Patent Application
20150056940
1. Field
Various features relate generally to wireless communications apparatus and more particularly to circuits and methods for removing interfering signals in a low noise amplifier of a wireless receiver.
2. Background
Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be accessed by access terminals adapted to facilitate wireless communications, where multiple access terminals share the available system resources (e.g., time, frequency, and power). Examples of such wireless communications systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems and orthogonal frequency-division multiple access (OFDMA) systems. A base station may provide the access terminal with access to a radio access network (RAN) using one or more radio access technology (RAT).
Responsive to increasing demand for greater functionality in apparatus including cellular telephones, smart phones, global positioning satellite (GPS) navigators, media players and the like, a growing number of wireless service operators are deploying RANs using a variety of RATs, at least some of which may interfere with one another. Many access terminals are configured for use with multiple RATs and/or may encounter different RATs while communicating on a preferred RAN. Coexistence issues can arise when the different RATs employ or share the same band of frequencies. For example, the wireless fidelity (WiFi) standard for local wireless communications defined by the Institute Of Electrical And Electronic Engineers (IEEE) as IEEE 802.11 may interfere with a wide area network (WAN) employing cellular network technologies. WiFi co-existence with WANs can present challenges to WAN sensitivity in radio frequency (RF) receivers.
Accordingly, there is an ongoing need for improved interference elimination circuits and devices.
In an aspect of the disclosure, a method and an apparatus are provided. The apparatus and method may be employed in a wireless networking environment. The apparatus may include a low-noise amplifier in high frequency RF receiver.
In an aspect of the disclosure, the apparatus includes a common-gate amplification circuit including a metal-oxide semiconductor field effect transistor (MOSFET), which may have a source terminal that is configured to receive an RF signal from a transmission line, and a series resonance comprising capacitance connected in series with an inductance. The series resonance may provide a low impedance path to ground for interfering RF components in the RF signal.
In an aspect of the disclosure, the series resonance is tuned to provide a high impedance to a band of frequencies centered on a frequency of interest. The interfering RF components may be characterized by frequencies outside the band of frequencies centered on the frequency of interest. The interfering RF components may include a harmonic of a frequency in the band of frequencies centered on the frequency of interest. The interfering RF components may include a harmonic generated in the transmission line. The band of frequencies may be centered on the frequency of interest corresponds to a band of frequencies associated with a first RAN. The interfering RF components may include a signal transmitted by a second RAN.
In an aspect of the disclosure, the signal transmitted by the second radio access network includes a carrier signal that is a harmonic of a frequency in the band of frequencies centered on the frequency of interest. The second RAN may include a WiFi network.
In an aspect of the disclosure, an output of the common-gate amplification circuit is down-converted using a local oscillator frequency corresponding to the frequency of interest. The interfering RF components may include a signal that has a frequency that is a harmonic of a local oscillator frequency.
In an aspect of the disclosure, a parallel resonance may be configured to reduce gain of frequencies outside the band of frequencies centered on the frequency of interest. The parallel resonance may include a second capacitance connected in parallel with a degeneration inductance that matches the transmission line.
In an aspect of the disclosure, a method of wireless communication includes providing an RF signal received from an antenna to an input of a common-gate amplification circuit, shunting the interfering RF component to ground through a resonating circuit coupled to the input of the common-gate amplification circuit, and passing the band of frequencies through the common-gate amplification circuit. The RF signal may include information encoded in a band of frequencies and an interfering RF component.
In an aspect of the disclosure, the resonating circuit may include a capacitance that is connected in series to an inductance. The capacitance and the inductance may have values selected to cause the resonating circuit to provide a low impedance path to ground for a frequency corresponding to the interfering RF component.
In an aspect of the disclosure, a parallel resonance may be provided at an output of a common source low noise amplifier that drives the transmission line. The parallel resonance may include a second capacitance connected in parallel with a degeneration inductance associated with the transmission line.
