DE1043420B - Phase modulator, in which circles are detuned in the rhythm of the modulation through variable capacities - Google Patents

Description

GERMAN

The invention relates to a phase modulator in which circles in the cycle through variable capacitances the modulation can be detuned.

Phase modulators that incorporate a variable capacitance circuit are known. They make use of the well-known fact that an oscillation circuit does not change its amplitude, or only changes it very little, when it is detuned about the resonance position. The relationship between amplitude and phase of an oscillating circuit is shown in FIG. 1. It can be seen from it that with a detuning of ± 1 (45 ° detuning) the amplitude changes only by 30 ° / ₀ , while the phase angle changes within the range of ± 45 °. How far this phase curve can be controlled depends on the required distortion factor, which in turn is determined by the linearity of the phase curve. It should be assumed in the following that the ± 1 detuning also corresponds to the required distortion factor, so that the modulator generates a phase angle deviation of ± 45 °.

Phase and frequency modulation are now through the relationship

fm

Δφ ₀ = phase angle deviation in radians,

Af ₀ = frequency deviation in Hz,

fm = modulation frequency in Hz,

linked together. A frequency-modulated oscillation can therefore be understood as a phase-modulated oscillation with the angular deviation Δφ ₀ = Af Jfm .

In the case of radios in the VHF band that work with frequency or phase modulation, there is always a certain one Frequency deviation prescribed. So z. B. radiotelephones have a frequency deviation of ± 15 kHz without having an impermissibly high distortion factor. If you now put the entrance The maximum phase deviation of ± 45 ° mentioned above is based on a modulation frequency of 1000 Hz a frequency deviation of

Af ₀ = Αψ ₀ ■ fm =

45
360

1000 = 125 Hz.

In order to get the required stroke, you start with a very low frequency and multiply the frequency, until you get to the desired end frequency, since with the frequency multiplication also the Frequency deviation with is multiplied. In the above example, the frequency would be increased more than a hundredfold must in order to achieve the required frequency deviation. This is a major disadvantage of phase modulation, the is eliminated to a considerable extent by the invention.

Phase modulator, in which by

variable capacitance circles can be detuned in the rhythm of the modulation

Applicant:

Telefunken GmbH,
Berlin NW 87, Sickingenstr. 71

Dipl.-Ing. Klaus Sann, Ulm / Danube,
has been named as the inventor

According to the invention, in a phase modulator in which a circuit is detuned in time with the modulation by a variable capacitance, several circuits each equipped with a variable capacitance are combined into a subcritically coupled filter which is tuned in such a way that the ripple of its phase response is in the range of Αφ = 45 · (2 »—1) ⁰ practically vanishes, where η denotes the number of circles.

When using a three-circuit filter according to the invention, this would mean that a completely linear phase deviation of ± 112.5 ° results. In the case of a four-circuit filter, on the other hand, which is shown in FIG. 2, the linear phase deviation amounts to ± 157.5 °. If you put the latter value in the equation Αψ ₀ = Af _o jfm , you get a frequency deviation of around 440 Hz with a negligibly small distortion factor in contrast to the relatively high distortion factor with the 45 ° detuning of a single circuit. In order to arrive at a correct result, one must consider the single and four-circle filters with the same distortion factor. The single-circuit filter results in a distortion factor of 4% with a phase deviation of ± 20 °, whereas the four-circuit filter only achieves a distortion factor of 4 ° / ₀ with a phase deviation of ± 200 °, i.e. ten times the phase deviation of the individual circuit.

As an exemplary embodiment, FIG. 2 shows a phase modulator with a four-circuit filter. Via the tube 1, the high frequency reaches the filter, which consists of four identically structured circuits I, II, III, IV, each of which is equipped with a variable controllable capacity. The four circles are coupled to one another in a subcritical manner via the coupling capacitors C _S1 , C ₆₂ , C _713. This filter is then adjusted so that the ripple of its phase response is in the range of

809 678/232

/ ίφ = 45 (2η - i) ⁰ practically vanishes. The modulation voltage U _mod is fed to all four circuits in phase.

The junction capacitance of a silicon area diode is particularly suitable as a variable capacitance. The silicon diode has first, very small losses, about 0.6 ° / ₀ at 10 MHz, and secondly a low TK their capacity, which is about +100 x 10 ^'6. Also, the increase in attenuation with increasing temperature for these diodes is negligible.

Claims (2)

Patent claims: 1. Phase modulator, consisting of several modulators connected in series, which, from the From the modulation side, they are connected in parallel, characterized in that several circuits, each equipped with a variable capacitance, are combined to form a subcritically coupled filter and the coupling is balanced in such a way that the ripple of its' phase response is in the range of A φ = 45 · (2n —1) ⁰ practically disappears, where η denotes the number of circles. 2. Phase modulator according to claim 1, characterized in that silicon area diodes as variable capacitances are used. Considered publications:
German patent specification No. 844 322. 1 sheet of drawings