GB2118389A

GB2118389A - Signal generator arrangement

Info

Publication number: GB2118389A
Application number: GB08207833A
Authority: GB
Inventors: Sidney Joseph Hewitt
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1982-03-17
Filing date: 1982-03-17
Publication date: 1983-10-26
Also published as: GB2118389B

Abstract

A signal generator arrangement, particularly for performing frequency division at microwave frequencies, comprises a first oscillator 1, a mixer 3 having two input ports one of which is fed from the first oscillator, and an injection-lockable oscillator 4 (Gunn or Impatt type) which feeds a signal to the other input port of the mixer, the injection- lockable oscillator being arranged to receive, for frequency locking purposes a signal 5 derived from the mixer 3 whereby the signal fed from the injection-lockable oscillator to the said other input port of the mixer is phase locked to a sub-multiple of the frequency of the first oscillator. As shown, the sub-multiple frequency fo can be locked to a reference frequency 8 by a phase- locked loop 6-11. An offset frequency can be incorporated (Figure 3). <IMAGE>

Description

SPECIFICATION Signal generator arrangement This invention relates to signal generator arrangements and more especially it relates to frequency divider arrangements for use at frequencies in the UHF band or at frequencies higher than the UHF band.

Frequency division techniques utilizing logic devices are well known more especially for use at frequencies below the ultra high frequency (UHF) band but division of frequencies much above the UHF band cannot satisfactorily be performed with currently available logic circuits.

According to the present invention a signal generator arrangement comprises a first oscillator, a mixer having two input ports one of which is fed from the first oscillator, and an injection lockable oscillator which feeds a signal to the other input port of the mixer, the injection lockable oscillator being arranged to receive, for frequency locking purposes a signal derived from the mixer whereby the signal fed from the injection lockable oscillator to the said other input port of the mixer is phased locked to a sub-multiple of the frequency of the first oscillator.

Thus it will be appreciated that the arrangement effectively operates as a frequency divider wherein the frequency of the injection lockable oscillator is set to a su b-m u Itiple of the first oscillator.

Preferably it is arranged that the injection lockable oscillator operates at a frequency which is half of the frequency of the first oscillator.

The injection lockable oscillator may be a free running oscillator having a natural frequency close to a sub-harmonic of the said first oscillator and which responsively to the signal to the signal derived from the mixer, is 'pulled', so as to be phase locked thereto, whereby the frequency of operation is a precise sub-harmonic of the said first oscillator.

The arrangement may include a phase detector responsive to a reference signal and to the frequency of the injection lockable oscillator, for providing in the presence of a phase difference therebetween, a feedback control signal which is applied to the said first oscillator for phase locking purposes, whereby the said first oscillator is constrained to be phase locked to the reference frequency signal.

The signal received by the injection lockable oscillator, may be derived from the said mixer via mixer means having two input ports, one of which is fed from the said mixer and the other of which is fed with an off-set frequency, whereby the first oscillator is constrained to produce one of two side bands, corresponding either to a multiple of the reference signal frequency plus the off-set frequency, or to a multiple of the reference frequency minus the off-set frequency.

The mixer means may be a single side band modulator, which is operative to determine the side band produced.

The injection lockable oscillator may in accordance with one embodiment of the invention com prise first combiner means having two input ports and one output port, amplifier means, second combiner means having one input port and two output ports, wherein one input port of the first combiner means is fed with a signal derived from the said mixer for phase locking purposes, the output port of the first combiner means being coupled to the input port of the second combiner means via the amplifier means, one output port of the second combiner means being coupled to the other input port of the first combiner means and the other output port of the second combiner means being arranged to feed the said other input port of the said mixer.

The said one output port of the second combiner means may be coupled to the said other input port of the first combiner means via an attenuator and a transmission line.

In accordance with an alternative embodiment of the invention the injection lockable oscillator may comprise a microwave oscillator, a circulator which is fed from the microwave oscillator, and fed also with the signal derived from the said mixer for phase locking purposes, the circulator being arranged to feed the said other input port of the said mixer.

The microwave oscillator may be either a Gunn diode oscillator, an impatt oscillator, or a transistor oscillator.

