Patent Application
20070223615
The present invention relates generally to multi-band radio system architectures. More particularly, the present invention relates to radio system architectures for supporting multiple band receive diversity.
Technological advances over the last several years have enabled manufacturers to develop smaller and more portable devices, rich in features and miserly on power consumption. Cellular phones and wireless enabled personal digital assistants (PDA's) are examples of such devices, which are now pervasive in modem society due to their portability and convenience, making wireless telecommunication a ubiquitous means for transferring information between users.
While voice communication has been the primary use of cellular phones, mainly due to transmission rate limitations, communication standards have emerged which enable higher bandwidth applications. Such applications include viewing streamed video such as television programming, and real-time Internet browsing capabilities. Two main communication standards are in use today, which can support both voice and data communication; GSM (global system for mobile communications) and WCDMA (wideband code division multiple access), both of which are multi-band.
Preferably, a wireless device is multi-standard compliant such that the single device can be used virtually anywhere regardless of the type of standard that is predominantly used. Otherwise, the user would need to carry at least two different wireless devices, each dedicated to operating with a specific telecommunication standard. Therefore, a multi-standard compliant device is highly desired.
Other components of wireless device 10 include the GSM/EDGE (enhanced data for global evolution) front end block 20 and the WCDMA front end block 22. Both blocks 20 and 22 include standard and well known receive and transmit path circuits. It is noted that the details of GSM front end block 20 and WCDMA front end block 22 are not shown, since
In the presently shown example of
While not shown, WCDMA front end block 22 includes duplexers for selectively connecting the three bidirectional lines 24 to either the respective input ports (IN5 to IN7) or output ports (OUT3 to OUT5).
As can be seen in
Diversity, more specifically receive diversity, is a function where a signal can be received by the wireless device from two antennas in parallel. This feature is typically used to achieve higher data rates in areas where signal strength is not optimal, and processing of both received signals by the base-band processor can effectively improve receive performance. In an environment with large buildings for example, a signal received by the primary antenna may be sub-optimal due to interference from reflections. The signal received by the secondary antenna can be processed by the base-band processor using various algorithms to effectively combine and optimize the overall received signal. Because the RF transceiver is typically multi-standard and multi-band compliant, receive diversity for as many of these standards and bands should be supported as well. As will be shown in
In order to support all three WCDMA bands, three receive sub-paths (for IMT/PCS/850) are required. Accordingly, the SP3T antenna switch will selectively couple the second antenna 52 to one of the three sub-paths connected to WCDMA receive front end block 56. The WCDMA receive front end block 56 includes most of the same receive circuits that are used in WCDMA front end block 22, and converts the single ended input signals into respective differential signals. The WCDMA receiver 58 performs the same receive functionality as RF transceiver 14, but is dedicated to receiving the WCDMA 850, WCDMA PCS and WCDMA IMT signals at its input ports IN1, IN2 and IN3 respectively. WCDMA receiver 58 then interfaces with digital base-band processor to provide the received data for further processing.
The primary disadvantage of wireless device 50 is the requirement of WCDMA receiver 58. As previously noted, RF transceiver 14 does not have a single spare input port, let alone three spare input ports, for receiving the additional three WCDMA bands. WCDMA receiver 58 is a relatively large component that uses precious board space, which can restrict the overall form factor and size of the final product. Furthermore, the cost of WCDMA receiver 58 can be in the range of dollars/device, which is a significant cost overhead for implementing wireless device 50. Therefore, adding WCDMA receiver 58 is a significant premium for implementing receive diversity. Because the additional WCDMA receiver 58 is required, the baseband processor 102 must have the capability to interface with both the RF transceiver 104 and WCDMA receiver 58. This adds complexity and may place restrictions on the type of baseband processor which can be used.
