A tunable loadline is disclosed. In an exemplary embodiment, an apparatus includes an amplifier configured to output an amplified signal having a selected power level and a first impedance network coupled to receive the amplified signal at an input terminal and generate a first output signal having a first power level at a first output terminal. The first impedance network being configured to load the amplified signal to convert the selected power level to the first power level. The apparatus also includes a second impedance network configured to selectively receive the first output signal and generate a second output signal having a second power level at a second output terminal. The second impedance network being configured to combine with the first impedance network to load the amplified signal to convert the selected power level to the second power level.

BACKGROUND

The present application relates generally to the operation and design of transmitters, and more particularly, to the operation and design of area efficient transmitters.

Wireless devices are becoming increasing more complicated and now routinely provide multi-mode and multi-band operation. To support such operation, a typical wireless device may include multiple power amplifiers to amplify signals for each mode/band. For example, a multi-mode multi-band wireless device may be configured for wireless communications using multiple communication technologies, such as Global System for Mobile Communications (GSM), Wideband Code Division Multiple Access (WCDMA), Classroom 2000 (C2K), and Long Term Evolution (LTE). In a typical implementation, a wireless device may include one amplifier for low band (LB) GSM, one amplifier for LB WCDMA/LTE/C2K, one amplifier for medium band (MB) GSM, and one amplifier for MB WCDMA/LTE/C2K. Unfortunately, this four power amplifier configuration utilizes significant circuit area.

Therefore, it would be desirable to have a way to amplify signals in a multi-mode multi-band transmitter that utilizes less circuit area than conventional configurations comprising multiple amplifiers.

DETAILED DESCRIPTION

FIG. 1shows an exemplary embodiment of a transmitter100comprising a power amplifier configuration that includes a novel tunable loadline112for use in a wireless device. The transmitter100comprises a baseband (BB) processor102, a digital-to-analog converter (DAC)104, a baseband filter106, a mixer (or up-converter)108, a power amplifier (PA)110, the novel tunable loadline112, antenna switch114, and an antenna116.

During operation, the BB processor102outputs digital signals118for transmission. The digital signals118are input to the DAC104and converted to an analog baseband signal120. The analog signal120is input to the baseband filter106to generate a filtered signal122that is input to the mixer108. The mixer108operates to up-covert the filtered baseband signal122to a radio frequency (RF) signal124based on a local oscillator (LO) signal. The RF signal124is input to the PA110to generate an amplified RF signal126that is input to the novel tunable loadline112. The tunable loadline112has at least two outputs (P1-Pn) that are coupled to the antenna116by the antenna switch114. A loadline (LL) control signal134controls the operation of the tunable loadline112and a switch (Swt) control signal136controls the operation of the antenna switch114.

In various exemplary embodiments, the novel tunable loadline112operates to change the loading at the output of the amplifier110so as to change the power level of the signals that are output from the loadline112and input to the switch114. For example, the loadline112can be configured to set the signal line128to have a power level of P1and to set the signal line130to have a power level of Pn. In an exemplary embodiment, P1is greater than Pn such that P1is a power level suitable for transmitting signals on a GSM communication network and Pn is a power level suitable for transmitting signals on a WCDMA communication network. Thus, the tunable loadline112makes it possible to output signals at different power levels utilizing the single amplifier110. This allows the transmitter100to operate in multi mode/bands while utilizing less circuit area than conventional transmitters having multiple amplifiers. A more detailed description of various exemplary embodiments of the novel tunable loadline112is provided below.

FIG. 2shows an exemplary embodiment of a novel tunable loadline200configured for use in a wireless device. The tunable loadline200comprises first202, second204, third206, and fourth208matching circuits. The first matching circuit202is configured to receive an amplified signal from the amplifier110at terminal234. The amplified signal at terminal234has a selected power level output from the amplifier110. The output of the matching circuit202is input to a series of switches210-220. The switches210-220operate to switch the output of the matching circuit202to other circuits based on the loadline control signal134. For example, each of the switches210-220can be individually controlled by the LL control signal134to operate in an open or closed position. When in the closed position, a switch directs the output of the first matching circuit202through the switch to other circuit elements. When in the open position, the output of the first matching circuit is not propagated beyond the open switch.

During operation, the switches216-220operate to direct the output of the first matching circuit202to corresponding output terminals228-232based on the LL control signals134. For example, the switch216directs the output of the first matching circuit202to the output terminal228. This output has a first power level determined by the selected output power of the amplifier110and the first matching circuit202. For example, this output terminal may be used to output signals at a first power level in a first frequency band. Similarly, the switches218and220are utilized to output signals at power levels in other frequency bands.

The switches210-214operate to direct the output of the first matching circuit202to corresponding matching circuits204-208based on the LL control signals134. For example, the switch210directs the output of the first matching circuit202to the second matching circuit204. The second matching circuit204combines with the first matching circuit202to provide an impedance combination that appears at the output of the amplifier110at terminal234. The output of the second matching circuit204is provided at an output terminal222and has a power level determined by the selected output power of the amplifier110and the combination of the first202and second204matching circuits. For example, this output terminal may be used to output signals at a second power level in a first frequency band. Similarly, the switches212and214are utilized to output signals at other power levels in other frequency bands through the combination of their respective matching circuits (i.e.,206,208) with the first matching circuit202. Accordingly, the tunable loadline200can be tuned to output signals in selected frequency bands having selected power levels based on the control of the switches210-220in response to the LL control signal134.

