DE1272464B - Filter with amplitude, frequency and phase changeable transmission path and its use as a delay line - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY GERMAN W7WW> PATENTAMT Int. Cl .:

H 03 h

EDITORIAL

German class: 21g-34

Number: 1272 464

File number: P 12 72 464.0-35 (J 30586)

Filing date: April 9, 1966

Opening day: July 11, 1968

The invention relates to a filter with a transmission path that can be changed in terms of amplitude, frequency and phase and its use as a delay line with adjustable delay.

To achieve frequency filtering with the desired frequency response, it is, for example, after Meinke / Gundlach, "Taschenbuch der Hochfrequenztechnik", 1962, p. 213 ff., Known, several Parallel or series resonance circuits with resonance frequencies and bandwidths that differ from one another to interconnect. The calculation of such composite filter networks becomes very easy complicated and confusing if the transmission path to be implemented does not have a simple behavior having. If the transmission path of a filter is to be changed during operation, the physical quantities of individual switching elements are changed. For certain purposes of communications engineering, in speech synthesis, for example, is a rapid and continuous change in the Transfer of filters required.

Networks with filtering characteristics have already become known in technology, in which a signal to be worked out by means of adding or subtracting mixer circuits and under With the help of delay loops is obtained.

For example, U.S. Patent 2,629,818 gives e.g. B. a circuit arrangement for processing pulse signals of a given pulse duration and given pulse spacing, which are transmitted by means of a modulated carrier frequency. An oscillator with half the carrier frequency is provided on the receiving side. A first, subtractively acting mixer stage superimposes the received modulated carrier frequency with a locally generated half carrier frequency and thus generates an intermediate frequency which in turn contains the modulation component of the received carrier. This intermediate frequency is passed through a feedback amplifier, in whose feedback path a delay is looped. The task of the feedback is to achieve sufficient amplification without the provision of a large number of amplifier stages. The delay is used to limit the feedback circulations of the processed signals. From the output of the feedback amplifier, the signals obtained are fed to a second subtractively acting mixer stage, in which they are superimposed a second time with the locally generated half the carrier frequency. The subtractively generated output signal of this second mixer stage is thus the recovered modulus filter with a transmission path that can be changed in terms of amplitude, frequency and phase and its use as a delay line

Applicant:

International Business Machines Corporation, Armonk, N.Y. (V.St.A.)

Representative:

Dipl.-Ing. G. Brügel, patent attorney,

7030 Boeblingen, Sindelfmger Str. 49

Named as inventor: Winslow Rodeck Remley, Bethesda, Md. (V. St. A.)

Claimed priority: V. St. v. America 9 April 1965 (446 840)

lation signal of the received carrier. The object of this invention is thus a sensitive, selective demodulator for carrier-frequency transmitted signals. The frequency of the oscillator at the receiving end may be regarded as constant, at least over a longer period of time. This is changed Frequency only if you want to switch to the reception of another station.

Another network that also works with two mixers, one subtracting and one adding, and a delay loop is described in the article "Signal Processing Techniques for Surveillance Radar Sets" by Fowler, Uzzo and R u ν i η in the IRE Transactions on Military Electronics, April 1961, pp. 103-108. According to this work ( Fig. 11) , a carrier frequency / 1 is fed to a frequency discriminator via a first mixer, a delay line and a limiting amplifier. At the same time, the output signal from the amplifier mentioned is fed back via a second mixer to the second input of the first mixer. The output of an oscillator with the fixed frequency / 1 is connected to the second input of the second * mixer. The output signal of the first mixer has the frequency / 2 = / 3 - / 1, where / 3 is the output frequency of the second mixer. / 3 is the sum in the second mixer

IHHi / W

from / 1 + / 2. The job of the loop with the two mixers and the delay line is (corresponding to page 106 of the paper, bottom left column) a »frequency modulation«, i.e. frequency conversion from / 1 to / 2. This is the solution of stability problems in feedback Amplifiers with a high degree of feedback enabled. Particular attention should be paid to the design the oscillator for generating the fixed frequency / l, which is the second input of the second Mixer is fed. It is a quartz oscillator with a constant frequency.

