DE1236603B - Broadband frequency modulator - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

H03c

German class: 21 a4- 14/01

Number: 1 236 603

File number: N 22233 IX d / 21 a4

Filing date: October 20, 1962

Open date: March 16, 1967

The invention relates to a broadband modulator, consisting of two oscillators of different frequencies, which are frequency modulated by the modulation voltage, preferably in phase opposition, and a mixer in which the difference frequency between the two, serving as the output voltage of the modulator Oscillators is obtained.

It is known that frequency-modulated signals are free from distortion in multi-channel transmission particularly high demands are made. The linearity of the modulator characteristic must be in this Trap to be particularly large. The linearity of the previous broadband modulators, in which the reflector voltage a klystron operated as a matched load with a large electronic bandwidth with the Signal voltage is modulated, for example, is not for a high quality multi-channel transmission sufficient. So it is known that the linearity of such modulation klystrons by the insertion to improve suitable reactances in the load circuit. But since the oscillator frequency is right in this case is high, this requires waveguide parts that require a mechanically very complicated adjustment, which often has to be readjusted over time. As a result of such a | klystron modulator The high frequencies used are also used for transposition into the intermediate frequency position a second microwave oscillator is necessary, which is both unstable and hassle-free such an arrangement is significantly increased.

Furthermore, so-called push-pull modulators are known in which two are variable in frequency Oscillators are connected in push-pull in such a way that when the frequency of one oscillator decreases under the influence of the modulation voltage, that of the other increases by the same amount. Such modulators are very useful for modulating small numbers of channels, however, they are not suitable as downright broadband modulators for the following reasons: To avoid distortion To avoid the second degree, the frequency deviations of the two oscillators would have to be perfect be identical. However, it cannot be because of the difference in frequency between the two Oscillators for the modulation is crucial. Even if second order distortions are relative can be kept small by choosing the center frequency of the two oscillators very high, additional instabilities would thereby call into question the usefulness of the modulator.

To eliminate these difficulties, a broadband modulator is now proposed according to the invention-broadband frequency modulator

Applicant:

Nippon Electric Company Ltd., Tokyo

Representative:

Dipl.-Ing. M. Bunke, patent attorney,

Stuttgart 1, Schloßstr. 73 B

Named as inventor:
Sukehiro Ito,
Yoshito Ueno, Tokyo

Claimed priority:

Japan November 8, 1961 (40 326)

gene, which is characterized, that for the center frequency of the oscillators / ₁₀ and / ₂₀ for the modulation voltage e _x and e _{2 of} the two oscillators and their tank circuit capacitances C ₁ and C ₂ and their bias for their capacitance diodes V ₁ or V ₂ and constants k the equation

/ ₂₀ e ₂ ² l2C ₂ + - =

is applicable. - ^

The invention is to be explained in more detail below with reference to the figures. '*

In FIG. 1 shows a broadband frequency modulator according to the invention. It consists of the two oscillators 11 and 12 with a tunable frequency. A mixer 13 is connected to the two oscillators 11 and 12 in such a way that the difference frequency of the two frequencies of the oscillators 11 and 12 is obtained in it. Furthermore, the two oscillators 11 and 12 have a common input circuit 14 , the task of which is to change the frequencies of the oscillators 11 and 12 in the rhythm of the modulation frequency supplied via the terminals 36. This modulation frequency

709 519/199

can either be an audio frequency or a multi-channel frequency mixture be. The oscillator 11 has a negative resistance 16, for example a tube, a transistor or a diode with negative resistance. An inductance lies parallel to this 18 and a capacitance 19, both of which are effectively connected to the negative resistor 16, so that they represent a tank circuit 17 in cooperation with the negative resistance. A capacitance diode 20 with a corresponding voltage source 21 connected in series and a high-value resistor 22 are parallel to the capacity 19 of the tank circuit 17. One to the jhochohmigen resistor 22 in the Voltage source 21 parallel capacitance 23 provides a low frequency for oscillator 11 Impedance and one for frequencies of the input signal high impedance. One side of the tank circuit is earthed at point 24 as shown.

The other variable-frequency oscillator 12 is constructed in a similar manner. It consists of one negative resistance 26 and a tank circuit 27, which in turn consists of an inductance 28, a capacitance 29 and a capacitance diode 30 with a corresponding voltage source 31 and a high-resistance Resistor 32 with parallel capacitance 33 is there and at one end, such as shown at which point 34 is grounded.

