DE1930187A1 - Phase locking circuit - Google Patents

Description

DR. ING. E. HOFFMANN · DIPL. ING. W-. EITLE DR. RER. NAT. K. HOFFMANN

PATENT LAWYERS
D-8000 MÖNCHEN 80 MARIA-THERESIA-STÜXSSE 6 TELEPHONE (0811) 441061 1930187

North American Rockwell Corporation, Ξ1 Segundo, Calif .. / USA

Phase giant! Circle

The present invention relates to a phase locked loop - especially for digitally controlled phase error signals - to determine the phase of incoming Signals for locking the phase of a reference signal with respect to the phase of an input signal.

In many cases it is necessary to get the phase of an incoming signal or another phase to bring it into synchronization with the same. Typical; Examples of this type are the acquisition of a command signal in data transmission systems and phase lock demodulators with frequency-modulated systems.

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Known systems of this type use a phase locked loop. in which the input signal offset with noise and other external signals - a multiplier. or phase detector is supplied, which has an output signal of a continuously variable at its second input voltage controlled oscillator receives. The multiplier or the phase detector then produces an output signal that .. is proportional to the phase error or in a certain function - for example a sine function is the phase error between the input signal, and the output signal of the voltage controlled oscillator, is available. This error signal is then generally a low pass filter; supplied, whereby the phase difference corresponding equilibrium current component is generated. The filtered Phase error signal is then a C-Ieichstromver-. more fed and used to control the frequency of the voltage controlled Oscillator is used, the frequency of which is preferably a linear function, that of. the low-pass filter, supplied DC voltage signal is. . . . . .-

Although such systems are in principle satisfactory work, difficulties arise anyway. So are, for example in the voltage controlled oscillator im general varactor diodes or similar elements built into the voltage controlled oscillator for the purpose of a to influence the linear dependency relationship. It surrendered however, there are very great difficulties in achieving a satisfactory linear dependency relationship. However, even if the linearity problem is solved, is the frequency shift per volt change in voltage am Input of the input signal not big enough to get a to ensure satisfactory operation. The operation

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of the voltage controlled oscillator is also either unstable or in some "cases - especially in Use of crystals - 'overstable.'

Another problem arises with regard to the requirements for the voltage level of the control signal, which is fed to the voltage controlled oscillator. The loop gain in a typical phase row The loop generally requires a DC amplifier with a high gain factor, for example 30 ÖÖO. Ordinary DC amplifiers show however, in a known manner, voltage drifts, instabilities, etc.

Accordingly, it is an object of the present invention to provide a phase locked loop that incorporates the aforesaid Does not have disadvantages and a satisfactory one using relatively simple assemblies Operation enabled.

According to the invention this is achieved in that a Frequency shift oscillator is provided which is between a first and second frequency with continuous Phase air generation of the reference signal switchable is, wherein the two frequencies are above and below the frequency of the input signal and that in.Aabigkeit the input signal and the reference signal Controlled switching devices are provided through which the phase frequency shift oscillator of its first to its second frequency and vice versa as a function of the difference in the phases of the two signals is switched.

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The output of the low-pass filter is with a sign detector connected by which it is determined as soon as the phase error signal in one of the two Directions exceed a certain threshold value, whereby the frequency shift oscillator is controlled in dependence thereon.

Result from the training according to the invention see various advantages. First, it eliminates the need for a high gain DC amplifier to use. Furthermore, the complicated voltage is expensive, te oscillator by a simple one Dual frequency oscillator replaced. The need for linearity is thus eliminated, so that with very narrow band design a crystal oscillator is used without the problem of excessive stability occurring. ■ · ■

Further details of the invention are to be found in the following explained in more detail using an exemplary embodiment and will be described, reference being made to the accompanying drawings. Show it:

Fig. 1 is a block diagram of a known phase locked loop with a voltage controlled oscillator; and

Fig. 2 is a block diagram of a phase locked loop according to "

the invention. . ■

In the following, on the drawing '- in particular Fig. 1 - Reference is made in which a known Phase lock loop e .'- 1O is shown.

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, searching phase of the input signal a (t), which can also contain noise and other interfering signals, is fed via a line 11 to a multiplier or phase detector 12, which is continuously fed via a second line 13 as the second input signal of the output signal b (t) variable voltage. controlled oscillator ^ k received · The phase detector produces an output signal c (t) which is proportional to the phase error or in a certain function - for example a sine function - to the phase error. This phase error signal is fed to a low-pass filter 15, which is a simple RC circuit, the output signal e (t) of which is a direct current signal / which corresponds to the difference in the phases of the signals a (t) and b (t) Oscillator 1 ^ supplied to control its frequency.

Assuming that the input signal a (t) through the following equation.

a (t) = Asin (u _Q t + Q, _± ) (1)

and the "signal b '(t)" by the equation

b (t) = Bcos (ω ■ t + θ _ο ) (2) '

is shown, then results in the product facility working phase detector 12 an output signal c (t), the by the following equation

c (t) = ABsin (üJ ₀ ± + 9 _i ) cos (^ _o t + Q _Q ) (3) = 1 / 2AB / sin (2cJ _Q t + Q ₁ + 9 ₀ ) +

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can be reproduced. It will be understood that the output of phase detector 12 has a component proportional to the difference in the phases of the input signals. The low-pass filter 15 eliminates the second harmonic 2 u> , leaving only the DC component sin (0. - θ) ^ As long as sin (Q ^ - & ₀ ) is small, which is usually the case, this expression can be replaced by (Θ. - θ) can be replaced. Accordingly, the output signal e (t) of the low-pass filter 15 can be given by the following formula;

■ ■ e (t) = 1 / 2ABsin (Q ₁ - ^θ ₀ >

be replaced, where K is a constant and θ. the phase

". ■ III fc *

error is.

