Abstract:
Embodiments of apparatuses, systems and methods relating to a mixer having high second- and third-order intercept points are disclosed. Other embodiments may be described and claimed.

Description:
TECHNICAL FIELD 
     Embodiments of the present invention relate generally to the field of radio-frequency communication devices, and more particularly, to a mixer with high second-order and third-order intercept points. 
     BACKGROUND 
     Field-effect transistor (FET) mixers are used in radio-frequency (RF) communication devices to convert signals from one frequency range to another based on a local oscillator (LO) signal. For example, a FET mixer in a receive chain may shift a received RF signal into an intermediate frequency (IF) signal for further processing by the receiver circuitry. A FET mixer in a transmit chain may convert an IF signal into an RF signal for wireless transmission. Performance of a FET mixer may be judged by a variety of factors including isolation, ease of integration, power consumption, distortion, conversion efficiency, second-order intercept point, and third-order intercept point, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which: 
         FIG. 1  illustrates a mixer in accordance with some embodiments. 
         FIG. 2  illustrates a radio frequency balun in accordance with some embodiments. 
         FIG. 3  illustrates a receiver in accordance with some embodiments. 
         FIG. 4  illustrates a transmitter in accordance with some embodiments. 
         FIG. 5  is a flowchart depicting a frequency conversion operation in accordance with some embodiments. 
         FIG. 6  illustrates a wireless communication device in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Various aspects of the illustrative embodiments will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. However, it will be apparent to those skilled in the art that alternate embodiments may be practiced with only some of the described aspects. For purposes of explanation, specific devices and configurations are set forth in order to provide a thorough understanding of the illustrative embodiments. However, it will be apparent to one skilled in the art that alternate embodiments may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative embodiments. 
     Further, various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the present disclosure; however, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation. 
     The phrase “in one embodiment” is used repeatedly. The phrase generally does not refer to the same embodiment; however, it may. The terms “comprising,” “having,” and “including” are synonymous, unless the context dictates otherwise. 
     In providing some clarifying context to language that may be used in connection with various embodiments, the phrases “A/B” and “A and/or B” mean (A), (B), or (A and B); and the phrase “A, B, and/or C” means (A), (B), (C), (A and B), (A and C), (B and C) or (A, B and C). 
     The term “coupled with,” along with its derivatives, may be used herein. “Coupled” may mean one or more of the following. “Coupled” may mean that two or more elements are in direct physical or electrical contact. However, “coupled” may also mean that two or more elements indirectly contact each other, but yet still cooperate or interact with each other, and may mean that one or more other elements are coupled or connected between the elements that are said to be coupled to each other. 
       FIG. 1  illustrates a mixer  100  in accordance with some embodiments. The mixer may include a node  104  that is to receive a local oscillator (LO) signal. The node  104  may be coupled with an amplifier  108  to amplify the LO signal. The amplifier  108  may be coupled with voltage supply  110  and ground. An output of the amplifier  108  may be coupled with a capacitor  118  to provide an amplified LO signal. The capacitor  118  may be coupled with gates of transistors  112  and  116  to provide the gates with an LO drive signal that is based on the amplified LO signal. The transistors  112  and  116  may be field-effect transistors (FETs) such as, but not limited to, metal semiconductor FETs (MESFETs), pseudomorphic high-electron mobility transistors (PHEMTs), metal-oxide-semiconductor FETs (MOSFET), etc. In an embodiment using a gallium arsenide (GaAs) technology, the capacitor  118  may work to level-shift the amplified LO signal in a manner such that the LO drive signal is centered around a FET pinch-off voltage of the transistors  112  and  116  to increase frequency conversion efficiency. In an embodiment using a silicon technology, the capacitor  118  may be a DC-blocking capacitor used in combination with an active biasing circuit that may be employed to bias the gates of the transistors  112  and  116  as desired. 
     The mixer  100  may further include a radio frequency (RF) balun  120 . The RF balun  120  may include primary windings  124 , including first primary winding  124 _ 1  and second primary winding  124 _ 2 , and secondary windings  128 , including first secondary winding  128 _ 1  and second secondary winding  128 _ 2 . The first primary winding  124 _ 1  may be electromagnetically coupled with first secondary winding  128 _ 1 , while the second primary winding  124 _ 2  may be electromagnetically coupled with second secondary winding  128 _ 2 . The primary windings  124  and the secondary windings  128  may be designed to accommodate specifically-contemplated design frequencies of the RF signals and intermediate frequency (IF) signals. As used herein, design frequencies may be frequencies within design constraints of the mixer  100  for a particular signal. 
