency.

The device according to the invention for displaying a large number of signals, that come from different signal sources are used; in doing so, the samples of each Signals staggered in time using the time division multiplex method.

Embodiments of the invention are shown in the drawing and will be described in more detail below described. It shows

F i g. 1 shows a basic block diagram of a device for the frequency-selective display of a signal,

F i g. 2 to 5 the time processes for four signals different frequency,

6 shows a basic circuit diagram of the comparator in the device according to FIG. 1,

F i g. 7 the dependence of the output pulse repetition frequency of the isolating stages on the input signal frequency,

F i g. 8 the required number of separation stages depending on the ratio of the cutoff frequencies,

F i g. 9 shows a basic block diagram of a device for the frequency-selective display of a large number of Signals according to the time division multiplex method,

10 shows a frequency plan when using the Device according to Fig. 9 for signal display in one Carrier frequency system.

The basic circuit of a device for frequency-selective display of a signal according to the invention is based on the block diagram of FIG. 1 emerged. The temporal processes at points a, b, c etc. indicated by arrows are shown in FIG. 2 to 5 in the corresponding lines a, b, c for four signals of different frequencies.

According to the sampling theorem, a signal is only

Contains frequencies in a limited frequency band of B Hz, where B is also the highest signal frequency, by taking short samples spaced apart by

γα shown in full. So that the sampling times do not coincide with the zero crossings of the signal in the event of an unfavorable phase position, the sampling frequency must practically be more than twice as large as the highest signal frequency. In the embodiment according to Fi g. 1, a sampling frequency of fr = 10 kHz is selected. In the case of the sampling of an oscillation shown in FIG. 2, line b , the frequency of which has the theoretical maximum value of 5 kHz = = y, this becomes clear

half the peak values are sampled.

To facilitate understanding of the operation of the device according to FIG. 1, the signal source G may initially only emit a single sinusoidal signal oscillation, the frequency of which may be 5000 Hz = £ p, 3850 Hz = j £, 3333 Hz = ώ or 2500 Hz = ^

(Figs. 2 to 5, line a). The signal is sampled by the electronic switch 5, which is open in the idle state and of short control pulses (Fig. 2 to 5, line d) of the pulse generator P at the rate of the sampling frequency fr = 10 kHz each for a duration of about 0, 5 μβ is closed. After the switch 5, samples of different amplitude and polarity are created, which follow each other at a distance of 100 μ5 (Figs. 2 to 5, line b).

The samples are fed to an amplitude discriminator A , which only emits a pulse if the samples exceed a certain threshold value. The threshold value is set to the mean value of the signal to be displayed over time, i.e. to its zero line in the case of a pure alternating current signal. (In the case of a signal with a direct current component, this is eliminated by suitable setting of the threshold value) The amplitude discriminator advantageously consists of a so-called Schmitt trigger K, which is followed by an AND element Ui . As is well known, the Schmitt trigger is an asymmetrical, bistable multivibrator whose output signal can only assume two different values, depending on whether the input voltage exceeds or falls below the set threshold value.

so In the present case the flip-flop is brought into one stable state by positive samples and the other by negative samples. The rectangular output oscillation of the Schmitt trigger (Fig. 2 to 5, line c) reaches one input of the

AND element Ui, at the other input of which the control pulses from pulse generator P (Fig. 2 to 5, line fly). At the output of AND element U 1 - which is also the output of amplitude discriminator A - appears for every positive sample Pulse while the negative samples are suppressed (Figs. 2 to 5, line e).

The comparator V only delivers a pulse when the one output pulse amplitude discriminator A in time with the sampling frequency for missing previous or subsequent pulse. This comparison of successive pulses is expediently served by an EXCLUSIVE-OR element E, one input of which is a delay element L 1 acting as a memory

is upstream; the running time of the delay element is equal to the reciprocal sampling frequency fr-. The EXCLUSIVE-OR element, at the two inputs of which two pulses, which are derived from f), only emits an output pulse if the two input information items are different from one another; this is the case with every change of sign of the scanning samples, that is, with every zero crossing of the / signal oscillation. The mean pulse repetition frequency at the output of the comparator V is thus rv. '·. . ■ ; ■■ , ·.

Equation (1) is therefore only valid in the range between the two limit frequencies / "and Z _n , that is within an octave: ·.: ■ .., ·. .; :., '■, ■. · ■; .. , - ■'.

10

15th

20th

25th

where / is the frequency of the signal oscillation to be displayed (FIGS. 2 to 5, line g). '

The EXCLUSIVE-OR element can be built up from three simple logic elements from two anticoincidence GHedern £ 1 and £ 2, whose outputs with the inputs of an OR gate £ 3 are connected (Fig. 6). In this circuit, the element £ 1 registers a change in sign of the samples from positive to negative values, while the other term £ 2 changes the sign from shows negative after positive values.

