Linear and polar dual mode transmitter circuit

Method and apparatus for configuring a transmitter circuit to support linear or polar mode. In the linear mode, a baseband signal is specified by adjusting the amplitudes of in-phase (I) and quadrature (Q) signals, while in the polar mode, the information signal is specified by adjusting the phase of a local oscillator (LO) signal and the amplitude of either an I or a Q signal. In an exemplary embodiment, two mixers are provided for both linear and polar mode, with a set of switches selecting the appropriate input signals provided to one of the mixers based on whether the device is operating in linear or polar mode. In an exemplary embodiment, each mixer may be implemented using a scalable architecture that efficiently adjusts mixer size based on required transmit power.

TECHNICAL FIELD

The disclosure relates to integrated circuits (IC's), and more specifically, to techniques for designing a transmitter circuit capable of dual-mode linear and polar operation.

BACKGROUND

Modern wireless communications devices often support signal transmission and reception over multiple radio frequency bands, using one of several distinct communications protocols or standards. For example, a single cellular phone may communicate using any or all of the WCDMA, CDMA, GSM, EDGE, and LTE standards for cellular telephony, over any frequency bands allotted for such communications.

In a communications device, radio-frequency (RF) circuitry is typically provided to upconvert a baseband signal to a particular radio frequency band for wireless transmission. The RF circuitry supporting each frequency band and/or wireless standard typically must satisfy different design constraints. For example, for certain modulation formats, it may be advantageous to use a linear architecture for upconverting the baseband signal, e.g., in-phase and quadrature components of the baseband signal are multiplied with corresponding in-phase and quadrature components of a local oscillator signal. Alternatively, for other modulation formats, it may be advantageous to use a polar architecture for upconverting the baseband signal, e.g., a single baseband signal having real amplitude is multiplied with a local oscillator signal having variable phase.

To accommodate multiple modulation formats, it would be desirable to provide a communications device capable of operation in both linear and polar modes, while minimizing unnecessary replication of component circuitry.

SUMMARY

An aspect of the present disclosure provides a method for upconverting a baseband signal comprising: in a linear mode, mixing a baseband in-phase (BB I) signal with a local oscillator in-phase (LO I) signal using a primary mixer; in the linear mode, mixing a baseband quadrature (BB Q) signal with a local oscillator quadrature (LO Q) signal using a secondary mixer; in the linear mode, combining the outputs of the primary and secondary mixers to generate an upconverted signal; and in a polar mode, mixing a baseband amplitude (BB) signal with a phase-modulated local oscillator (LO) signal using the primary mixer.

Another aspect of the present disclosure provides an apparatus for upconverting a baseband signal comprising: a primary mixer configured to, in a linear mode, mix a baseband in-phase (BB I) signal with a local oscillator in-phase (LO I) signal, the primary mixer further configured to, in a polar mode, mix a baseband amplitude (BB) signal with a phase-modulated local oscillator (LO) signal; and a secondary mixer configured to, in the linear mode, mix a baseband quadrature (BB Q) signal with a local oscillator quadrature (LO Q) signal.

Yet another aspect of the present disclosure provides an apparatus for upconverting a baseband signal comprising: primary means for mixing a baseband in-phase (BB I) signal with a local oscillator in-phase (LO I) signal in a linear mode, and for mixing a baseband amplitude (BB) signal with a local oscillator (LO) signal in a polar mode; and secondary means for mixing a baseband quadrature (BB Q) signal with a local oscillator quadrature (LO Q) signal in the linear mode, and mixing the BB signal with the LO signal in the polar mode.

Yet another aspect of the present disclosure provides a computer program product for instructing a transmitter to upconvert a baseband signal, the transmitter comprising a primary mixer for multiplying a first baseband signal with a first local oscillator signal and a secondary mixer for multiplying a second baseband signal with a second local oscillator signal, the product comprising: computer-readable medium comprising: code for causing a computer to, in the linear mode, digitally generate a baseband in-phase signal as the first baseband signal; and code for causing a computer to, in the polar mode, digitally generate a baseband amplitude signal as the first baseband signal.

DETAILED DESCRIPTION

FIG. 1depicts an implementation of a known transmitter100for a device. InFIG. 1, baseband input signals BB I (in-phase) and BB Q (quadrature-phase) are provided to low-pass filters103.1and103.2. Both signals BB I and BB Q may be differential (rather than single-ended) signals, and, unless otherwise noted, such signals may generally be represented in the accompanying figures by the use of two signal lines rather than one. The output signals of the low-pass filters103.1and103.2are provided to mixers104.1and104.2, which modulate the filtered baseband signals to a higher frequency by multiplying with differential local oscillator signals LO I and LO Q, respectively.

