The invention relates to the field of frequency multipliers.
Frequency multipliers are a basic building block in Radio Frequency Integrated Circuits (RFICs), such as are typically used in radio transceivers, imaging, and RADAR systems. However, most frequency multipliers have no conversion gain. To achieve a positive gain, a reflector is provided to reflect power back to the output signal.
However, such reflectors are typically unmatched to the input impedance, resulting in reflective loss at the input. To overcome this, additional components are typically added, which increase the cost and size of the chip, and which also introduce signal loss. Furthermore, increasing the number of components on the chip reduces the operative bandwidth of the chip and introduces processing errors resulting from non-compliance with the required tolerances.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the figures.
The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope.
There is provided, in accordance with an embodiment, a system comprising: a frequency multiplier configured to receive an incoming radio frequency signal having a fundamental frequency, and to output an outgoing radio frequency signal having an output frequency that is an even multiple of the fundamental frequency; an input transformer comprising a multiplier-side inductor configured to provide the incoming radio frequency signal, in a differential mode, to the frequency multiplier at the fundamental input frequency; a direct current bias source configured to bias the frequency multiplier, thereby producing the outgoing radio frequency signal and multiple harmonic signals of the fundamental signal; and a reflector comprising a capacitor configured to resonate with the multiplier-side inductor at the output frequency, and reflect back a portion of the multiple harmonics signals having the output frequency back to the multiplier.
In one embodiment, the direct current bias source is connected at a point of symmetry with respect to the multiplier-side inductor and the frequency multiplier.
In one embodiment, the multiplier-side inductor provides a radio frequency choke to the frequency multiplier.
In one embodiment, the capacitor is connected at a point of symmetry with respect to the multiplier-side inductor, thereby positioned at a virtual ground with respect to the incoming radio frequency signal.
In one embodiment, the reflector consists of the capacitor coupled to the multiplier-side inductor.
In one embodiment, the even multiple of the fundamental input frequency comprises twice the fundamental input frequency.
In one embodiment, the capacitor comprises a switch capacitor that is configured to resonate with the multiplier-side inductor at multiple different fundamental frequencies.
In one embodiment, an inductance Lout of the multiplier-side inductor complies with:
Z
in=(zoutN2∥jωLink2)+jωLin(1−k2)=Zsource*
In one embodiment, a capacitance of the capacitor Cref is:
where the fundamental frequency is f0.
In one embodiment, the reflector is configured to attenuate an odd harmonic signal produced by the frequency multiplier.
There is provided, in accordance with an embodiment, a method comprising: coupling an incoming radio frequency signal having a fundamental input frequency through a multiplier-side inductor; providing the incoming radio frequency signal to a frequency multiplier in a differential mode; biasing the frequency multiplier to produce multiple harmonic signals of the fundamental signal comprising an outgoing radio frequency signal having an output frequency that is an even multiple of the fundamental frequency, resonating, via a capacitor coupled to the multiplier-side inductor, at the output frequency, thereby reflecting back a portion of the multiple harmonics signals having the output frequency; combining the reflected harmonics with the outgoing radio frequency signal; and outputting an outgoing radio frequency signal.
In one embodiment, the direct current bias source is connected at a point of symmetry with respect to the multiplier-side inductor and the frequency multiplier.
In one embodiment, the method further comprises providing a radio frequency choke to the frequency multiplier.
In one embodiment, the method further comprises providing a virtual ground to the incoming radio frequency signal, wherein the capacitor is positioned at the virtual ground.
In one embodiment, the reflector consists of the capacitor coupled to the multiplier-side inductor.
In one embodiment, the method further comprises the even multiple of the fundamental input frequency comprises twice the fundamental input frequency.
In one embodiment, the method further comprises the capacitor comprises a switch capacitor that is configured to resonate with the multiplier-side inductor at multiple different fundamental frequencies.
In one embodiment, the method further comprises an inductance Lout of the multiplier-side inductor complies with:
Z
in=(zoutN2∥jωLink2)+jωLin(1−k2)=Zsource*
In one embodiment, a capacitance of the capacitor Cref is:
where the fundamental frequency is f0.
In one embodiment, the method further comprises attenuating an odd harmonic signal produced by the frequency multiplier.
In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the figures and by study of the following detailed description.
Exemplary embodiments are illustrated in referenced figures. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below.
A system and method are described herein to provide a compact, high gain reflector for use with a frequency multiplier. The reflector comprises a capacitor that is symmetrically positioned with respect to an inductor of an impedance-matched input transformer, and configured to resonate with the inductor at the desired output frequency. This serves to capture and reflect back a common mode signal that would otherwise be lost, such as the desired even harmonic signals. The symmetry of the design provides a virtual ground to isolate the reflector to differential mode signals, such as the input signal and any undesired odd harmonic signals.
