IE45589B1 - Improvements in or relating to quartz-controlled high-frequency oscilliators - Google Patents

Abstract

1529549 Automatic frequency control SIEMENS AG 26 July 1977 [17 Sept 1976] 31203/77 Heading H3A In an a.f.c. loop for locking a controlled oscillator 4 to a crystal controlled reference source 1, the output from the reference source 1 is fed via a divider or multiplier 2 to a mixer 41 in the controlled oscillator and the output from the mixer is compared with a harmonic or subharmonic of the reference signal in a comparator 6 to produce the required control signal for the oscillator 4.

Description

The invention relates to quartz-controlled highfrequency oscillators of the type having a regulating circuit which controls said oscillator, using a reference Signal that is considerably lower than the output of the oscillator circuit.

Micro-wave carrier supply systems are constructed largely with free-running oscillators whose output is synchronised by use of a special regulating circuit using a reference signal of considerably lower frequency than the - I oscillator output frequency, Such regulating circuits are subject to special requirements, and should comprise as few components as possible, preferably all of a simple nature, involve a minimum of technical adjustments, and should have characteristics such that the output has a low noise content, ' is free from secondary frequencies, and effects a simple frequency change.

It is'difficult to adequately satisfy all these requirements in carrier supply systems exhibiting direct frequency multiplication, based on a quarts oscillator £0 working.at. approximately 100 MHz used to synchronise oscillators of up to e.g. 2 GHz and a following frequency multiplier, or using a synchronised oscillator operating in the carrier frequency range, wherein a frequency or phase comparison is carried out at the carrier frequency.

One object of the present invention Is to provide an oscillator construction that avoids the problems which occur with the above-described circuits, to give low noise and high stability, without a low resistance to secondary frequencies and the need for high adjustment outlay or high component costs. -245588 The invention consists in a quartz-controlled highfrequency oscillator in which a reference sign'al of considerably lower frequency is provided by a quartz-controlled reference oscillator and used in a regulating circuit to control a free-running high-frequency oscillator, said quartz oscillator feeding a reference signal via a frequency multiplier or frequency divider to an amplifier that is followed by a filter, the output signal from said filter being fed to a harmonics mixer which is connected in, the free-running high-frequency oscillator and produces’a comb of harmonics of the driving signal from said filter, the intermediate frequency obtained from the harmonics mixer being fed via a selective amplifier to be compared with a selected harmonic or sub-harmonic of the quartz oscillator in the regulating circuit.

The particular advantages which are achieved by a construction in accordance with the invention are as follows :The reference signal requires to be of only very low magnitude, and is produced in a particularly simple manner. The harmonics mixer which produces the harmonics and intermediate frequency is likewise very simple in construction; it preferably consists of a simple Schottky diode in a glass housing, which is installed in a cavity resonator of the high-frequency oscillator. No time-consuming adjustment is necessary. The phase or frequency comparison, which may be effected selectively for carrier supply systems with or without service call modulation, is itself carried out at a low frequency position and is therefore able to be effected - 3 particularly simply and at a favourable cost* Furthermore» the regulating concept corresponding to the invention can produce very high secondary frequency attenuations,*, namely 90 dB and more* The adjustment, outlay S is low, and stability or noise problems do not occur during adjustment of the regulating circuit, as the multipliers employ only Schottky diodes, and there are no multipliers using capacitance diodes involved. A clearly defined frequency change can be achieved by a suitable selection of the multiplication factor of the frequency multiplier v connected following the quartz oscillator, or by limiting the oscillator tuning range to determinate frequency bands. Finally, a high degree of reliability is achieved by the tolerance insensitivity of the regulating loop and the low loading and number of the components. Xt is also possible to attain the fixed multiplication factors in carrier supplies of- existing systems by an appropriate selection of the multiplication factors and intermediate frequency to enable existing quartz crystals to be re-used.

The invention will now be further described with reference· to the drawings, in which iFigure 1 is a simplified block schematic circuit diagram illustrating one exemplary embodiment of the invention; and Figure 2 is a graphical representation of the frequency spectrum of the signals in the harmonics mixer.