Some examples of the invention will now be described solely by way of example with reference to the accompanying drawings in which; Figure 1 is a block schematic diagram of a signal generator arrangement; Figure 2 is a block schematic diagram of a signal generator arrangement phase locked to a reference frequency; Figure 3 is a generally schematic block diagram of a signal generator arrangement including frequency off-set means; Figure 4 is a block schematic diagram of an injection lockable oscillator suitable for use with the arrangements shown in Figure 1,2 and 3; and Figure 5 is a block diagram of an alternative injection lockable oscillator which is usable with the arrangements shown in Figures 1,2 and 3.

Referring now to Figure 1, a frequency generator arrangement comprises an oscillator 1, which provides an output signal on a line 2 and one input signal for a mixer 3. The mixer 3, is fed with another input signal from an injection lockable oscillator 4, whereby the mixer 3 provides an output signal on a line 5, which is fed to the injection lockable oscillator 4forfrequency locking purposes. The injection lockable oscillator 4, is arranged normally to operate at a frequency at or about FO. The oscillator 1 is arranged to provide a frequency of 2FO.The mixer 3 thus receives input signals from the oscillator 1 and the injection lockable oscillator 4, at 2FO and FO respectively whereby one side band signal from the output of the mixer 3 on the line 5 will be at the frequency FO and will serve to pull the injection lockable oscillator 4 so that its frequency is synchronised precisely to the frequency FO.

The frequency from the injection lockable oscillator 4, is provided on an output line 6 and is thus exactly half of the frequency on the output line 2 from the oscillator 1. The signal generator arrangement may thus be considered to operate as a frequency divider.

It may be desirable that the signal generator should be locked to a stable frequency and an arrangement in which phase locking is achieved is shown in Figure 2, wherein parts of the figure which correspond to Figure 1 bear where appropriate the same numerical designations. Referring now to Figure 2, the signal at the frequency FO on the line 6, is fed to a phase detector 7 which is fed via a line 8 with a stable reference signal at a frequency of FO precisely. An output signal on a line 9, is fed via a filter 10 which serves to smooth the signal on line 9, to provide on a line 11, a control signal which is utilized to control the frequency of the oscillator 1 such that phase differences between the signals on the lines 6 and 8 respectively tend to zero. The frequency on the line 2 will be an exact multiple of the frequency on the line 6.The precise frequency generated will be determined by the stable reference on line 8. Thus if the injection lockable oscillator 4 is arranged normally to operate at a frequency which approximates to half of the frequency of the oscillator 1 then the signal on the line 5 will serve as a synchronising signal which effectively pulls the frequency of the injection lockable oscillator 4 so that it is constrained to be a precise sub-harmonic of the frequency generated by the oscillator 1.

For some applications, it is desirable that the output frequency on the line 2 is off-set by an off-set frequency. An arrangement for achieving an output frequency which is off-set, is shown in Figure 3, wherein parts corresponding to Figures 1 and 2, bear as appropriate the same numerical designations.

Referring now to Figure 3, an arrangement is shown wherein a single side band modulator 12, is coupled in series with the line 5 between the mixer 3 and the injection lockable oscillator 4. The single sideband modulator is fed with a modulating signal on a line 13 having a frequency FM. It will therefore be apparent that the frequency on the output line 2 will be N.FO * FM. N will be determined by the natural frequency of oscillation of the injection lockable oscillator 4 and if it is arranged that the injection lockable oscillator 4 is arranged normally to run at approximately half the frequency of the oscillator 1,then N will be equal to 2. It is also apparent that the output signal may either be N.FO-FM or N.FO + FM. Which of these two side bands is provided will be determined by the design of the single side band modulator 12.Thus it is apparent that the single side band modulator may be designed to produce either the upper side band or the lower side band. In an alternative arrangement the side band may be determined by means of a filter and in this case the single side band modulator 12 may be replaced with an alternative design of mixer.

It will be apparent that the injection lockable oscillator 4 may take any suitable form, and two suitable forms are shown in Figures 4 and 5 respectively.

Referring now to Figure 4, one form of injection lockable oscillator arrangement comprises a power combiner 13, which is arranged to receive on the line 5, an injection locking input signal and to provide an output signal on a line 14foran amplifier 15. The output of the amplifier 15 is fed via a line 16 to an inputterminal of a further power divider 17, having output lines 18 and 6 respectively. It will be appreciated that the lines 5 and 6 correspond to those shown in Figures 1 and 2. The line 18 is arranged to feed an attenuator 19 which is connected to an input port 20 of the combiner 13. The arrangement shown in Figure 4, will oscillate at a frequency determined by the time constant around the loop including the attenuator 19.The arrangement is arranged normally to operate at a frequency which is near to the required frequency and which therefore will be influenced by the injection locking signal applied via the line 5, which serves to pull the operating frequency as necessary.

