WO2017148505A1

WO2017148505A1 - Mixing circuit to reduce the phase noise and frequency offset variance in local oscillators

Info

Publication number: WO2017148505A1
Application number: PCT/EP2016/054248
Authority: WO
Inventors: Paul FERRAND
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2016-02-29
Filing date: 2016-02-29
Publication date: 2017-09-08
Also published as: CN108781057A; CN108781057B

Abstract

Apparatus for improving an operating frequency of an oscillating output signal by averaging deviations of operating frequencies of at least two oscillating input signals. The apparatus comprises electrical circuit(s) adapted to: (a) Mix together, by a mixer circuit, at least a first and a second oscillating input signals. Each of the input signal having a common input operating frequency and the mixed signal having a resultant operating frequency. Each of the input operating frequencies is centered around a common nominal frequency with a frequency deviation and the resultant operating frequency is centered around a multiple of the nominal frequency. (b) Divide, by a divider circuit, the resultant operating frequency of the mixed signal to create an output signal having an operating frequency centered around the nominal frequency with an averaged frequency deviation which is an average of the frequency deviations of the at input signals. (c) Output the output signal.

Description

MIXING CIRCUIT TO REDUCE THE PHASE NOISE AND FREQUENCY OFFSET VARIANCE IN LOCAL OSCILLATORS

BACKGROUND

The present invention, in some embodiments thereof, relates to reducing frequency deviation effects of an oscillating signal and, more specifically, but not exclusively, to reducing frequency deviation effects of an oscillating signal by averaging the deviation effects of at least two oscillating input signals, in particular an oscillating input signal and a delayed oscillating signal created by delaying the oscillating input signal.

Oscillating signals are a basic building block in a variety of demanding applications, for example, reference signals for analog circuits and/or clocks for digital circuits. Such applications may often require accurate low-noise oscillating signals that can be generated with minimal power consumption and maintained accurate over a range of frequencies as well as over time.

Accuracy of the oscillating signals may be extremely important in digital communications systems, in particular in wireless communications systems where a plurality of mobile transceivers communicate with one or more base stations. Each transceiver includes a transmitter and a receiver which may require an accurate and precise reference frequency with low frequency drift characteristics to communicate with the base station(s). Timing circuit and/or components, for example, crystal oscillators, clock generators and the likes are typically used to provide the requisite reference frequencies, however the generated frequency of the oscillating signals tend to drift over time and temperature.

SUMMARY

According to an aspect of some embodiments of the present invention there is provided an apparatus for improving an operating frequency of an oscillating output signal by averaging deviations of operating frequencies of two or more oscillating input signals. The apparatus comprises one or more electrical circuits adapted to mix together, by a first mixer circuit (Ml), at least a first and a second oscillating input signals, each having a common input operating frequency, to create a mixed signal having a resultant operating frequency. Each of the input operating frequencies is centered around a common nominal frequency with a frequency deviation and the resultant operating frequency is centered around a multiple of the nominal frequency. The one or more electrical circuits divide, by a divider circuit, the resultant operating frequency of the mixed signal to create an output signal which has an output operating frequency centered around the nominal frequency with an averaged frequency deviation which is an average of the frequency deviations of the at least first and second oscillating input signals. The one or more electrical circuits then output the output signal.

The first mixer circuit (Ml) and/or the divider circuits are configured to receive two or more additional oscillating input signals to create the output signal.

Optionally, the apparatus includes one or more delay circuit configured to delay the first input oscillating signal received from an oscillating circuit to generate the second oscillating input signal as a delayed version of the first oscillating input signal.

The frequency deviation comprises a frequency offset from the center of the nominal frequency and/or a phase noise. The frequency offset is randomly distributed around the nominal frequency of the oscillating input signals and the phase noise relates to random frequency variation processes over time with respect to the nominal frequency.

The one or more electrical circuits further include a high pass filter, HPF, being configured to remove one or more low frequency component of the mixed signal.

The divider circuit comprises a second mixer (M2) to create the output signal and one or more low-pass filters, LPF, configured to remove one or more high frequency component from the output signal.

The divider circuit further includes a feedback path configured to create a feedback signal from the output signal. The feedback signal is fed back into the second mixer (M2) which is configured to mix the mixed signal and the feedback signal.