     The RF balun  120  may operate to differentially couple a single-ended RF signal at node  132  with drains of transistors  112  and  116 . The RF balun  120  may be constructed as a compact balun with accurate amplitude and phase balance. The RF balun  120  may further, in conjunction with capacitors  144  and  148 , as discussed below, operate as a diplexer to separate the single-ended RF signal, at node  132 , and differential IF signal, at nodes  136  and  140  or nodes  152  and  156 . The nodes  136  and  140  or nodes  152  and  156  may also be referred to as a differential IF signal interface. 
     At design frequencies of the IF signal, the secondary windings  128  may act as short circuits. Capacitors  144  and  148  may provide ground returns at design frequencies of the RF signal, while maintaining high impedances at design frequencies of the IF signal. This may allow the IF signal to be separated from the RF signal at nodes  152  and  156 , which may also be referred to as RF grounding ports  152  and  156 . Due at least in part to this method of separation of IF and RF signals at nodes  152  and  156 , the impedance at nodes  152  and  156  may not affect a balance of the mixer  100 . 
     In some embodiments, additional RF grounding at nodes  152  and  156  may be provided through the addition of LC segment  160 , including capacitor  164  and inductor  168 , and LC segment  172 , including capacitor  176  and inductor  180 . These LC segments may be designed to resonate at design frequencies of the RF signal to provide the additional RF grounding at nodes  152  and  156 , respectively. 
     In various embodiments, capacitors  184 ,  188 , and  192  may be coupled, in parallel, with first secondary winding  128 _ 1 , second secondary winding  128 _ 2 , and primary windings  124 , respectively. The capacitors  184 ,  188 , and  192  may facilitate tuning of the RF balun  120  at the desired RF frequency ranges. Furthermore, in some embodiments inductors  194  and  196  may be provided to increase RF-to-IF and LO-to-IF signal isolation. 
     The mixer  100  may be a monolithic mixer with all of the elements integrated in a single integrated circuit. The integrated circuit may have a substrate composed of a semiconductor material such as, but not limited to, gallium arsenide (GaAs), silicon, aluminum gallium arsenide (AlGaAs), gallium nitride (GaN), aluminum gallium nitride (AlGaN), indium phosphide (InP), silicon carbide (SiC), etc. 
     The mixer  100 , as described, may have a number of high-performance characteristics. For example, the mixer  100  may have desirable linearity, e.g., a high IIP2 of greater than approximately 60 dBm and a high IIP3 of greater than approximately 30 dBm, and low conversion loss. Furthermore, these performance characteristics may be obtained while using relatively low LO drive levels allowing for integration of the amplifier  108  in the same integrated circuit with the remaining components of the mixer  100  while still using relatively low direct current (DC) power consumption as compared to a typical bipolar complementary metal oxide semiconductor (BiCMOS) quad FET mixer having comparable linearity. 
     The topology of the mixer  100  may allow for some flexibility as to the type of IF circuit differentially interfaced with mixer  100  at nodes  152  and  156  or nodes  136  and  140  such as differential IF amplifiers or various baluns such as, but not limited to, a lumped LC balun or a wire-wound balun. 
       FIG. 2  illustrates the RF balun  120  in accordance with some embodiments. The RF balun  120 , as shown in  FIG. 2 , includes a first concentric structure  204  that has a pair of transmission lines concentrically oriented to implement the first primary winding  124 _ 1  and the first secondary winding  128 _ 1 ; and further includes a second concentric structure  208  that has another pair of transmission lines concentrically oriented to implement the second primary winding  124 _ 2  and the second secondary winding  128 _ 2 . The first concentric structure  204  may be coupled with the second concentric structure  208  by a connection  212  that is coupled with the primary windings  124  at interior portions of the respective concentric structures. Other embodiments may use other types of RF baluns. 
       FIG. 3  illustrates a receiver  300  in accordance with some embodiments. The receiver  300  may be a dual-channel receiver with receive channels  304 _ 1  and  304 _ 2 . The receiver  300  may include an RF front-end  308  having circuitry configured to provide various signal processing operations with respect to RF signals received from one or more antennas. These signal processing operations may include, e.g., amplification, impedance matching, filtering etc. 
