Cancellation of anti-resonance in resonators

Briefly, in accordance with one embodiment of the invention, a resonator such as an electromechanical resonator may be coupled with a cancellation network to reduce and/or cancel an anti-resonance effect in the resonator, which may be due to, for example, a static capacitance inherent in the resonator. Cancellation of an anti resonance effect from the resonator response may allow a resonance effect of the resonator to be a predominant effect to allow the resonator to be utilized as a bandpass filter having a relatively higher Q, for example in a bandpass sigma-delta modulator that may be utilized in a digital RF receiver.

TECHNICAL FIELD

Subject matter herein generally may relate to digital communication (Class 375), and particularly may relate to reduction and/or cancellation of anti-resonance in resonators that may be utilized in sigma-delta modulators, although the scope of the claimed subject matter is not limited in this respect. In one or more particular embodiments, subject matter herein may relate to delta modulation (Subclass 247), although the scope of the claimed subject matter is not limited in this respect.

BACKGROUND

Communication systems have widely used surface acoustic wave (SAW) resonators due to their higher quality (Q) factors which typically are difficult to achieve with active filters. Recent developments in micro-mechanical resonators have allowed micro-mechanical resonators to replace SAW resonators since such micro-mechanical resonators tend to be less bulky than SAW resonators. However, micro-mechanical resonators often have limited resonant frequencies, typically on the order of hundreds of megahertz (MHz). Advances in bulk acoustic wave (BAW) resonator technology have allowed such BAW resonators to be utilized with conventional CMOS technology, and furthermore such BAW resonators have higher resonant frequencies typically in the gigahertz (GHz) range, allowing BAW resonators to be utilized in cellular and wireless local area network (WLAN) applications. Such resonators may exhibit both resonance characteristics and anti-resonance characteristics, where the resonance characteristic may provide a bandpass filter type function, and where the anti-resonance characteristic may provide a notch filter type function.

It will be appreciated that for simplicity and/or clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, if considered appropriate, reference numerals have been repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are set forth to provide a thorough understanding of claimed subject matter. However, it will be understood by those skilled in the art that claimed subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, components and/or circuits have not been described in detail.

In the following description and/or claims, the terms coupled and/or connected, along with their derivatives, may be used. In particular embodiments, connected may be used to indicate that two or more elements are in direct physical and/or electrical contact with each other. Coupled may mean that two or more elements are in direct physical and/or electrical contact. However, coupled may also mean that two or more elements may not be in direct contact with each other, but yet may still cooperate and/or interact with each other.

It should be understood that certain embodiments may be used in a variety of applications. Although the claimed subject matter is not limited in this respect, the circuits disclosed herein may be used in many apparatuses such as in the transmitters and/or receivers of a radio system. Radio systems intended to be included within the scope of the claimed subject matter may include, by way of example only, wireless personal area networks (WPAN) such as a network in compliance with the WiMedia Alliance, wireless local area networks (WLAN) devices and/or wireless wide area network (WWAN) devices including wireless network interface devices and/or network interface cards (NICs), base stations, access points (APs), gateways, bridges, hubs, cellular radiotelephone communication systems, satellite communication systems, two-way radio communication systems, one-way pagers, two-way pagers, personal communication systems (PCS), personal computers (PCs), personal digital assistants (PDAs), and/or the like, although the scope of the claimed subject matter is not limited in this respect.

Types of wireless communication systems intended to be within the scope of the claimed subject matter may include, although are not limited to, Wireless Local Area Network (WLAN), Wireless Wide Area Network (WWAN), Code Division Multiple Access (CDMA) cellular radiotelephone communication systems, Global System for Mobile Communications (GSM) cellular radiotelephone systems, North American Digital Cellular (NADC) cellular radiotelephone systems, Time Division Multiple Access (TDMA) systems, Extended-TDMA (E-TDMA) cellular radiotelephone systems, third generation (3G) systems like Wideband CDMA (WCDMA), CDMA-2000, Universal Mobile Telecommunications System (UMTS), and/or the like, although the scope of the claimed subject matter is not limited in this respect.