The feedback path further includes an amplifier being configured to restore a signal amplitude level of the feedback signal to equal a signal amplitude level of the mixed signal.

Optionally, the feedback path includes a multiplier being configured to multiply the operating frequency of the feedback signal to match the operating frequency of the mixed signal.

Optionally, the apparatus includes one or more delay circuits configured to amplify the output signal to increase a signal amplitude level of the output signal to compensate for attenuation of the signal amplitude level during the mixing and the dividing. According to an aspect of some embodiments of the present invention, there is provided a method for improving an operating frequency of an oscillating output signal by averaging deviations of operating frequencies of at least two oscillating input signals. The method comprises:

- Receiving at least a first and a second oscillating input signals having a common input operating frequency centered around a common nominal frequency with a frequency deviation.

Mixing together, at a first mixer (Ml), the at least first and second oscillating input signals to create a mixed signal having a resultant operating frequency centered around a multiple of the nominal frequency.

Dividing, at a divider circuit, the resultant operating frequency of the mixed signal to create an output signal which has an output operating frequency centered around the nominal frequency with an averaged frequency deviation which is an average between the frequency deviations of the at least first and second oscillating input signals. - Outputting the output signal.

The divider circuit comprises a second mixer (M2) being configured for creating the output signal and a feedback path configured to create a feedback signal from the output signal. The feedback signal is fed back into the second mixer (M2) which is configured to mix the mixed signal and the feedback signal.

Unless otherwise defined, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

In the drawings: FIG. 1 is a schematic illustration of an exemplary apparatus for improving frequency characteristic(s) of an oscillating output signal, according to some embodiments of the present invention;

FIG. 2 is a flowchart of an exemplary process of improving frequency characteristic(s) of an oscillating output signal, according to some embodiments of the present invention;

FIG. 3 is a schematic illustration of an exemplary apparatus for improving frequency characteristic(s) of an oscillating output signal using two input signals, according to some embodiments of the present invention;

FIG. 4 is a schematic illustration of a power density chart presenting a gain reduction for an exemplary oscillating output signal created by averaging two oscillating input signals, according to some embodiments of the present invention;

FIG. 5 is a schematic illustration of an exemplary apparatus for improving frequency characteristic(s) of an oscillating output signal using four input signals, according to some embodiment of the present invention; and

FIG. 6 is a schematic illustration of an exemplary apparatus for improving frequency characteristic(s) of an oscillating output signal using a delayed input signal, according to some embodiment of the present invention. DETAILED DESCRIPTION

The present invention presents apparatuses, systems and methods for improving one or more frequency characteristics of an oscillating signal, for example, accuracy, stability and/or variation over time and/or temperature by reducing one or more deviation effects of the operating frequency of the oscillating signal. The deviation effects may include, for example, a frequency offset and/or a phase noise (also referred as phase drift). The frequency offset may be manifested as a deviation from a center of a nominal frequency and for multiple oscillating signals in practical applications may typically be randomly distributed around the nominal frequency center. The phase noise may be typically characterized in practical application as random phase noise processes such as stochastic, rapid, short-term fluctuations in the phase of the oscillating signal.

The frequency characteristic(s) of the oscillating signal may be improved by averaging the deviation effects of two or more input oscillating signals having a common nominal operating frequency to create an output signal. Due to the random nature of the deviation effects, i.e. the random distribution of the frequency offset and the phase noise random processes, averaging the deviation effects may significantly improve the frequency characteristics of the output signal.

Improving the frequency characteristic(s) of the oscillating signal by averaging the deviation effects of the two or more input signals may present significant benefits compared to existing methods currently used for improving the frequency characteristic(s). One benefit may be reduced cost by using two or more low-end oscillating circuits as sources for the oscillating input signals as opposed to using an expensive high-end oscillating circuit which may have one or more improved frequency characteristic(s), for example, temperature compensation and/or frequency tracking. Another benefit may be reduced complexity (and possibly cost) of the oscillating circuit by avoiding use of one or more phase noise reduction circuits, for example, phase tracking circuits.

