DE2034207C - Circuit arrangement for changing the frequency deviation of frequency and phase modulated signals - Google Patents

Description

40

The invention relates to a circuit arrangement for changing the frequency deviation of frequency and phase modulated signals.

In order to achieve maximum operation in frequency or phase modulation systems with a large frequency deviation To achieve this, it is often desirable to keep the cut-off frequency of the demodulator below the value Press, which is at least required when using the usual FM demodulation. For this were different methods developed, namely demodulators with frequency modulated feedback and phase-locked demodulators. Both methods work so that the IF signal is effectively with a bandwidth is filtered that is lower than would be allowed with conventional deniodulation systems.

In contrast, the invention is based on the object of creating a circuit arrangement with which allows a real change in the frequency deviation of an incoming FM or PM signal.

This object is achieved according to the invention in that for processing the frequency or phase-modulated signals two channels are provided and each channel a delay element and a Mixer, in which the input signal is mixed with the delayed signal of the other channel and that from at least one of the channels an output signal is derived, the frequency of which compared to the frequency of the input signal according to the Delay times of the delay elements is shifted. In a preferred embodiment of the Invention is still em from the output signal to stabilize the amplitude of the input signal Serving feedback signal derived.

The circuit arrangement according to the invention, the frequency deviation of an incoming FM or PM signal reduced or increased according to the principle of synthetic phase isolation (SP /). The Principle of synthetic phase isolation exists darn by mixing an input signal with a over aeerunassvibration and further mixing one Auseefiiterten sum or difference signal with the Input signal or the difference or summation signal the first mix an output signal with the Frequency of the input signal to gain that he. independent of the phase of the input signal Phase has. A cutoff frequency or threshold. shift only takes place if the circuit arrangement according to the invention for reducing-u frequency deviation is used. This circuit order but can be used for other purposes, such as a system transition in the intermediate frequency range. can also be used to extend the frequency deviation. The signal with reduced Frequency deviation can then be through a filter -inem usual demodulator are supplied. This procedure works in the same way as all methods of expansion of the FM or "M threshold" Signals with a large frequency deviation, because the minimum bandwidth of a system is twice as much the information frequency, and the frequency deviation must be quite large if there is a reduction of the frequency deviation have a benefit

The present invention was prompted by the desire to use the technique of synthetic phase isolation in an FM receiver by threshold expansion. The correlation bandwidth of this regenerative arrangement is mastered by the designer as well as the ratio of the time delays, i.e. the increase in the phase characteristic. The noise bandwidth of the apparatus for the reduction of the frequency sweep can ^cli: be n, as in the conventional receivers with threshold shift, without having to bring jedich such a great sacrifice in signal distortion and signal suppression because to be used for signal processing, no circuit arrangement, the saturation effects shows how a limiter, a discriminator or a degenerative, frequency-modulated oscillator.

Another application of the circuit arrangement according to the invention can be found in communication systems using satellites. This is where connections to the spacecraft are made high modulation index transmissions are used. The same information is often encountered with relay links together, in which use is made of a lower modulation index. The technology of Changing the frequency swing can be seen as a low-distortion transformation between these two system elements to be used. The significant distortion caused by demodulation and re-modulation are conditional, with a circuit

arrangement according to the invention avoided because here such demodulation and remodulation does not take place!:.

Further details and configurations of the invention can be found in the following description, in which the invention on the basis of the embodiments shown in the drawing closer is described and explained. The characteristics to be taken from the description and the drawing can in other embodiments of the invention individually or collectively in any Combination find application. ' It shows

F i g. 1 shows the block diagram of a first circuit arrangement according to the invention,

F i g. Figure 2 shows the block diagram of a further embodiment of the invention which is only a reduction the frequency deviation enables

F i g. 3 shows a diagram of the amplitude of the output signal the circuit arrangement according to FIG. 2 as a function of the frequency.

F i g. 4 the reproduction of a frequency plan that identifies the optimal frequencies to achieve the greatest possible Bandwidth shows, and

5A and 5B are diagrams of the amplitude and phase behavior of the two filters r ₅ and r _{6 of} the circuit arrangement according to FIG. 2.

It can be assumed that the circuit arrangement 10 zr.r change of the frequency deviation according to F i g. 1 the following input and output signals having:

V ,, _in = cos (ο, t + Φ)

V _out = COS (ci ₂ f + (-)).