The reflector disclosed herein may be used for incoming signals having frequencies spanning from X-band range of 8-12 GigaHertz (GHz) up to the millimeter-wave range, reaching as high as 300 GHz. In other embodiments, incoming signals may have lower or higher frequencies than the aforementioned range.
Reference is now made to
Frequency multiplier 104 may comprise any suitable even multiplier. For example, in the non-limiting illustration of
A direct current (DC) bias source Vbias is provided at a central tap to bias transistors 104a and 104b, comprising frequency multiplier 104, and produce the outgoing RF signal at the desired output frequency, as well as multiple harmonic signals k*f0 for k=2, 3, 4 . . . of the fundamental signal f0. Vbias may be selected to optimally bias transistors 104a and 104b and may be provided at the central tap as a virtual ground for the incoming RF signal. A typical value for Vbias applied to bipolar transistors may range from 0.6 volts (V) to 0.9V, covering known class B and class A biasing modes.
Vbias is connected at a point of symmetry with respect to Lout and therefore, does not affect the incoming RF signal that is coupled through Lout in differential mode. To multiplier 104. Referring to
For example, the characteristics of Vbias may be selected to push transistors 104a and 104b into a class-a mode of operation and drive a relatively high current for signal components having the frequency 2f0. In another mode of operation, Vbias may be selected to push transistors 104a and 104b to produce a high desired harmonic signal relative to the fundamental output signal.
At least one of the components produced by frequency multiplier 104, as driven by Vbias, is the desired multiplied output RF signal having a frequency of 2f0. This desired output signal and any desired reflected even harmonic signals may be tapped out of multiplier 104 as the outgoing RF signal, such as by using a wire. The output signal may be sent through an additional transformer balun TR2 to create an output differential signal.
However, another portion of this desired even harmonic multiple RF output signal is leaked back in common mode, together with the other harmonics produced by distorting the incoming RF signal. Additionally, a portion of the odd harmonic multiple RF output signal is leaked back in differential mode This common mode portion of the signal having the desired output frequency 2f0 would typically be lost.
A reflector 106, comprising a capacitor Cref, is connected at a point of symmetry with respect to Lout that provides a virtual ground for the incoming differential RF signal. Cref is positioned is configured to resonate with Lout to create a ‘short’ at the desired output frequency 2f0, and thereby capture and reflect back a portion of the multiple harmonics signals having the output frequency back to multiplier 104. Cref is configured to reflect the common mode, even harmonic components back to frequency multiplier 104, whereas the differential mode, odd harmonic components are not affected by Cref and are attenuated due to their phase. Thus, this common mode reflected portion of the signal is transferred back to multiplier 104 and combined with the outgoing RF signal to improve the gain of frequency multiplier 104.
By utilizing Lout of input transformer 102 to couple with Cref and resonate at the desired output frequency, in one embodiment, reflector 106 may consist of only Lout coupled to Cref, and thus, since Lout comprises an intrinsic component of input transformer 102, the only additional component required to implement reflector 106 and improve the gain of multiplier 104 is Cref resulting in a compact, cost effective design that avoids unwanted effects from additional components, such as inductors that introduce loss and could create undesired magnetic coupling.
Additionally, due to the preservation of phase by reflector 106, any other common mode signals having even frequency multiples 2kf0 for k=2,3,4 . . . constructively interfere with the resonating 2f0 common mode component, and are at least partially captured and reflected back to frequency multiplier 104, while the desired even multiple is fully reflected. Conversely, any odd harmonic components produced by multiplier 104, such as having the fundamental frequency, destructively interfere in reflector 106, and are attenuated.
Advantageously, the symmetric configuration of the reflector, comprising Lout coupled with Cref, and Vbias with respect to multiplier 104 precludes any effect by Vbias and/or the reflector on the incoming differential signal, As stated above, the reflector is only sensitive to common mode signals. Furthermore, Cref is positioned at a virtual ground with respect to the incoming differential RF signal.
Thus, Vbias may be selected according to the intrinsic properties of multiplier 104 to produce the desired output signal at 2f0. Lin and Lout may be selected to have a combined impedance Zin that matches the source impedance, such as may be produces by an earlier stage, to reduce reflective loss at the input. Cref may be selected to resonate with Lout at 2f0.
