BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
FIGS. 1A and 1B illustrate simplified operations of a receiver switch in accordance with an embodiment of the invention.
FIG. 2 illustrates a CMOS switch using a switched resonator at a TX mode, in accordance with an embodiment of the invention.
FIG. 3 illustrates a CMOS switch using a switched resonator at RX mode, in accordance with an embodiment of the invention.
FIG. 4A illustrates a multi-stacked switch at a TX path, in accordance with an embodiment of the invention.
FIG. 4B illustrates a simplified equivalent model of on state switch using a body floating technique switch with signal flow, in accordance with an embodiment of the invention.
FIG. 5 illustrates exemplary receiver switch simulation results, in accordance with an embodiment of the invention.
FIGS. 6A and 6B illustrate exemplary transmit switch simulation results, in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
Embodiments of the invention may provide for CMOS RF antenna switches, which may also be referred to as SP4T CMOS switches. The CMOS RF antenna switches in accordance with embodiments of the invention may provide for one or more of multi-band operation, high power level handling, and integration with other devices and circuits. Generally, the CMOS RF antenna switch may include at least one receiver switch and at least one transmit switch. The receiver switch may utilize one or more switched resonators, as will be described in further detail below. The transmit switch may utilize or otherwise employ a body substrate tuning technique, as will also be described in further detail below.
Description of a Receiver Switch
In accordance with an embodiment of the invention, the CMOS RF antenna switch, and in particular, the receiver switch component of the RF antenna switch will be now be described in further detail with reference to FIGS. 1-3. FIGS. 1A and 1B provide an illustrative example of an operation of a simplified CMOS RF antenna switch having a transmit switch 102 and a receiver switch 104, in accordance with an embodiment of the invention. As shown in FIGS. 1A and 1B, a CMOS RF antenna switch may comprise an antenna 100 in communication with at least one transmit switch 102 and at least one receiver switch 104. As shown in FIG. 1A, when the transmit switch 102 is ON (e.g., enabled), thereby providing a transmit signal to the antenna 100, the receiver switch 104 is OFF (e.g., disabled). Likewise, as shown in FIG. 1B, when the receiver switch 104 is ON (e.g., enabled), thereby allowing reception of a receive signal from the antenna 100, the transmit switch 102 is OFF (e.g., disabled). According to an embodiment of the invention, the antenna 100 may be a single multi-mode (e.g., RX and TX), multi-band antenna, although a plurality of distinct antennas may be utilized according to other embodiments of the invention.
Still referring to FIGS. 1A and 1B, the receiver switch 104 may be in the form of a switched resonator, according to an embodiment of the invention. This switched resonator may provide distinctly different equivalent circuits, depending on whether the receiver switch 102 is ON or OFF, respectively. In FIG. 1A, when the receiver switch 104 is OFF, an LC resonant circuit may be formed in accordance with an embodiment of the invention. The LC resonant circuit may block the transmit signal provided from the transmit switch 102 in the ON state, thereby maximizing the power of the signal transmitted via antenna 100. According to an embodiment of the invention, the LC resonant circuit may include at least one inductor 106 in parallel with at least one capacitor 108. The value of the inductor 106 may be sufficiently large, perhaps over 5 nH, depending on the desired operating frequency of the resonant circuit. It will be appreciated that while the LC resonant circuit is illustrated as a parallel resonant circuit in FIG. 1A, other embodiments of the invention may utilize a series resonant circuit as well (e.g., an RLC resonant circuit).
On the other hand, in FIG. 1B, when the receiver switch 104 is ON, a filter may be formed, according to an embodiment of the invention. The filter may be a low-pass filter, with a certain cutoff frequency characteristics according to an embodiment of the invention. In addition, the filter may include a very small inductor 110 value at the desired operating frequency in order to provide for a low insertion loss. Accordingly, the filter 104 may provide for the reception, with low insertion loss, of at least a portion of the receive signal provided from the antenna 100. While the above-described filter is illustrated as a low-pass filter, it will be appreciated that other embodiments of the filter may be a bandpass filter, a high-pass filter, or the like.