Finally, the essay "Some Studies on Delayed Feedback Circuits" by H. S e k i is in the

F i g. 1 the basic block diagram of such a filter,

F i g. 2 a modified version using a Hartley single sideband modulator,

F i g. 3 the use of a modulated carrier as a control signal,

F i g. 4 an example of a signal to be filtered,

F i g. 5 the frequency spectrum of the in FIG. 4 signal shown,

F i g. 6 shows the course over time of a control signal chosen as an example,

F i g. 7 shows the frequency spectrum of the in FIG. 6 control signal shown,

F i g. 8 the frequency spectrum of the loop

Proceedings of the IRE, April 1958, pp. 758 to 763, 15 revolving signal after zero, one, two and four To pay attention. In it are in general circulation,

Thoughts also suggested delayed feedback loops as the basis of narrow band filters. Unfortunately, this work does not go into as much detail as the two previous references.

It is an object of the present invention, compared with the stated prior art, to provide a Specify a filter that is particularly suited to the requirement that the transmission can be changed quickly.

F i g. 9 shows the real part of the transmission path as a function of the frequency during use a control signal according to FIG. 6,

F i g. 10 the immediate part of the transmission path as a function of the frequency during use a control signal according to FIG. 6 and

11 shows the level as a function of the frequency at the output of the filter when using a response response according to amplitude, frequency and phase 25 control signal according to FIG. 6th

enough. Such a filter using a filter according to FIG. 1, the signal to be filtered becomes ν dem

Multiplier circuit, which, in addition to the input of the overall arrangement of the filter via fundamental frequencies and the simple sum and / or line 2, is also supplied via line 1 or difference frequencies with the! Combinations- a periodic control signal u , which emits the higher-order frequencies, is explained. ₃₀ transmission path of the filter controls.

According to the invention, this object is thereby achieved. The control signal u can be generated by any

solved that the signal to be filtered and a control known arrangement are generated. In the pre-signal, the course of which determines the transmission path of the added embodiment of the FiI filter according to the invention, a multiplier circuit is added, however, this control signal u certain introduces, which generates a product signal that is subject to the restrictions. First, it must repeat itself with both fundamental frequencies and the sum and period T. Second, the highest difference frequencies of the simpler and higher order frequency component of the control signal u must be less than that that contains this product signal at the first input k . . . , ,, ·. .. τ >> · <-. ·· j γ »j ·

a superposition circuit is fed, whose Ύ ^{be 'where k} g ^{anzzahl "lst} g · ^{The reasons for this} output via a retarder and a frequency limitations 40 are explained in the description of the converter to the second input of the Uberlagerungs- action.

circuit is fed back, the two signals for the present invention is the meaning

In the superimposition circuit, additively or subtractively of the word "periodic" in the control signal u are not superimposed, so that the delay of the superimposition circuit, the delay and 45, is limited by its strict mathematical definition. The “periodic” side frequency converter loop formed here of a basic signal should also include signals which are almost the same perioperiod of the control signal and the frequency conversion of the frequency converter is equal to the reciprocal value of the basic period of the control signal
and that between the output of the overlay 50
circuit and the input of the frequency converter
a line branches off to the input of a bandpass filter,
whose bandwidth is at most equal to the reciprocal of the basic period of the control signal and

the output of which forms the output of the filter. 55 short period T of the control signal u enables relatively special embodiments of the invention are large bandwidths.

The signal υ to be filtered is mixed with the control signal u in a multiplier circuit 3. It can simply be a multiplicative mixer or product modulator belonging to the known state of the art. Such a circuit is z. B. described in S ea 1 y, "Electronic Computing Circuits", 1958, p. 266 ff.

The output signal of the multiplier circuit 3 is a broadband signal, which apart from the two supplied Basic frequencies and the simple sum and difference frequencies also the sum and higher order difference frequencies.

are you. It should therefore also include the use of control signals that move slowly change from period to period. The fed through line 2 to be filtered

k (k +1) signal ν is limited to the frequency band from ψ to. The reasons for this are also explained in the description of the mode of operation. One

characterized in that an amplitude-modulated carrier signal is used as the control signal and / or that a Hartley single sideband modulator is used as the multiplier circuit is provided.