In an aspect of the disclosure, a wireless device includes means for amplifying an RF signal received from an antenna, and means for shunting an interfering RF component of the RF signal to ground. The means for shunting may include a resonating circuit coupled to an input of the common-gate amplification circuit. The RF signal may be received at an input of a common-gate amplification circuit. The RF signal may include information encoded in a band of frequencies and/or on a plurality of carriers and/or subcarriers. The means for amplifying may be configured to provide an amplified version of the RF signal to a local oscillator used to down-convert the band of frequencies.
In the following description, specific details are given to provide a thorough understanding of the various aspects of the disclosure. However, it will be understood by one of ordinary skill in the art that the aspects may be practiced without these specific details. For example, circuits may be shown in block diagrams in order to avoid obscuring the aspects in unnecessary detail. In other instances, well-known circuits, structures and techniques may not be shown in detail in order not to obscure the aspects of the disclosure.
Several aspects of electrical circuits, assemblies, ICs, and IC packaging will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as “elements”). These elements may be implemented in, or interact with electronic hardware, computer software, or any combination thereof.
The various concepts presented throughout this disclosure may be implemented across a broad variety of telecommunication systems, network architectures, and communication standards. Certain aspects of the discussions described below are described in relation to Global System for Mobile Communications (GSM), and in relation to 3rd Generation Partnership Project (3GPP) protocols and systems, and related terminology may be found in much of the following description. However, those of ordinary skill in the art will recognize that one or more aspects of the present disclosure may be employed and included in one or more other wireless communication protocols and systems.
The mobile device 102 may be configured to communicate with a first access point (AP) 104 to obtain services from a first network through RAN 114 and to communicate with a second AP 106 to obtain services from a second network associated with RAN 116. Each RAN 114 and 116 may provide voice and/or data services for subscribed users. RANs 114 and 116 may be operated by the same or different network operators. The geographical areas covered by RANs 114 and 116 may differ in size and/or may at least partially overlap. In one example, RAN 116 may be a WiFi network that covers a substantially smaller area than a GSM network 114. The access terminal 102 may be deployed in a location where multiple accessible cells or RANs 114 and 116 are available and the access terminal 102 may be configured to access a plurality of networks, and/or a single core network through multiple access points 104 and 106. Accordingly, the access terminal 102 may be capable of receiving wireless communications signals on different carrier frequencies and/or in different sub-bands associated with the carrier frequencies. It will be appreciated that information may be encoded on one or more subcarriers found in a band of frequencies.
Each of the APs 204, 210 and/or 222 may include, or be referred to as a base station, a base transceiver station, a radio access point, an access station, a radio transceiver, a basic service set, an extended service set, a Node B, an evolved Node B (eNB), a wireless hub, a WiFi Access Point (WAP) or by some other suitable terminology. Each AP 204, 210 and/or 222 may support a RAN that provides access to core network services provided by one or more network operators. RANs may be implemented using any suitable RAT and may be compatible or comply with telecommunication standards employing a variety of modulation and multiple access techniques. By way of example, RANs associated with the APs 204, 210 and/or 222 may include one or more of Universal Terrestrial Radio Access (UTRA) employing CDMA or one of its variants, such as Wideband-CDMA (W-CDMA); GSM employing TDMA, Time Division Synchronous Code Division Multiple Access (TD-SCDMA), Long Term Evolution (LTE) which is a set of enhancements to the Universal Mobile Telecommunications System (UMTS), Evolved UTRA (E-UTRA), Wi-Fi, IEEE 802.16 (WiMAX), IEEE 802.20, and Flash-OFDM employing OFDMA. RANs may also include one or more of Evolution-Data Optimized (EV-DO) or Ultra Mobile Broadband (UMB). An access terminal 202 may support multiple antennas to handle different network technologies. For example, an access terminal 202 may have different antennas for a 3GPP defined network, a WiFi network and/or a Bluetooth network.
