Patent Application
20070232241
The present invention relates to electronic circuits that are radio frequency (“RF”) transceivers; in particular at different times the circuit is required to either transmit RF power to an antenna port or to receive RF power from the antenna port and amplify the signal in a low noise amplifier (“LNA”) on one or more separate frequency bands.
In recent years the use of wireless communications systems has increased significantly. Cellular and cordless telephone systems are ubiquitous. Portable wireless data devices are indispensable to many businesspeople and can be used to send and receive e-mails, surf the Internet and perform location based services. And fixed wireless local area networks (“LANs”) are becoming more and more popular as ongoing development increases the throughput rate of the systems. While such wireless communications systems may use different technologies to meet the needs of various applications and customers, all of them employ RF transceivers to send and receive information. Thus, more and more transceivers are being developed as the wireless marketplace expands.
For many power amplifiers 18, the transmitted signal at the antenna 12 must be matched to a 50 ohm impedance level, which represents the impedance of the antenna 12. Normal transmit powers for common devices such as cell phones and wireless LAN devices are in the 100s of mW to 1 or more Watts. This means that large voltage swings exist at the antenna of these devices.
In order to switch high voltages with low RF attenuation of the signal, special devices such as GaAs high electron mobility transistor (“HEMT”) switches (including “DPHEMPT” switches) or Silicon on Saphire (“SOS”) switches are typically employed. PIN diodes have also been used for this application, but they have the drawback that they draw significant current whereas the aforementioned SOS and HEMT technologies do not draw significant current. Note that none of the aforesaid technologies widely used to implement the transmit/receive switches shown in
In the past, researchers have sought ways to integrate the transmit/receive switch function into standard CMOS or BiCMOS IC processes. At low power levels, a low voltage MOS switch is capable of implementing this function. In addition, there have been several researchers who demonstrated the use of floating MOS switches in which breakdown of the switch to the substrate is avoided by using MOS devices in a CMOS well and then resonating the well to substrate capacitance at the frequency of the transmit signal. See, e.g., Feng-Jung Huang and Kenneth K. O, “Single-Pole Double-Throw CMOS Switches for 900-MHz and 2.4-GHz Applications on p− Silicon Substrate,” IEEE Journal of Solid-State Circuits, Vol. 39, No. 1, January 2004; and Niranjan A. Talwalkar, C. Patrick Yue, Haitao Gan, and S. Simon Wong, “Integrated CMOS Transmit-Receive Switch Using LC-Tuned Substrate Bias for 2.4-GHz and 5.2-GHz Applications,” IEEE Journal of Solid-State Circuits, Vol. 39, No. 6, June 2004. However, all of these approaches create a large voltage stress either between the substrate and the well or between the well and the source and drain junctions. This can damage or destroy the switch, thereby rendering the transceiver inoperable. Therefore, the long term reliability of these approaches is questionable.
Thus, there is a need to provide transceiver switching solutions which address these and other issues.
The instant application provides a system and method of creating a transmit/receive switch function using a BiCMOS or CMOS IC process, which allows for a single chip architecture. This includes silicon-based MOS and BJT transistor shunt switches and silicon diode-based shunt switches preferably formed using CMOS or BiCMOS technology. Such shunt switch devices are not required to withstand the voltage swings found at the antenna of the device in
In accordance with one embodiment of the present invention, a transceiver module is provided. The module comprises an antenna node, a transmit path, a receive path and at least one switchable impedance. The transmit path is electrically connected to the antenna node and comprises a power amplifier. The receive path is electrically coupled to the antenna node and comprises a low noise amplifier. The switchable impedance comprises a switch electrically coupled to the transmit path and the receive path. The switchable impedance is configured to switch between a first state that substantially reflects power in the transmit path from the antenna node and a second state that substantially reflects power in the receive path from the antenna node. The switch is a silicon based shunt switch coupled to ground and is selected from the group consisting of a silicon-based MOS switch, a silicon-based bipolar switch and a silicon-based diode. Furthermore, the transceiver module is formed on a single, unitary substrate.