Furthermore, the use of such a filter as a delay line with a controllable delay specified. For this purpose, the multiplier circuit is provided with a control signal that can be varied in terms of its frequency fed;

An embodiment of the filter according to the invention is described below with reference to the drawings explained. It shows

Note that the lowest difference frequency is greater than zero, since the highest frequency component

k
nent of the control signal u is smaller than γ , and the lowest frequency component of the filter to be filtered

k
Signal υ is greater than - = ■. This is important to the

Avoid loss of information during processing.

The output signal of the multiplier circuit 3 is fed via a line 4 to a summing superposition circuit 5 forwarded. This adds the output signal of the multiplier circuit 3 with the Signal that consists of a delay 6, an amplifier 7 and a frequency converter 8 in a Loop runs around. The output signal of the superimposing circuit 5 is repeated again and again sent through the loop. The superposition circuit 5 can also be a Acting known prior art circuit, such as those cited above, for example Reference by S e a 1 y, p. 251 ff, is described.

In the preferred embodiment of the filter according to the invention, a delay 6 is used to set the total delay of the signal circulating in the loop to the time T , which is equal to the period of the control signal u used . The design of this retarder 6 is irrelevant. It can e.g. B. to a magnetic drum, a magnetic tape, an electronic, a magnetostrictive delay line od. Like. Act.

An amplifier 7 has the task of the overall amplification of the signal circulating in the loop to keep close to the value one. The amplifier 7 is one of the prior art corresponding broadband amplifier.

The last link in the loop of the exemplary embodiment according to the invention contains a frequency converter 8, which offsets the frequencies of the circulating signal by an amount equal to the reciprocal

value γ of the loop delay T. Such a

Frequency converter can consist of a superposition circuit in conjunction with an oscillator of the

Frequency γ exist. Frequency converter of this type

are also well known. In the illustrated exemplary embodiment, the frequency converter 8 receives via a line 10 synchronization signals. These have the task of maintaining a stable phase relationship between the control signal κ on line 1 and the output signal of the frequency converter 8 to maintain. The filter output is formed by a bandpass filter 11 connected to the signal circulation loop. In the selected exemplary embodiment, the amplitude transmission path should of the bandpass filter 11 in the

k (k + 1)
frequency range from γ to a factor of one. This factor does not have to be strictly adhered to. It is important, however, that it has a constant size over the entire frequency range in order to avoid distortion of the output signal.

An expanded embodiment of the filter according to the invention is shown in FIG. 2 shown. It is the multiplier circuit 3 according to FIG. 1 by a combination of two phase shifters 31 and 32, two multipliers 33 and 34 and a subtracter 35 have been replaced. From the circuits 31 to 35 existing arrangement is known as a Hartley single sideband modulator, such as it is given in S e a I y, "Electronic Computing Circuits", 1958, pp. 555 ff. While only the Difference frequencies in the output signal of the multiplier circuit 3 to the output signal of the in FIG. 1 contribute to the filter shown, the difference frequencies in the output signal on line 4 are missing of the in FIG. Hartley single sideband modulator shown in FIG. Only the corresponding sum frequencies are included. To form a filter output using these sum frequencies, the frequency converter 8 must be designed so that the frequency of the circulating in the loop

Signals reduced by γ and not as in the one in FIG. 1 is enlarged.

In some applications, phase Ψ of the transmission path G (/) is important.

Ψ = daily

-1

Real part G (f)
Imaginary part G (/) "

In other applications, only the amplitude transmission path P (/) is important.

P (f) = [real part G (/)] ² + [imaginary part G (/)] ² .