     Each of the receive channels  304  may include a bandpass filter  312 _ 1  and  312 _ 2  coupled with the RF front-end  308  and configured to provide a bandpass response to limit the RF signal to the desired design frequencies. The bandpass filters  312  may be coupled with a mixer block  316 . 
     The mixer block  316  may include mixers  320 , which may be similar to and substantially interchangeable with mixer  100  described above. In some embodiments, the mixer block  316  may be monolithically integrated into a single integrated circuit. 
     Mixer  320 _ 1  may be coupled with the bandpass filter  312 _ 1  and a local oscillator  324 . Similarly, mixer  320 _ 2  may be coupled with the bandpass filter  312 _ 2  and the local oscillator  324 . Each of the mixers  320  may be configured to generate a respective differential IF signal based on the LO signal, received from the local oscillator  324 , and on respective single-ended RF signals received from the bandpass filters  312 . 
     In some embodiments, the mixer block  316  may include output amplifiers  328  configured to amplify respective outputs of the mixers  320 . Output amplifiers  328  may be coupled with respective bandpass filters  332  that are configured to provide bandpass responses to limit the respective differential IF signals to the desired design frequencies, which are typically lower frequencies than the RF signal design frequencies to facilitate signal processing operations. 
     The receiver  300  may further include an IF backend  336  coupled with the bandpass filters  332 . The IF backend  336  may have circuitry configured to provide various signal processing operations with respect to the IF signals. These signal processing operations may include, e.g., amplification, impedance matching, filtering, etc. 
     The receiver  300  may further include analog-to-digital converters  340 . The digital converter  340 _ 1  may receive the analog IF signal of the receive channel  304 _ 1  and convert it to a digital signal for further processing by, e.g., a baseband processing block. In a similar manner, digital converter  340 _ 2  may receive the analog IF signal of the receive channel  304 _ 2  and convert it to a digital signal for further processing by, e.g., a baseband processing block. 
       FIG. 4  illustrates a transmitter  400  in accordance with some embodiments. The transmitter  400  may include an IQ modulator having an in-phase (I) path  404  and a quadrature (Q) path  408 . 
     The in-phase path  404  may include a digital-to-analog converter DAC  412  that receives a digital signal from, e.g., a baseband processor, that represents an in-phase portion of an IF signal to be transmitted. The DAC  412  may generate a differential analog signal that represents the in-phase portion of the IF signal to be transmitted. This signal may be provided to an amplifier  416  that amplifies the signal and provides it to a mixer  420  of mixer block  424 . 
     Similarly, the quadrature path  408  may include a DAC  428  that receives a digital signal from, e.g., the baseband processor, that represents a quadrature portion of the IF signal to be transmitted. The DAC  428  may generate a differential analog signal that represents the quadrature portion of the IF signal to be transmitted. The signal may be provided to an amplifier  432  that amplifies the signal and provides it to a mixer  436  of the mixer block  424 . 
     The mixer block  424 , similar to mixer block  316 , may be monolithically integrated into a single integrated circuit. The mixer block  424  may include a splitter  440  that receives an LO signal from a local oscillator  444 . The splitter  440  may provide a first LO signal to the mixer  420  and a second LO signal, which is out of phase from the first LO signal by ninety degrees, to the mixer  436 . The mixers  420  and/or  436  may be similar to and substantially interchangeable with mixer  100 . 
     The mixers  420  and  436  may output respective RF signals that are combined and provided to RF front-end  448 . The RF front-end  448  may include circuitry that conditions the RF signal by, e.g., filtering the RF signal. The RF front-end  448  may provide the conditioned RF signal to a power amplifier  452  that amplifies the RF signal for subsequent over-the-air transmission. 
     In some embodiments, the transmitter  400  may also include a transmit observation path  456  that includes another mixer  460 . The mixer  460  may generate a differential IF signal based on the RF signal that is output from the power amplifier  452 . This IF signal may be fed back to the DACs  412  and  428  and may be used to adjust various transmit characteristics of the transmitter  400 . 
     The mixer  460  may include a similar topology, or a different topology from the mixers  420  and  436 . In some embodiments, the mixer  460  may be incorporated into the mixer block  424  with the mixers  420  and  436 . 
