This application is a 35 U.S.C. §371 National Phase Entry Application from PCT/EP2010/055259, filed Apr. 21, 2010, and designating the United States.
The present invention discloses an improved tunable signal source.
The demand for tunable signal sources with low phase noise and a wide tuning range is growing, particularly tunable signal sources which can be used in higher frequency ranges, e.g. at 60 GHZ and above. Such a signal source can be used in a variety of technical fields such as, for example, radars and telecommunications.
One commonly used approach to obtain a high frequency signal source is to design a low frequency VCO, Voltage Controlled Oscillator, and to then apply frequency multipliers to up-convert the frequency of the VCO. Although it in this way is relatively easy to obtain an improvement in phase noise performance compared to a high frequency VCO, the phase noise degrades by 6 dB at every doubling of the oscillation frequency. This phase noise degradation, which accompanies an increase in frequency, can be alleviated by using a mixer and a fixed frequency oscillator in order to up-convert the frequency. Unfortunately, this approach has the drawback of having a relatively small tuning range, since the absolute tuning range determined by the low frequency VCO is unchanged in the frequency up-conversion.
As explained above, there is a need for a high frequency signal source which has improved properties with respect to phase noise and tuning range compared to previously known such signal sources.
A purpose of the present invention is to offer such a high frequency signal source. This purpose is met by the present invention in that it discloses a frequency tunable signal source which comprises a first and a second oscillator, each of which has as its output a signal at a fundamental frequency and at least one signal at a harmonic frequency of the fundamental frequency.
The frequency tunable signal source of the invention also comprises a mixer with a first and a second input port as well as an output port, and further comprises a control unit which controls ON/OFF switches, by means of which switches two of said signals are switchably connected to the first input port and the other two signals are switchably to the other input port, with one switch for each signal.
In addition, the frequency tunable signal source also comprises a third oscillator which produces an output signal which is connected to a third input port of the mixer, and at least one of the first, second and third oscillators is a VCO, a Voltage Controlled Oscillator.
By means of the invention, as will be explained in the detailed description given in this text, a frequency tunable signal source with low phase noise is obtained, which can be used at high frequencies.
In one embodiment of the frequency tunable signal source of the invention, the third oscillator is a fixed frequency oscillator, an FFO.
In one embodiment of the frequency tunable signal source of the invention, at least one of the first and second oscillators is a VCO.
In one embodiment of the frequency tunable signal source of the invention, one of the first and second oscillators is an FFO.
The invention will be described in more detail in the following, with reference to the appended drawings, in which
The invention will be described in detail below, and the terms “fundamental frequency” and “harmonic frequency” will be used. These terms can briefly be defined as follows: A periodic signal can be expressed by means of, for example, a Fourier series with the components N*f0, where f0 is the signal's fundamental frequency and N is an integer. Thus:
N=1 gives us the signal's fundamental frequency, also known as the first harmonic, and
N=2 gives us the signal's second harmonic, and
N=3 gives us the signal's third harmonic, etcetera.
The embodiment 100 also comprises a mixer 120 with a first 121 and a second 122 input port as well as an output port 124. The output signals from the two VCOs 105, 115 are connected pair-wise to the input ports 121, 122 of the mixer via ON/OFF switches shown as S1-S4 in
As those skilled in the field will understand, which of the four output signals that are connected to which input port (via an ON/OFF switch) depends on which results that are desired as output signals from the mixer 120. In principle, any of the signals f1, f2, f1′, f2′, can be input to either one of the input ports 121, 122, or in fact to of both the input ports 121, 122 of the mixer.
However, in the example given in
The signal at the fundamental frequency f1 of the first VCO 105 and the signal at the fundamental frequency f2 of the second VCO 115 are connected to the first input port 121 and the second input port 122 of the mixer 120 respectively via the switches S1 and S4 respectively; the signal at the second harmonic frequency f1′ of the first VCO 105 and the signal at the second harmonic frequency f2′ of the second VCO 115 are connected to the mixer's second input port 122 and first input port 121 respectively via the switches S2 and S3, respectively.
