Electrical generator or motor structure – Non-dynamoelectric – Charge accumulating
Reexamination Certificate
2001-04-20
2003-07-29
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Charge accumulating
C333S186000, C333S197000, C310S311000
Reexamination Certificate
active
06600252
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods and subsystems for processing signals utilizing a plurality of vibrating micromechanical devices.
2. Background Art
The need for passive off-chip components has long been a key barrier against communication transceiver miniaturization. In particular, the majority of the the high-Q bandpass filters commonly used in the RF and IF stages of heterodyning transceivers are realized using off-chip, mechanically-resonant components, such as crystal and ceramic filters and SAW devices, as illustrated in FIG.
1
. Due to higher quality factor Q, such technologies greatly outperform comparable filters implemented using transistor technologies, in insertion loss, percent bandwidth, and achievable rejection. High Q is further required to implement local oscillators or synchronizing clocks in transceivers, both of which must satisfy strict phase noise specifications. Again, as illustrated in
FIG. 1
, off-chip elements (e.g., quartz crystals) are utilized for this purpose.
Being off-chip components, the above mechanical devices must interface with integrated electronics at the board level, and this constitutes an important bottleneck against the miniaturization of super-heterodyne transceivers. For this reason, recent attempts to achieve single-chip transceivers for paging and cellular communications have utilized alternative architectures that attempt to eliminate the need for off-chip high-Q components via higher levels of transistor integration. Unfortunately, without adequate front-end selectivity, such approaches have suffered somewhat in overall performance, to the point where they so far are usable only in less demanding applications.
Given this, and recognizing that future communication needs will most likely require higher levels of performance, single-chip transceiver solutions that retain high-Q components and that preserver super-heterodyne-like architectures are desirable.
Recent demonstrations of vibrating beam micromechanical (“&mgr;mechanical”) resonator devices with frequencies in the VHF range and Q's in the tens of thousands have sparked a resurgence of research interest in communication architectures using high-Q passive devices as disclosed in the above-noted patent application entitled “Device Including A Micromechanical Resonator Having An Operating Frequency and Method of Extending Same.” Much of the interest in these devices derives from their use of IC-compatible microelectromechanical systems (MEMS) fabrication technologies to greatly facilitate the on-chip integration of ultra-high-Q passive tanks together with active transistor electronics, allowing substantial size reduction.
FIG. 2
illustrates a comparison of MEMS and SAW wherein MEMS offers the same or better high-Q frequency selectivity with orders of magnitude smaller size. Indeed, reductions in size and board-level packaging complexity, as well as the desire for the high performance attainable by super-heterodyne architectures, are principal drivers for this technology.
Although size reduction is certainly an advantage of this technology (commonly dubbed “RF MEMS”), it merely touches upon a much greater potential to influence general methods for signal processing. In particular, since they can now be integrated (perhaps on a massive scale) using MEMS technology, vibrating &mgr;mechanical resonators (or &mgr;mechanical links) can now be thought of as tiny circuit elements, much like resistors or transistors, in a new mechanical circuit technology. Like a single transistor, a single mechanical link does not possess adequate processing power for most applications. However, again like transistors, when combined into larger (potentially, VLSI) circuits, the true power of &mgr;mechanical links can be unleashed, and signal processing functions with attributes previously inaccessible to transistor circuits may become feasible.
The Need for High Q in Oscillators
For any communications application, the stability of the oscillator signals used for frequency translation, synchronization, or sampling, is of utmost importance. Oscillator frequencies must be stable against variations in temperature against aging, and against any phenomena, such as noise or microphonics, that cause instantaneous fluctuations in phase and frequency. The single most important parameter that dictates oscillator stability is the Q of the frequency-setting tank (or of the effective tank for the case of ring oscillators). For a given application, and assuming a finite power budget, adequate long- and short-term stability of the oscillation frequency is insured only when the tank Q exceeds a certain threshold value.
Given the need for low power in portable units, and given that the synthesizer (containing the reference and VCO oscillators) is often a dominant contributor to total transceiver power consumption, modern transceivers could benefit greatly from technologies that yield high-Q tank components.
The Need for High Q in Filters
Tank Q also greatly influences the ability to implement extremely selective IF and RF filters with small percent bandwidth, small shape factor, and low insertion loss. As tank Q decreases, insertion loss increases very quickly, too much even for IF filters, and quite unacceptable for RF filters. As with oscillators, high-Q tanks are required for RF and IF filters alike, although more so for the latter, since channel selection is done predominantly at the IF in super-heterodyne receivers. In general, the more selective the filter, the higher the resonator Q required to achieve a given level of insertion loss.
Micromechanical Circuits
Although mechanical circuits, such as quartz crystal resonators and SAW filters, provide essential functions in the majority of transceiver designs, their numbers are generally suppressed due to their large size and finite cost. Unfortunately, when minimizing the use of high-Q components, designers often trade power for selectivity (i.e., Q), and hence, sacrifice transceiver performance. As a simple illustration, if the high-Q IF filter in the receive path of a communication subsystem is removed, the dynamic range requirement on the subsequent IF amplifier, IQ mixer, and A/D converter circuits, increases dramatically, forcing a corresponding increase in power consumption. Similar trade-offs exist at RF, where the larger the number or greater the complexity of high-Q components used, the smaller the power consumption in surrounding transistor circuits.
The Micromechanical Beam Element
To date, the majority of &mgr;mechanical circuits most useful for communication applications in the VHF range have been realized using &mgr;mechanical flexural-mode beam elements, such as shown in
FIG. 2
with clamped-clamped boundary conditions. Although several micromachining technologies are available to realize such an element in a variety of different materials, surface micromachining has been the preferred method for &mgr;mechanical communication circuits, mainly due to its flexibility in providing a variety of beam end conditions and electrode locations, and its ability to realize very complex geometries with multiple levels of suspension.
U.S. Pat. No. 6,049,702 to Tham et al. discloses an integrated passive transceiver section wherein microelectromechanical (MEM) device fabrication techniques are used to provide low loss, high performance switches. Utilizing the MEM devices also makes possible the fabrication and use of several circuits comprising passive components, thereby enhancing the performance characteristics of the transceiver.
U.S. Pat. No. 5,872,489 to Chang et al. discloses an integrated tunable inductance network and method. The network utilizes a plurality of MEM switches which selectively interconnect inductance devices thereby providing a selective inductance for a particular circuit.
U.S. Pat. No. 5,963,857 to Greywall discloses an article comprising a micromachined filter. In use, the micromachined filters are assembled as part of a radio to miniaturize the size of the radio.
U.S. Pat. No
Brooks & Kushman P.C.
Dougherty Thomas M.
The Regents of the University of Michigan
LandOfFree
Method and subsystem for processing signals utilizing a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and subsystem for processing signals utilizing a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and subsystem for processing signals utilizing a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3093396