Referring now toFIG. 1, a diagram of a resonator and cancellation network in accordance with one or more embodiments will be discussed. As shown inFIG. 1, circuit100may include resonator110and cancellation network112in combination. The resonant frequency function of resonator110allows circuit100to function as a bandpass filter circuit with a relatively high Q factor. Typically, resonator110may exhibit two modes of resonance, a series mode of resonance and a parallel mode of resonance. In a series mode resonance, the impedance of resonator110may be at a minimum value, and/or admittance may be at a maximum value, which may occur at a frequency referred to as a resonant frequency. Likewise, in a parallel mode resonance, the impedance of resonator110may be at a maximum value, and/or admittance may be at a minimum value, which may occur at a frequency referred to as an anti-resonant frequency. An example of a response of resonator110exhibiting a resonance characteristic and an anti-resonance characteristic is shown inFIG. 3. For operation of circuit100as a bandpass filter, the resonant frequency characteristic may provide such a function. The anti-resonant frequency characteristic, however, in some applications, may be deleterious to the operation of resonator110, for example where resonator110is utilized in a sigma-delta modulator such as sigma-delta modulator526shown, for example, inFIG. 6where circuit100may function as a bandpass filter, although the scope of the claimed subject matter is not limited in this respect.

In one or more embodiments, resonator110may be realized as an electromechanical resonator. For example, resonator110may be a micro-electromechanical system (MEMS) type resonator, a crystal type resonator, a ceramic type resonator, a surface acoustic wave (SAW) type resonator, a bulk acoustic wave (BAW) type resonator, a film bulk acoustic resonator (FBAR) type resonator, and so on. Such electromechanical type resonators may generally provide a higher Q factor, higher accuracy of resonant frequencies, and greater temperature stability. In one or more embodiments, resonator110may be realized on a silicon substrate, for example via a micromachining process. In one particular embodiment, resonator110may be realized on an integrated complementary metal oxide semiconductor (CMOS) type circuit, and/or bipolar CMOS (BiCMOS) type circuit, although the scope of the claimed subject matter is not limited in this respect.

Cancellation network112may be utilized in circuit100to cancel the anti-resonance of resonator110, for example to provide a more idealized bandpass filter response. In accordance with one or more embodiments, amplifier114may receive an input116at non-inverting input118, and inverting input120of amplifier114may be coupled to ground. Non-inverting output122of amplifier114may be coupled to resonator110, and inverting output124of amplifier114may be coupled to cancellation network112. The outputs of resonator110and cancellation network112may be coupled to node126wherein resonator110and cancellation network112may be presented with the same load ZL128, and/or the same effective load, and share a common output VOacross load128at node126. It should be noted that the various connections shown inFIG. 1are merely one arrangement of circuit100, and other arrangements of the connections may be utilized. For example resonator110may be coupled to inverting output124and cancellation network may be coupled to non-inverting output122, and the scope of the claimed subject matter is not limited in this respect.

Referring now toFIG. 2, a diagram of an equivalent circuit for a resonator and a cancellation network in accordance with one or more embodiments will be discussed.FIG. 2shows circuit100ofFIG. 2where resonator110may be represented by equivalent circuit elements. The series mode resonance characteristic may be represented by a series RLC circuit comprising resistor Rm212, capacitor Cm214, and inductor Lm216, which may provide an ideal, and/or a somewhat ideal, transfer function for resonator110. A parallel mode resonance characteristic may be represented by static capacitance Cp210and Cm214. Static capacitance210may be an inherent characteristic of resonator110, which may be modeled, for example, as a capacitance coupled in parallel with the RLC circuit comprising resistor212, capacitor214, and inductor216. Static capacitance210may alter the ideal transfer function of resonator110, for example by introducing two transmission zeroes into the transfer function of resonator110. Cancellation capacitor CC218of cancellation network112may be utilized to reduce and/or eliminate the effects of static capacitance210of resonator210, for example where resonator110may be utilized to provide a bandpass filter function in a sigma-delta modulator such as sigma-delta modulator526ofFIG. 5andFIG. 6, although the scope of claimed subject matter is not limited in this respect. For example, such an arrangement of circuit100using resonator110and cancellation network112may be utilized in circuits to emphasize the resonance characteristic of resonator112and to deemphasize the anti-resonance characteristic of resonator112, although the scope of claimed subject matter is not limited in this respect.