(D

The input signal is kept at constant amplitude by a circuit 12 for automatic gain control [ AGC] in order to ensure linear processing of the signal in the circuit arrangement 10. The output signal of the AVR 12 is fed to two parallel channels 14 and 16. The channel 14 contains a bandpass filter (r,) 18, the output signal of which is fed to a mixer (Mi) 20. The output signal of the mixer 20 is fed to _{a further bandpass filter (r 2).} In the channel 16 there is a bandpass filter (τ 1) 24, the output signal of which is _{fed to a mixer (M 2} ) 26. The output signal from this mixer 26 is fed to a further bandpass filter U ₄ ) 28. The output signal of the r ₂ filter 22 is mixed with the output signal of the r, filter 24 in the M ₂ mixer 26, while the output signal of the T ₄ filler 28 is mixed with the output signal of the τ, filter 18 in the M, - Mixer 20 is mixed, the output signal of the! -, - filter 22 is fed in a feedback loop 30 via a rectifier 32 and a DC amplifier 34 of the A I / ^ circuit 12 in order to keep the amplitude of the input signal constant.

When operating the circuit arrangement 10 according to FIG. I the bandpass filters 18, 22, 24 and 28 act as delay lines. Since these are band passes, they only transmit the lower sciten bands of the _{signals supplied by the M 1} - uiu ¹ M ₂ mixers 20 and 26. The r, filter 18 causes a delay i,. while the r, filter 24 causes a delay r ₃ , so that the output signals of the bandpass filters 18 and 24 take the following form:

COS [fi, (f- T ₁ ) + 0]

cos [ei, (r-Tj) + 0].

The Mj mixer 26 mixes the output signal of the bandpass filter 24 according to equation (4) with the output signal V _out according to equation (2), which results in the following value _{for the output signal of the M 2 mixer 26:}

cos [(m, -,., ₂ ) f - C ₁ T ₃ + 0 - ff] . (5)

_{The delay T 4} caused by the bandpass filter 28 leads to the following signal:

COS [(.D ₁ - ,,, ₂ ) (t - T ₄ ) - ei, T ₃ 4 - 0 - (-)] . (6)

The signal according to equation (6) is converted to

COS [(ei, - Ci ₂ ) '~'' ¹ I ^T 4 +''' 2 ^T 4 ~ '''l ⁷ 3 + ^fl> - ^] ■ O)

The signal given by the equation (7) is then converted into the delayed output signal in the mixer 20 of the bandpass filter 18 are mixed according to equation (3), so that the door is the output signal of the Μ, mixer 20 the following expression gives:

COS [ci ₂ f - ei, T ₁ + 0 + ei, T ₄ - cj-, T ₄ + ei, T ₃ - 0 + H].

(2) This expression can be transformed into

COS [(D ₂ f - Ci ₁ T ₁ + ei, T ₄ - Ci ₂ T ₄ + Ci ₁ T ₃ + (-)] . (9)

The signal according to equation (9) is then delayed by the bandpass filter 22 by the time τ, as a result of which an output signal

COS [(D ₂ t - O ₂ r-, - (D ₁ T ₁ + Ci ₁ T ₄ - (D- T ₄ + (D ₁ T ₁ + - ff])

(10)

results, which, according to the assumption made at the beginning, is equal to the output signal V _out according to equation (2). Solving this equation gives:

- (D ₂ T ₂ - (D ₁ T- + Cl ₁ T ₄ - Cl ₂ T ₄ + (D ₁ T ₃ = 0 (D ₁ [T ₄ + T ₃ - Tj] = Cl ₂ [T ₂ + T ₄ ]

(H)

Accordingly, a careful choice of the delay times caused by the bandpass filters 18, 22. 24 and 38 are conditional, the frequency <·., A value

uo , which is either larger or smaller air, (D _1. The circuit arrangement 10 according to FIG

(15 make transitions between different signal systems possible without the need for demodulation and subsequent new modulation of simials.

F i g. 2 shows the block diagram of an embodiment of the invention which only allows a reduction in the frequency deviation. An input signal is fed to a circuit 42 for automatic gain control in order to ensure linear processing in the circuit arrangement. The signal is fed from the AVR 42 to two parallel channels 41 and 43. The channel 41 contains a mixer (M ₃ ) 44. The output signal of the ^ /., Mixer 44 is fed to a bandpass filter (r 1) 46. The channel 43 contains a mixer (M ₄ ) 48. The output signal of the / VZ ₄ mixer 48 is fed to a bandpass filter (rj 50. The output signal of the r ₍₎ bandpass 46 is _{mixed in the M 4} mixer 48 with the input signal , while the output signal of the Tj bandpass 50 is mixed with the input signal in the / VZ, mixer 44. The output signal of the τ ,, bandpass 46 is also fed into a feedback loop 52 via a rectifier 54 and a DC amplifier 56 of the A ΚΛ circuit 42. The bandpass filters 40 and 50 operate as delay lines during the operation of the stroke reducer 40 according to FIG.