In an alternative arrangement shown in Figure 5, the injection lockable oscillator comprises a single port oscillator 21 coupled via a line 22 to a circulator 23. An injection locking signal is applied via the line 5 to the circulator 23 and an output signal is produced on the line 6. In the arrangement shown in Figure 5, a signal is fed from the single port oscillator 21 to the output line 6, the frequency of the single port oscillator being pulled so as to be synchronised with the injection locking input signal applied on the line 5. The arrangement shown in Figure 5 is quite well known and it will be appreciated by those skilled in the art that the single port oscillator may comprise a transistor oscillator, a Gunn diode oscillator, or an impatt oscillator.

A signal generator as just before described has the advantage that signals may be produced at microwave frequencies which are related to a standard reference frequency or to the frequency of a controlled oscillator and which are true submultiples of the frequency. Therefore it will be appreciated that the function of frequency division may be provided by the arrangement shown at frequencies within or above the UHF band.

CLAIMS (Filed on 17.2.83) 1. A signal generator arrangement comprising a first oscillator, a mixer having two input ports one of which is fed from the first oscillator, and an injection lockable oscillator which feeds a signal to the other input port of the mixer, the injection lockable oscillator being arranged to receive, for frequency locking purposes a signal derived from the mixer whereby the signal fed from the injection lockable oscillator to the said other input port of the mixer is phase locked to a sub-multiple of the frequency of the first oscillator.

2. A signal generator arrangement as claimed in claim 1 wherein the injection lockable oscillator is adapted to operate at a frequency which is half of the frequency of the first oscillator.

3. A signal generator as claimed in claim 1 or claim 2 wherein the injection lockable oscillator is a free running oscillator having a natural frequency close to a sub-harmonic of the said first oscillator and which responsively to the signal derived from the mixer, is 'pulled', so as to be phase locked thereto, whereby the frequency of operation is a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. frequency divider. It may be desirable that the signal generator should be locked to a stable frequency and an arrangement in which phase locking is achieved is shown in Figure 2, wherein parts of the figure which correspond to Figure 1 bear where appropriate the same numerical designations. Referring now to Figure 2, the signal at the frequency FO on the line 6, is fed to a phase detector 7 which is fed via a line 8 with a stable reference signal at a frequency of FO precisely. An output signal on a line 9, is fed via a filter 10 which serves to smooth the signal on line 9, to provide on a line 11, a control signal which is utilized to control the frequency of the oscillator 1 such that phase differences between the signals on the lines 6 and 8 respectively tend to zero. The frequency on the line 2 will be an exact multiple of the frequency on the line 6.The precise frequency generated will be determined by the stable reference on line 8. Thus if the injection lockable oscillator 4 is arranged normally to operate at a frequency which approximates to half of the frequency of the oscillator 1 then the signal on the line 5 will serve as a synchronising signal which effectively pulls the frequency of the injection lockable oscillator 4 so that it is constrained to be a precise sub-harmonic of the frequency generated by the oscillator 1. For some applications, it is desirable that the output frequency on the line 2 is off-set by an off-set frequency. An arrangement for achieving an output frequency which is off-set, is shown in Figure 3, wherein parts corresponding to Figures 1 and 2, bear as appropriate the same numerical designations. Referring now to Figure 3, an arrangement is shown wherein a single side band modulator 12, is coupled in series with the line 5 between the mixer 3 and the injection lockable oscillator 4. The single sideband modulator is fed with a modulating signal on a line 13 having a frequency FM. It will therefore be apparent that the frequency on the output line 2 will be N.FO * FM. N will be determined by the natural frequency of oscillation of the injection lockable oscillator 4 and if it is arranged that the injection lockable oscillator 4 is arranged normally to run at approximately half the frequency of the oscillator 1,then N will be equal to 2. It is also apparent that the output signal may either be N.FO-FM or N.FO + FM. Which of these two side bands is provided will be determined by the design of the single side band modulator 12.Thus it is apparent that the single side band modulator may be designed to produce either the upper side band or the lower side band. In an alternative arrangement the side band may be determined by means of a filter and in this case the single side band modulator 12 may be replaced with an alternative design of mixer. It will be apparent that the injection lockable oscillator 4 may take any suitable form, and two suitable forms are shown in Figures 4 and 5 respectively. Referring now to Figure 4, one form of injection lockable oscillator arrangement comprises a power combiner 13, which is arranged to receive on the line 5, an injection locking input signal and to provide an output signal on a line 14foran amplifier 15. The output of the amplifier 15 is fed via a line 16 to an inputterminal of a further power divider 17, having output lines 18 and 6 respectively. It will be appreciated that the lines 5 and 6 correspond to those shown in Figures 1 and 2. The line 18 is arranged to feed an attenuator 19 which is connected to an input port 20 of the combiner 13. The arrangement shown in Figure 4, will oscillate at a frequency determined by the time constant around the loop including the attenuator 19.The arrangement is arranged normally to operate at a frequency which is near to the required frequency and which therefore will be influenced by the injection locking signal applied via the line 5, which serves to pull the operating frequency as necessary. In an alternative arrangement shown in Figure 5, the injection lockable oscillator comprises a single port oscillator 21 coupled via a line 22 to a circulator 23. An injection locking signal is applied via the line 5 to the circulator 23 and an output signal is produced on the line 6. In the arrangement shown in Figure 5, a signal is fed from the single port oscillator 21 to the output line 6, the frequency of the single port oscillator being pulled so as to be synchronised with the injection locking input signal applied on the line 5. The arrangement shown in Figure 5 is quite well known and it will be appreciated by those skilled in the art that the single port oscillator may comprise a transistor oscillator, a Gunn diode oscillator, or an impatt oscillator. A signal generator as just before described has the advantage that signals may be produced at microwave frequencies which are related to a standard reference frequency or to the frequency of a controlled oscillator and which are true submultiples of the frequency. Therefore it will be appreciated that the function of frequency division may be provided by the arrangement shown at frequencies within or above the UHF band. CLAIMS (Filed on 17.2.83)