In accordance with another embodiment of the present invention, a transceiver module comprises an antenna node, a transmit path, a receive path and at least one switchable impedance means. The transmit path is electrically connected to the antenna node and comprises a power amplifier. The receive path is electrically coupled to the antenna node and comprises a low noise amplifier. The switchable impedance means comprising switch means electrically coupled to the transmit path and the receive path. The switchable impedance means is configured to switch between a first state that substantially reflects power in the transmit path from the antenna node and a second state that substantially reflects power in the receive path from the antenna node. The transceiver module is formed on a single, unitary substrate.
In accordance with yet another embodiment of the present invention, a transceiver module comprising an antenna node, a frequency multiplexer and a plurality of transceivers is provided. The frequency multiplexer is coupled to the antenna node and the plurality of transceivers is each coupled to the antenna node via the frequency multiplexer. Each transceiver is configured to operate at a separate frequency, and each transceiver comprises a transmit path and a receive path. The transmit path is electrically connected to the antenna node. The transmit path comprises a power amplifier and at least one switchable impedance. The receive path is electrically coupled to the antenna node. The receive path comprises a low noise amplifier and at least one switchable impedance. Each switchable impedance is configured to switch between a first state that substantially reflects power back toward the antenna node and a second state in which signal power is transmitted along its respective path and comprising a switch. The switch is a silicon based shunt switch coupled to ground and is selected from the group consisting of a silicon-based MOS switch, a silicon-based bipolar switch and a silicon-based diode. Furthermore, the transceiver module is formed on a single, unitary substrate.
In accordance with a further embodiment of the present invention, a transceiver module comprising an antenna node, a transmit path and a receive path is provided. The transmit path is electrically connected to the antenna node. The transmit path comprises a power amplifier, a transformer coupled to the power amplifier, and a switchable impedance coupled to the transformer. The switchable impedance is in a high impedance state in a first mode of operation that is a receive mode and is in a low impedance state in a second mode that is a transmit mode. The receive path is electrically coupled to the antenna node. The receive path comprises a low noise amplifier and a switchable impedance that is in a high impedance state in the receive mode and a low impedance state in the transmit mode. Each switchable impedance comprises a silicon based shunt switch coupled to ground and is selected from the group consisting of a silicon-based MOS switch, a silicon-based bipolar switch and a silicon-based diode. Furthermore, the transceiver module is formed on a single, unitary substrate.
FIGS. 1(c)-1(m) illustrates reactive networks for use in transceiver switching circuits in accordance with aspects of the present invention.
FIGS. 8(a)-8(f) illustrate shunt switch types for use in the present invention.
In describing the preferred embodiments of the invention illustrated in the appended drawings, specific terminology will be used for the sake of clarity. However, the invention is not intended to be limited to the specific terms used, and it is to be understood that each specific term includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.
The present invention does not involve overall transceiver system architecture design, but rather addresses transceiver switching circuitry that may be employed in different transceiver architectures. A generalized discussion of transceiver architecture design may be found in “Transceiver System Design for Digital Communications,” by Scott R. Bullock, ©1995, ISBN 1-884932-40-0, the entire disclosure of which is hereby expressly incorporated by reference herein.
One of the critical issues addressed by the present invention involves avoiding high voltage swings that can occur during operation of an RF transceiver. As explained above, excessive voltages can adversely affect transceiver components, causing degradation in performance or even overall system failure.
While embodiments of the present invention employ MOS, BJT or diode switches in the transceiver, it is very important to avoid subjecting them to a high voltage stress. According to one aspect of the invention, this can be done by using shunt switches to reflect or transmit power across the transmitter or receiver portions of the transceiver as needed. That is, switches are connected to a low RF swing node and are in their low impedance state during the transmit operation.
Preferably electrically coupled between the PA section 42 and the antenna 44 are a first reactive device 48, a shunt switch 50 and a second reactive device 52, and preferably electrically coupled between the LNA section 46 and the antenna 44 are a third reactive device 54, a shunt switch 56, and a fourth reactive device 58. Another reactive device 60 may also be electrically coupled between the antenna 44 and the PA section 42 and the LNA section 46 as shown, for example to help provide impedance matching with the antenna 44 or for protection against electrostatic discharge at input or output pins. While the reactive devices 48, 52, 54, 58 and 60 are shown, any or all of these devices may be omitted in a particular design.