The differential outputs of the mixers104.1and104.2are combined and coupled to a balun primary element101.1of balun101. Balun101also includes a balun secondary element101.2electromagnetically coupled to the balun primary element101.1. The balun101functions to convert a differential signal across the balun primary element101.1to a single-ended signal at node101.2aof the balun secondary element101.2, wherein the other node101.2bof the balun secondary element101.2is coupled to a ground voltage. InFIG. 1, the balun primary and secondary elements are shown as mutually coupled inductors, although the techniques of the present disclosure need not be limited to implementations of baluns as mutually coupled inductors.

InFIG. 1, the node101.2aof the balun secondary element101.2is coupled to an amplifier120. Such an amplifier may include a pre-driver amplifier, driver amplifier, or power amplifier, that performs the function of amplifying the signal prior to transmission over the air via an antenna (not shown).

One of ordinary skill in the art will realize that the components in the transmitter100are shown for illustrative purposes only, and that a transmitter may generally be implemented using any of a number of alternative architectures not shown. For example, a transmitter may omit the balun element101, and/or adopt additional filters and gain elements not shown. The techniques of the present disclosure are contemplated to be applicable to such alternative architectures not shown.

One of ordinary skill in the art will also appreciate that the circuit blocks depicted in the accompanying figures are intended only as functional illustrations, and are not meant to depict the degree to which certain functions may be integrated with each other. For example, in certain exemplary embodiments, a single integrated circuit (IC) may be provided that implements all of the functions of the baseband filters, the mixers, and the balun, while a separate IC may be provided that implements the function of the amplifier. Alternatively, all functional components shown may be implemented discretely, or together in a single chip. Such exemplary embodiments are contemplated to fall within the scope of the present disclosure.

In modern wireless devices, a single transmitter may be designed to accommodate multiple operating frequency ranges and/or wireless standards. For example, a transmitter may be designed to accommodate frequency ranges such as 824-914 MHz (used for wireless standards such as GSM850, GSM900, JCELL), and 1710-1980 MHZ (used for wireless standards such as DCS, PCS, IMT). The transmitter may also be designed to support multiple modulation formats, e.g., Gaussian minimum-shift keying (GMSK), quadrature amplitude modulation (QAM), quadrature phase-shift keying (QPSK), etc. To accommodate multiple frequency ranges, standards, and/or modulation formats, a single transmitter architecture may be alternately configured to support either a linear mode of operation or a polar mode of operation, as further described hereinbelow.

FIG. 2depicts an exemplary embodiment of a transmitter200supporting both linear and polar modes.

In linear mode, a baseband module260provides digital baseband signals BB I (digital) and BB Q (digital) to digital-to-analog converters (DAC's)150.1and150.2, respectively. The DAC's150.1and150.2output analog differential baseband signals BB I (analog) and BB Q (analog) to upconversion module210. BB I and BB Q contain the in-phase and quadrature components, respectively, of the signal to be transmitted. Within the upconversion module210, BB I and BB Q are filtered by filters103.1and103.2, respectively, and mixed with in-phase and quadrature local oscillator signals LO I and LO Q, respectively, using mixers104.1and104.2. One of ordinary skill in the art will appreciate that, in linear mode, the modulated information is contained in the amplitudes of the BB I and BB Q signals.

In polar mode, the baseband module260provides digital baseband amplitude signal BB (digital) to DAC250.1, which generates a single analog differential baseband signal BB (analog) for input to upconversion module220. Within the upconversion module220, BB (analog) is filtered by filter203.1, and mixed with a single local oscillator signal LO using mixer204.1. One of ordinary skill in the art will appreciate that, in polar mode, the modulated information is contained in the amplitude of the BB signal, as well as in the phase of the LO signal.

One of ordinary skill in the art will appreciate that to select between operation in linear mode and operation in polar mode, a variety of techniques may be employed. For example, in an exemplary embodiment (not shown), a switch may be provided to couple the balun101.1to either the output of upconversion module210or the output of upconversion module220. In an alternative exemplary embodiment (not shown), one of the upconversion modules210and220may be selectively powered off and on, e.g., by a digital signal (not shown) generated by the baseband module260. Such exemplary embodiments are contemplated to be within the scope of the present disclosure.

While the transmitter200depicted inFIG. 2may support operation in either linear or polar mode, it requires separate instances of circuitry for the linear mode upconversion module210and the polar mode upconversion module220. It would be desirable to provide an even more efficient transmitter implementation that minimizes the replication of component circuitry.

FIG. 3depicts a transmitter300according to the present disclosure, wherein a single upconversion module310is provided for both linear and polar modes. Upconversion module310includes two signal paths310.1and310.2.