Averaging the frequency characteristics of the two or more oscillating input signals is done by first mixing the input signals using a first mixing circuit to create a mixed signal and dividing the mixed signal using a divider circuit to restore the nominal operating frequency for the output signal. The mixed signal has a resultant operating frequency which is a multiple of the nominal operating frequency. The mixed signal may be driven through a high pass filter (HPF) configured to remove one or more low frequency components from the mixed signal which are created by the first mixing circuit while mixing the input signals. The mixed signal is then driven into the divider circuit which may include a second mixing circuit coupled with a feedback path feeding back the output signal to provide a feedback signal to the second mixing signal. The second mixing circuit is configured to create the output signal by mixing the mixed signal and the feedback signal. The divider circuit may further include a low pass filter (LPF) configured to remove one or more high frequency components from the output signal which are created by the second mixing circuit while mixing the mixed signal and the feedback signal. The divider circuit may further include an amplifier on the feedback path configured to restore an amplitude level for the feedback signal to the nominal amplitude level of the input signals.

Optionally, one or more delay circuits are used to delay one or more of the input signals to create one or more delayed signals which are delayed versions of the input signals. The delayed signal(s) may be used in conjunction with the input signal(s) to create the output signal.

Optionally, the divider circuit includes a multiplier configured to multiply the feedback signal. The multiplier may be required in the event when more than two oscillating input signals are used to create the output signal where the number n of input signals is a power of 2. When mixing n input signals having a common nominal frequency the resultant operating frequency of the mixed signal is the nominal frequency multiplied by n. In order to properly adjust the feedback signal before it enters the second mixing circuit the feedback signal may be multiplied to have the same nominal frequency as the mixed signal.

Optionally, the output signal is amplified to increase a signal amplitude level of the output signal to compensate for attenuation of the signal amplitude level during the mixing and the dividing.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

The present invention may be a system, a method, and/or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing.

Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network.

The computer readable program instructions may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions. Reference is now made to FIG. 1 which is a schematic illustration of an exemplary apparatus for improving frequency characteristic(s) of an oscillating output signal, according to some embodiments of the present invention. An exemplary apparatus 100 includes a mixing circuit 110 which receives a plurality of oscillating input signals 102A through 102N having an operating frequency centered around a common nominal frequency and a divider circuit 120 which drives out an oscillating output signal 106 having an operating frequency centered around the same common nominal frequency. Each of the input signals 102 may be received from, for example, an oscillator circuit. The mixing circuit 110 includes one or more mixers (Ml) 112 for mixing the two or more input signals 102 and an HPF 114 for removing one or more low frequency components from the mixed signal coming out of the mixer(s) (Ml) 112 to create a mixed signal 104.

Optionally, the mixing circuit includes one or more delay circuits 116 for delaying one or more of the input signals 102 to create one or more delayed signals which are delayed versions of the input signal(s) 102 to be driven into the mixer(s) (Ml) 112.

The mixed signal 104 is divided in the divider circuit 120 using a mixer (M2) 122 which mixes together the mixed signal 104 with a feedback signal 108 received through a feedback path feeding the output signal 106 back into the divider circuit 120. The feedback path includes an amplifier 126 for restoring an amplitude level of the feedback signal 108 to a nominal amplitude level of the input signals 102.

Optionally, the feedback path includes a multiplier 128 to multiply the operating frequency of the feedback signal 108. The multiplier 128 may be required to multiply the operating frequency of the feedback signal 108 to equal the operating frequency of the mixed signal 104 when more than two input signals 102 are used to create the mixed signal 104. The signal coming out of the mixer (M2) 122 is driven through an LPF 124 which removes one or more high frequency components of the mixed signal to create the output signal 106.

Optionally, the apparatus 100 includes one or more output amplifiers 130 to restore an amplitude level of the output signal 106 to create an amplified output signal 107. The amplitude level of the output signal 106 may need to be restored since it may be attenuated compared to the input signals 102 due to the mixing and/or the dividing operations performed in the mixer circuit 110 and /or the divider circuit 120. Reference is also made to FIG. 2 which is a flowchart of an exemplary process of improving frequency characteristic(s) of an oscillating output signal, according to some embodiments of the present invention. A process 200 for improving frequency characteristic(s) of the oscillating output signal 106 may be done by averaging the frequency characteristic(s) of one or more of the oscillating input signals 102 using the exemplary apparatus 100.