The reactive devices 48, 52, 54, 58 and 60 are most preferably formed as reactive networks, which may include various combinations of capacitors, inductors and transmission lines. Such reactive networks may be constructed to achieve a predetermined impedance at one or more frequencies. Preferably, the reactive networks are selected or adjusted to maximize power transfer along the path from the antenna to the receiver in receive mode and along the path from the transmitter to the antenna in the transmit mode. The specific configurations of reactive networks are not critical to the invention, and may be selected based on engineering design parameters. Nonetheless, several specific reactive network configurations are illustrated in FIGS. 1(c)-1(m) by way of example only. For instance, FIGS. 1(c), 1(d) and 1(e) illustrate an inductor, a capacitor, and a parallel inductor/capacitor configuration.
Returning to
Now the operation of the shunt switches 50 and 56 during receive and transmit modes will be explained. During receive mode, the antenna 44 will input power from a received signal into the circuit 40. For efficient transceiver operation, it is most desirable for the transmit side 41 of the circuit 40 (e.g., PA section 42, reactive devices 48 and 52, and shunt switch 50) to reflect as much power back toward the antenna 44 as possible. Conversely, it is most desirable for the receive side 43 of the circuit 40 (e.g., LNA section 42, reactive devices 54 and 58, and shunt switch 56) to pass through as much power as possible from the antenna 44. Thus, it is most preferable for the shunt switch 50 of the transmit side 41 to be set in a low impedance state while the shunt switch 56 is set in a high impedance state during receive mode. By way of example only, the shunt switch 50 may be logically “closed” to achieve the low impedance state (e.g., such as can be modeled with a small resistor) and the shunt switch 56 may be logically “opened” to achieve the high impedance state (e.g., such as can be modeled by a small capacitor, as many switches appear capacitive in a high impedance state).
During transmit mode it is most desirable for the receive side 43 to reflect as much power toward the antenna 44 as possible, while it is most desirable for the transmit side 41 to pass through as much power as possible from the PA section 42 to the antenna 44. Thus, in this case, the shunt switch 56 may be logically closed to achieve the low impedance state while the shunt switch 50 may be logically open to achieve the high impedance state. Here, during transmit, the shunt switch 50 must be able to withstand the full RF+DC voltage swing at its terminal connected to node 51 while in a logically open state, while the shunt switch 56 is protected from a large voltage swing by having both of its terminals at a voltage near or at ground. For example, switch 56 can be implemented using a very low breakdown voltage MOS device while switch 50 may require the use of a high breakdown voltage BJT switch.
For either shunt switch 50 or shunt switch 56, when the low impedance state is entered, it is desirable to reflect as much power as possible. Thus, while a reflection of 75-80% of power is acceptable, most preferably at least 90% or more of the power is reflected during the low impedance state. The exact degree to which power is reflected is a function of the impedance of the switch in the low impedance state and the specific reactive networks connecting the switch to the antenna node. Conversely, when either shunt switch 50 or shunt switch 56 is in the high impedance mode, it is desirable to dissipate as little power in the switch as possible as the goal in the open state is to transfer as much of the power as possible from the antenna to the selected module (42 or 46). It is possible to increase power transmission by increasing the impedance presented by the switch in its off state at the desired RF signal frequencies. Thus, as shown in
Similarly, circuit 402 includes a transmit side 412 having a power amplifier section 422 electrically coupled to the antenna 44 through the reactive devices 482 and 522 and shunt switch 502. The circuit 402 also includes receive side 432 having a low noise amplifier section 462 that is coupled as well to both the antenna 44 and the user device. The LNA section 462 electrically couples to the antenna 44 through the reactive devices 542 and 582 and shunt switch 562. Reactive device 602 is also preferably electrically coupled between the transmit and receive sides and the antenna 44. Here, the reactive devices 601 and 602 may be configured as frequency diplexers to optimize operation of the circuits 401 and 402 at two different frequencies or frequency bands.
