FI86119B - Device for the creation of two oscillator signals - Google Patents

Description

1 86119

Device for generating two local oscillator signals

The invention relates to an apparatus for generating two local oscillator signals, the apparatus comprising first and second microwave local oscillators, each controlled separately by its own phase-locked control loop, comprising a subharmonic mixer for mixing or sampling a sample taken from the local oscillator signal. to compare the phase of the mixed signal and the phase of the reference oscillator signal and to adjust the frequency of the local oscillator based on the phase comparison.

In a microwave radio operating on the "full duplex" principle, two independent local oscillators with microwave frequencies are required if the duplex interval, i.e. the distance between the local oscillator frequencies of the transmitter and the receiver, is not always constant. Since the phase-locked loops 20 are unable to process microwave frequency signals, the phase-locked operation of the microwave oscillator requires some means to lower its frequency sufficiently for the phase-locked loops. One way is to mix the oscillator frequency in the microwave range to a lower frequency using a subharmonic mixer. The so-called however, generating a pumping or mixing signal is not very easy, as its frequency must also be relatively high in some cases.

30 In some previous solutions, the local oscillators of the transmitter and receiver have been completely separate, which is an expensive solution due to the large number of components operating at the microwave frequency. A more cost-effective solution has been found by using the same local oscillator for the 35 transmitters and receivers, but the resulting intermediate frequencies are related to the difference between the transmission and reception frequencies (duplex interval).

In principle, it is possible, at least with parametric frequency dividers 5, to divide the local oscillator signal in the microwave range to a lower frequency for phase-locked loops, but this solution is also expensive.

On the other hand, splitting or mixing high frequencies into lower frequencies could be avoided by using lower frequency local oscillators as well as multipliers that raise the oscillator frequency to the desired local oscillator frequency, but such multipliers are expensive and reduce the achievable frequency raster.

In summary, the disadvantages of the known solutions are either the expensive structure or the binding of intermediate frequencies to the duplex interval. Fixed pre-division or multiplication, in turn, reduces the frequency raster achievable by changing the divider terms of other frequency dividers that may be associated with the phase lock circuits.

The object of the invention is a solution which avoids the above-mentioned problems. This is achieved by a device of the type described in the introduction, which according to the invention is characterized in that the mixing signals of the subharmonic mixers are harmonic multiples of the same oscillator signal.

The basic idea of the invention is to use the receivers as pump signals of the sub-harrow mixers associated with the transmission local oscillators with harmonics of the same oscillator frequency. In this way, instead of two, only one circuit for generating the pump signal of the subharmonic mixer required for the phase locking of the local oscillator is required. Since such circuitry operates in or near the microwave range, it is considerably expensive, so that the invention achieves significant cost savings.

When different harmonic frequencies of the same oscillator are used as the pumping signals of the subharmonic mixers, the interfering mixing results that would occur if the same pumping signal frequency were used for both mixers in the case where the output frequency difference is large. When using the same pumping signal frequency, the frequency difference of the local oscillator signals could be increased only by increasing the frequency of the pumping signal, and the frequencies coming to the frequency dividers in the 10 phase-locked loops so much that they may not be able to process them.

In one embodiment of the invention, each phase-locked loop has a frequency divider connected between the subharmonic mixer and the phase comparator, the output frequency of which can be changed by changing the output frequency of the local oscillator.

In another embodiment of the invention, the reference oscillator signals fed to the phase comparators of the different phase-locked loops can be divided by independently controlled frequency dividers. These frequency dividers can be used to determine the frequency steps at which the frequency can be shifted from one frequency (channel to another).

The invention will now be described in detail by means of an exemplary embodiment with reference to the accompanying figure, which shows a block diagram of a device according to the invention.

The microwave frequency, voltage controlled oscillators 1 and 2 act as local oscillators of the transmitter and receiver, respectively, generating local oscillator signals f1 and fosc2. The frequency range of oscillators 1 and 2 may typically be, for example, 10-20 GHz. In addition, a sample signal is derived from the output signal of the oscillator 1 to the subharmonic mixer 3, where it is mixed to a lower frequency f3. Mixer 3? The output signal, i.e. the scrambled signal f3, is fed to a sub-4 86119 pass filter 7, which passes the scrambling result with the lowest frequency and filters out all upper scrambling results from the signal f3. The filtered signal f3 is applied to a frequency divider 12, where the frequency f3 5 is divided by the divider term N1 and formed as the output frequency f5 of the divider 12, which is input to the second input of the phase comparator 11. A reference oscillator signal fREF1 is applied to the second input of the phase comparator 11. The phase comparator 11 compares the phases of the signals f5 and fREr1 to form a voltage signal VC1 proportional to the phase difference, which is supplied by the amplifier 6 to the frequency control input of the voltage-controlled oscillator 1. Thus, a phase-locked loop adjusting the frequency of the oscillator 1 is formed.