Since the two mixers 44 and 48 provide the lower sideband, the phases of the two signals fed to the mixers are subtracted. Since it is the case with the circuit arrangement 40, provided that the level of the input signal is sufficiently high. is an oscillating loop, it works in such a way that the phase shift along the closed loop is 2 η η . The frequencies of the output signals of the bandpass filters 46 and 50 must always add up to the frequency of the input signal. The way in which they are distributed, however, depends on the delay values imposed by the bandpass filters 46 and 50. A derivation of the mode of operation of the circuit arrangement 40 according to FIG. 2 follows.

The input signal of the stroke reducer 40 is stabilized with the aid of the A KR-SchalHing 42 so that linear processing is guaranteed. When as input signal

(12)

and as an output signal

given input signal is mixed. The output signal from the mixer 48 is then

■ i
₅ ^ / I ² B cos ["., (Z - t") + ". ₀ τ ,, + 0 (Z) - 0 (I - t ")

After a delay τ i in bandpass filter 50, there becomes: _{| 0} signal according to equation (16)

K ₁ (Z) = * A ¹ Ii cos [.. ,, (z - T ₅ - t ") +", "t" + 0 (Z - T ₅ ) - 0 (Z - T ₅ - τ ,, ) + (-Ht- T ₅ - r ,,)]

= ß cos [t. ,, z + «(ζ)].
From equation (17) it follows that ¹ A ¹ = 4

25 (-) {!) = - ,,,, [r ₅ + T ₁₁ ] + ... "τ ,, + 0 (Z - T ₅ )

- Φ (I -T ₅ - r ") 4- W (Z - T ₅ - r"). (I '))

The static and dynamic parts of these expressions can be resolved as follows:

"1 [ ^T 5 + T (J = '" (IT ,,

" ¹ I - '" (I

The frequency <·· _{2 of} the signal K ₂ (Z) is given by du;

III, = .

'"2

The dynamic termc require

W (Z) = 0 (ZT ₅ ) -

_{T (i} )

V ₁ (Z) = B cos [<■ -, ζ 4- W (Z)] (13) so The system function is then door phascnmodulii- '-.

Signals

is accepted, then is at the exit

of the Mi bandpass 44 a lower sideband of the ,,, "_ _r , 1 - e ~ ^r " ^s

Form ^{H (s)} = ^e - M

γ / IBcos [K - ₍ . ,,) Z + 0 (Z) - W (Z)]. (14) The first part of this expression can be ignoriei

After a delay T ₆ in the bandpass filter 46, the ^we [ ^the ; Y ^eiI "^." M is a simple delay ur signal according to equation (14) to ^T * and. accordingly it is the system function

6o for gain and phase calculation

F ₂ (Z) = ~ AB cos [(,., "- ™, Kf - T ₆ )

(15)

The output signal of the bandpass filter 46 given by the equation (15) is _{fed to the jV / 4} mixer 48, in which it is set here with the jw for 5 by the equation (12), so the result

H ¹ I '- ' ~ " ^e ~ '"' ^H
v '"' ~ ~ f _ _ε -; ,,, <ίΤΓίΤ ·

The conjugate complex expression is then the amplitude and phase transfer functions are then given by

and it follows that the square of the Reinforcement

sin y- /

. Γ Ϊ "

sin y /

3 / ι - 1 2 / ι

f.

(37)

(38)

sin '(! 2 -. rj
sin * (1 2 - .. {r., - t- r "

(27)

Accordingly, with phase modulation, the amplitude is independent

sin \! <■ <τ ,,

sin I 2-Mr, 4- r "l

(28) As can be seen, the amplitude slowly increases up to / ^ j / u and then goes asymtotically for / = 2j

to infinity. The phase dependency is only a delay and therefore has no effect on the signal. F i g. 3 shows a graphical representation of the amplitude of the output signal of the circuit arrangement 40 as a function of the input modulation frequency for various values of n. The amplitude is essentially constant up to frequency values of the order of magnitude

For small values of «■■ (r_ _s + O, equation (28) is reduced

(39)

The Phascnabluiiigkei! results in / u

,,,) = tan

K.

(30)

The resolution into real and imaginary parts then results

= 12. ·,

(31)

A delay of r _{5 was} previously neglected, and consequently it is the phase characteristic of the system function for phase-modulated signals

(32)

In order to normalize the derived formula for purposes of illustration, the following parameters used:

/ 1 =

+ T ₆ ).