Thus, two transceivers can operate on two different frequency bands. Each circuit 401 and 402 preferably operates in the same manner as circuit 40 of
During transmit mode at the first frequency or frequency band, it is most desirable for the receive side 431 to reflect as much power toward the antenna 44 as possible, which it is most desirable for the transmit side 411 to pass through as much power as possible from the PA section 421 to the antenna 44. Thus, in this case, the shunt switch 561 may be logically closed to achieve the low impedance state while the shunt switch 501 may be logically open to achieve the high impedance state. Here, during transmit, the shunt switch 501 must be selected to handle the full transmit voltage swing at node 511, while the shunt switch 561 is protected from the large voltage swing by shunting node 571 to ground. It should be understood that operation of the circuit 402 at a second frequency or frequency band occurs in similar fashion to that of circuit 401 at the first frequency/band. In this case it is preferable for the reactive device 601 to reflect power away from the circuit 401 and toward the antenna 44, while the reactive device 602 admits power to and from the circuit 402. In sum, the shunt switches on the paths leading to all of the non-selected (inactive) modules are preferably placed into a low resistant state while the switch on the path leading to the selected (active) module is placed in a high impedance state. The respective reactive devices should be selected to maximize power transfer between the antenna and the particular modules for the active and inactive states.
As shown in the figure, the power amplifier 106 may include a base bias generator, including a reference transistor 108 coupled to a current source 110, a MOS transistor 112, and an operational amplifier 114. The base bias generator is used to bias BJT transistor 122, which is the principal output device of the power amplifier. While an exemplary configuration of power amplifier is provided, the invention is not limited to any particular power amplifier configuration. In this case, instead of having a switch at node 51 as in
A second node 116 is also coupled to the antenna node 104. The second node 116 is adapted to take signals received by the antenna and provide them to the user device, where they may be subsequently processed or otherwise employed in the operation of the user device. Between the antenna node 104 and the second node 116 is LNA 118, which amplifies the signals received by the antenna 104 prior to passing them to through the second node 116.
The transceiver switching circuit 100 includes additional components which are electrically coupled between either the power amplifier and the antenna node 104 or between the LNA 118 and the antenna node 104. These components include shunt switches.
For instance, the transmission path between the power amplifier and the antenna node 104 preferably includes a first shunt switch 120 coupled to the input node 107 of the power amplifier final stage transistor 122. The switch 120 may be, e.g., a MOS type switch where the drain is coupled to the power amplifier output node, the gate is coupled to a transmit enable (“
In particular, FIGS. 8(a)-8(f) illustrate different ways to implement shunt switches in the embodiments of the present invention. While examples of shunt switches such as in
As explained above,
Returning to
Inductor 124, which may be used as a “choke,” preferably couples the collector of the transistor 122 to the power source, and inductor 126 preferably couples the emitter of the transistor 122 to ground. The transistor 122's collector (or drain if a MOSFET transistor is used) is also desirably coupled to one end of inductor 128, while the other end of the inductor 128 is coupled to node 130. A capacitor 132, which may be used as a DC block, is preferably disposed between the node 130 and the antenna node 104. A capacitor 134 may also be coupled between the node 130 and ground, while a resistance 136, such as a 50Ω resistance, either may be coupled between the antenna node 104 and ground or may simply represent the load of the antenna at the node 104.
As mentioned above, additional circuitry may be electrically disposed between the antenna node 104 and the LNA 118. In the present embodiment, such circuitry includes an inductor 138 coupled between node 130 and node 140. A second shunt switch 142 is also coupled to the node 140. The switch 142 may be, e.g., a MOS switch where the drain is coupled to the node 140, the gate is coupled to a receive enable (“
In the present embodiment, when the circuit 100 is to receive a signal from the antenna, the shunt switch 120 is preferably activated to be in a low impedance or logical “on” state, coupling the node 107 to ground. Thus, the base of transistor 122, which would be the gate if a MOS transistor is used instead, is also shorted to ground, and the transmit side of the transceiver circuit 100 reflects power back toward node 130 because the transistor 122 is a high impedance when in the OFF state.
In this case, the portion of the received signal from the antenna that flows through inductor 128 is reflected by the large impedance mismatch between the antenna impedance and the impedance of the base-collector (or drain-gate) capacitance of the transistor 122 in series with the matching capacitor 134. The input impedance looking into inductor 128 from the antenna node 104 is reasonably high as long as the transistor 122 collector capacitance is sufficiently small. Therefore, very little current, and hence little power, will flow from the antenna through inductor 128.
During receive mode, the switch 142 is preferably placed in a logical off state, acting as an open circuit and providing high impedance. Thus, the signal received by the antenna is coupled through an impedance matching network, including inductor 138 and capacitor 144, to the LNA 118, where it is amplified and passed to the node 116. The capacitor 144 is desirably selected to have an optimal noise figure and to match the input impedance from the antenna with the LNA 118.