1. A signal generator arrangement comprising a first oscillator, a mixer having two input ports one of which is fed from the first oscillator, and an injection lockable oscillator which feeds a signal to the other input port of the mixer, the injection lockable oscillator being arranged to receive, for frequency locking purposes a signal derived from the mixer whereby the signal fed from the injection lockable oscillator to the said other input port of the mixer is phase locked to a sub-multiple of the frequency of the first oscillator.

precise sub-harmonic of the said first oscillator.

4. A signal generator arrangement as claimed in any preceding claim including a phase detector responsive to a reference signal and to the frequency of the injection lockable oscillator, for providing in the presence of a phase difference therebetween, a feedback control signal which is applied to the said first oscillator for phase locking purposes, whereby the said first oscillator is constrained to be phase locked to the reference frequency signal.

5. A signal generator arrangement as claimed in any preceding claim wherein a signal received by the injection lockable oscillator, is derived from the said mixer via mixer means having two input ports, one of which is fed from the said mixer and the other of which is fed with an off-set frequency, whereby the first oscillator is constrained to produce one of two side bands, corresponding either to a multiple of the reference signal frequency plus the off-set frequency, or to a multiple of the reference frequency minus the off-set frequency.

6. A signal generator arrangement as claimed in any preceding claim wherein the mixer means is a single side band modulator, which is operative to determine the side band produced.

7. A signal generator arrangement as claimed in any preceding claim wherein the injection lockable oscillator comprises first combiner means having two input ports and one output port, amplifier means, second combiner means having one input port and two output ports, wherein one input port of the first combiner means is fed with a signal derived from the said mixer for phase locking purposes, the output port of the first combiner means being coupled to the input port of the second combiner means via the amplifier means, one output port of the second combiner means being coupled to the other input port of the first combiner means and the other output port of the second combiner means being arranged to feed the said other input port of the said mixer.

8. A signal generator arrangement as claimed in claim 7 wherein the said one one output port of the second combiner means is coupled to the said other input port of the first combiner means via an attenuator and a transmission line.

9. A signal generator arrangement as claimed in any of claims 1 to 6 wherein the injection lockable oscillator comprises a microwave oscillator, a circulator which is fed from the microwave oscillator, and fed also with the signal derived from the said mixer for phase locking purposes, the circulator being arranged to feed the said other input port of the said mixer

10. A signal generator arrangement as claimed in claim 9 wherein the microwave oscillator is either a Gunn diode oscillator, an impatt oscillator, or a transistor oscillator.

11. A signal generator arrangement substantially as herebefore described with reference to the accompanying drawings.