Of course, wireless device 50 can be implemented in a configuration where WCDMA receiver 58 is not required. However, this would require a replacement for RF transceiver 14 which has the capability to receive the additional receive sub-paths for supporting tri-band receive diversity. More specifically for wireless device 50, RF transceiver 24 would need to be replaced with a different RF transceiver having an additional three input ports for receiving the WCDMA 850, WCDMA PCS and WCDMA IMT signals provided by WCDMA receive front end block 56. Unfortunately, this solution would be more costly since two different RF transceivers would need to be manufactured; one for non-diversity wireless devices and one for diversity enabled wireless devices. Those skilled in the art will understand that flexible use of a single chip for multiple applications, ie. non-diversity and diversity implementations is far more cost effective.
Alternately, a single RF transceiver having numerous input ports to anticipate future expansion can be used. Unfortunately, such an RF transceiver will still have a finite number of input ports, which may be insufficient for unforeseen future expansion. Furthermore, there is a practical limitation to the number of input ports and associated circuits, which can be implemented on an RF transceiver. Too many unused input ports will waste silicon area and ultimately add to the RF transceiver cost.
It is, therefore, desirable to provide a wireless device architecture, which can efficiently use the same RF transceiver for any number of standards and bands in diversity and non-diversity applications.
It is an object of the present invention to obviate or mitigate at least one disadvantage of previous RF transceiver interface architectures. In particular, it is an object of the invention to provide a flexible RF transceiver receive interface for sharing a physical input port with at least two input signals.
In a first aspect, the present invention provides a signal interface circuit for a receiving component. The signal interface circuit includes filter means and a switch circuit. The filter means receives a first wireless transmission signal and a second wireless transmission signal for providing corresponding first and second wireless transmission signal outputs. The switch circuit receives the first and the second wireless transmission signal outputs for providing a differential output signal corresponding to one of the first and second wireless transmission signal outputs.
According to an embodiment of the present aspect, the filter means includes a first differential output SAW filter and a second differential output SAW filter. The first differential output SAW filter receives the first wireless transmission signal and provides a first differential output signal corresponding to the first wireless transmission signal output. The second differential output SAW filter receives the second wireless transmission signal and provides a second differential output signal corresponding to the second wireless transmission signal output. The switch circuit includes a first 2:1 RF switch circuit and a second 2:1 RF switch circuit. The first 2:1 RF switch circuit receives first phases of the first differential output signal and the second differential output signal, and selectively passes one of the first phases. The second 2:1 RF switch circuit receives second phases of the first differential output signal and the second differential output signal, and selectively passes one of the second phases, where the differential output signal corresponding to the passed first and second phases.
According to another embodiment of the present aspect, the filter means includes a first single-ended output SAW filter and a second single-ended output SAW filter. The first single-ended output SAW filter receives the first wireless transmission signal and provides a first single-ended output signal corresponding to the first wireless transmission signal output. The second single-ended output SAW filter receives the second wireless transmission signal and provides a second single-ended output signal corresponding to the second wireless transmission signal output. The switch circuit includes a 2:1 RF switch circuit for receiving the first and the second single-ended output signals and for selectively passing one of the first and the second single-ended output signals to a balun, where the balun provides the differential output signal.
In a second aspect, the present invention provides a multi-standard compliant wireless device for receiving first and second transmission signals. The wireless device inlcudes a signal interface circuit, and an RF transceiver. The signal interface circuit receives the first and the second transmission signals and selectively passes one of the first and the second transmission signals as a selected input transmission signal. The RF transceiver has first and second input ports each configured for receiving either the first or the second transmission signals, the RF transceiver receiving the selected input transmission signal at the first input port.
In an embodiment of the second aspect, the first and the second transmission signals are provided by an antenna switch coupled to an antenna, and the signal interface circuit includes filter means and a switch circuit. The filter means for receiving the first transmission signal and the second transmission signal, the filter means provides corresponding first and second transmission signal outputs. The switch circuit receives the first and the second transmission signal outputs and provides a differential output signal corresponding to one of the first and second transmission signal outputs.