As shown at 210, the process 200 starts with receiving at the mixer(s) (Ml) 112 two or more of the input signals 102 which are at least partially independent of each other. The oscillating input signals 102 all have a common operating frequency centered around the nominal frequency and may each include one or more deviations (deviation effects), for example, a frequency offset and/or a phase noise. Each of the input signals 102 may be represented as described in equation 1 below:

Equation 1:

Where each of the input signals 102 is defined as having a frequency which

may indicated as operating frequency of the input signals and may further include a phase noise expressed as a continuous-time phase process θ\ where i stands for the index of the input signals 102A through 102N. The frequency a); is composed of the nominal frequency expressed as ω_ε = 2πf_c and may further include a frequency offset ω_έ = 2πfϊ. Both oscillating input signals have a common amplitude level A.

The frequency offsets ω_έ of the input signals 102 are assumed to be randomly distributed around a nominal frequency ω_ε = 2πf_c with finite variance σ². The phase noise processes of the input signals 102 are assumed to be random processes with a

mean of and an autocorrelation of where

represent different points in time and β is an autocorrelation expectation parameter factor related to each of the input signals 102. The parameter β is a feature of the local oscillator and will be different for different oscillators. While the present invention may apply to any type of phase noise, the assumptions made herein above closely represent typical, realistic systems and may further represent a worst case scenario since the evolution of the input signals is unpredictable. The phase noise processes so defined are generated as:

Equation 2:

Where is a Gaussian process wrapped on the circle such that i = {1,2} and

is the Dirac delta function. As discussed, the characteristic of the resulting random process, may be a Wiener process with the following expectation and autocorrelation values:

Equation 3:

In the mixing circuit, the signals 102 are mixed at the filter (Ml) 112 and filtered at the HPF 114 to create a mixed signal 104 which has a resultant operating frequency which is the sum of the operating frequencies of all the input signals 102. Since the operating frequency of all the input signals 102 has a common nominal frequency, the resultant operating frequency of the mixed signal 104 expressed as s_M (t) is a multiple, of the operating frequency of the input signals 102 and is directly related to

the input signals 102 expressed in equation 4 below.

Equation 4:

As shown at 220, the mixed signal 104 is divided using the divider circuit 120 to create the output signal 106 s'(t) which is expressed as shown in equation 5 below. Equation 5:

Developing equations 1 and 5 for the divider circuit 120 in which the mixed signal 104 is mixed with the feedback signal 108 (with restored nominal amplitude level) produces equation 6 below.

Equation 6:

As evident the output signal 106 is an oscillating signal having a frequency which is the average of the frequencies ω_1; ... , ω_η of the input signals 102 with a phase noise process which is the average of the phase noise processes of the input signals

102. Developing the equations 1 through 6 may be complex for the general n order (n input signals 102) and is therefore generalized hereinabove while presented in detail hereinafter for lower order embodiments of the present invention.

As shown at 230, the output signal 106 is driven out of the apparatus 100 to be used for one or more of a plurality of applications, for example, a reference clock for digital circuits, a modulation clock for a radio frequency (RF) transceiver and the likes.

The operating frequency characteristics of the output signal 106 may be significantly improved by averaging the deviation(s) of the input signals 102 in order to reduce the deviation(s). The output signal 106 has an operating frequency which is centered on the nominal frequency ω_ε but may include reduced deviation(s) (deviation effects) due to the averaging of the deviation among the two or more input signals 102. The random nature of the deviation(s), i.e. the random distribution of the frequency offset among the input signals 102 operating frequency ω_ορ ; and the random nature of the phase noise processes allow the averaging operation to statistically reduce the

deviation effects. The reduced deviation may be characterized as follows. The variance of the frequency offse of each of the input signals 102 S; (t) may be represented as σ².

The output signal 106 s'(t) will have an operating frequency with a variance of σ²/n . Similarly, the autocorrelation of the phase noise process of the output signal 106 is also divided by n and is equal to

The reduced deviations of the output signal 106 may increase an amplitude noise to some extent, however one or more amplification circuits such as the output amplifier 130 may be applied to the output signal 106 to restore an amplitude level of the output signal 106 in order to remove and/or reduce the amplitude noise and thus improve a signal to noise ratio of the output signal 106. Furthermore both the mixing circuit 110 and the divider circuit 120 may induce at least some signal power loss, however the noise level remains constant and thus achieving a higher signal to noise ratio for the output signal 106. The output signal may be further amplified to restore the amplitude level of the output signal 106 which may be attenuated during the mixing and dividing operations.