The access terminal 202 may be connected to one or more of the APs 204, 210 and 222 and the antenna 220 may receive or detect signals from multiple APs 204, 210 and 222 at any given time. In one example, the access terminal 202 may be connected to the Internet through a WAP 222 while associated with a packet-switched (PS) network, such as LTE, through eNB 204 and/or with a circuit-switched (CS) network for data and voice calls through base station 210. The access terminal 202 may be registered with an E-UTRAN through the eNB 204 and a packet data network (PDN) gateway 210 may provide connectivity between the access terminal 202 and one or more external packet data networks such as the Internet 216. The access terminal 202 may be registered with a CS network through the base station 210 in order to obtain voice and data services through a CDMA-2000 network, for example. In one example, a general packet radio service (GPRS) system permits 2G, 3G and W-CDMA mobile networks to transmit IP packets to external networks such as the Internet 216 using a gateway function which may include a serving GPRS support node (SGSN) 214 to provide interworking services including access to an external packet switched networks such as the Internet 216.
Each of the APs 204, 210 and 222 may communicate with the access terminal 202, using predefined carrier frequencies and bands of frequencies. In some instances, frequency bands used by one of the APs 204, 210 and/or 222 may overlap frequency bands used by the other APs 204, 210 and/or 222. Although wireless networking protocols may include provisions that accommodate and avoid interference caused by overlapping frequency bands, interference may affect the operation of the antenna and the amplifiers and signal processors that extract signals from modulated carriers.
Referring again to
Spatial multiplexing may be used to transmit different streams of data simultaneously on the same frequency. The data steams may be transmitted to a single mobile device 102 to increase the data rate or to multiple mobile devices 102 to increase the overall system capacity. This is achieved by spatially precoding each data stream and then transmitting each spatially precoded stream through a different transmit antenna on the downlink. The spatially precoded data streams arrive at the mobile device 102 with different spatial signatures, which enables the mobile device 102 to recover the one or more the data streams.
Receiver circuits in an access terminal 202 may be connected to one or more antennas 220, may receive a plurality of signals on carrier signals that have different or the same frequency, and may be subject to interference from signals received through the one or more antennas 220. According to certain aspects described herein, the access terminal 202 may be configured to eliminate, minimize or compensate for interference before down-conversion at a local oscillator. A local oscillator is a circuit that is used to convert an RF signal of interest to a lower frequency in a process referred to herein as down-converting the RF signal. In one example, a signal carried on a 5 GHz carrier may be down-converted to a signal that is encoded on a lower frequency carrier, known as an intermediate frequency, prior to decoding the RF signal.
A multi-port device 302 may include a plurality of ports 312a, 312b, 312c and 312d that receive RF signals at one or more carrier frequencies. For example, two ports 312a and 312b may receive RF signals on 2.6 GHz carriers corresponding to band B38 (HB1) band B7 (HB3) respectively, one another port 312c may receive an RF signal on a 2.3 GHz carrier corresponding to band B40 (HB4), and another port 312d may receive an RF signal on a 2.5 GHz carrier corresponding to band B41 (HB2). In the illustrated example, a signal-of-interest designated as HB2 is received at a first port 312d, and provided through a low-noise amplifier 316 and an interface circuit 318 to the transmission line 306. The transmission line communicates the current-amplified HB2 signal to a device 304 having a low-noise amplifier (LNA) that is configured to down-convert the HB2 signal using a mixer 320 and associated local oscillator 326. The operation of down-converting mixer 320 may be affected by interfering signals and/or carriers associated with one or more of the other ports 312a, 312b and/or 312c. In the illustrated example, an interfering or jammer RF signal received at a second input port 312b may be coupled to the transmission line 306 through transformer 318.