According to an aspect of the present embodiment, the filter means includes a first differential output SAW filter and a second differential output SAW filter. The first differential output SAW filter receives the first transmission signal and provides a first differential output signal corresponding to the first transmission signal output. The second differential output SAW filter receives the second transmission signal and provides a second differential output signal corresponding to the second transmission signal output. The switch circuit indudes a first 2:1 RF switch circuit and a second 2:1 RF switch circuit. The first 2:1 RF switch circuit receives first phases of the first differential output signal and the second differential output signal, and selectively passes one of the first phases. The second 2:1 RF switch circuit receiving second phases of the first differential output signal and the second differential output signal, and selectively passes one of the second phases, the differential output signal corresponding to the passed first and second phases.
In a further embodiment of the present aspect, the filter means includes a first single-ended output SAW filter and a second single-ended output SAW filter. The first single-ended output SAW filter receives the first transmission signal and provides a first single-ended output signal corresponding to the first transmission signal output. The second single-ended output SAW filter receives the second transmission signal and provides a second single-ended output signal corresponding to the second transmission signal output. The switch circuit includes a 2:1 RF switch circuit for receiving the first and the second single-ended output signals and for selectively passing one of the first and the second single-ended output signals to a balun, the balun providing the differential output signal.
In yet another embodiment, the switch circuit includes a 2:1 integrated differential RF switch circuit for receiving the first differential output signal and the second differential output signal, the differential RF switch circuit selectively passing one of the first differential output signal and the second differential output signal as the differential output signal.
In another embodiment, the multi-standard compliant wireless device further includes a receive diversity circuit for providing a receive diversity signal to the second input port. The receive diversity circuit includes a second signal interface circuit for receiving a first diversity signal and a second diversity signal, and selectively passes one of the first diversity signal and the second diversity signal as the receive diversity signal. The receive diversity circuit includes a second antenna switch coupled to a second antenna for providing the first diversity signal and the second diversity signal. The second signal interface circuit includes filter means and a switch circuit. The filter means receives the first diversity signal and the second diversity signal, and provides corresponding first and second diversity signal outputs. The switch circuit receives the first and the second diversity signal outputs and provides the receive diversity signal corresponding to one of the first and second diversity signal outputs. The filter means includes a first differential output SAW filter and a second differential output SAW filter. The first differential output SAW filter receives the first diversity signal and provides a first differential output signal corresponding to the first diversity signal output. The second differential output SAW filter receives the second diversity signal and provides a second differential output signal corresponding to the second diversity signal output.
In aspects of the present embodiment, the switch circuit includes a first 2:1 RF switch circuit and a second 2:1 RF switch circuit. The first 2:1 RF switch circuit receives first phases of the first differential output signal and the second differential output signal, and selectively passes one of the first phases. The second 2:1 RF switch circuit receives second phases of the first differential output signal and the second differential output signal, and selectively passes one of the second phases, where the differential output signal corresponding to the passed first and second phases. The filter means includes a first single-ended output SAW filter for receiving the first diversity signal and for providing a first single-ended output signal corresponding to the first diversity signal output, and a second single-ended output SAW filter for receiving the second diversity signal and for providing a second single-ended output signal corresponding to the second diversity signal output. The switch circuit includes a 2:1 RF switch circuit for receiving the first and the second single-ended output signals and for selectively passing one of the first and the second single-ended output signals to a balun, where the balun providing the differential output signal. Alternately, the switch circuit includes a 2:1 integrated differential RF switch circuit for receiving the first differential output signal and the second differential output signal, the differential RF switch circuit selectively passing one of the first differential output signal and the second differential output signal as the receive diversity signal.