Some embodiments of the present invention are provided through examples, which present possible embodiments and/or preferred embodiments. Reference is now made to FIG. 3 which is a schematic illustration of an exemplary apparatus for improving frequency characteristic(s) of an oscillating output signal using two input signals, according to some embodiments of the present invention. An apparatus 100 A which is a specific variant of the exemplary apparatus 100 receives two oscillating input signals 102A and 102B having an operating frequency centered around a common frequency and creates an output signal 106 A having an operating frequency centered around the nominal frequency with reduced deviation(s). The apparatus 100A includes a mixing circuit 110A and a divider circuit 120A. The two input signals 102A and 102B s₂ (t) are expressed in equation 7 below.

Equation 7:

The input signals 102A s₁ (t) and 102B s₂ (t) are mixed together at a mixer (Ml) 112A to create a pre-filter mixed signal 103A s_M (t) which is expressed in equation 8 below.

Equation 8:

The pre-filter mixed signal 103A includes two frequency components.

The first frequency component is centered around a sum of the nominal frequency ω_ε of the input signals 102A and 102B at and the second frequency component

is centered around a difference of the nominal frequency ω_ε of the input signals 102A and 102B at

The pre-filter mixed signal 103A is then driven into an HPF 114A which removes the low fr

equency component of the pre-filter mixed signal 103 A to create a mixed signal 104A which is expressed in equation 9 below.

Equation 9:

The HPF 114A may be adapted to clearly discriminate between the high frequency component ω₁ + ω₂ and the low frequency component ω₁— ω₂. In typical practical applications of interest for the present invention, the difference between may be extremely large and allowing the HPF to

properly separate the two frequency components in an optimal manner.

The mixed signal 104A is then driven into the divider circuit 120 A which divides the operating frequency of the mixed signal 104A to create the output signal 106A. The divider circuit 120 A includes a mixer (M2) 122A which mixes the mixed signal 104A with a feedback signal 108A to create the steady state output signal 106A. The mixer (M2) 122A is configured to reduce the operating frequency of the mixed signal 104A in order to form an operating frequency centered around the nominal frequency for the output signal 106A. The output signal 106A is expressed as s'(t) as shown in equation 10 below.

Equation 10:

The output signal 106 A is driven through a feedback path in the divider circuit 120 A which includes an amplifier 126A. The amplifier 126 A restores the amplitude level of the output signal 106A to create the feedback signal 108 A having a nominal amplitude level equal the amplitude level of the mixed signal 104A. The amplifying factor of the amplifier 126 A is thus set at 4/.A². In the steady state, the intermediate output signal s(t) of the mixer (M2) 122A is therefore the feedback signal 108A mixed with the mixed signal 104A as expressed as shown in equation 11 below.

Equation 11:

The signal coming out of the mixer (M2) 122A is then driven into an LPF 124A which removes a high frequency component

οf the mixed signal to create the output signal 106A. The output signal 106A may therefore be expressed as shown in equation 12 below.

Equation 12:

Combining equations 10 and 12 produces the expression in equation 13 below. Equation 13:

Equation 13 translates to two terms as expressed in equation 14 below.

Equation 14:

As evident from equation 14 the deviations (deviation effects) are reduced for the output signal 106 by averaging the deviation(s) of the input signal 102A and 102B using the apparatus 100A.

Based on the assumptions presented before, the phase noise processes

are random processes, for example they may be Wiener processes, with a mean of 0 and an autocorrelation where E[. ] denotes the

expectation operator and β is a parameter. Since both the phase noise processes are independent, the autocorrelation of the resulting phase noise process of the output

signal 106A is expressed in equation 15 below.

Equation 15

This translates to a reduction in noise variance the output signal 106A. This gain reduction is shown through the power spectral density of one of the input signals 102A and 102B compared to the averaged output signal 106A.

Reference is now made to FIG. 4 which is a schematic illustration of a power density chart presenting a gain reduction for an exemplary oscillating output signal created by averaging two oscillating input signals, according to some embodiments of the present invention. A relative power density chart 400 presents power density graphs for an oscillating output signal created by averaging two oscillating input signals using an apparatus such as the apparatus 100A. A graph 410 presents a relative power density characteristic of an oscillating output signal such as the oscillating output signal compared to a graph 420 which presents a relative power density characteristic of an oscillating input signal such as the oscillating input signals 102A and 102B. As evident from the chart 400, the graph 410 associated with the averaged output signal 106 presents a 3dB noise reduction compared to the graph 420 associated with one of the original input signals 102A and 102B.