       FIG. 5  is a flowchart depicting a frequency conversion operation  500  that may be done by any of the above-described mixers in accordance with some embodiments. At block  504 , the frequency conversion operation  500  may include receiving a first signal. In an embodiment in which the frequency conversion operation  500  is done in the context of a transmit operation, the receiving of the first signal may be receiving, by a mixer, e.g., mixer  100 , a differential IF signal. In an embodiment in which the frequency conversion operation  500  is done in the context of a receive operation, the receiving of the first signal may be receiving, by a mixer, e.g., mixer  100 , a single-ended RF signal. 
     At block  508 , the frequency conversion operation  500  may include receiving an LO signal. In some embodiments the LO signal may be conditioned by, e.g., being amplified with an amplifier such as amplifier  108 . 
     At block  512 , the frequency conversion operation  500  may include generating a second signal. The generating of the second signal may be based on the first signal, received at block  504 , and the LO signal, received at block  508 . 
     In an embodiment in which the frequency conversion operation  500  is done in the context of a transmit operation, the generating of the second signal may be generating, by a mixer, e.g., mixer  100 , a single-ended RF signal based on the LO signal and the differential IF signal. In an embodiment in which the frequency conversion operation  500  is done in the context of a receive operation, the generating of the second signal may be generating, by a mixer, e.g., mixer  100 , a differential IF signal based on the LO signal and the single-ended RF signal. 
     A block diagram of an exemplary wireless communication device  600  incorporating one or more mixers  604 , which may be similar to mixers  100 ,  320 ,  420 ,  436 , and/or  460 . The wireless communication device  600  may further include an antenna structure  608 , a duplexer  612 , a transmitter  616 , a receiver  620 , a main processor  624 , and a memory  628  coupled with each other at least as shown. The mixers  604  are shown as being in both the transmitter  616  and the receiver  620 ; however, other embodiments may have mixers  604  in one or the other. Further, while the wireless communication device  600  is shown with transmitting and receiving capabilities, other embodiments may include devices with only receiving or transmitting capabilities. 
     In various embodiments, the wireless communication device  600  may be, but is not limited to, a mobile telephone, a paging device, a personal digital assistant, a text-messaging device, a portable computer, a desktop computer, a base station, a subscriber station, an access point, a radar system, a satellite communication device, or any other device capable of wirelessly transmitting/receiving RF signals and benefitting from frequency conversion operations as described herein. 
     The main processor  624  may execute a basic operating system program, stored in the memory  628 , in order to control the overall operation of the wireless communication device  600 . For example, the main processor  624  may control the reception of signals by receiver  620  and the transmission of signals by transmitter  616 . The main processor  624  may be capable of executing other processes and programs resident in the memory  628  and may move data into or out of memory  628 , as desired by an executing process. 
     The transmitter  616 , which may be similar to and substantially interchangeable with transmitter  400  in some embodiments, may receive outgoing data (e.g., voice data, web data, e-mail, signaling data, etc.) from the main processor  624  and may generate RF signal(s) to represent the outgoing data. The RF signals may then be provided to the duplexer  612  and transmitted over the air by the antenna structure  608 . 
     The receiver  620 , which may be similar to and substantially interchangeable with receiver  300 , may receive the incoming RF signals and provide incoming data transmitted by the RF signals to the main processor  624  for further processing. 
     In various embodiments, the antenna structure  608  may include one or more directional and/or omnidirectional antennas, including, e.g., a dipole antenna, a monopole antenna, a patch antenna, a loop antenna, a microstrip antenna or any other type of antenna suitable for over-the-air transmission/reception of RF signals. 
     Those skilled in the art will recognize that the wireless communication device  600  is given by way of example and that, for simplicity and clarity, only so much of the construction and operation of the wireless communication device  600  as is necessary for an understanding of the embodiments is shown and described. Various embodiments contemplate any suitable component or combination of components performing any suitable tasks in association with wireless communication device  600 , according to particular needs. Moreover, it is understood that the wireless communication device  600  should not be construed to limit the types of devices in which embodiments may be implemented. 
     Although the present disclosure has been described in terms of the above-illustrated embodiments, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. Those with skill in the art will readily appreciate that the teachings of the present disclosure may be implemented in a wide variety of embodiments. This description is intended to be regarded as illustrative instead of restrictive.