When the circuit 100 is in transmit mode, switch 120 is preferably placed in a high impedance state, acting as an open circuit while in a logical off state. Switch 142 is preferably placed in a low impedance state, acting as a short circuit while in a logical on state. With switch 120 in high impedance mode, current desirably flows through capacitor 123 to the input of the power amplifier transistor 122, is amplified by the transistor 122, and is coupled to the antenna node 104 through inductor 128, and capacitors 134 and 132. With the switch 142 in low impedance mode, the inductor 138 becomes part of the impedance matching network for the power amplifier 106 that includes inductor 128 and capacitor 134. No excessive, damaging voltage appears across switch 120 or switch 142 during transmit mode due to their shunt configurations and because switch 120 is ahead of high gain transistor 122, thereby ensuring a highly reliable circuit.
As shown in
Regardless of which configuration is used, the structure of
When switching into transmit mode, a possible short circuit at the power amplifier device output could occur, preventing proper operation of the circuit 200. In order to avoid this, the switch 202 is placed in a low impedance state, which creates a parallel resonant circuit with capacitor 204 across inductor 210 that results in the overall impedance from node 208 to ground being high at the resonant frequency. By choosing capacitor 204 to parallel resonate with inductor 210 at the desired transmit frequency, the impedance seen looking into the branch of capacitor 204, inductor 210 and capacitor 206 will have a high impedance and will not significantly load down the power output device. This circuit achieves the goal of improved direction of the antenna power to the LNA during receive mode while still making sure that all of the shunt switches see a very small voltage during the transmit mode as both switches 202 and 142 are in their low resistance state during transmit mode. In the present embodiment, the circuit 200 is configured to operate across a limited frequency range, in particular the band for which capacitor 206 and inductor 210 are in series resonance and the band for which capacitor 204 and inductor 210 are in parallel resonance.
In some situations, an additional degree of freedom is desired in the order to select optimal values for all of the components in both transmit and receive modes. This can be achieved by removing inductor 138 from being a part of the transmission matching network. Another embodiment of the present invention employing such a configuration is shown in
As shown, circuit 300 is similar to circuit 200 and also includes another shunt switch, namely switch 302 in series with capacitor 304. The switch 302 enables modification of the input impedance to a branch through which power should not flow. The capacitor 304 preferably couples the drain of the switch 302 to node 130. The source of the switch 302 may be coupled to ground, or, alternatively as shown by the dotted line, to the drain of switch 142 and node 140. The gate of switch 302 is coupled to the receive enable signal line. As with switches 202 and 142, switch 302 is in the low resistance state during transmit mode and is a shunt switch; therefore none of these three switches will see a high voltage stress even during transmit operation.
Capacitor 304 is desirably selected to resonate in parallel with inductor 138 at the desired transmit frequency. This removes the loading presented by inductor 138 from the transmission matching network, thereby facilitating its optimal design. During receive mode, switch 302 is placed in a high impedance state. During transmit mode, switch 302 is placed in a low impedance state. Neither switch 142 nor switches 302 or 202 will see significant voltages during the transmit mode because they are both in a low impedance state.
In accordance with another aspect of the invention, other reactive devices may be used in the power amplifier output matching. For example, the pi match, the T match, etc., may be employed. Similarly, additional matching networks can be used at the input to LNA 118. For example, the pi match, the T match, etc., may be employed here as well. See FIGS. 1(c)-1(m) for examples of reactive networks that may be employed. Note that the LNA matching network can be connected to the antenna node 104 with either an inductor or a capacitor and the parallel resonator enable by switch 302 in the embodiment of
In accordance with another aspect of the present invention, for all of the places where a resonant circuit (either series or parallel) is formed, the center frequency of that resonant circuit can be adjusted by adding in additional reactive elements with additional switches to move the center frequency of the resonance electronically. Although the bandwidth of the technique is may be constrained to some extent due to the resonant operation, by electronically switching the center frequency it can be extended to cover wider bandwidths. This may also be of particular interest for applications with different transmit and receive frequencies, or which employ multiple bands of transmit and/or receive frequencies.
The antenna port or node can actually be part of a larger circuit. For example, as with the embodiment of
As shown in
Similar to the embodiments described above, the circuit 400 also includes a second node 408 coupled to the antenna node 404. The second node 408 is adapted to take signals received by the antenna and provide them to the user device, where they may be subsequently processed or otherwise employed in the operation of the user device. Between the antenna node 404 and the second node 408 is LNA 410, which amplifies the signals received by the antenna 404 prior to passing them to through the second node 408.