Reference is now made to FIG. 5 which is a schematic illustration of an exemplary apparatus for improving frequency characteristic(s) of an oscillating output signal using four input signals, according to some embodiment of the present invention. While in the present document apparatuses using 2 or four inputs are described, it will be clear that configurations are also possible having 3 signals as input. An apparatus 100B which is a specific variant of the exemplary apparatus 100 receives four oscillating input signals 102A, 102B, 102C and 102D having an operating frequency centered around a common frequency and creates an output signal 106B having an operating frequency centered around the nominal frequency with reduced deviation(s). The operation of the apparatus 100B is similar to the operation of an operation of an apparatus such as the apparatus 100A with one exception relating to multiplying the operating frequency of a feedback signal 108B to equal a frequency of an operating frequency of a mixed signal 104B. The apparatus 100B includes a mixing circuit HOB and a divider circuit 120B. The four input signals 102A- 102D are mixed using a two stage mixer (Ml) 112B to first mix each pair 102A-102B and 102C- 102D followed by mixing the output of the two mixers (Ml) 112B in a mixer (Ml) 112C. The four input signals 102A

102B s₂ (t), IOC s₃ (t) and 102D s₄ (t) are represented as shown in equation 16 below.

Equation 16:

The pre-filter mixed signal 103B is then driven into an HPF to remove the low frequency components of the pre-filter mixed signal 103B in order to create the mixed signal 104B. The mixed signal includes four lower frequency components centered around 2f_c and one high frequency component centered around The low frequency

components are removed by the HPF 114B and the mixed signal 104A includes only the high frequency component with an amplitude equal to A⁴/8. The

signal 104B is fed into a mixer (M2) 112B in the divider circuit 120B which mixes the mixed signal 104B with the feedback signal 108B to create an intermediate output signal. The intermediate output signal goes through an LPF 124B which removes the high frequency component of the output signal to create the output signal 106B. The output signal 106B is fed back into the divider circuit 120B and goes into an amplifier which restores an amplitude level of the feedback signal 108B to a nominal amplitude level equal to that of the mixed signals 104B. The feedback signal 108B is driven into a multiplier 128A which multiplies the operating frequency of the feedback signal 108B by 4 so it would equal the operating frequency of the mixed signal 104B which is 4 times the nominal operating frequency of the input signals 102A-102B due to the two stage mixer (Ml) 112B and 112C.

Following the same equations presented for the apparatus 100 A, the averaged output signal 106B is expressed in equation 17 below.

Equation 17:

As evident from equation 17 the deviations (deviation effects) are reduced for the output signal 106 by averaging the deviation(s) of the input signals 102A-102D using the apparatus 100B.

Optionally, a plurality of embodiments exist for an apparatus such as the apparatus 100 for receiving any order n oscillating input signals to create an output signal such as the output signal 106. The apparatus 100 may use multi stage mixers (Ml) such as the mixer (Ml) 112 in a mixing circuit such as the mixing circuit 110 coupled with an appropriate multiplier such as the multiplier 126 in a divider circuit such as the divider circuit 120. The output signal 106 may also be taken from the amplifier 126 rather than the low pass filter (LPF) 124.

Reference is now made to FIG. 6 which is a schematic illustration of an exemplary apparatus for improving frequency characteristic(s) of an oscillating output signal using a delayed input signal, according to some embodiment of the present invention. An apparatus lOOC which is a specific variant of the exemplary apparatus 100 receives one oscillating input signal 102A. It is possible to reduce phase noise by using a single oscillator and in particular by mixing the oscillating input signal 102A from said oscillator with a delayed version of itself. In this case the two processes related to the input oscillating signals 102A and to the delayed input oscillating signal 102A1 are not independent. In such a configuration the degree of reduction of the phase noise will depend on the delay. In addition, the degree of reduction of the phase noise may also depend on the process itself. The apparatus lOOC includes a delay circuit 116A configured to delay the input signal 102A of a predefined period of time (delay) to create a delayed signal 102A1 which is a delayed version of the input signal 102A. The delay can have different values and can be chosen based on the local oscillator used for generating the oscillating input signal and on the desired degree of phase noise reduction. In addition or alternatively, the amount of delay may depend on physical constraints: the amount of delay determines indeed the size of the delay circuit. Therefore, the available space in the apparatus will set an upper limit to the dimension of the delay circuit and consequently to the amount of the delay which can be achieved. The amount of delay will be the result of a tradeoff between phase noise reduction and circuit size. The input signal 102A is mixed together with the delayed signal 102A1 in a mixer (Ml), such as the mixer (Ml) 112A, to create a pre-filtered mixed signal 103C. The signal flow through the apparatus lOOC from the mixer (Ml) 112A is then similar to that of the apparatus 100A.