When multiple RF signals 312a, 312b, 312c and/or 312d are received on different carrier frequencies by one or more antennas 220, co-existence issues may arise. Some co-existence issues may relate to the mixing down of jammer signals that have frequencies at harmonics of the local oscillator (LO) 326 used to obtain a baseband signal from the signal of interest 312d. In one example, the jammer signal may be a WiFi signal detected by an antenna 220 on a carrier frequency of 5 GHz. As illustrated in
One approach to reducing the impact of the jammer signal is to provide a parallel resonance at the source of the common-source amplifier 316 to reduce the gain at an out-of-band frequency. The parallel resonance may be formed by adding a capacitance 322 in parallel with a degeneration inductor 324, which is used to match the impedance of an input of the amplifier 302. The parallel resonance formed from the inductance 324 and capacitance 322 may operate as a filter that reduces the gain at the out-of-band frequency and may therefore ameliorate the problems attributable to the jammer signal. An inductance-capacitance (LC) value may be selected to obtain low pass filtering in order to attenuate the higher frequencies. However, noise figure degradation of 0.1 dB-0.2 dB or higher may result.
In some examples, the series resonant circuit 504 may be tunable and can be digitally controlled to resonate at one of a plurality of frequencies corresponding to various potential jamming signals. The series resonant circuit 504 may be tuned by varying the inductance 508 or capacitance 510. An example of a digitally programmable capacitance element 520 is depicted in
In some examples, a plurality of series resonant circuits 504 may be provided, each series resonant circuit 504 being tuned to target a specific interferer. In some instances, there may be multiple interferers that desensitize the receiver. For example, interferers may be present at 5.4 GHz and 7 GHz in the system.
The low noise amplifier 624 may be configured to drive a mixing circuit 628 that down-converts the signal of interest using a local oscillator 626. The LNA 624 may be a common-gate amplifier. A signal received from the transmission line 606 is provided to a source terminal of a transistor 624a in the LNA 624. In accordance with certain aspects disclosed herein, a series resonance 630 may be connected to the source terminal of the transistor 624a. The series resonance 630 may have an inductance 632 that is series connected with a capacitance 634 such that the series resonance 630 is tuned to provide a low impedance path to ground for certain targeted frequencies. The series resonance 630 may be tuned through the selection of the values of inductance 632 and capacitance 634. In one example, the series resonance 630 may be tuned to shunt signals having a frequency around a harmonic of the frequency of the local oscillator 626 and/or to filter harmonics generated in the transmission line 606.
The series resonant circuit 630 may be combined with the parallel resonance 614 to improve the out-of-band jammer signal rejection characteristics of the receive chain. The series resonant circuit 630 may be provided after or near the termination impedance 622 of the transmission line 606 and/or at or near the input to the LNA 624, while other filters are deployed to improve the rejection of signals at one or more harmonic frequencies of the local oscillator 626 and/or signals at frequencies that are not harmonics of the local oscillator frequency. For example, the load of the LNA 624 may be a parallel resonant circuit 636 that provides a high impedance at the carrier frequency of the signal of interest and provides a low impedance path to the jammer signal. In another example, a combination of the parallel resonant circuit 614 and the series resonant circuit 630 may be employed, and may yield a 16 dB or better rejection of interfering harmonics for the entire receive chain, and without incurring a significant noise figure penalty.
In some examples, a plurality of series resonant circuits 630 may be provided, each series resonant circuit 630 being tuned to target a specific interferer. Alternatively or additionally, the combination of the series resonant circuit 630 with the parallel resonance 614 may be configured to improve the out-of-band jammer signal rejection characteristics of the receive chain when multiple interferers are present. According to one aspect, one resonant circuit 614 or 630 may be tuned to reject one interferer when there are multiple interferers that can desensitize the receiver, and the other resonant circuit 630 or 614 may be tuned to reject interferers at other frequencies. For example, there may be interferers at 5.4 GHz and 7 GHz in the system, and the parallel resonant circuit 614 may be tunable to reject only the 5.4 GHz interferers, in which case the series resonant circuit 630 may be tuned to reject the 7 GHz interferer.