When input signal116is applied to amplifier114, current flowing through static capacitance210may be flowing in one direction and current flowing through cancellation capacitance may be flowing through cancellation capacitor218in an opposite direction due to the opposite phase polarities of non-inverting output122and inverting output124of amplifier114. Since such currents are combined at node126, such currents cancel out at load128. As a result, the anti-resonance characteristic provided by static capacitance210may be reduced and/or eliminated, which may result in the series resonance effect of the RLC circuit as a predominant characteristic in the response of circuit100, for example as shown inFIG. 4. Such a cancellation of the anti-resonance characteristic may occur, for example, where the value of cancellation capacitor218matches, or at least nearly matches, the value of static capacitance210, although the scope of claimed subject matter is not limited in this respect. In such an arrangement, cancellation capacitor218may provide a negative capacitance with respect to the capacitance of static capacitance210, wherein the cancellation capacitor218may effectively reduce and/or remove the response provided by static capacitance210. It should be noted that, while in one embodiment cancellation network112may be realized by cancellation capacitor218, any device and/or circuit element that is capable of presenting a negative capacitance with respect to static capacitance218may be utilized to realize cancellation network112. For example, cancellation network112may comprise a diode having a capacitance matched or nearly matched to static capacitance210to cancel out, or at least partially cancel out, an anti-resonance characteristic provided by static capacitance210, and the scope of the claimed subject matter is not limited in this respect. Thus, by matching cancellation capacitor218to static capacitance210, cancellation of anti-resonance from the response of resonator110may be achieved, although the scope of claimed subject matter is not limited in this respect.

In one or more embodiments, cancellation of an anti-resonance response of resonator110with cancellation network112may occur in a current domain at node126as a result of the outputs of resonator110and cancellation network112being connected at node126coupled to resistor128. As a result, no load matching is required at the output circuit100since cancellation of anti-resonance may occur at a single resistor. Cancellation of anti-resonance may be provided via matching, and/or nearly matching an impedance of cancellation network with an impedance of an inherent component in resonator110that creates an anti-resonance effect in a response of resonator110. As shown inFIG. 2, cancellation network112may comprise cancellation capacitor218having a value that matches, and/or nearly matches, the capacitance value of static capacitance210, wherein current flowing through cancellation capacitor218has the same magnitude, or nearly the same magnitude, as current flowing through static capacitance210, but with an opposite polarity, such that the two currents may cancel, and/or nearly cancel, when combined at node126, although the scope of the claimed subject matter is not limited in this respect.

Referring now toFIG. 3, a diagram of a response of a resonator showing resonance and anti-resonance in accordance with one or more embodiments will be discussed. As shown inFIG. 3, transfer function310of resonator110may be plotted as admittance (Y), for example in units of siemens, versus frequency (f), for example in units of hertz. Peak admittance312may occur at a resonant frequency, fr, which may correspond to a series resonance characteristic of resonator110. Minimum admittance314may occur at an anti-resonant frequency, fa, which may correspond to a parallel resonance characteristic of resonator110, and which may be referred to as anti-resonance.