In the exemplary embodiment, the evaluation of the output pulses from the comparator V is carried out by two isolating stages T1 and T2 connected in series. Each isolating stage only emits a pulse if two pulses arrive at its input one after the other at the sampling frequency h. In principle, such a separating stage has a very similar structure to the comparator V ₁ instead of the EXCLUSIVE-OR element £ but an AND element t / 2 or t / 3. For the delay element L 2 or L 3 connected upstream of one input of the AND element t / 2 or t / 3, as with the delay element Li in the comparator, the condition that its running time is equal to the reciprocal sampling frequency / 7 · applies. This ensures that two pulses which occur one after the other at the input of an isolating stage at the rate of the sampling frequency appear simultaneously at the two inputs of the relevant AND element; in this case the AND gate emits a pulse. The mean pulse repetition frequency at the output of the first separation stage Tl is. :

■. · ■ - Ti = .4 /.-/ τ, (η

where / is the frequency of the oscillation to be displayed and Zrd the sampling frequency.

The highest possible pulse repetition frequency that can occur at the output of the first separation stage is the sampling frequency (Zi = Zr = IO kHz, FIG. 2, line i). If we put in equation (1)

Within this range there is a linear relationship between the mean pulse frequency i \ at the output of the first separating stage and the frequency to be displayed / For example, for / = 3850 Hz there is an average pulse repetition frequency of /, = 5400 Hz (Fig. 3, line i) and for / = 3333 Hz an average pulse repetition frequency of / 1 = 3333 Hz ( Fig. 4, line #. ·.: ■■ ■ .. · ■ ■ '■■, · ... _: ·· _: · _; . · '.'·;'..; ....

When two isolating stages Ti and T2 are connected in series, the second isolating stage only emits a pulse if three pulses follow one another at the input of the first isolating stage at the rate of the sampling frequency. The mean pulse repetition frequency at the output of the second separating stage 72 is

(2)

In a very similar way to equation (1), an upper limit frequency / _o and a lower limit frequency / "can be derived from equation (2), at which / 2 assumes the highest possible pulse repetition frequency or becomes zero:

for / = / „= -ψ = 5kHz, J ₂ = f _T =

1OkHz

(Fig. 2, line 0
and

for / = / "= - ^ ¹ - 3.333 kHz becomes / ₂ = 0

(Fig. 4, line /): ■■. \ - ■: / ■ "'/'. .. ·. ''; ^: ' / Ί V-; j "

When using two isolating stages, the upper limit frequency / _{o is the} same as for a single stage; the lower limit frequency / _u , however, is higher. Equation (2) is therefore valid in a smaller area than equation (1):

door

= 2 (3 / -'Jr) fr

55 s' * 4 ·]

(2 a)

this gives an upper limit frequency for the signal frequency to be displayed.

:. · ■ / = / o = ^ Y = 5 kHz.

The smallest possible pulse repetition frequency at the output of the first separating stage is Zi = O (FIG. 5, line i); Inserting this value in equation (1) results in a lower limit frequency for the signal frequency to be displayed, for example, for / = 3850 Hz there is an average pulse repetition frequency of / 2 = 3100 Hz (FIG. 3, line 1).

From the equations (1) and (2) the law of formation for the mean pulse repetition frequency / "can be seen, which occurs with η isolating stages connected in series at the output of the last isolating stage:

/ "= 2 (n + I) / - n / _T

H.

= 2.5 kHz.

for

ID

The frequencies are expediently related to the sampling frequency / V in equation (3); then,. ■ _; .

fr

■ -i.fr '

for

The relationship, given by equation (4), between the mean pulse repetition frequency / "and the frequency to be displayed / - both related to the sampling frequency fr - is shown in FIG. 7 plotted for / I = 1, 2, 4, oo successive separation stages. The solid lines apply in the discussed area between the lower limit frequency

f. =

2 (n + 1)

fr

(5)

and the common upper limit frequency

JO ry JT

So within the cut-off frequencies, the separation stages show the behavior of a high-pass filter.

From the two equations (5) and (6), the required number η of the separation stages can be calculated for a certain ratio of the limit frequencies:

η =

/ u

/ u

- 1

η as a function of

is in Fig. 8 shown.

The dash-dotted straight line in FIG. 7 applies to / 7 = 00, i.e. That is, with an infinite number of separation stages, the lower and upper limit frequencies coincide and the displayed signal frequency is equal to half the sampling frequency; the pulse repetition frequency at the output of the last isolating stage is equal to the sampling frequency (the prerequisite is that the signal oscillation is not sampled at its zero crossings). To the right of the dash-dotted straight line are in FIG. 7 for / J = I, 2, 4 drawn dashed lines, which are symmetrical to the corresponding solid lines. For example, for / "= 0.7 / 7- and / = 0.3 f _{T, the} same pulse repetition frequency is obtained at the output of the first separating stage, namely Zi = 0.2 fr. The roof-shaped frequency characteristic is repeated with the integer multiples of the upper limit frequency f _o as a singular point The separation stages thus show the behavior of a bandpass filter if one goes beyond the upper limit frequency; the sampling theorem no longer applies in this area.