Also shown in
As in the embodiments of
The circuit 400 of
In circuits where the RF block to be switched has a transformer at its output, instead of a series switch, the connection of the transformer to RF ground may be broken as shown in
In particular,
As shown, the circuit 500 includes a first section 502 adapted for the 2.4 GHz band of the 802.11b and g standards and a second section 504 adapted for the 4.9-5.85 GHz band for the 802.11a standard. Each of the sections 502 and 504 includes an LNA, namely LNA 506 for section 502 and LNA 508 for section 504, where the LNAs 506 and 508 are adapted for operation at the respective frequency band. Each of the sections 502 and 504 preferably also includes a power amplifier, namely power amplifier 510 for section 502 and power amplifier 512 for section 504. As with the LNAs 506 and 508, the power amplifiers 510 and 512 are preferably adapted for operation at the respective frequency band.
The section 502 preferably also includes a reactive network of elements 514 and 516 in conjunction with switches 518, 520 and 522. The elements 514 and 516 may comprise, by way of example only, quarter wavelength transmission lines or pseudo quarter wavelength lines (ones approximated by a finite number of inductors and capacitors). In one example, the elements 514 and 516 comprise pi or tee LC lumped networks. Other examples of reactive networks which may be employed are illustrated in FIGS. 1(c)-1(m). The switches 518, 520 and 522 are most preferably shunt switches, where the shunt switch 518 is for activating/deactivating the LNA 506, the shunt switch 520 is for activating/deactivating the power amplifier 510, and the shunt switch 522 is for activating/deactivating the first section 502 generally. Examples of such shunt switches are provided in FIGS. 8(a)-8(f).
The section 504 preferably also includes a reactive network of elements 524 and 526 in conjunction with switches 528, 530 and 532. As with elements 514 and 516, the elements 524 and 526 may comprise, by way of example only, pseudo quarter wavelength lines. In one example, the elements 524 and 526 comprise pi or tee LC lumped networks, although other reactive networks such as in FIGS. 1(c)-1(m) may be employed. The switches 528, 530 and 532 are most preferably shunt switches, where the shunt switch 528 is for activating/deactivating the LNA 508, the shunt switch 530 is for activating/deactivating the power amplifier 512, and the shunt switch 532 is for activating/deactivating the second section 504 generally. As above, examples of such shunt switches are provided in FIGS. 8(a)-8(f).
As shown in
During operation, one power amplifier or one LNA of the circuit 500 is preferably active at a time. The other active components are preferable placed in a state to reflect power away from them. This is done using the shunt switches. By way of example only, if the circuit 500 is to receive a signal in the 2.4 GHz band, switches 520, 528, 530 and 532 are preferably placed in a low impedance state so that most or all of the power is reflected away from PA 510, PA 530 and LNA 508. Here, the shunt switches 518 and 522 are preferably placed in a high impedance state so that most or all of the power passes from the antenna 544 to the LNA 506.
In another example, if the circuit 500 is to transmit a signal in the 5.5 GHz band, switches 518, 520, 522 and 528 are preferably placed in a low impedance state so that most or all of the power is reflected away from the PA 510, the LNA 506 and the LNA 508. Here, the shunt switches 530 and 532 are preferably placed in a high impedance state so that most or all of the power passes from the PA 512 to the antenna 544.
Thus, it can be seen that
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. By way of example only, while MOS switches may be illustrated in the figures for certain embodiments, BJT or diode switches may be employed instead. In addition, while the circuits presented above were described in a single-ended configuration, the invention is not so limited and is equally applicable to differential configurations as well. Furthermore, any of the embodiments according to the present invention are preferably implemented in single chip architectures. As discussed above, features in the embodiments described herein may be incorporated into other embodiments. For instance, any of the reactive networks may be used in any of the embodiments herein. Similarly, any of the shunt switch configurations may be used in any of the embodiments herein.
This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/777,473 filed Feb. 28, 2006 and entitled “A Narrow Band BiCMOS Transmit Receive Switching Scheme for use in Radio Frequency Transceivers,” the entire disclosure of which is hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 60777473 | Feb 2006 | US |