As is also shown in
In addition, although the FFO 125 is used in this embodiment to obtain a shift upwards in frequency, the FFO 125 can of course also be used to obtain virtually any other shift, such as, for example a shift downwards in frequency.
The control unit 110 operates to cause the switches S1-S4 to be in the ON or OFF position depending on which frequency it is desired to have as the output frequency of the mixer 120.
In addition, the table of
As those skilled in the art will realize, a vast number of combinations are possible with a tunable signal source of the invention, depending on how the frequency ranges of the VCOs 105 and 115 are chosen and how the VCOs are set (i.e. controlled by means of a tuning voltage) within their respective ranges, in combination with how the FFO 125 is chosen, as well as how the switches S1-S4 are set.
However, suitably, the frequency ranges of the two VCOs 105 and 115 are chosen so that the frequency combinations shown in the table in
Thus, with the values exemplified above of the ranges of f1 and f2, a frequency range of 14-22 GHz can be covered “seamlessly”. An additional “upwards shift” can then be obtained by means of the frequency f3 of the FFO 125. As can be seen, the invention offers a tunable signal source with a wide tuning range.
It should be pointed out that the invention can be varied in a wide variety of ways with respect to the kinds of oscillators used: in the embodiment 100 of
In an alternative embodiment 300 of the invention shown in shown in
The fundamental frequency f2 as well as the second harmonic f2′ of the FFO 315 are both connected to the second input port 122 of the mixer 120 via respective ON/OFF switches S2 and S4, and the fundamental frequency f1 as well as the second harmonic f1′ of the VCO 105 are both connected to the first input port 121 of the mixer 120 via respective ON/OFF switches S1 and S3. All of the ON/OFF switches are controlled by the control unit 110 in order to obtain the desired output frequency at the output port 124 of the mixer 120. Again, in similarity to the embodiment 100 of
If, as an example, the tuning range of the VCO 105 is chosen to be in the range of 8-10 GHZ and the FFO 315 has a fundamental frequency of 6 GHz, the following combinations are among those that can be obtained by means of the switches S1-S4:
As can be seen, the frequency combinations f1, 2f1−f2, f1+f2, 2f1, f1+2f2, cover the whole frequency region of 8˜22 GHz. Those frequency bands and the settings of the switches S1-S4 which are necessary to obtain them are shown in the table of
Turning now to the issue of the phase noise performance of the tunable signal source of the invention, one requirement is that the oscillator which is used to up-shift the signal (such as the FFO 125 in
The three input-port mixer denoted as 120 in the embodiments shown in
Thus, in a preferred embodiment, the invention uses a single mixer with three input ports. One example 500 of such a mixer is shown in
The differential input signal of a first oscillator at frequency f1 is input at the bases of the emitter coupled pairs, Q5 with Q6 and Q7 with Q8, while the input signals at frequencies f2 from a second of the other two oscillators is input to the bases of one transistor in each of the pairs Q1-Q2 and Q3-Q4, with the differential signal at frequency f3 from the third oscillator being input at the base of the other transistor in these pairs. It should be pointed out that the input-ports for the signal at frequency f1 and the signal at f3 can be exchanged.
The invention is not limited to the examples of embodiments described above and shown in the drawings, but may be freely varied within the scope of the appended claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2010/055259 | 4/21/2010 | WO | 00 | 10/17/2012 |
Publishing Document | Publishing Date | Country | Kind |
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WO2011/131237 | 10/27/2011 | WO | A |
Number | Name | Date | Kind |
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7701300 | Park et al. | Apr 2010 | B2 |
8543055 | Cook et al. | Sep 2013 | B1 |
8543077 | Rafi et al. | Sep 2013 | B2 |
Number | Date | Country |
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2136238 | Sep 1984 | GB |
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Zhang, P., et al., “A New RF Front-End and Frequency Synthesizer Architecture for 3.1-10.6 GHz MB-OFDM UWB Receivers”, Circuits and Systems, 2005, 48th Midwest Symposium on Cincinnati, Ohio, Aug. 7-10, 2005, Piscatway, NJ, US, Aug. 7, 2005, pp. 1119-1122, XP010895338. |
Number | Date | Country | |
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20130038376 A1 | Feb 2013 | US |