Referring now toFIG. 4, a diagram of a response of a resonator and a cancellation circuit showing a cancellation, at least in part, of anti-resonance in accordance with one or more embodiments will be discussed. As shown inFIG. 4, transfer function410of resonator112and cancellation network112in combination may be plotted as admittance (Y), for example in units of siemens, versus frequency (f), for example plotted in units of hertz. Peak admittance412may occur at a resonant frequency, fr, where cancellation network112may reduce at least in part and/or remove an anti-resonance effect as shown inFIG. 4. Cancellation of anti-resonance with cancellation network112may result in circuit100having a more ideal bandpass filter response with a relatively higher Q factor and center frequency at or near frequency fras shown inFIG. 4, although the scope of the claimed subject matter is not limited in this respect.

Referring now toFIG. 5, a block diagram of a an intermediate-frequency (IF) digitization receiver including a bandpass sigma-delta modulator that may utilize a resonator and a cancellation network in accordance with one or more embodiments will be discussed. Receiver500may be a radio-frequency (RF) receiver utilized, for example, in a cellular telephone type device, a wireless local area network (WLAN) type device, and/or the like. An RF signal may be received via antenna510, filtered with RF filter512, and amplified with low-noise amplifier (LNA)514. The signal may then be passed through image-rejection (IR) filter (IR FILTER)516where the signal may be demodulated using demodulator518and oscillator (fLOI)520. A channel may be selected by passing the signal through channel filter (CHANNEL FILTER)522and then amplified via variable gain amplifier (VGA)524. Digitization of the signal may be accomplished via bandpass sigma-delta modulator (BP SDM)526to provide a digitized form of the signal to digital signal processor (DSP)528for baseband processing of the signal. DSP528may control the gain of VGA524via control line530, and may provide output532in response to the received signal, which may be, for example, data contained within the received signal, although the scope of claimed subject matter is not limited in this respect. Bandpass sigma-delta modulator526for digitization of the IF signal may be realized using circuit100to provide a bandpass filter function, for example using an electromechanical resonator type device for resonator110, where an anti-resonance characteristic of resonator may be reduced and/or removed via cancellation network112, although the scope of the claimed subject matter is not limited in this respect.

In one or more embodiments, receiver500may be part of a transceiver of a wireless local or personal area network (WLAN or WPAN) communication system. For example, receiver500may be utilized in a mobile or remote unit such as a mobile computer and/or information handling system, a desktop computer, and/or a cellular telephone, and digital signal processor528may provide baseband and/or media access control (MAC) processing functions. In one embodiment, DSP528may comprise a single processor, including filtering, and/or alternatively may also comprise a baseband processor and/or an applications processor, although the scope of the claimed subject matter is not limited in this respect. DSP528may couple to a memory (not shown) which may include volatile memory such as DRAM, non-volatile memory such as flash memory, and/or alternatively may include other types of storage such as a hard disk drive, although the scope of the claimed subject matter is not limited in this respect. Some portion or all of the memory may be included on the same integrated circuit DSP528, and/or alternatively some portion and/or all of the memory may be disposed on an integrated circuit and/or other medium, for example a hard disk drive, that is external to the integrated circuit of DSP528, although the scope of the claimed subject matter is not limited in this respect.

Receiver500may receive signals via antenna510that are received, for example from a remote access point and/or base station (not shown) via wireless communication link. In an alternative embodiment, receiver500may include two or more of antennas510, for example to provide a spatial division multiple access (SDMA) system and/or a multiple input, multiple output (MIMO) system, although the scope of the invention is not limited in this respect. The remote access point may couple with network so that receiver may receive information from the network, including devices coupled to the network, by communicating via the wireless communication link. Such a network may include a public network such as a telephone network and/or the Internet, and/or alternatively the network may include a private network such as an intranet, and/or a combination of a public and/or a private network, although the scope of the claimed subject matter is not limited in this respect. Communication between receiver500and the remote access point may be implemented via a wireless personal area networks (WPAN) such as a network in compliance with the WiMedia Alliance, a wireless local area network (WLAN), for example a network compliant with a an Institute of Electrical and Electronics Engineers (IEEE) standard such as IEEE 802.11a, IEEE 802.11b, IEEE 802.11n, IEEE 802.16, HiperLAN-II, HiperMAN, Ultra-Wideband (UWB), and so on, although the scope of the claimed subject matter is not limited in this respect. In another embodiment, such communication between may be at least partially implemented via a cellular communication network compliant with a Third Generation Partnership Project (3GPP or 3G) standard, a Wideband CDMA (WCDMA) standard, and so on, although the scope of the claimed subject matter is not limited in this respect.