According to a further embodiment of the present aspect, the second signal interface circuit receives a third diversity signal, and selectively passes one of the first diversity signal, the second diversity signal and the third diversity signal. The filter means includes a first differential output SAW filter, a second differential output SAW filter and a third differential output SAW filter. The first differential output SAW filter receives the first diversity signal and provides a first differential output signal corresponding to the first diversity signal output. The second differential output SAW filter receives the second diversity signal and provides a second differential output signal corresponding to the second diversity signal output. The third differential output SAW filter receives the third diversity signal and provides a third differential output signal. The switch circuit includes a 3:1 integrated differential RF switch circuit for receiving the first differential output signal, the second differential output signal and the third differential output signal. The 3:1 integrated differential RF switch circuit selectively passing one of the first differential output signal, the second differential output signal and the third differential output signal as the receive diversity signal.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:
Generally, the present invention provides a transceiver interface architecture where the same RF transceiver can be used in wireless devices that support any number of standards and bands, with or without receive diversity implementation. Each input port of the RF transceiver is preferably wide-band in nature and has the correct frequency selectivity, can be shared by a number of input signals, which effectively expands the number of available input ports. Input port sharing can be realized with virtual ports that receive two or more input signals and selectively pass one signal to the physical input port. The use of virtual ports allows for flexible wireless design implementations using the same RF transceiver, and in particular, for receive diversity implementations that inherently require dedicated input ports. The use of low cost and small area virtual ports obviates the need for larger, dedicated, and more costly RF receivers.
In this present example, RF transceiver 104 has seven input ports, which is typical for a quad-band GSM and tri-band WCDMA implementation. In order to accommodate diversity, a 2:1 virtual port 120 is inserted between input port IN6 and the WCDMA PCS and WCDMA IMT signals from WCDMA front end block 112, and a 3:1 virtual port 122 is inserted between input port IN7 and the WCDMA PCS, WCDMA IMT and WCDMA 850 diversity signals from WCDMA receive front end block 118. Virtual port 120 can selectively pass one of the WCDMA PCS or WCDMA IMT signals to input port IN6, which effectively frees input port IN7 for use by virtual port 122. Virtual port 122 can selectively pass one of the three received WCDMA signals to input port IN7 in receive diversity operation. For example, if virtual port 120 passes the primary WCDMA IMT signal received from WCDMA front end block 112 to input port IN6, then virtual port is correspondingly controlled to pass the secondary WCDMA IMT signal received from WCDMA receive front end block 118 to input port IN7.
However, according to another embodiment of the invention, the input ports of RF transceiver 104 are preferably wideband inputs, similar to those described in commonly owned U.S. patent application Ser. No. 11/297,335 filed on Dec. 9, 2005, the contents of which are entirely incorporated by reference. Therefore, two or more input signals each at different frequencies can be received by the wideband input, provided they are within the operating frequency range of the wideband input. Accordingly, input port IN7 is also preferably a wideband input and the correct frequency selectivity for receiving any one of the three WCDMA signals.
GSM/EDGE front-end block 110 includes a receive section and a transmit section. The receive section includes four receive SAW filters 200, 202, 204 and 206, for receiving the GSM 850, GSM 900, GSM DCS and GSM PCS signals respectively from antenna switch 106. Each SAW filter provides a band-selection and differential output corresponding to its single ended input signal, which are coupled to input ports IN1, IN2, IN3 and IN4. The transmit section includes a pair of baluns 208 and 210, and a quad-band GSM/EDGE power amplifier (PA) module 212. Balun 208 receives a differential output signal from output port OUT1 and generates a corresponding single-ended output, while balun 210 receives a differential output signal from output port OUT2 and generates its own corresponding single-ended output. PA module 212 amplifies the signals from baluns 208 and 210 and provides the amplified signals to antenna switch 106. GSM/EDGE front end block 110 is a standard configuration that is known in the art. In fact, antenna switch 106 and SAW filters 200, 202, 204 and 206 can be purchased as an integrated package for integration/assembly into wireless device 100.