FIG. 2 illustrates an illustrative example of an operation of an RF antenna switch 200 in transmit (TX) mode. In particular, FIG. 2 includes an antenna 100 in communication with the transmit switch 102 and the receiver switch 104. According to an embodiment of the invention, the transmit switch 102 may comprise signal paths for one or more transmit signals. For example, as shown in FIG. 2A, there may be two signal paths that is, signal paths TX1 and TX2 controlled by switches M1204 and M2206, respectively. The switches M1204 and M2206 may comprise one or more CMOS switches. Likewise, the receiver switch 104 may include signal paths RX1 and RX2, as controlled by switches M3208, M4210, M5212, M6214, M7216, M8218, and M9220, which may each comprise one or more CMOS switches.
In FIG. 2, according to an embodiment of the invention, the RF antenna switch 200 is illustrated as operating in TX mode for signal path TX1. With this TX mode configuration for transmit switch 102, switch M1204 is closed and switch M2206 is open. In addition, the receiver switch 104 forms an resonant circuit, described in further detail below, by closing switches M3208, M4210 while opening switches M5212, M6214, and M7216 to provide a high impedance point at node 232. In addition, although not illustrated as such in FIG. 2, switches M8218 and M9220 may also be closed to bypass leakage signals to ground ion order to protect the low-noise amplifier (LNA) from such leakage signals. One of ordinary skill in the art will recognize that in FIG. 2, signal path TX2 could have been enabled instead of signal path TX1 without departing from embodiments of the invention. It will also be appreciated that the configuration of the transmit switch 102 and receiver switch 104, including the numbers of transmit and receive signal paths, may be varied without departing from embodiments of the invention.
In the configuration illustrated in FIG. 2, the power handling capability of the transmit switch 102 may be based upon the impedance of the resonant circuit and the source-to-drain breakdown voltage of cascaded switches M5212, M6214 M7216 of the receiver switch 104. In other words, the maximum transmit power of the transmit switch 102 may be dependent upon the impedance and breakdown characteristics of the receiver switch 104.
According to an embodiment of the invention, the resonant circuit may be an LC parallel resonant circuit formed by inductors L1222, L2224 in parallel with capacitor C1226. In order to provide the desired blocking during the TX mode configuration to maximize the transmit signal power, the inductance value of inductor L2224 may be sufficiently large. However, the ratio of the value of inductors L1222 and L2224 may be related to the power handling of the transmit switch 102. Accordingly, if the value of L1222 is too small, then a large voltage swing may be above the source-to-drain breakdown voltage of switches M5212, M6214, and/or M7216, which are intended to be open to provide a high impedance point at node 232. Therefore, the value of the inductor L1222 may be selected to yield the optimum voltage swing for the TX mode and low insertion loss for the RX mode.
In accordance with an embodiment of the invention, FIG. 3 provides an illustrative operation of an RF antenna switch 300 in transmit (RX) mode. As shown in FIG. 3, both switch M1204 and switch M2206 of the transmit switch 102 are open to isolate antenna 100 from transmit signal paths TX1 and TX2, respectively. However, in enabling receive signal path RX1, switches M3208, M4210, and MS 218 are open, while switches M5212 and M6214 are closed. Further, to bypass leakage signal to ground to protect the low noise amplifier (LNA), switch M9220 may be closed. One of ordinary skill in the art will recognize that signal path RX2 could have been enabled instead of signal path RX1 without departing from embodiments of the invention.
Still referring to FIG. 3, a low-pass filter may be formed using inductor L1222 and capacitor C2228. If low insertion loss is a primary consideration, then the inductor L1222 value may be as small as possible. However, as described above with respect to FIG. 2, the value of inductor L1222 impacts the voltage swing of the TX mode, and thus, the value of inductor L1222 may be selected to provide the optimum voltage swing for the TX mode and low insertion loss for the RX mode.
Dual Band operation
As described with reference to FIGS. 1-3, the receiver switch 104 (e.g., switched resonator) may provide for an LC resonator in the TX mode and an LC lowpass filter for the RX mode. In addition, as shown in FIGS. 2 and 3, there may be two transmit signal paths TX1 and TX2 and two receive signal paths RX1 and RX2. It will be appreciated, however, that fewer transmit or receive paths may be included as desired without departing from embodiments of the invention. In accordance with an embodiment of the invention, TX1 and RX1 may be provided for GSM band (e.g., 900 MHz) communications and TX2 and RX2 may be provided for DCS/PCS band (e.g., 1.9 GHz) communications, although different bands may be utilized as well. In addition, more than two bands-perhaps three or four bands-may also be supported without departing from embodiments of the invention.