The phase of the transmission can then be disregarded. In applications of the last-mentioned type, it can be useful to use a special periodic control signal u. F i g. 3 shows a block diagram of a filter which contains a device for generating such a particularly type of control signal w. This is produced by means of an amplitude modulator 12, to which a carrier signal is fed via a line 13 and a modulation signal with the period T is fed via a line 14. The modulation signal is given by:

E (t) = VPlfJP).
The carrier signal is given by:

2nnt
cos .

η is an integer chosen so that γ is greater than the highest frequency component of E (t) and such that the sum of γ and the highest

Frequency component of E (t) is less than γ. This restriction with regard to the selection of η is necessary to ensure that all frequency components in the output signal of the amplitude modulus

lators 12 fall in the frequency band from 0 to γ. The output signal of the amplitude modulator 12 via the line 1 is therefore:

E (t) cos

2ntlt

It serves as a control signal that controls the transmission path of the filter controls.

7 8

Although each of the three mentioned embodiments, for example, let the input signal to be filtered ν (t)

Examples of the filter according to the invention a signal given by:

. Circulating loop from a superposition circuit 5, v (t) = B cos (2π ft + Θ)

a delay 6, an amplifier 7 and a _Ώ ,., ° _,. .,. , ...

Contains frequency converter 8, it _{goes without saying that the 5} ^{= RealteÜ VOn} Beexp (2njf _o t _{+ J} e).

Applying the principles of the invention not B is equal to the amplitude of the signal to be filtered,

is limited to this element arrangement. The , . _{Freauenz the zw} i _sc h _s - and ^{(fc + 1)} reads

through these elements functions performed are ^{Jo seme t T} * i ^vsaz> is ^the New York Convention-acres _{χ T,}

the delaying of successive parts of a pro and Θ the phase of the signal to be filtered. F i g. 4th

duct signal, the offset of the frequency on each _{other- I0} shows the signal to be filtered as a function of time

following parts of the product signal by amounts that and F i g. 5 as a function of frequency, i.e. H. be

proportional to the frequency spectrum experienced by these parts,

Because the control signal u (i) has the period T can be superimposed on the delayed ones

and frequency-shifted parts For example, j Fourier series with the fundamental frequency 1 could be

the function of the signal loop through an i ₅ ^H T

long delay line with multiple distributed to be pressed. In other words, that has

Tapped, a frequency converter on each down control signal u (i) the form:

handle and a superposition circuit for _k combination -

rening of the output signals of all frequency converters _u (t) - Σ A _n cos (+ φ λ + —2-

are executed. 20 "= · V ^ " J 2

While a preferred embodiment and two modifications thereof have been described above A _n is the amplitude of the η-th harmonic, the following explanations give _{d fundamental frequency> φ its phase and} A. der an example of the operation of an embodiment ^M "2 of the invention as well a description of the effective DC levels of u (t) .Figure 6 shows an example of a typical control signal as a function of the

For the filter according to FIG. 1 is the following time ahead. In it are:

set: ^ ₃ ^ ^ ₁ ^ ₃ ^ ₁

1. The control signal u returns with the period T ₃₀ ² 2 4 4, that is, u (t) = u (t + η t), wherein η is a whole number ^ _Λ. 4; ■ · · A _n = 0, and Φ _1; Φ ₂ , ..., Φ _η = 0.

2. The highest frequency component in the control

signal «is smaller than £, where ft also ^ ^ f ^{7 ze} & ^a frequency spectrum of this control

is an integer. Using the well-known simple trigo-

3. The signal to be filtered υ is metric in its bandwidth

on the frequency band from - = to be ^

_borders . _o cos χ ■ cos y = y [cos (x + y) + cos (x - y)]

4. The bandpass filter 11 has a transmission path

with the factor one in the frequency band of it is easy to prove that the product v (t) ■ u (t)