The voltage controlled oscillator 14 changes its. '■''_ Frequency K radians per second per volt of the control voltage. Accordingly, if the amplifier 16 ^ has a gain. A, then the change in frequency Au) of the oscillator 14 can be given by the following equation

AO = AK _o e (t) -V.,. (5)

be reproduced. By solving the equations ti · and for e (t) and substitution gives see

= e (t) =

AK

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As a typical example of phase lock on a 1800 Hz signal, assume that it varies + 5.Hz and a phase lock, within a range of 1 ° should be reached. If these values are substituted in Equation 7 results.

m ^K o ^A - θ ~ - 2 7Γ / 30Ο

Known product detectors, for example the phase detector 12, have K values of the order of magnitude of 0.1 or less with regard to practical excitations - such as overloading. If, for reasons of stability, a crystal oscillator is used whose frequency has been reduced to 180 Hz by halving the frequency, it can be assumed that K is about 0.1 Hz per volt or f = 2Tf (0.1) = 0.6 . Substituting these values in equation 8 and solving for A results in

α 1SOO 1800 , v

^{A =} ^ iT ⁼ 0.1 χ 0.6 = 30,000. (9)

As has already been mentioned, a / gives a strengthener with such a high gain factor significant difficulties due to instabilities, drifts, etc.

In the following, reference should be made to Fig. 2 may be referred to in

which illustrated a phase locked loop according to the invention is, whereby-the problems that arise through avoidance one DC amplifier 16 and one continuous variable controlled oscillator 1 '^ are avoided, The voltage controlled oscillator 1 ^ f is replaced by a simple frequency shift oscillator 17, which is in the Is able to generate two chosen frequencies. The frequency

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Displacement oscillator 17 must be able to from one frequency to another abruptly with continuous rather Jump phase. With such a design, the output signal of the low-pass filter 15 is a sign detector 18 zuzuf.t, which determines whether the phase error signal in one of the two directions a exceeds a certain threshold. The output signal of the sign detector 18 - for example a simple one Flip-flop circuit can be switched from one state to the other by the output signal of the low-pass filter 15 is switched - a switch 19 which is the frequency of the frequency shift "oscillator 1? controls. The switch 19 is continuously on or off so that the frequency shift oscillator 1? vibrates on one or another frequency of its two frequencies. -

If -the phase of the frequency shift oscillator output signal 17 the phase of the input signal lags behind on the line 11, the switch 19 causes a switchover to the higher frequency on which it is so long remains until the phase of that signal reaches the phase of the input signal on line 11. hat * Once the phase of the frequency shift oscillator output signal 17 leads the phase of the input signal from line 11 by a certain value, causes the Switch 19 that the frequency shift oscillator 17 is switched to his_lower frequency on which it remains until the input signal of the line 11 is reached in phases. In this way, the Phase of the signal on line 13 continuously within-- '

ORIGINAL

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half a predetermined value of the phase of the input signal of the line ΊΊ held. '.

Let the advantages of the present invention be discussed. Not only does the need eliminate itself a provision of a DC amplifier, but also the provision of a complex continuously variable voltage controlled oscillator with its linearity condition. In addition, it can be used for narrow band operation - For example, in command signal acquisition Crystal oscillator for the frequency shift oscillator 17 used without too high a Stability occurs.

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Claims (1)

Pat e nta'n's sayings 1*. , / Phase lock loop - especially for digitally controlled Phase error signals - to determine the Phase of incoming signals to lock the phase of a reference signal with respect to phase of an input signal, thus g e k e η η show net, that a frequency shift oscillator (1 ^) is provided is that between a first and second frequency with continuous phase for generating the reference signal is switchable, the two frequencies above and lie below the frequency of the input signal, and that depending on the input signal and the reference signal controlled switching devices, (19) are provided by which is the phase frequency shift oscillator (17) of its first to its second frequency and vice versa in Depending on the difference in the phases of the two signals is switched. 2 »phase control loop according to claim 1, characterized in that g e k e η η ζ e ich η e t that the switching devices (19) multiply the input signals and reference signals. 3 · phase control loop according to claim 1 or 2, characterized g e k e η η ζ e i ch η e t that the switching devices (19) have a low-pass filter (15) which has a direct current signal proportional to the phase error of the two signals lets through. 4. phase locked loop according to claim 3 »thereby" ge: -, k e η η ζ e i e h η e t that the switching device (19) one of has the DC signal fed device, 9098 86/1007 which determines whether the phase error is a certain Value exceeds in either direction, and which one or the other of the two signal-identifying States created. 5 · Phase locked loop according to claim ^, characterized in that the switching device (19) a device (19) which switches the oscillator (17) ″ from a first to a second frequency causes, as soon as the phase error signal has a certain Value exceeds. 6. phase control loop according to one of the preceding claims, characterized in that the g e k e η nze ic h η e t The oscillator (17) is switched to its higher frequency as soon as the phase of the reference signal matches the phase of the input signal lagging, and is locked to its low frequency as soon as the phase of the reference signal of the Phase of the input signal leads. 7. Phase locked loop according to one of the preceding Arisprüche, thereby ge k e η η ζ ei c h η e t that the Switching devices (19) have a phase detector (12). 8. Phase locked loop according to claim 1, characterized in that the switching device (19) one controlled the input signal and the reference signal Has device which determines whether the difference in the Phase exceeds a certain value in one of the two directions and which the oscillator (14) of its first switches to its second frequency as soon as the difference exceeds a certain value. 90 98 86/1007 Le-β rs e j te