InFIG. 3, when the transmitter300operates in linear mode, signal path310.1upconverts the in-phase baseband signal BB I using the in-phase local oscillator signal LO I, while signal path310.2upconverts the quadrature baseband signal BB Q using the quadrature local oscillator signal LO Q. When the transmitter300operates in polar mode, signal path310.1upconverts the baseband amplitude signal BB using the local oscillator signal LO, while signal path310.2is shut off.

In an exemplary embodiment, the baseband module360may generate BB I (digital) in linear mode, and BB (digital) in polar mode. In an alternative exemplary embodiment (not shown), digital or analog switching means may be provided to select BB I as the input to signal path310.1in linear mode, and to select BB as the input to signal path310.1in polar mode.

In an exemplary embodiment, the LO I/LO signal may be generated by a single frequency synthesizer (not shown), which can be alternately configured to generate an unmodulated local oscillator signal (LO I) during linear mode, and a modulated local oscillator signal (LO) during polar mode.

One of ordinary skill in the art will appreciate that in polar mode, the transmitter300effectively selects only one of the two signal paths used in linear mode, and supplies the selected signal path with the appropriate baseband and local oscillator signals for polar mode. This implementation avoids the need to provide separate upconversion modules, such as modules210and220depicted inFIG. 2, for dual mode polar and linear operation.

While the transmitter300avoids some of the replication of circuitry found inFIG. 2, the functionality afforded by the signal path310.2may also be reused during operation in polar mode. As further described herein, certain advantages may be afforded by employing in polar mode both of the signal paths used in linear mode.

FIG. 4depicts an exemplary embodiment of a transmitter400according to the present disclosure, wherein a single upconversion module440is designed to support both linear and polar modes. Upconversion module440includes first signal path440.1and second signal path440.2. Switches410.1and410.2are provided to select between either linear mode or polar mode, as described hereinbelow. Switches420.1and420.2are further provided to select between operation in either linear or polar mode.

In linear mode, the first signal path440.1multiplies the BB I signal derived from the baseband module460with the LO I signal. Switches410.1,410.2,420.1, and420.2are configured to allow the second signal path440.2to multiply the BB Q signal derived from the baseband module460with the LO Q signal, by coupling a first differential input of the mixer404.2to BB Q, and a second differential input of the mixer404.2to LO Q.

In polar mode, the baseband module460provides a single differential baseband signal BB to upconversion module440. In an exemplary embodiment, the other baseband signal BB Q may be disabled in polar mode (not shown). The switches410.1and410.2are configured in polar mode to couple the differential ends of the BB signal from the first signal path440.1to the first differential input of mixer404.2in the second signal path440.2. Furthermore, the switches420.1and420.2are configured to couple the differential ends of the LO signal to the second differential input of mixer404.2. Using this switch configuration, the upconversion module440mixes the signal BB with the local oscillator signal LO using both mixers404.1and404.2in polar mode.

One of ordinary skill in the art will appreciate that alternative exemplary embodiments wherein the upconversion module440is designed to work with only the BB Q and LO Q signals in polar mode are also contemplated to be within the scope of the present disclosure. In fact, the designations of “I” and “Q” in this specification, in the claims, and in an arbitrary circuit design are generally interchangeable.

By employing the same two signal paths in both linear and polar mode, the architecture of transmitter400offers several advantages over the architectures of transmitters200and300. For example, the transmitter400requires only two separate mixers404.1and404.2, as compared to the at least three mixers104.1,104.2, and204.1required by the dual-mode transmitter200. This leads to less die area being consumed by the transmitter400, as well as to a simpler circuit design. Fewer mixers may also result in fewer parasitic elements loading the balun101.1, allowing for the use of a single balun across a broad frequency range, e.g., from 800 MHz to 2 GHz.

Furthermore, compared to the transmitter300, an advantage of the transmitter400is that, for equivalent levels of transmit power, each of the two signal paths440.1and440.2will consume approximately half of the total current consumed by the single mixer signal path310.1in polar mode. As the voltage drop across each signal path circuit element is related to the corresponding current flow in each element, the parallel-coupled signal paths440.1and440.2may require less voltage supply headroom than the single signal path310.1in polar mode. Thus transmitter400may advantageously operate with a lower voltage supply than transmitter300. One of ordinary skill in the art will also appreciate that providing two signal paths440.1and440.2effectively doubles the available size of the mixer used for upconverting the baseband signal BB, compared to the embodiment wherein only one of the signal paths is employed.