The integrating evaluation circuit B at the output of the last isolating stage contains, for example, a capacitor that is converted from the amplified direct current pulses with impressed current to a voltage

value is charged that _{: is} proportional to its repetition frequency and thus to the frequency of the signal oscillation to be displayed; this voltage can then be displayed by a high-impedance direct current instrument calibrated in Hertz. However, a digitally operating device can also be used to display the frequency, for example a counter which counts the number of pulses emitted by the last separation stage during a sufficiently long period of time. - .;

. The device shown in FIG. 1 can be used with particular advantage for displaying a large number of signals originating from different signal sources using the time division multiplex method; such an arrangement is shown in the basic block diagram of FIG. 9 shown. An electronic switch Si to Sm is assigned to each of the m signal sources G i to Gm. The electronic switches close briefly at the rate of the sampling frequency / 7-, their closing times being offset from one another within a sampling period. Control pulse sequences Fi to Fm, which are offset in time and supplied by the pulse supply PV , are used to control the electronic switches. The actual device for frequency selection, namely the amplitude discriminator A, the comparator V and the separation stages Ti to Tn, are used several times. The second input of the AND gate Ui in the amplitude discriminator A (FIG. 1) is to be supplied with a pulse train F with the repetition frequency mfr in accordance with the pulse repetition frequency of the temporally interconnected samples. The output pulses of the last separation stage Tn are distributed to the evaluation circuits Bi to Bm by the electronic switches SB i to SB m, which are controlled by the pulse trains Fl to Fm in synchronism with the corresponding switches 51 to S m. AND gates can serve as electronic switches SBi to SBm.

A preferred field of application of a device according to FIG. 9 are carrier frequency systems with out-of-band signal transmission. In this case, a signal oscillation is used for the transmission of switching signals, the frequency of which is, for example, 3850 Hz, i.e. above the transmitted voice band of 300 to 3400 Hz. The level of this signal oscillation in the high-level high sampling method (working current method) is approximately -4.3 dBmO, ie level -4.3 dB based on 1 mW at the relative level 0. If the sampling frequency Zr = 10 kHz, the result is When using two isolating stages, a lower limit frequency / = 3333 Hz, as shown in the frequency diagram of FIG. 10. The speech oscillations (hatched area) are practically suppressed and when the signal oscillation / _s = 3850 Hz occurs, pulses with an average repetition frequency of 3100 Hz appear at the output of the second isolating stage. The evaluation circuits contain a sensitive DC relay that indicates whether the signal oscillation is present or not. Such a central signal evaluation device on the receiving side of a carrier frequency system can, for example, be assigned to 120 channels; be: a sampling frequency of 10 kHz then the sum pulse repetition frequency is 1.2 MHz. The central evaluation device replaces the complex signal receivers assigned to each individual channel in known carrier frequency systems, each of which has a filter and an amplifier for filtering out and amplifying

809 521 /

Signal oscillation included.

Another area of application is the transmission of data in a large number of channels Carrier frequency system in which not all channels are occupied at the same time; a smaller one is sufficient Number of data receivers as channels are available. The determination of whether there is data in a channel be transferred or not, take over

10

simple evaluation circuits B 1 to B m (FIG. 9), which then cause the relevant channel to be forwarded to a data receiver.

Finally, a device according to FIG. 9 can also be used in time division switching systems, where the required by periodic connection of lines to a multiplex rail Samples already exist.

In addition 5 sheets of drawings

Claims (1)

Patent claims: 1. Device for displaying a signal of a certain frequency which is above the frequency band ^r > of a mixture of other signals and between an upper and lower limit frequency (f <J,!) , The ratio of the limit frequencies being less than 2, using samples of the signal mixture, whose repetition frequency is twice as large as the upper limit frequency, an amplitude discriminator, which only emits a pulse when the samples exceed a threshold value corresponding to the time average of the signal to be displayed, an r> comparator, which only generates a pulse emits when the pulse preceding or following an output pulse of the amplitude discriminator at the rate of the sampling frequency is missing and an integrating evaluation circuit, in particular for electrical communication technology, characterized in that the comparator (V) has one or more separation stages (Ti to T / ^ are downstream, each n Only emit a pulse if two 2 ^r > pulses arrive at their input one after the other at the rate of the sampling frequency, whereby the number η of the separation stages is derived from the condition