At step 704, the interfering RF component is shunted to ground through a series resonance circuit coupled to the input of the common-gate amplification circuit. The resonance circuit may include a capacitance that is connected in series to an inductance. The capacitance and the inductance may have values that are selected to cause the resonance circuit to provide a low impedance path to ground for a frequency corresponding to the interfering RF component. The interfering RF component may have a frequency that is a harmonic of a local oscillator used to down-convert the band of frequencies. Further, the capacitor and/or inductor may be tunable by using a switched network for capacitors and switched ports for inductors. The interfering RF component may include a signal that has a frequency that is a harmonic of a local oscillator used to down-convert the band of frequencies. The interfering RF component may include a signal that is increased in the transmission line.
In an aspect of the disclosure, the series resonance circuit is tunable. In one example, the series resonance circuit may be tuned to target one of a plurality of potentially interfering RF components in the RF signal. In another example, the series resonance circuit is one of a plurality of series resonance circuits connected to the source of the MOSFET, each series resonance circuit being tuned to provide a low impedance path to ground for a different interfering RF component in the RF signal. In an aspect of the disclosure, a parallel resonance circuit is used to target an interfering RF component in the RF signal that is different from interfering RF components targeted by one or more series resonance circuits.
At step 706, the band of frequencies is passed through the common-gate amplification circuit. According to certain aspects described herein, the RF signal may be filtered before it is transmitted over a transmission line. The RF signal may be filtered before the transmission line by providing the RF signal to a parallel resonance that may be provided at a source terminal of a common source low noise amplifier that drives the transmission line, for example. The parallel resonance may have a second capacitance connected in parallel with a degeneration inductance that may be used to match the impedance of an input of the amplifier.
According to certain aspects described herein, the RF signal received from the antenna is amplified using a current amplifier, and an output of the current amplifier is provided to a first end of a transmission line. The RF signal may be filtered using a parallel resonance coupled to a source terminal of a transistor in the current amplifier. The input of the common-gate amplification circuit may be coupled to a second end of the transmission line. The parallel resonance may comprise a second capacitance connected in parallel with a degeneration inductance that is configured to provide impedance matching of an input port that receives the RF signal from the antenna.
The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any implementation or aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term “aspects” does not require that all aspects of the disclosure include the discussed feature, advantage, or mode of operation. The term “source/drain” terminal of a transistor may be either the source or the drain of the transistor. Whether it is actually the source or the drain depends on the voltages applied to the various terminals of the transistor when it is in operation. Moreover, the term “VDD” represents the circuit's power supply voltage, and “VSS” represents the circuit ground.
The terms wafer and substrate may be used herein to include any structure having an exposed surface with which to form an IC according to aspects of the present disclosure. The term “die” may be used herein to include an IC. A die may include one or more circuits. The term substrate is understood to include semiconductor wafers. The term substrate is also used to refer to semiconductor structures during fabrication, and may include other layers that have been fabricated thereupon. The term substrate includes doped and undoped semiconductors, epitaxial semiconductor layers supported by a base semiconductor, or semiconductor layers supported by an insulator, as well as other semiconductor structures well known to one skilled in the art.
One or more of the components, steps, features and/or functions illustrated in
Also, it is noted that the embodiments may be described as a process that is depicted as a flowchart, a flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. A process is terminated when its operations are completed. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination corresponds to a return of the function to the calling function or the main function.
The various features of the invention described herein can be implemented in different systems without departing from the invention. It should be noted that the foregoing aspects of the disclosure are merely examples and are not to be construed as limiting the invention. The description of the aspects of the present disclosure is intended to be illustrative, and not to limit the scope of the claims. As such, the present teachings can be readily applied to other types of apparatuses and many alternatives, modifications, and variations will be apparent to those skilled in the art.
