Patent Application
20080252521
1. Field of the Invention
This invention relates generally to a transceiver array employing beam-forming and, more particularly, to a transceiver array employing digital beam-forming that includes a plurality of vertically integrated semiconductor wafers.
2. Discussion of the Related Art
Transceiver arrays are widely used in wireless communications, radar applications and sonar applications. A transceiver array is an array of transceiver channels each including an antenna where the channels combine to provide a directional beam for both transmitting and receiving purposes, including beam scanning. As the directivity of the array increases, the gain of the array also increases.
Various types of transceiver arrays are known in the art that provide beam steering. One known transceiver array type includes mounting individual transceiver front-end channels on a mechanical device that moves to provide beam steering or scanning.
Another known transceiver array type is a phased array. A typical phased array includes an antenna in each channel that is connected to a phase shifter, and a power combiner for adding the signals together from the antennas. The phase shifters control either the phase of the excitation current of the antenna for transmission or the phase of the receive signals. When the signals are combined, a beam is formed in a particular direction. Particularly, a transmit beam is formed in space, and a receive beam adds coherently if the signals are received from a particular region of space. The radiation pattern of the transceiver array is determined by the amplitude and phase of the current at each of the antennas. If only the phase of the signals is changed and the amplitude of the signals is fixed, the beam can be steered.
The known transceiver arrays of these types are typically expensive, bulky, consume a relatively large amount of power, etc.
In order to alleviate some of the disadvantages of the known transceiver arrays, digital beam-forming systems have been developed in the art that eliminate the need for the phase shifters to provide beam steering. The digital beam-forming systems digitally provide beam steering. One advantage of digital beam-forming is that once the RF information from each channel is captured in the form of a digital stream, digital signal processing techniques and algorithms can be used to process the data in the spatial domain.
Digital beam-forming is based on the conversion of the RF signal at each antenna into two streams of binary base-band signals representing in-phase and quadrature-phase channels. The digital base-band signals represent the amplitude and phases of signals received at each antenna in the array. The beam-forming is provided by weighting each digital signal from the channels, thereby adjusting their amplitude and phase so that when they are added together they form the desired beam. Thus, the linear phase weight applied to the digitized signal at each channel can make the antenna beam appear as if it is steered to different angular directions.
As mentioned above, each transmit/receive module 16 includes a plurality of components. Typically, the components in the transmit/receive module 16 are discrete integrated circuit components mounted to a printed circuit board. Because so many components are required in the transmit/receive module 16, the size of the array 10, the component insertion losses and power consumption are significant.
In accordance with the teachings of the present invention, a transceiver array is disclosed that employs vertically integrated circuits in one or more wafers. The array includes a digital wafer having digital circuits. A plurality of RF cubes are formed to the digital wafer, where each RF cube includes an antenna wafer and at least one lower wafer, and where each RF cube represents a separate channel of the array. The antenna wafer includes a patch antenna and a resonating cavity. The at least one lower wafer includes high frequency RF integrated circuits and intermediate frequency RF integrated circuits. The array has application as a front-end for a digital beam-forming system.
Additional features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.
The following discussion of the embodiments of the invention directed towards a transceiver array that employs digital beam-forming and includes vertically integrated RF channels is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses.
On the receiver side of the channel 36, the receive signal is amplified by a low noise amplifier (LNA) 42. The amplified receive signal from the LNA 42 is sent to a mixer 44 that down-converts the high frequency receive signal to an intermediate frequency (IF) signal. The mixer 44 receives a mixer signal from a local oscillator (LO) 46 to provide the frequency down-conversion. In one non-limiting embodiment, the receive signal is about 22 GHz and the IF signal is about 2.4 GHz. The IF signal from the mixer 44 is then sent to a band-pass filter 50 that filters the IF signal to be within a particular frequency band. The filtered signal from the band-pass filter 50 is then amplified by an IF amplifier 52.
The IF signal is then sent to an analog-to-digital (A/D) converter 56 in the digital wafer 34 that converts the analog signal to a digital signal for digital signal processing. The digital signal from the A/D converter 56 is then filtered by a band-pass filter 58, and down-converted to a base-band signal suitable for digital beam-forming by a digital down-conversion device 60. The digital base-band signal is then applied to a weighting junction 62 that weights the signal for beam-forming and beam steering purposes in a manner that is well understood to those skilled in the art. All of the weighted signals from all of the channels 36 are added by a summer 64, and the combined signal is processed by a beam-forming digital signal processor 66.