15 The frequency of oscillator 2 is adjusted by a corresponding phase-locked loop. From the output signal f03C2 of the oscillator 2, a sample signal is taken, which is mixed in the sub-harmonic mixer 5 to a lower frequency f4. The output signal f4 of the mixer 5 is filtered in the low-pass filter 20 and divided in the frequency divider 13 by the divider term N2 and a signal f6 is generated, which is fed to the second input of the phase comparator 14. The phase comparator 14 compares the phase of the signal f6 with the phase of the reference oscillator signal fREF2, generating a voltage signal Vc2 proportional to the phase difference, which is applied by the loop amplifier 10 amplified to the frequency control input of the oscillator 2. The reference oscillator signals fREF1 and fREF2 are formed by the respective divider circuits 15 and 17 at the output frequency fREF of the reference oscillator 16.

The pumping or mixing signals required by the subharmonic mixers 3 and 5 are generated in the same oscillator 4 and each mixer operates from each other,. regardless of the harmonic multiples of the output frequency of the oscillator 4. The frequency of the oscillator 4 is preferably 1 GHz, the harmonic multiples being 2 GHz, 5 86119 3GHz, etc. The reference oscillator frequencies and the frequencies f3 and f4 are typically in the order of a few tens of megahertz. The local oscillator frequencies are foscl and are chosen so that the frequency occurs close to one of the 4 harmonic frequencies of the oscillator-5.

In the device according to the invention, the output frequencies of the local oscillators 1 and 2 of the transmitter and receiver can be selected independently of each other by changing the divider terms N1 and N2 and 10 of the frequency dividers 12 and 13, if necessary by adjusting the frequency of the oscillator 4.

In some cases, oscillator 16, its multiplied signal can be used as oscillator 4, or oscillator 4 can be phase-locked to oscillator 16, 15, whereby all frequencies present are derived from oscillator 16. The best implementation depends on the output hair f and the requirements set.

The divider terms R1 and R2 of dividers 15 and 17 are preferably interchangeable, with the result that it is also possible that the frequency steps at which the frequencies of the transmitter and receiver can be changed can be set independently of the transmitter and receiver.

The figure and the related description are intended to illustrate the present invention only. The details of the device according to the invention may vary within the scope of the appended claims.

Claims (5)

6 86119 An apparatus for generating two local oscillator signals, the apparatus comprising first (1) and 5 second (2) microwave local oscillators, each controlled separately by its own phase-locked control loop, comprising a subharmonic mixer (3, 5) for mixing and sampling 10 of the local oscillator signal 11, 14) for comparing the phase of said mixed signal and the phase of the reference oscillator signal and adjusting the frequency of the local oscillator (1, 2) on the basis of the phase comparison, characterized in that the mixing signals of the sub-harmonic mixers (3, 5) are harmonic multiples of the same oscillator signal . Device according to claim 1, characterized in that each phase-locked loop comprises a low-pass filter (7, 9) connected to the output of the subharmonic mixer (3, 5) for separating the lowest frequency mixing result into said mixed signal. Device according to Claim 1 or 2, characterized in that each phase-locked loop comprises a frequency divider (12, 13) connected between the subharmonic mixer (3, 5) and the phase comparator (11, 14), and that the frequency dividers (12, 13) ) divisor terms (N1, N2) can be changed independently. Device according to claim 1, 2 or 3, characterized in that each phase-locked loop comprises a frequency divider (15, 17) connected between the reference oscillator (16) and the phase comparator (11, 14), and in that the frequency dividers (15) , 17) the terms divisor (R1, R2) can be changed independently of each other. Device according to one of the preceding claims, characterized in that the mixing signals and the reference signals for the phase comparators are generated by the same oscillator. 7 86119