^ _to (k + 1) _{and with the factor zero except} . is given by:

half of this area. The Fourier transformer 45 _{ίΑ (. Λ} _ BA ₀ ,,. Tion of the filter output signal ο (t) behaves ^{(τ) 'U {)} ~ 2 ^cos ^ ⁿ Jo ^{l +>} then the Fourier transform to filter the Signals v {t) according to the equation _{:, .. +} B_ ^ _A Ε03 Λ _π / _υί ι Θ [ ^2πΗΐ Ι Φ) S {o (i)} = | 3 {«(i)} [w (/ T ² ) -jM (/ r ² )] 2n = i "V T" J

| _5o

Where ^ {} is the Fourier transform and, B Λ ( _fi . _N 2nnt

i is the HiI- + _Τ Σ / .cos ^ i + β

(mi) f {f) /

Bert transformation of 'u (i) for ί = / T ² . Included

is the Hilbert transformation of u (t) in Fig. 8a shows a frequency spectrum of this profach ii (t) with a phase shift of 90 °. ₅₅ duct signal, as it is at the input of the delay 6

appears. During each revolution in the loop

From the above equation it follows that the delayed the delay 6 the phase of each component transmission path G (/) of the filter is given by: nent of the product signal by an amount 2 π J ₀ T.

The frequency converter 8 increases the frequency of each

G (/) = '4γγττγ = 4 "[« (/ Γ ² ) -M / T ² )]. ^6o component by an amount - which corresponds to a phase

The generality of this relationship could be demonstrated mathematically by shifting each component by the amount If. But it is a match. F i g. 8b shows a frequency spectrum of the subject to explain the operating principles of the present product signal after one cycle in the loop, using an example that shows the same type of signals ν and control signals to be filtered after two cycles u and F i g. 8 d after four rounds. F i g. 8 used as a whole. taken shows that as a result of each revolution in

the loop the whole product signal towards higher

will.

shifted the amount ψ

Frequencies around

while the phase of each component of the product signal is delayed _{by 2.T 1} Z _{0 T.}

As already stated, a secondary condition of the filter according to the invention is that the pass band of the bandpass filter 11 only covers the frequency band from - = to includes. This frequency band is indicated by the dashed lines in FIG. 8 indicated. In addition, FIG. 8 that by means of the frequency converter 8 successive, different components of the product signal are shifted into this frequency band during each revolution. Therefore, after four revolutions this frequency band contains all information of the original product signal. The interaction of all signal level contributions within this frequency band ψ to --- = ^ leads to the generation of the filter output signal oU). Its frequency spectrum is given by:

is a function of frequency. The imaginary part of the transmission path is shown in FIG. The total emitted level is given by:

ρ (/ τ ² ) = ^ -1 μ (/ τ ² ) -jo (/ γ ² ) ¹²

u ² (/ T ² ) ü ² (fT ² )

Γ BA ₀
L ~ 2

BA ₁

BA ₂

-2.τ / "η

'Hf-Jo) is * Dirac's delta function, which is used to align the spectral line to the frequency J _0. Since the spectrum of the signal to be filtered was B e ^{J <J} 6 (f - f ₀ ) , and since the spectrum of the filter output signal divided by the spectrum of the signal to be filtered gives the filter transmission path, its transmission path is at the

arbitrary frequency / in the band ^ to ^ - ± _ ~ given by:

This simply corresponds to a quarter of the square of the current envelope of the control signal »(F). F i g. 11 shows the level at the filter output with the one shown in FIG. 6 control signal shown.

The exact position of the filter transmission path in the frequency spectrum is determined by the phase relationship between the control signal ii and the frequency offset caused by the frequency converter 8. The phase shift caused is an integral multiple of 2 rr. If the frequency shift caused by the frequency converter 8 should lag behind the control signal u , the functions shown in FIGS. 9, 10 and 11 would be shifted to the left in the frequency spectrum.

At this point it seems useful to examine some of the reasons for the general restrictions with regard to the input signals u and ν :

1. The control signal ii (t) must be periodic so that an orderly interaction between the

signals circulating in the loop.