WCDMA front-end block 112 also has a receive section and a transmit section. The receive section includes low noise amplifiers (LNA) 220, 222 and 224 having singled-ended outputs coupled to filter means, implemented as SAW filters 226, 228 and 230. LNA's 220, 222 and 224 receive WCDMA 850, WCDMA PCS and WCDMA IMT signals from antenna switch 106. SAW filter 226 is shown as providing differential signals to input port IN5, however, SAW filters 228 and 230 are shown to provide either differential or single-ended signals to virtual port 232. Virtual port 232 passes one of the WCDMA PCS and WCDMA IMT signals in differential format, to input port IN6. As will be shown later, the configuration of the signal interface circuit 234 consisting of SAW filters 228 and 230 and virtual port 232, can be implemented in different ways depending on the desired format of the input signal (ie. Single-ended or differential). Virtual port 232 is presently shown as a separate component from WCDMA front end block 112, but can easily be integrated as part of WCDMA front end block 112. It is noted that LNA's 220, 222 and 224 and SAW filters 226, 228 and 230 are available
The transmit section includes SAW filters 240, 242 and 244 receiving differential signals from output ports OUT3, OUT4 and OUT5 respectively, each providing single-ended outputs to corresponding power amplifiers 246, 248 and 250. In the present example, power amplifier 246 provides the WCDMA IMT signal, power amplifier 248 provides the WCDMA PCS signal, and power amplifier 250 provides the WCDMA 850 signal. The input section and the output section of WCDMA front end block 112 share a set of three bi-directional lines 252 via duplexers 254, 256 and 258, which provide isolation and filtering. Each of the three bidirectional lines 252 are connected to antenna switch 106 for receiving/providing the WCDMA signals.
Now a description of the receive diversity signal path follows. First, it is noted that input port IN7 has been illustrated near the bottom of RF transceiver 104 instead of between IN6 and OUT3 as previously illustrated in
In WCDMA receive diversity operation, duplexers 254, 256 and 258 are switched to couple bi-directional lines 252 to LNA's 220, 222 and 224, and antenna switch 106 will couple antenna 108 to one of the LNA's 220, 222 and 224, depending on which WCDMA signal standard is being used. Those of skill in the art will understand that the appropriate switching is controlled by the base-band processor. If the signal is a WCDMA PCS signal, then virtual port 232 will be configured to pass the WCDMA PCS signal from SAW filter 228 to input port IN6. Concurrently, antenna switch 116 will couple secondary antenna 114 to one of the LNA's 276, 278 and 280 depending on which WCDMA signal standard is being used. In the present example where the signal is a WCDMA PCS signal, secondary antenna 114 will be coupled to LNA 278 via preselector 272. Accordingly, virtual port 288 will pass the WCDMA PCS signal provided by SAW filter 284 to input port IN7.
Virtual ports 232 and 288 perform the same function, that is, they both perform a switching operation to pass one of several input signals to one output. The main functional difference is that virtual port 232 performs a one of two selection while virtual port performs a one of three selection.
Therefore, due to the effective input port expandability of RF transceiver 104 provided by virtual ports 232 and 288, no additional WCDMA receiver is required. The diversity input signal path can now be provided directly to the RF transceiver 104. This provides two major advantages. First, the board space cost and component cost for the wireless device 100 is reduced, since virtual port components will cost much less and occupy less board area than a dedicated receiver chip. Second, the virtual ports allow the same RF transceiver to be used for diversity and non-diversity implementations of wireless devices. Therefore, the RF transceiver manufacturer can realize the benefits of economies of scale when the same chip can be used in a multiplicity of wireless device designs.
According to one embodiment of the present invention, virtual ports 232 and 288 can be implemented with standard RF switches. RF switches are exclusively used for electrically coupling an antenna to one of several different input/output signal paths. In fact, antenna switches 106 and 116 are standard RF switches which differ only in that switch 106 provides a one of nine selection while switch 116 provides a one of three selection. RF switches are specifically designed for antenna switching operation, as there are electrical parameters which must be carefully considered for RF switching applications. For example, in applications where both WiFi and Bluetooth connectivity is desired, isolation between ports can be between 18 dB to 35 dB.