When the switch 40 is in the transmit mode, the digital signal processor 66 provides a digital signal to be transmitted to the summer 64 that is distributed to the several weighting junctions 62 in the various channels 36 so as to provide the desired weighting to the transmit signal for beam-forming and directional purposes. The digital signal from the weighting junction 62 is then sent to a digital-to-analog (D/A) converter 70, provided on the digital chip 34, in the transmit side of the channel 36. The analog signal from the D/A converter 70 is then sent to a band-pass filter 72 to filter the signal to be within the desired frequency band. The filtered signal from the band-pass filter 72 is then sent to a mixer 74 for frequency up-conversion purposes to convert the signal to a high frequency signal for transmission. The mixer 74 receives a frequency signal from a local oscillator (LO) 76 to provide the up-conversion. The high frequency signal from the mixer 74 is then filtered by another band-pass filter 78 and amplified by an LNA 80. A power amplifier 82 then amplifies the high frequency signal that is sent to the antenna 38 for transmission purposes.
The amplifiers 42, 52, 80 and 82 can include MEMS tunable matching networks that can tune the response of the amplifiers. Particularly, a broadband amplifier can be used, and it can be tuned to different bands by tuning the MEMS matching network. Further, the band pass filters 50, 72 and 78 can be MEMS tunable band-pass filters. Additionally, evanescent mode filters can be used for the band-pass filters 50, 72 and 78, which can also be tunable.
As is well understood in the art, each digital signal, whether a receive signal or transmit signal, would include both an in-phase portion and a quadrature-phase portion. Further other transceiver components, such as low-pass filters and amplifiers, may be provided in the transceiver array 30 depending on the specific application.
Although the specific embodiment for the RF cube 102 shows the patch antenna 116, the present invention contemplates any suitable antenna for any of the applications discussed herein. For example, other types of antennas may be applicable including printed dipoles, printed Vivaldi antennas, (PIFA), slot antennas, spiral antennas, loop antennas, printed inverted F antennas, etc. Further, the configuration of the patch antenna 116, or any of the other antennas mentioned above, can be both linearly and circularly polarized.
The MMIC wafer 112 includes a metallized or back plane layer 124 having a feed slot 126 formed therethrough. The receive signal resonates within the cavity 120 and propagates through the feed slot 126 and is received by an RF MMIC circuit 128 formed on the MMIC wafer 114. Likewise, the transmit signal is sent through the feed slot 126 from the circuit 128 to resonate within the cavity 120 to be transmitted by the patch antenna 116. The MMIC circuit 126 includes the various circuits in the wafers 32.
The RF MMIC circuit 128 is intended to represent any RF integrated circuit or circuits fabricated on the wafers 112 and 114 that are compatible with silicon and III-V semiconductor wafers. For example, the RF MMIC circuit 128 can include microelectro-mechanical switches or other microelectro-mechanical systems. RF MEMS components provide tunability, such as tunable matching networks for amplifiers and tunable filters, and therefore result in tunable RF cubes which can be used in a multi-band digital beam forming array. Further, the RF cube architecture disclosed herein can be integrated on-wafer with an evanescent mode filter to allow for a complete, high performance, wafer-scale, transmit/receive, tunable module for digital beam forming arrays. Combining a tunable high-cube evanescent mode filter with the RF cube 120 on-wafer results in a high-performance architecture because these types of evanescent mode filters can be used to isolate the RF from the local oscillator signal and the intermediate frequency signal at the mixers, and also eliminate all of the higher harmonics generated by the active elements of the circuit.
An antenna 142 is deposited on a top surface of the antenna wafer 132, and a resonating cavity 144 is formed within the wafer 132. The antenna 142 is intended to represent any of the antennas referred to above. RF integrated circuits 146 are provided on both sides of the lower RF wafer 134 and include integrated circuit components as discussed above. Any one of the integrated circuits 146 can be an RF MEMS integrated in the transceiver module 130, as discussed above. Further, IF integrated circuits 148 are provided on a bottom surface of the intermediate frequency RF wafer 136, where the IF integrated circuits 148 include the IF components in the transceiver array. Digital integrated circuits 150 are provided on both sides of the digital wafer 140. Various RF vias 152, typically made of gold (AU), extend through the various wafers 132-140, as shown, to provide the electrically coupling between the various circuits.
The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.