FIG. 5depicts another exemplary embodiment according to the present disclosure. InFIG. 5, a baseband module560generates digital output signals BB1and BB2, which are converted to analog baseband signals BB I/BB and BB Q/BB by digital-to-analog converters550.1and550.2, respectively. In linear mode, baseband module560provides a digital version of BB I at digital output BB1, and a digital version of BB Q at digital output BB2. In polar mode, baseband module560provides a digital version of BB at both digital outputs BB1and BB2. As the baseband module560effectively selects the baseband input to the transmitter500depending on the operating mode, there is no need to perform such selection using analog switches, e.g., switches410.1and410.2in transmitter400.

FIG. 6depicts a transmitter600, wherein a mixer640and LO buffer620having selectable size are provided to implement the techniques of the present disclosure. Further details of a mixer and LO buffer having selectable size may be found in U.S. patent application Ser. No. 12/209,164, earlier referenced herein. In an exemplary embodiment, the scalable mixer architecture shown in mixer640ofFIG. 6may be used for each of the mixers404.1and404.2in transmitter400. One of ordinary skill in the art will appreciate, however, that the mixer architecture described with reference toFIG. 6need not be employed in the linear and polar dual mode transmitter architectures described hereinabove, and that the scope of the present disclosure is contemplated to include mixer architectures not explicitly disclosed herein. Note while the signal leads of the transmitter600are shown as single lines for simplicity, inFIG. 6such single lines may generally denote either single-ended or differential-ended signals.

In the transmitter600, mixer640is composed of sub-mixers640.1through640.N, and LO buffer630is composed of associated sub-LO buffers630.1through630.N. Note each of the sub-mixers640.1through640.N shown may include a plurality of separate mixer circuits (not shown) including, e.g., an I mixer and an inverse I mixer for differential processing, and a Q mixer along with inverse Q mixer. Similarly, each of the sub-LO buffers630.1through630.N shown may include a plurality of separate LO buffer circuits (not shown) for each of the plurality of separate mixer circuits.

InFIG. 6, the local oscillator signal is generated by an LO generator650, which includes a frequency divider651coupled to the output of a frequency synthesizer652, which is in turn coupled to a crystal oscillator654.

InFIG. 6, the sub-mixers640.1through640.N and sub-LO buffers630.1through630.N may be selectively enabled or disabled by a baseband processor610controlling control signals EN.1through EN.N, respectively. Each sub-mixer mixes a corresponding buffered LO signal with a baseband signal612aderived from DAC612in the baseband processor610, and filtered by selectable baseband filters620.1through620.N. The mixed and combined output signals of the sub-mixers are coupled via a balun101to an amplifier120for further transmission, e.g., over an antenna (not shown).

In the transmitter600, the baseband processor610may select which of the sub-mixers, sub-LO buffers, and baseband filters to enable, based on criteria including, e.g., total gain of the transmit power required to be delivered to the driver amplifier. For example, to operate in a lowest gain mode, only sub-mixer640.1, sub-LO buffer630.1, and baseband filter620.1may be enabled, with the remaining sub-mixers, sub-LO buffers, and baseband filters being disabled. This mode may correspond to operating the transmitter600with a mixer and LO buffer of minimum size. To operate in a highest gain mode, all of sub-mixers640.1through640.N, sub-LO buffers630.1through630.N, and baseband filters620.1through620.N may be enabled. This mode may correspond to operating the transmitter600with a mixer and LO buffer of maximum size. One of ordinary skill in the art will appreciate that a mixer and LO buffer of an intermediate size may be obtained by enabling a corresponding subset of the sub-mixers and sub-LO buffers.

In an exemplary embodiment, each of the sub-mixers640.1through640.N may be nominally identically sized to allow accurate control of the gain step size available to the transmitter600.

FIG. 7depicts an exemplary embodiment of a method700according to the present disclosure. Note the exemplary embodiment shown inFIG. 7is meant to be illustrative only, and is not meant to limit the scope of the present disclosure to any particular exemplary embodiment shown. Furthermore, the order of the steps shown inFIG. 7should not be construed as limiting the techniques disclosed to any particular sequence of steps.

At step710, in linear mode, the method mixes the baseband quadrature (BB Q) signal with the local oscillator quadrature (LO Q) signal using a primary mixer.

At step720, in linear mode, the method mixes the baseband in-phase (BB I) signal with the local oscillator in-phase (LO I) signal using a secondary mixer.

At step730, in polar mode, the method mixes the baseband quadrature (BB Q) signal with the local oscillator quadrature signal (LO Q) signal using the primary mixer.

At step740, in polar mode, the method mixes the baseband quadrature (BB Q) signal with the local oscillator quadrature signal (LO Q) signal using the secondary mixer.

At step750, the method combines the outputs of the primary and secondary mixers to generate the upconverted signal.

A number of aspects and examples have been described. However, various modifications to these examples are possible, and the principles presented herein may be applied to other aspects as well. These and other aspects are within the scope of the following claims.