The input signal, for example a multichannel mixture, arrives at terminals 36 of the input circuit 14 on the primary turns of the transformer 37. The secondary winding of the transformer 37 is grounded at its center. There are variable resistors to the two halves of the secondary winding 41 and 42 connected in parallel. The amplitudes of the in the two halves of the secondary winding induced voltages can thus be adjusted by the wiper contacts. Thus, the Capacitors 43 and 44 on the capacitance diode 20 and 30 of the oscillators 11 and 12, respectively The amplitude of the modulating input voltage can be set individually. Since the frequency of the Oscillator 11 by the resonance frequency of the tank circuit 17 and thus by the capacitance of the diode 20 is determined, the oscillator frequency is frequency modulated by the input voltage. In the same The oscillator 12 is also frequency modulated. Since now the phases of the frequency modulating the oscillator Voltage through the counter-traction transformer 37 with its grounded secondary center tap are opposite to one another, is the Modulation voltage for oscillator 11 positive if the modulation voltage for oscillator 12 is negative. So when the oscillator 11 has a frequency deflection due to the modulation voltage Experiences higher frequencies, the oscillator 12 is at the same time by the same amount shifted to lower frequencies. In this way, then, the two oscillators with respect to the frequency is modulated in push-pull. One of the input channels is therefore obtained at the output 46 of the mixer 14. voltage proportional voltage resulting from the difference between the frequencies of the two Oscillators 11 and 12 results.

The inductance 18 of the tank circuit 17 and the capacitance 19 of the same in the oscillator 11 are now denoted by L ₁ or C ₁ and the variable capacitance of the diode 20 by B ₁ and its bias voltage by V ₁ and the modulation voltage effective at the diode 20 by C. ₁ sin pt, then applies to the frequency Z _{1 of} the oscillator 11

J ₁ - γ

It should be noted that in the event that the angular frequency ρ in the expression ε _λ sin pt is within the audio frequency, this expression is the through

ίο the modulating signal represents impressed information itself and that if the angular frequency ρ lies within the carrier frequency and the amplitude ^ is changed by the signal of the information or, in other words, if the expression e _x sin pt represents an amplitude-modulated subcarrier, then there is the amplitude e _x the change in time of the envelope of the angular frequency ρ of the carrier frequency again.
Furthermore, the following applies to the capacitance O _{1 of} the diode 20

Here, K is a constant according to the explanations given in the RC Review, 1959, March, pp. 58 to 85, which is independent of the diode 20 or its direct current or alternating current bias. The oscillator frequency / _{] 0 of} the oscillator 11 is therefore in the event that the modulation voltage is equal to zero, that is to say e _t sin pt = 0

/ 10 = τ—

2π L ₁ C ₁

This is the center frequency of the frequency-modulated oscillator 11. If one sets pt = χ for sin, then the following applies for the oscillator frequency of the oscillator 11

Λ Μ =

L ₁ C ₁

7 _Χ + e _x x

Although this expression is a

If it is a function of e _x and other independents, it can be seen as a function of χ alone.

The function Z ₁ W can be converted into a Maclaurin series if

Ie ₁ ^ l < V ₁ (5)

is applicable.

Because within this range the function is infinitely differentiable and the remainder R _n according to the Maclaurin series converges with increasing η to 0. It is therefore true

1!

2!

n \

φ) _

Equation (6) shows the relationship between the modulating input signal e _x χ and the oscillator

frequency Z ₁ (X) if one considers e _t as a constant. It roughly reflects the relationship between the modulating input signal and the frequency deviation of the oscillator 11. The first expression on the right hand side of equation (6) is:

/ i (0) = / ₁₀ , (7)

because e _x χ = 0 when x = 0. Zio ^{can be seen from} equation (3). The second expression is the oscillator 11 modulating signal is opposite. The center frequency Z20 i ^st thus given by

Z20 -

2π 1 / L ₂ (C ₂ + -IL

K Zio ei x

A mathematically analogous treatment of this equation gives for

1!

"1 +

pi

(8th)

\ 2π

15th

'V, -e ₉ x

and is thus proportional to the modulation voltage Ij ₁ X. This element represents a frequency deviation from the center frequency of the oscillator 11, which is proportional to the modulating signal.

This expression therefore represents the frequency modulation component required. The third Expression reads

The function / ₂ (x) can in turn be converted into a Maclaurin series if

e ₂ x |

is, thus results for

3 KZ

₁₀ <

2C ₁ + -J.
1 / F ₁

2!

(9)

The first link on the right
chung (6 ') is again

Z ₂ (O) = Z ₂₀ ;

applies to the second term

and is proportional to the square of the modulation voltage e _x χ. The third and the following terms are proportional to the third and higher order modulation voltages. The second and the following terms therefore represent the second and higher order distortions in frequency modulation.