As the number of signal paths at the antenna 100 increases, however, the power handling capability of the transmit switch 102 may drop. Accordingly, in a single-pole multi-throw switch, it may be desirable to decrease the number of signal paths at the antenna 100. For instance, as shown in FIGS. 2 and 3, RX1 and RX2 of the receiver switch 104 may share one LC parallel resonator at the antenna 100 front end, where the LC parallel resonator is comprised of inductors L1222, L2224 and capacitor C1226. As described above, the LC parallel resonator may block the transmit signals from TX1 and TX2 at either band. Instead of having a switched resonator with two switched transmission zeros at dual bands, the LC parallel resonator described above may have only one transmission zero, which may be at 1.5 GHz with a wide band, according to an embodiment of the invention. In addition, the LC parallel resonator may provide for −13 dB, −25 dB and −14 dB return loss at 900 MHz, 1.5 GHz, and 1.9 GHz, respectively.
Description of a Transmit Switch
The transmit switch 102 in FIGS. 2 and 3 will now be described in further detail with reference to FIGS. 4A and 4B. In particular, FIG. 4A illustrates a transmit switch 102 structure for switch M1204 at TX1 and switch M2206 at TX2 according to an exemplary embodiment of the invention. As shown in FIG. 4A, switches M1204 and M2206 may include stacked transistors such as CMOS transistors 402, 404, and 406 stacked (e.g., cascaded) from source to drain. By stacking transistors 402, 404, and 406 from source to drain, the cumulative breakdown voltage can be increased since it is split among the transistors 402, 404, and 406, thereby providing for a higher power blocking capability. Such a high power blocking capability may be necessary, for example, at switch M2206 at TX2 when switch M1204 at TX1 is closed to transmit a signal. While FIG. 4 illustrates three stacked transistors, it will be appreciated that fewer or more stacked can be cascaded as well.
However, by stacking the transistors 402, 404, and 406, the insertion loss of the transmit switch 102 may be increased. Accordingly, as shown in FIG. 4A, a body floating technique, which includes connecting high resistor 408, 410, and 412 values at the body substrate, may be applied to the transmit switch 102 in accordance with an embodiment of the invention With such a body floating technique, the transistors 402, 404, and 406 may use a deep N-well structure, perhaps of a 0.18-um CMOS process, which may be immune to potential latch ups due to connecting high resistor 408, 410, 412 values at the body substrate. The resistors 408, 410, 412, which may also be referred to as body floating resistors, may reduce the insertion loss by blocking leakage current to the substrate ground.
FIG. 4B illustrates signal flow at on single stage switch—for example, transistor 402, 404, or 406. As the size of a transistor 402, 404, 406 increases, the parasitic capacitance value becomes high enough so that source-to-body 452 and drain-to-body 454 parasitic capacitor with body floating resistor 456 may be used as signal path c at the ON state. However, if the body is grounded, signal path c in FIG. 4B is bypassed to the ground, which results in degraded insertion loss.
Simulation results
FIG. 5 illustrates simulation results for the operation of an exemplary multi-band (e.g., 900 MHz, 1.9 GHz) receiver switch 104 in accordance with an embodiment of the invention. These simulation results illustrate the insertion loss 502, the isolation 504 from the antenna 100 to the TX, and the isolation 506 between RX1 and RX2. In particular, the insertion loss 502 is illustrated by the top solid line. The isolation 504 measured between the antenna 100 and the TX is illustrated by the middle line. Likewise, the isolation 506 between RX1 and RX2 is illustrated by the bottom line.
FIG. 6 illustrates simulation results for the operation of an exemplary multi-band transmit switch 102. In particular, the simulation results in FIGS. 6A illustrate the power handling capability while FIG. 6B illustrates the isolation from the antenna 100 to the RX. In both FIGS. 6A and 6B, the solid lines represent simulations at the first band of 1.9 GHz while the circled lines represent simulations at the second band of 900 MHz.
One of ordinary skill in the art will recognize that the simulation results are provided by way of example only. Indeed, the transmit switch 102 and the receiver switch 104 may be configured for other bands of operation as well. Accordingly, the simulation results may likewise be provided for other bands of operations without departing from embodiments of the invention.
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Patent Application
20070281629