Referring now toFIG. 6, a block diagram of a second order bandpass sigma-delta modulator that may utilize a resonator and a cancellation network in accordance with one or more embodiments will be discussed. Bandpass sigma-delta modulator526as shown inFIG. 6may be a second order bandpass sigma-delta modulator and may be utilized, for example, as bandpass sigma-delta modulator526of receiver500ofFIG. 5, although the scope of the claimed subject matter is not limited in this respect. Although bandpass sigma-delta modulator526ofFIG. 6is shown as a second order modulator, other orders may be within the scope of the claimed subject matter, for example first order, third order, fourth order, and so on, and the scope of the claimed subject matter is not limited in this respect. A continuous time signal {circumflex over (x)}(t), such as an IF signal of receiver500, may be applied to summer612, the output of which may be applied to bandpass filter function614that may be provided by circuit100via resonator110in combination with cancellation network112. The output of circuit100maybe applied to quantizer616to provide a discrete time version y(n) of the continuous time signal at output618. Output618may be fed back through delay function620to provide a delayed output622to digital-to-analog converter (DAC)624and to DAC626. DAC624may provide a return-to-zero (RZ) signal, and DAC626may provide a half-delayed return-to-zero (HRZ) signal. Delay for one sampling period may be provided by discrete time delay function620, for example, to avoid metastability and to provide sufficient time for quantizer616to settle. AlthoughFIG. 6only describes a second-order sigma-delta modulator with a single-bit quantizer, higher-order multi-bit sigma-modulator may be realized in a similar arrangement.

Referring now toFIG. 7, a circuit level structural diagram of a bandpass sigma-delta modulator in accordance with one or more embodiments will be discussed. Bandpass sigma-delta modulator700may be substantially similar to bandpass sigma-delta modulator526ofFIG. 5andFIG. 6, with functional blocks being implemented with circuit blocks and/or elements. At least some circuit components of bandpass sigma-delta modulator700may be realized on a semiconductor chip710fabricated, for example, using a standard CMOS process. Input transconductor (Gm)712may be utilized to convert an input signal from voltage to current, for example so that summation with the feedback signals received from DAC730and/or DAC732may be performed in the current domain at nodes734and736. After summation, the current signals may be converted back to voltage by a current-to-voltage converter (I/V)714, for example to drive resonator110and/or cancellation network112which may be disposed off of chip710or on chip710. The outputs of resonator110and cancellation network112may be combined at node126and applied to ground through resistor RL718to provide an input signal to variable gain amplifier (VGA)716. Alternatively, resistor RL718and variable gain amplifier (VGA)716may be replaced by a transimpedance amplifier. VGA716may also be utilized, for example, to provide phase regulation or compensation of the signal prior to quantization. Phase regulation or compensation may also be realized by a separate phase regulator following variable gain amplifier (VGA) or transimpedance amplifier and before the quantization. Since VGA716may present a relative higher input impedance, resistor718may be the effective load seen at node126and may be analogous to load128ofFIG. 1, although the scope of claimed subject matter is not limited in this respect.

Quantization by quantizer616and delay function620ofFIG. 6may be realized with four serially connected dynamic latches, latch (LATCH1)720, latch (LATCH2)722, latch (LATCH3)724, and latch (LATCH4)726. Latch720may function as quantizer616, for example to provide one-bit quantization. Latch722, together with latch720, may function as delay function620to provide one sampling period delay. In an alternative arrangement, Latch720and latch722may be replaced by a comparator or one-bit quantizer that has one sampling period delay. Latch724and latch726may generate RZ and control signals for DAC730, and latch724may generate HRZ control signals for DAC732. DAC730and/or DAC732may be current-switched digital-to-analog converters to provide current summation at node734and node736. In one or more embodiments, the circuit of latch720may be arranged to reduce kickback noise. Bandpass sigma-delta modulator700may provide a digital output via latch (OUTPUT LATCH)728, which may be, for example, a D flip-flop, although the scope of the claimed subject matter is not limited in this respect.