By exchanging the indices 2 for 1, this results in the same way for the oscillator 12

and the third link is given by

Z ₂ = jzmr-rz -.—--. (10

(60
the sliding

1!

3 ^ / ₂₀ e ₂ ² x ² [2C ₂ +

If the diode 30 has the same characteristics as the diode 20 in the oscillator 11, the constant K is also the same for the two diodes, and it applies

2!

(T)

where for the modulating input signal the same expression unpt, but with the opposite sign, _{i.e. -e 2} sin /; /, applies, since the phase of the signal corresponds to the

The broadband frequency modulator 10 has an output frequency which is equal to Zi ^- Z ₂ and is produced in the mixer 13. The frequency-modulated frequency F obtained at the output terminals 46 of the mixer 13 is. ^

F- \ f, m - /. M + ^ Um-JiM

f " ( Q) -Z ₂ " (Q)] 2!

72!

(10)

To create this equation, add or (50 apply. The first term on the right-hand side that Maclaurin's terms can be subtracted from the other of the equation, provided that equations (5)

1
2π

/In

This expression represents the center frequency of the broadband modulator according to the invention. The second Member means:

^Kx

1!

/? 0f 2

- ^{3 /} . , K \

where C ₁ and e _{2 have the} same sign and io or - e ₂ sin pt is expressed. the

are proportional to each other, since the antiphase equation (12) represents the frequency-modulated output

of the two modulation voltages for the oscillator output, which is generated by the broadband frequency modulator

11 or 12 can already be achieved by e _x x or <? J sin pt or - e _% x 10.

The third link is called

2!

2Kx ²
64

6 / ^ ₁ Q +

KK ^

Zsso ^ ² 2 C ₁

] / T / ₂ C ₁

KY

(13)

This term represents the second-order distortion at the output of the broadband frequency modulator. In order to keep the second-order distortion as low as possible, it is sufficient to use the constants C ₁ C ₂ , L ₁ L ₂ , V ₁ V ₂ , e _x e ₂ to be chosen so that they correspond to the following equation

7 Γ -4-

ζ. C ₁ ^ p

α:

- ⁶ ICs

{c. + φτ

(14)
suffice.

Since the distortions originating from the third and higher harmonics, which are represented by the third and the following links in the chain, are small compared to the distortion originating from the second harmonic, they play practically no role in the problem at hand. It is therefore possible to significantly increase the linearity of the modulation characteristic in the present broadband frequency modulator 10. It must be emphasized that the center frequencies / ₁₀ and Z _{20 of} the oscillators 11 and 12 present in equation (14) are determined by equations (3) and (3 ') and that the constants K of the varactor diodes 20 and 30 are the same can be if their characteristics are the same.

In the broadband frequency modulator 10 according to the invention, the values for C ₁ C ₂ , L ₁ and L ₂ and V ₁ and K ₂ , C ₁ and e ₂ which satisfy equation (14) deviate according to the center frequencies f ₁₀ and / ₂₀ of Oscillators 11 and 12, the diodes 20 and 30 used and the negative resistors 16 and 26 used. Therefore these values are to be determined experimentally by measuring the oscillator frequencies. First, the values L ₁ and L _{2 of} the tank circuits 17 and 25 must be determined. The remaining constants, for example the diode bias voltages V ₁ and V _2, can be adjusted so that the center frequencies of the oscillators 11 and 12 _{reach the desired values for a given capacitance C 1} and C _{2 of} the tank circuits 17 and 27, as do the voltages e _x and e _{2 of} the modulation signal if it is a frequency-divided signal. Then a new adjustment is carried out for the constants C ₁ and C ₂ after the constants β _λ ε ₂ , V ₁ V _{2 have been established.} It may also be necessary to adjust the constants e _x and e _{2 again} after the constants C ₁ and C ₂ and V ₁ and K _{2 have been established.} By repeating these balancing processes several times, all constants C ₁ C ₂ , L ₁ L ₂ , V ₁ K ₂ , e _x and e _{2 can,} under certain circumstances, assume values so that they satisfy equation (14). On the basis of FIG. 2 another embodiment of a broadband frequency modulator 50 according to the invention will be explained. This also consists of two variable frequency oscillators and a mixer which is connected to these oscillators so that its output is equal to the difference between the two oscillator frequencies. The components 11, 12 and 13 are identical to those of FIG. 1, with the exception that in the tank circuit 27 'of the oscillator 12' the polarities of the varactor diode 30 'and the associated bias voltage source 31' differ from those of the polarities in the embodiment according to FIG. 1 shown are reversed. The input circuit 54 of the frequency modulator according to FIG. 2 consists of the variable resistors 55 and 56, which are directly parallel to the input terminals 36. One end of each of the two resistors is grounded at 57. Furthermore, the two resistors each have a sliding contact and are thus set in such a way that the oscillators 11 and 12 'receive the necessary modulation voltage. The advantage of the frequency modulator according to FIG. 2 consists in the fact that the two modulation voltages for the oscillators 11 and 12 'can be in phase. With such an arrangement it is therefore possible to completely prevent second-order distortions caused by the modulation characteristic by selecting the constants C ₁ , C ₂ , L ₁ , L ₂ , V ₁ , V ₂ , e _x and e _{2 in} such a way that that they