(33)

(34) When constructing the circuit arrangement 40 according to FIG. 2, the choice of the output frequencies with respect to the amount of reduction in the frequency deviation can be made independently, because the delay and

, ο the center frequency of a bandpass filter independent of each other are fin filters like bandpass filters 46 and 50. Effectively causes one delay and one constant phase shift and therefore introduces a constant into the previous analysis.

The effect of this constant phase shift is to change the mean operating frequency, however, this does not affect the dynamic behavior of the circuit arrangement 40.

The choice of frequencies, however, cannot be completely arbitrary because the bandpass filters 46 and 50 have to effect a signal separation. If the bandpass filter 40 is made narrow with respect to the bandpass filter 46, the main part of the swing reduction appears in the output signal V ₁ [I]. Because it's easier. To make narrow bandpasses at lower frequencies, the bandpass filter 50 is chosen so that its center frequency is lower than that of the bandpass filter 46. Fs is useful to determine the optimal frequencies that correspond to the maximum possible band-

5Q wide lead. If / _{u is} the center frequency of the bandpass filter 50, f _{h is} the center frequency of the bandpass filter 46, π is the reduction factor of the frequency deviation and B is the maximum bandwidth of the input signal, then the result for the in FIG. 4 for a maximum bandwidth and to prevent overlapping

In these equations »the ratio of the stroke reduction, while / which normalized for a total loop delay of one second Input modulation frequency is. So is

^l351

~ ■> * ~ TI '~ Jf

70-—.

If an input signal of 70 MHz is assumed, the following applies by definition

fa + h = 70.

Solving these three equations at the same time gives

140; V.

5 / V -2

(42)

L =

Λ =

70

(43)

(44)

(45)

The following table shows optimal frequencies for different values of n.

4 6 8

10

20th

100

35

31

30th

29.5

29.2

28.6

28.0

l "

26.2

27.2 27.5 27.6 27.7 27.9 28.0

43.8 42.8 42.5 42.4 42.3 42.1 42.0

Since the frequency values are so close, investigations on a circuit arrangement according to FIG. 2 the frequencies of 28 and MHz were selected for / „and f _h. This results in a maximum

10

Bandwidth of? 8 MHz. when η becomes large. For the investigations, T ₅ and τ ,, were chosen so that η = 3.

F i. G. 5Λ and 5 B show the amplitude and phase behavior of the two bandpass filters 5 (1 and 4 (i The increase in the l'hasenkurvc results in filter 5 ( a delay of 280 ns and for filter 4 <a delay of 130 ns. The predicted! Stroke reduction is accordingly

N =

28 () J-_T3O
Ί30

= 3.15.

The sub reaction of the circuit arrangement 4 (was made using an IF input sign :; '« of 70 MIIz by connecting its output to a spectrum analyzer. Then became A sinusoidal frequency modulation of 100 kHz is impressed on the IF input signal and the degree of modulation adjusted so that the first zero value for the carrier frequency resulted in the spectrum. Then wtirdi the IF signal of 70 MHz was fed directly to the Spckian analyzer, and it became the modification frequency again adjusted so that the first null value resulted for the wearer. The ratio of the The new modulation frequency to H) OkHz results in the reduction of the frequency deviation. The measured Wcrl yielded 3.3 and thus resulted in an accuracy of the prediction that met expectations. The investigations found that the circuit arrangement 4t cririhts a linear reduction without the necessity for demodulation. Therefore there is no demodulation threshold. the that Operation of the induction-like circuit arrangement

35, could stand in the way.

1 sheet of drawings

Claims (4)

Patent claims: 1. Circuit arrangement for changing the frequency deviation of frequency and phase modulated Signals, characterized in that for processing the frequency or phase modulated Signals two channels (14 and 16) are provided and each channel has a delay element (22 or 28) and a mixer (20 or 26), in which the input signal with the delayed Signal of the other channel is mixed, and that of at least one of the channels (e.g. 14) an output signal is derived, the frequency of which is compared to the frequency of the input signal is shifted according to the delay times of the delay elements (22 and 28). 2. Circuit arrangement according to claim 1, characterized in that the output signal a feedback signal used to stabilize the amplitude of the input signal is derived. 3. Circuit arrangement according to claim 1 or 2, characterized in that the delay elements are formed by bandpass filters which In each case, let the lower sideband of the fed you pass through 4. Circuit arrangement according to one of the preceding claims, characterized in that in each Kam '(14 and If) two delay elements (18 and 22 or 24 and 28) and the mixer (20 and 26) each arranged between the delay elements of the corresponding Kana's and that the signal emerging from the first delay element (18 or 24) of a channel is mixed with the output signal of the second delay element (28 or 22) of the other channel.