2. The highest frequency component in the control signal u must be less than -ψ so that the lowest frequency component in the product signal r (f) · u (t) is greater than zero.
The signal v (t) to be filtered must be limited to a frequency band of width - = ■ in order to prevent adjacent parts of the spectrum of the product signal from interfering with one another. For example, according to FIG. 8 a, if that is to

filtering signal ν exceeds the bandwidth -ψ,

(k - 1) Jt

the parts of the product signal from - t ~ to ψ

Σ A _n [cos (2πη / Τ + <!> „) - j sin (2.τη. / T + Φ _η )], and from ⁽ - ^/ ^ li to ^ - into the frequency

since the sine function leads the cosine function by 90 °, and there

band from -ψ to

spread out and one

_lnnfT =

for ί = JT ²

is obtained by substitution:

G (/) = y [U (ZT ² ) - ^

This is the transmission path of the filter according to the invention.

F i g. 9 illustrates the real part u (fT ² ) of the »filter transmission path when using the in FIG. 8 u. It can be seen that the shape of this real part corresponds to the shape of the control signal; /, but that the control signal is a function of time and the real part of the transmission path causes errors in the output signal. This error would then be added as the signals circulated in the loop.

4. The bandpass filter 11 must be in the frequency band of ■ ==

until

a constant transfer factor

to avoid distortion of the output signal. According to FIG. 8 would the filter output signal wrong components

λ η ·· j Cc-1) u- k λ Cc + 1) u · from the bands - ~ - to = ■ and ^ —ψ-— to

j- included if the frequency band of the bandpass filter 11 would spread over the range from ~ to. However, if the fre-

809 569/460

frequency band of the bandpass filter 11 is narrower than

the range γ to

- ~ -, the filter output would only be part of the in the F i g. 9 and 10 correspond to the transmission paths shown and only a part of the in F i g. 11 level shown at the output.

Although the above description of the operation of the invention on the basis of a specific Example using a specific control signal and a specific signal to be filtered is done, it should be expressly emphasized that the operating principles easily apply to the general case can be expanded to include any control signal and any signal to be filtered encompasses the general restrictions outlined above.

It should be apparent that this filter system is suitable for a wide variety of applications is. The filter system according to the invention can replace expensive conventional filters in many cases. However, the use of the filter system according to the invention is of particular interest in such cases in which very complicated transfer functions or time-varying transfer functions appear.

The use of the filter according to the invention as a continuously variable delay line is also of interest. Since in the known delay lines the physical elements within the delay line have to be adjusted, to change the delay time, they are only cumbersome or in certain applications complex to handle. Such known physical devices can be supported by the present Filters to be replaced. In the case of the filter according to the invention, it takes time to change the delay time only the control signal to be changed.

Claims (4)

Patent claims: 1. Filter with amplitude, frequency and phase changeable transmission path, characterized in that the signal to be filtered (r) and a control signal («), the course of which determines the transmission path of the filter, are fed to a multiplier circuit (3), which is a product signal - »which contains the two basic frequencies and the sum and difference frequencies of simple and higher order, that this product signal is fed to the first input of a superposition circuit (5), the output of which is sent via a delay (6) and a frequency converter (8) to the second input of the superimposing circuit (5) is fed back, the two signals in the superimposing circuit are additively or subtractively superimposed so that the delay of the loop formed by the superimposing circuit (5), the delay (6) and the frequency converter (8) of a basic period T of the control signal («) is the same and the frequency conversion of the frequency converter (8) is equal to the rez iproken value -ψ of the basic period T of the control signal (w) and that between the output of the superposition circuit (5) and the input of the frequency converter (8) a line branches off to the input of a bandpass filter (11) whose bandwidth is at most is equal to the reciprocal value ψ of the basic period T of the control signal (m) and the output of which forms the output of the filter. 2. Filter according to claim 1, characterized in that a multiplier circuit (3) Hartley single sideband modulator (31 to 35) is provided. 3. Use of the filter according to one of the preceding claims as a delay line with adjustable delay, characterized in that the multiplier circuit (3) has a Frequency variable control signal («) is fed. Considered publications: U.S. Patent 2,629,818; "IRE Transactions on Military Electronics", Vol. MIL-5 (April 1961), No. 2, pp. 103-108; “Proc. of the IRE, Vol. 46 (April 1958), No. 4, Pp. 758 to 763. For this purpose 2 sheets of drawings S »569/460 7. HO BundesdnidCMci Berlin