simultaneously satisfy equations (5), (5 ') and (14).

In FIG. 3 shows a further exemplary embodiment of a wide web frequency modulator 60 according to the invention. This consists of the two oscillators 11 'and 12 ", which are essentially constructed in the same way as the oscillators shown in the previous exemplary embodiments. A mixer 13 is connected to these two oscillators. It produces the difference between the two oscillator frequencies. There is also an input circuit 64 connected to the two oscillators, so that they are changed in frequency according to the incoming modulation voltage Contains capacitance and that finally a radio frequency blocking inductance 65 is arranged between the capacitance diode 20 and the high-resistance resistor 22 , the end of the inductance in the vicinity of the diode 20 being grounded by a capacitance 651. A bias voltage source 21 for the diode 20 is constructed in this way that a terminal 211 , not shown s power supply with a voltage of 150 V, which also serves other purposes, the current flow in a Zener diode 218, which is parallel to the resistor 213 and at the point 24 , via the resistors 212 and 213 . causes a stabilized bias source of about 113 V to be tapped at terminal 218.4 of the Zener diode. The tube 16 'has an anode circuit 66 which is arranged in such a way that the output of the aforementioned 150-volt power supply via a coupling circuit comprising a resistor 662, a capacitor 663, a capacitor 664, and a further resistor via the terminal 661 665 and a further capacitor 666 and via an inductance 669, the task of which is to keep the output oscillation away from the decoupling circuit, is supplied to the anode of the 4p tube 16 '. The grid of the tube 16 'is connected to the tank circuit 17' via a coupling capacitance 67. In addition, it is grounded via the resistor combination 681 and 682 , the terminals 69 being provided in parallel to the resistor 682 for connecting an ammeter. A variable capacitance 29 'is arranged in the oscillator 12 ″ and serves as a capacitive element of the tank circuit 27 ″. Furthermore, a bias voltage source 31 ″ is arranged so that the voltage of -105 volts of a power supply unit, which is not shown and which serves as a negative voltage source for other purposes, flows through the series resistors 312, 314 and 315 via the input 311 caused, so that at a Zener diode 318, to which the series circuit of the resistors is connected in parallel with 314 and 315, a constant bias voltage of about -.. arises 13 volts, is taken off the 314 Λ of the potentiometer 314 through the wiper contact far as the other constructional details of the Oscillator 12 ″ with those of the oscillator 12 'according to FIG. 2 or of the oscillator 11 'match, they are provided with the same reference numerals as those of the oscillator 12' or their first digit 6 has been replaced by 7 and will not be explained further. It should be emphasized that since the tank circuit 17 'has no additional fixed capacitance, the frequency of the oscillator 11' is higher than that of the oscillator 12 ".

For example, the center frequencies of the oscillators 11 ', 12 "are 78 or 62 MHz, if the others Values of the circles correspond to the list given later.

The mixer 13 of the broadband oscillator consists of the transformers 83 and 84 for receiving the frequencies supplied by the oscillators 11 'and 12 "via the capacitors 81 and 82 , an output transformer 85 with the output terminals 46, a diode group 87 connected to the transformers 83, 84, is that they form a ring modulator along with them 85 connected so on. This is used for the amplitude modulation of the higher frequency greater at the lower frequency, which is obtained through the secondary winding of the transformer 84th the frequency higher lying is the connected in series secondary and primary windings of the transformer 83 between the two center taps of the secondary winding of the transformer 84 and the primary winding of the transformer 85. By means of the capacitance 88, which is parallel to the primary winding of the transformer 85 and together with this forms an oscillating circuit, the lower sideband of the amplitude-modulated electrical Schw ingung or an electrical oscillation of the difference between the frequencies of the two oscillators 11 'and 12 "at the output terminals 46 selectively obtained. If desired, the output of the frequency modulator can be amplified or frequency multiplied. The input circuit 64 is designed so that a resistor 91 is parallel to the input terminals 36, with which the input impedance of the frequency modulator is matched to the impedance characteristic of the input signal, and that an input terminal 36 is also connected directly via the capacitor 43 to the oscillator 11 ' while the other input terminal 36 is grounded. The potentiometer 92 and the resistor 93 are connected between earth and the one input terminal which is connected to the oscillator 11 '. A wiper contact of the potentiometer 92 is connected to the oscillator 12 "via the capacitor 44. In this way it is possible to set the ratio of the voltages modulating the oscillators 11 'and 12".