Although the input oscillating signal 102 A and the delayed input oscillating signal 102A1 are not independent, the apparatus of the invention allows to reduce the phase noise of the output signal as will be shown in the following for the case that the the phase noise process is random and in particular a Wiener process.

As an example, assume that the phase noise process in the oscillating input signal 102A is a Wiener process as described above. Considering the phase noise process at two time instants t and s, such that , the difference process verify W_t— W_s ~

The average of said process with a version of itself delayed by τ

leads to a new process W', which is not a Wiener process anymore. The resulting process has 0 mean and the step increment between any time instants t and s has the following characteristics:

Equation 18:

If the input oscillating signal 102 A and the delayed input oscillating signal 102A1 are observed over a time interval (t— s) < τ, the new process has a variance that is half of the original process, meaning that the phase noise of the input oscillating signal 102A is reduced of ½. For larger time intervals, the variance is reduced by a constant τ/2, which becomes smaller with time relative to the original variance In any case, the phase noise of the output signal will be reduced compared

to the phase noise of the input oscillating signal 102A.

More generally, the delay τ may be chosen based on the period over which the variance of the process should be statistically reduced or period of interest. Specifically, the delay may be set based on the number of symbols over which the phase noise is estimated. In particular, if a delay is set to be equal to the period of interest, the output signal will have a phase noise This period of interest will depend on the

application of the invention.

As an example, in a system where the phase noise is estimated every 10 symbols, choosing a delay of τ = 10 symbols, the phase noise process of the output signal will behave like a Wiener process of half the variance between each estimation.

The choice of the delay is thus dependent on the desired period for which we want a reduced variance in the process. As already mentioned above, in practice, the larger the values of the delay τ, the larger has to be the delay circuit. The choice of the delay involves a tradeoff between the available space on a circuit board and the delay or in other words the degree of phase noise reduction.

The apparatus described in figure 6 will produce the desired effect of reducing the phase noise and in particular variance noise if the oscillating input signal 102A is delayed by an amount of time larger than the period of interest.

Obviously a plurality of additional embodiments may be created for an apparatus such as the apparatus 100 which includes one or more delay circuits such as the delay circuit 116 to delay any number of oscillating input signals 102 such as the oscillating input signals 102. Furthermore any single input 102 may be delayed using multi stage delay circuits 116 to create additional one or more delayed signals such as the delayed signal 102A1. For example, a single input signal 102A may be received by the apparatus 100 which includes 3 delay circuits 116. The input signal 102A may be driven into a first delay circuit 116 to create a delayed signal 102A1. The delayed signal 102A1 may then be driven into a second delay circuit 116 to create a delayed signal 102A2 and the delayed signal 102A2 may then be driven into a third delay circuit 116 to create a delayed signal 102A3. The apparatus 100 may be used to receive the four signals 102A, 102A1, 102A2 and 102A3 in order to create the output signal 106.

The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

As used herein the term "about" refers to ± 10 %.

The terms "comprises", "comprising", "includes", "including", "having" and their conjugates mean "including but not limited to". This term encompasses the terms

"consisting of and "consisting essentially of.

The phrase "consisting essentially of means that the composition or method may include additional ingredients and/or steps, but only if the additional ingredients and/or steps do not materially alter the basic and novel characteristics of the claimed composition or method.

As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or

"at least one compound" may include a plurality of compounds, including mixtures thereof.

The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments.

The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". Any particular embodiment of the invention may include a plurality of "optional" features unless such features conflict.

Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range. Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases "ranging/ranges between" a first indicate number and a second indicate number and "ranging/ranges from" a first indicate number "to" a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting.