Reference is now made to
Referring to
Zin=(ZoutN2∥jωLink2)+jωLin(1−k2) (2)
For imaginary unit j, and sinusoidal angular frequency ω, and where the output impedance Zout may be represented by an impedance having a value of Zout*N2. Zin represents the impedance presented by transformer 102 and Zout represents the impedance presented by multiplier 104 and which may be determined from the intrinsic properties of transistors 104a and 104b. Thus, input transformer 102 may be selected to provide an impedance, Zin, that matches a source impedance Zsource corresponding to a previous stage to circuit 100 that introduces incoming RF signal to circuit 100, and thus equivalent to the complex conjugate of Zsource, or Zsource*. Using equations (1) and (2) above, the values for Lin and Lout, N and k comprising input transformer 102 may be determined from Zsource and Zout. Furthermore, since Zout is determined as the impedance of multiplier 104, Zout is significant only to differential signals, and is therefore ‘blind’ or not affected by capacitor Cref.
Reference is now made to
Thus, for a given value of Lout calculated above, and a fundamental input frequency f0, Cref may be determined, accordingly.
The following sequential steps describe an exemplary method for determining one or more components of the reflector of
Zin=(ZoutN2∥jωLink2)+jωLin(1−k2)=Zs*
As is evident from the symmetry of the design described above, the incoming differential signal at f0 is evenly distributed for input into transistors 104a and 104b of multiplier 104, and the direction of the incoming differential current oscillates in accordance with the reversing the polarity of the incoming signal. The symmetric positioning of Cref with respect to Lout and the central tap Vbias provides a virtual ground for multiplier 104, making Cref effectively invisible to the incoming differential signal. Similarly, Vbias as a DC supply does not affect the incoming differential signal, but merely pushes multiplier 104 to a state that produces higher harmonics of the incoming signal.
Thus the componentry added as part of the reflector of the circuit, namely Cref coupled to Lout, are passive components that do not affect the incoming differential signal, and are compact, thus occupy only a small portion of the circuit.
However, since Cref is coupled to Lout to resonate at 2f0, together they capture any common mode signals having even multiples of f0 that may have leaked from transistors 104a and 104b, such as due to any non-linear properties of transistors 104a and 104b. These captured common mode signals are added to and reflected back with the outgoing signal, while the desired harmonic is completely reflected due to the selection of the Cref, thereby improving the performance of multiplier 104 and increasing its gain. Furthermore, Cref is invisible to any differential mode signals, such as comprising any signal leakage by transistors 104a and 104b having odd multiples of f0 and resulting in their attenuation.
Vbias may be selected in accordance with the properties of transistor 104a and 104b to provide a relatively high current, or gain, in the second harmonic, 2f0. Thus, any leaked signal may be amplified, and signal components with even multiples of f0 may be captured and reflected back to the output.
Furthermore, the modality of the signals is preserved. Thus, common mode signals with even multiples of f0 are added via constructive interference, wherein the differential mode signals with odd multiples of f0 cancel each other out via destructive interference.
Optionally, Cref may comprise a switch capacitor that is configured to resonate with Lout at multiple different fundamental frequencies, and allowing circuit 100 to multiply signals having multiple different fundamental frequencies f0.
The reflector described above may be configured with any suitable multiplier circuit configuration. For example, referring to
Reference is now made to
An input transformer comprising a multiplier-side inductor coupled to an input-side inductor is provided to present an impedance Zin that matches a source impedance of a source that provides an incoming RF signal having a fundamental input frequency f0. The incoming RF signal is coupled through the multiplier-side inductor (Step 800). The incoming radio frequency signal is provided to a frequency multiplier in a differential mode (Step 802).
A DC bias source may bias the multiplier into a mode that produces multiple harmonics of f0, including an outgoing radio frequency signal having an output frequency that is an even multiple of the fundamental frequency, such as by pushing multiple transistors comprising the multiplier into class-a, class-b, or class-ab mode of operation to drive a current flow (Step 804). The multiple harmonics may additionally include odd harmonic signals in negative phase, and even harmonic signals that are in phase.
The multiple signals produced by the multiplier are collected and the odd harmonic signals are canceled, and the even harmonic signals are combined and added to the outgoing RF signal having frequency 2f0 (Step 806). A portion of the harmonic signals produced is leaked to the input transformer, were the even harmonic signals are leaked in common mode, and the odd harmonic signals are leaked in differential mode (Step 808).
A capacitor coupled to and symmetrically positioned with respect to the multiplier-side inductor resonates at the output frequency, thereby reflecting back the portion of the multiple harmonics signals having the output frequency, and attenuating the odd harmonic signals (Step 810). The reflected harmonics are combined with the outgoing signal to contribute to the output conversion gain (Step 812). The outgoing signal is tapped out of the multiplier circuit (Step 814).
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 market site, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.