Referring now toFIG. 8, a block diagram of an intermediate-frequency (IF) digitization receiver including a wideband bandpass sigma-delta modulator that may utilize a resonator and a cancellation network in accordance with one or more embodiments will be discussed. Receiver800illustrates one possible embodiment of a system that may utilize bandpass sigma-delta modulator526that utilizes resonator110and cancellation network112to cancel anti-resonance from the response of resonator110in accordance with one or more embodiments. Receiver800ofFIG. 8may be substantially similar to receiver500ofFIG. 5with the exception of including a wideband bandpass sigma-delta modulator526to digitize a wider signal band, for example the whole signal band, rather than a single channel. Blocks ofFIG. 8that are similar to blocks ofFIG. 5may perform a similar function in some embodiments. Antenna810may receive an RF signal that may be filtered with RF filter812and then amplified with LNA814. The amplified RF signal may then be filtered via IF filter816and demodulated using demodulator818and oscillator820. A wideband demodulated output may be provided to bandpass sigma-delta modulator526for analog-to-digital conversion of the wideband signal. The digitized wideband signal may be provided to DSP822for further digital signal processing, such as filtering and baseband signal processing, to provide an output824, although the scope of the claimed subject matter is not limited in this respect.

Referring now toFIG. 9, a block diagram of a radio-frequency (RF) digitization receiver including an RF wideband bandpass sigma-delta modulator that may utilize a resonator and cancellation network in accordance with one or more embodiments will be discussed. Receiver900illustrates one possible embodiment of a system that may utilize bandpass sigma-delta modulator526that utilizes resonator110and cancellation network112to cancel anti-resonance from the response of resonator110in accordance with one or more embodiments. Blocks ofFIG. 9that are similar to blocks ofFIG. 5may perform a similar function in some embodiments. In accordance with one or more embodiments, receiver900ofFIG. 9may implement RF digitization of a received RF signal. The RF signal may be received via antenna910, filtered via RF filter912, and amplified via LNA914. The amplified RF signal may be directly digitized via bandpass sigma-delta modulator526for analog-to-digital conversion of the RF signal. In such an embodiment, resonator110may have a resonant frequency tuned to the RF signal wherein resonant frequency of resonator110may correspond to a frequency or frequency band of the RF signal. The digitized RF signal may then be provided to DSP916for further digital signal processing, such as filtering and baseband signal processing, to provide output918, although the scope of the claimed subject matter is not limited in this respect. Narrow band IF digitization receiver500ofFIG. 5, wideband IF digitization receiver800ofFIG. 8, and/or RF digitization receiver900ofFIG. 9illustrate example systems where circuit100including resonator110and cancellation network may be utilized for cancellation of anti-resonance from resonator110. However, these are merely examples of applications for circuit100. Other applications for circuit100are contemplated as being within the scope of the claimed subject matter, and the scope of the claimed subject matter is not limited in this respect.

Although the claimed subject matter has been described with a certain degree of particularity, it should be recognized that elements thereof may be altered by persons skilled in the art without departing from the spirit and/or scope of the claimed subject matter. It is believed that cancellation of anti-resonance in resonators and/or many of its attendant advantages will be understood by the forgoing description, and it will be apparent that various changes may be made in the form, construction and/or arrangement of the components thereof without departing from the scope and/or spirit of the claimed subject matter or without sacrificing all of its material advantages, the form herein before described being merely an explanatory embodiment thereof, and/or further without providing substantial change thereto. It is the intention of the claims to encompass and/or include such changes.