Xn the block schematic circuit diagram shown in Figure l, a quartz-controlled stabilising oscillator produces a reference signal in a conventional frequency position in the 100 MHz range. This signal is then multiplied and/or divided by a factor m (where m is a whole number) in a following frequency multiplier or divider 2. The signal is then amplified in a subsequently connected amplifier 3, which is followed by a band-pass filter 7. The output of the band-pass filter 7 is fed to a harmonics mixer 4' with a Schottky diode, which mixer is integrated into the resonant circuit of a free‘5 running high-frequency oscillator 4. The high-frequency X oscillator 4 is regulated by a varactor diode in this embodiment, and the regulation and control of the oscillator is effected by a regulating circuit 6 in which a frequency or phase comparison is carried out, and which may be pro15 vided with an additional monitoring circuit U. One input of the regulating circuit 6 is supplied with an output from the quartz-controlled oscillator 1, this output being the desired harmonic pf^ that is obtained from the quartz oscillator output via a filter 8. A second input of the regulating circuit 6 is connected via a selective amplifier having single-circuit characteristics to receive both the output of the harmonics mixer 4' and the output of the filter 7, whilst the output of the regulating circuit 6 controls the varactor diode of the free-running oscillator 4 A comb of harmonics of the driving signal mf^ passed from the filter 7 is formed in the harmonics filter 4’.

(The frequency spectrum in the harmonics mixer 4’ is represented graphically in Figure 2). Xn the regulated state an output is produced, and the free-running - 5 45589 oscillator 4 oscillates with a displacement of pf^ next to ri-times the harmonic of the driving signal mf^. Here the multiplication factor or division factor £ preferably has a value of 1 or 2, but does not have to be a whole number.

In the harmonics mixer 4', the intermediate frequency which is formed in the frequency ρ£'σ that contains any frequency error of the free-running . oscillator 4, and after this has been selectively aqiplified in the amplifier 5, it is compared with the controlled frequency pf^ from the quarts oscillator 1 in · the regulating circuit 6. The regulating circuit 6 regulates the free-swinging oscillator 4 via its tuning diode, in such manner that the intermediate frequency signal pf’^ becomes equal in frequency to the harmonic ρ£^ of the quartz frequency. A monitoring device U in the regulating circuit S can be used to detect and report any desynchronisation of the free-running oscillator 4 and subsequently synchronise this oscillator· The mathematical relationship between the carrier frequency fT and the quarts frequency f is governed by the

Claims (8)

1. CLAIMS:1. A quartz-controlled high-frequency oscillator in which a reference signal of considerably lower frequency is produced by a quartz-controlled referen.ee 5 oscillator and used in a regulating circuit to control a free-running high-frequency oscillator, said quartz oscillator feeding a reference signal via a frequency multiplier or frequency divider to an amplifier that is followed by a filter, the output signal from said filter 10 being fed to a harmonics mixer which is connected in'the free-running high-frequency oscillator a nd produces a comb of harmonics of the driving signal from said filter, the intermediate frequency obtained from the harmonics mixer being fed via a selective amplifier to be compared with IS a selected harmonic or sub-harmonic of the quartz oscillator in the regulating circuit.

2. An oscillator as claimed in Claim 1, in which a frequency multiplier or divider is connected between tha. quartz oscillator and the regulating circuit to obtain 2o a selected harmonic or sub-harmonic of the quartz oscillator output.

3. An oscillator as claimed in Claim 1, Ιη which a selected harmonic is withdrawn from the quartz oscillator via a filter. rawxiA. j - 7 L· * 45889 • IS

4. An oscillator as claimed in any one of Claims 1 to 3, in which the harmonics mixer contains an element having a non-linear characteristic.

5. An oscillator as claimed in Claim 4» in which said non-linear element is a Schottky diode.

6. An oscillator as claimed in any one of the · preceding Claims» in which said free-running oscillator contains a varactor diode for regulation purposes· . ’ $

7. An oscillator as claimed in any one of the preceding Claims» in)which said harmonics mixer is. integrated into a resonator cavity in the free-running oscillator»

8. · A .quartz-controlled free-running. highfrequency oscillator» substantially as described with: reference to Figure 1.