In the broadband frequency modulator according to FIG. 3 are the individual components to achieve this the smallest possible distortion of the second degree of the input signal is selected as follows:

In input circuit 64: V resistor 91 250 Ω

Resistance 92 Λ variable from

• ^ 0 to 300 Ω

Resistance 93 75 Ω

Capacitor 43 and 44 each 1 μΡ

The frequency oscillators 11 'and 12 "contain the following items:

Half of a double triode 12 RLL 3 (12 AT 7) are used as tubes 16 'and 26'.

The windings 18 and 28 are each 3 mH.

The variable capacitance 29 'ranges from 0.8 to 7 pF. The varactor diodes 20 and 30 'are called Silicon diodes SD111 used. The capacity

709 519/199

Claims (1)

11 12 these diodes changes with a bias voltage. In the present embodiment, vari- change from 25 to 5 volts from 5 pF to 15 pF. able capacitance diodes as variable reactance elements specified. The inductance of such capacitance diodes Resistance 212 4 kΩ does not change noticeably with the one on them Resistor 312 33 kQ 5 lying bias. It should be emphasized that Resistor 315 8.2 kΩ the variable reactance elements also in other ways Λτ.τ · a * Aiii ini, n can be constructed. Resistance 213 10 KiI ™ ι ■ ι ·. - ^ _{A c} ~, ι ■ · ι j · _π .. _t Although the pipes in the third exemplary embodiment - Resistor 314 2 kΩ _{with its cathodes} grounded and the feedback Zener diodes 218, 318 each ₁₀ windings are placed on the cathode circuits RD-13 A also includes an anode or grid earthed circuit (IN 1513) and the jerk capacitors 23.33 3.3 μΡ coupling circuits on the anodes or the grid Capacitors 651, 751 90 pF are placed. It should also be emphasized that Windings 65, 75: 414 mH ^{15 in the dri "en} embodiment, each capacitive EIe- - _n ment that does not belong to the tank circuit is used Resistance 662 can be 5 kΩ, provided not only its stray capacitance Resistor 762 12 kΩ is sufficient for the tank circuit. Capacitors 664, 764 0.02 aF Capacitors 67.77 100 μΡ »Claim: Resistors 681, 781 10 kQ broadband modulator consisting of two oscillator gates of different frequencies, which by the Resistor 682, 782 Shunt ^ modulation voltage preferably in phase opposition resistors are frequency modulated, and a mixer, door 1 mA _{25 m} ^ _{61n d} j _ea j _s ^ output voltage of the modulator serving difference frequency of the two oscillators In the output circuit 63 there are the following individual won, thereby marked- parts: net that for the center frequency of the oscillators Capacitor 81 82 0 002 uF / _{10 or / 20} for the modulation voltage _{C 1} or e ₂ IVUIlUClIoClLUl oil. Oid Vjvui LA.JL ₁ ι · ι s ~ \ · ΐϊ j. ι ι-η ι ι * 3 ° of the two oscillators and their tank circuit Wmdungsverhaltnis capacities C ₁ or C ₂ and their bias of the transformer 84 4: 4 _{for their} capacitance diodes V ₁ or F ₂ and Turn ratio constants K the equation of the transformer 83 3: 3 Turn ratio 35, _p d _lc , K \ _P 4or \ ^K of transformer 85 5: 5 ■ / " ^e i ^ ^c i + y ™ J / 20 ^ ₂ ^ C ₂ - | - ^ As a diode group 87 four germanium diodes of the type SD 12H (IN 34A) capacitor 88, 5 pF. As already described, the broadband frequency modulator is according to the invention simple in structure. Its resulting frequency-modulated oscillation has practically no second distortion Degree. is applicable. Documents considered · French patent specification No. 908 726. 1 sheet of drawings