It is clear from the uPG2150T5L data sheet that such RF switches are designed and intended for antenna switching purposes only, since the stated electrical requirements are tailored to accommodate such applications. In particular, these switches are intended to be used in antenna applications incorporating the transmit path, where they are designed to handle signals of large power (˜30 dBm). Hence using such switches elsewhere in a wireless device would not be apparent to persons skilled in the art. Furthermore, the commercially available RF switches such as the NEC uPG2150T5L SP3T RF switch, are configured for passing single-ended signals, and not the differential signals received and provided by the RF transceiver. Hence the RF switches are inherently incompatible with the RF transceiver. However, according to the embodiments of the invention, such commercially available RF switches can be used to implement the previously described virtual ports. Also, in the embodiments of the present invention, the RF switches are used in the receive path only, where the power handling requirements are not stringent (<0 dBm).
RF switch 404 receives one phase of the differential WCDMA PCS signal at port “a” and one phase of the differential WCDMA IMT signal at port “b”. Similarly, RF switch 406 receives the other phase of the differential WCDMA PCS signal at port “a” and the other phase of the differential WCDMA IMT signal at port “b”. Although not shown, RF switches 404 and 406 each have two control inputs for controlling their respective internal switch circuits, for passing the signals from either ports “a” or “b” to port “c”. Port “c” of both RF switches 404 and 406 are coupled to input port IN6, which is differential. Both RF switches 404 and 406 are controlled at the same time such that only ports “a” or “b” from both switches are coupled to their respective port “c”. This can easily be done by having a first common control signal connected to the control ports of both switches for coupling port “a” to port “c”, and a second common control signal connected to the control ports of both switches for coupling port “b” to port “c”.
Since ports “a” of both switches receives the differential WCDMA PCS signal and ports “b” of both switches receives the differential WCDMA IMT signal, concurrent switching by both switches 404 and 406 will effectively provide differential signal switching functionality. RF switches 404 and 406 can be implemented with the NEC uPG2159T5K switch, or the Murata XM0825SR-TL1301—721 SPDT switch. The NEC switch is small at 1 mm by 1 mm in size, thus utilizing very little board space in comparison to a dedicated receiver which can be at least 5 mm by 5 mm. At a cost of about $0.35 per switch unit versus $3 per unit for a wireless receiver, the cost savings are significant.
Since two separate RF switches 404 and 406 are used in the embodiment shown in
The example implementation embodiments for virtual port 232 shown in
Therefore, the presently shown embodiment of
The inventive concept shown in FIGS. 6 to 8 are equally applicable to virtual port 288 shown in
Therefore, by employing the virtual port interfaces as described by the embodiments of the present invention, the same RF transceiver chip can be used in multiple wireless device designs, with or without receive diversity. With on-chip receive diversity, receive sensitivity and signal quality during WCDMA receive operations can be enhanced. By example, the receive diversity shown by the present embodiments can enhance HSDPA performance to achieve receive data rates up to 10.2 Mbps.
The presently shown examples of the invention embodiments are illustrated in a tri-band application with diversity. However, the embodiments are equally applicable to dual-band applications with diversity. In a dual-band application with diversity, the primary WCDMA paths would include two (not three) signal standards that are multiplexed to one input port. Correspondingly, the diversity path would include two signal standards. However, if the two standards are close in frequency, then a single RF switch with a balun can be used. This configuration has been illustrated in
For RF transceivers that do not have a seventh input port (IN7), tri-band implementation with diversity can still be implemented. Taking the example of
While the embodiments of the signal interface circuits are used in a receive diversity application, they can also be used for non-diversity applications, where the RF transceiver does not have sufficient physical input ports for receiving all the types of transmission signals that can be received.
The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.