Claims

1. An apparatus for improving an operating frequency of an oscillating output signal by averaging deviations of operating frequencies of at least two oscillating input signals, comprising:

at least one electrical circuit adapted to:

mix together, by a first mixer circuit (Ml), at least a first and a second oscillating input signals, each of the oscillating input signal having a common input operating frequency, to create a mixed signal having a resultant operating frequency, each of the input operating frequencies is centered around a common nominal frequency with a frequency deviation and the resultant operating frequency is centered around a multiple of the nominal frequency;

divide, by a divider circuit, the resultant operating frequency of the mixed signal to create an output signal which has an output operating frequency centered around the nominal frequency with an averaged frequency deviation which is an average of the frequency deviations of the at least first and second oscillating input signals; and

output the output signal.

2. The apparatus of claim 1, wherein the first mixer circuit (Ml) and/or the divider circuits are configured to receive at least two additional oscillating input signals to create the output signal.

3. The apparatus of any one of claims 1 to 2, further includes at least one delay circuit configured to delay the first input oscillating signal received from an oscillating circuit to generate the second oscillating input signal as a delayed version of the first oscillating input signal.

4. The apparatus of claim 1, wherein the frequency deviation comprises a frequency offset from the center of the nominal frequency and/or a phase noise, wherein the frequency offset is randomly distributed around the nominal frequency of the oscillating input signals and the phase noise relates to random frequency variation processes over time with respect to the nominal frequency.

5. The apparatus of any one of claims 1 to 4, wherein the at least one electrical circuit further includes a high pass filter, HPF, being configured to remove at least one low frequency component of the mixed signal.

6. The apparatus of any one of claims 1 to 5, wherein the divider circuit comprises a second mixer (M2) to create the output signal and at least one low pass filter, LPF, configured to remove at least one high frequency component from the output signal.

7. The apparatus of claim 6, wherein the divider circuit further includes a feedback path configured to create a feedback signal from the output signal, the feedback signal being fed back into the second mixer (M2), the second mixer (M2) being configured to mix the mixed signal and the feedback signal.

8. The apparatus of claim 7, wherein the feedback path further includes an amplifier being configured to restore a signal amplitude level of the feedback signal to equal a signal amplitude level of the mixed signal.

9. The apparatus of any of claims 7 to 8, wherein the feedback path further includes a multiplier being configured to multiply an operating frequency of the feedback signal to match the operating frequency of the mixed signal.

10. The apparatus of any one of claims 1 to 9, wherein the at least one electrical circuit is configured to amplify the output signal to increase a signal amplitude level of the output signal to compensate for attenuation of the signal amplitude level during the mixing and the dividing.

11. A method for improving an operating frequency of an oscillating output signal by averaging deviations of operating frequencies of at least two oscillating input signals, comprising:

receiving at least a first and a second oscillating input signals having a common input operating frequency centered around a common nominal frequency with a frequency deviation; mixing together, at a first mixer (Ml), the at least first and second oscillating input signals to create a mixed signal having a resultant operating frequency centered around a multiple of the nominal frequency;

dividing, at a divider circuit, the resultant operating frequency of the mixed signal to create an output signal which has an output operating frequency centered around the nominal frequency with an averaged frequency deviation which is an average between the frequency deviations of the at least first and second oscillating input signals; and

outputting the output signal.

12. The method of claim 11, further comprising adapting the first mixer circuit (Ml) and/or the divider circuit to receive at least two additional oscillating input signals to create the output signal.

13. The method of any one of claims 11 to 12, further comprising applying at least one delay circuit configured to delay the first input oscillating signal received from an oscillating circuit to generate the second oscillating input signal as a delayed version of the first oscillating input signal.

14. The method of any of claims 11 to 13, wherein the frequency deviation comprises a frequency offset from the center of the nominal frequency and/or a phase noise, wherein the frequency offset is randomly distributed around the nominal frequency of the oscillating input signals and the phase noise relates to random frequency variation processes over time with respect to the nominal frequency.

15. The method of any one of claims 11 to 14, wherein the divider circuit comprises a second mixer (M2) to create the output signal and a feedback path configured to create a feedback signal from the output signal, the feedback signal is fed back into the second mixer (M2) which is configured to mix the mixed signal and the feedback signal.