FIG. 3shows an exemplary detailed embodiment of a novel tunable loadline300configured for use in a wireless device. For example, the loadline300is suitable for use as the tunable loadline112shown inFIG. 1. The tunable loadline300is configured from the tunable loadline200and comprises two matching networks302and318.

The tunable loadline300is configured to adjust to the various operating modes of the wireless device to provide signal amplification compatible with operation at multiple power levels (for example, for use in GSM or WCDMA communication networks). As a result, a single amplifier can be utilized instead of using multiple amplifiers as in conventional multi-mode/band transmitters.

To transmit a signal in a WCDMA communication network, the tunable loadline300comprises a first impedance network302comprising a first inductor304connected between an input terminal306and a first output terminal308. The first impedance network302also comprises a first capacitor310connected between the first output terminal308and a signal ground. The first impedance network302is configured to receive an amplified WCDMA signal from the amplifier110at the input terminal306and pass this signal to a first switch312that directs the signal to an antenna through node314for transmission. In an exemplary embodiment, the first inductor304has a value of (3 nH) and the first capacitor310has a value of (10 pF) to provide a load to the amplifier110(to load the amplified signal at the input terminal306) of approximately 5 ohms. This configuration results in a transmit signal at terminal314having a transmit power of P2suitable for transmission in a WCDMA network.

To transmit a signal in a GSM communication network, the first switch312is opened and a second switch316is closed to direct the signal at the first output terminal308to a terminal326at a second impedance network318. The second impedance network318comprises a second capacitor320connected between the terminal326and the signal ground. The second impedance network318also comprises a second inductor322connected between the terminal326and a second output terminal324. In an exemplary embodiment, the second inductor322has a value of (13 nH) and the second capacitor320has a value of (1.7 pF) that combine with the first inductor304and first capacitor310to adjust the overall load to the amplifier110to approximately 2 ohms. For example, the second impedance network318is configured to combine with the first impedance network302to load the amplified signal at the input terminal306to convert the selected power level to the power level P1. This configuration results in a transmit signal at terminal324having a transmit power of P1suitable for transmission in a GSM network.

Since the specified GSM power is higher than the WCDMA power, the tunable loadline300operates to increase or decrease the load according to the selected transmission technology to allow a single amplifier (i.e., amplifier110) to be used to transmit signals within the specified power level for the transmission technology selected. In an exemplary embodiment, a controller or other entity at the wireless device outputs the LL control signal134to control the operation of the switches312and316to select the appropriate load for the amplifier based on the selected transmission technology. For example, to transmit signals at the appropriate power levels for WCDMA, the LL control line134closes the switch312and opens the switch316. This results in transmit signals having power levels suitable for WCDMA being output from the terminal314. Likewise, to transmit signals at the appropriate power levels for GSM, the LL control line134closes the switch316and opens the switch312. This results in transmit signals having power levels suitable for GSM being output from the terminal324.

FIG. 4shows an exemplary embodiment of a matching circuit400configured for use in the tunable loadline ofFIG. 3. For example, the matching circuit400is suitable for use as the matching circuit302shown inFIG. 3. The matching circuit400comprises an inductor402connected between the terminals306and308. A first variable capacitor404is connected between the terminal308and a signal ground. The first variable capacitor404is adjustable to allow the matching circuit400to be tuned to obtain desired operation at selected frequencies. The matching circuit400also comprises an optional variable capacitor406connected between the terminal306and the terminal308. The optional variable capacitor406is also tunable to obtain desired operation at selected frequencies.

FIG. 5shows an exemplary embodiment of a matching circuit500configured for use in the tunable loadline ofFIG. 3. For example, the matching circuit500is suitable for use as the matching circuit318shown inFIG. 3. The matching circuit500comprises an inductor502connected between the terminals326and324. A first variable capacitor504is connected between the terminal326and a signal ground. The first variable capacitor504is adjustable to allow the matching circuit500to be tuned to obtain desired operation at selected frequencies. The matching circuit500also comprises an optional variable capacitor506connected between the terminal326and the terminal324. The optional variable capacitor506is also tunable to obtain desired operation at selected frequencies.

FIG. 6shows an exemplary embodiment of a variable capacitor600configured for use in the matching circuits400and500shown inFIG. 4andFIG. 5. The variable capacitor600comprises capacitors C1through Cn that are connected to a first terminal602. The capacitors C1-Cn are further connected to transistor switches S1-Sn, respectively. The outputs of the transistor switches S1-Sn are connected to a second terminal604. The transistor switches S1-Sn are controlled by capacitor control (CC) signals606that are connected to the gate terminals of the transistor switches. The CC signals606are generated by a processor, controller, or other entity to control which of the switches S1-Sn are open and which are closed. In an exemplary embodiment, the capacitors C1-Cn have the same capacitance value. In other exemplary embodiments, each of the capacitors C1-Cn has a capacitance value that is set to any desired value.

During operation, the CC control lines606are set by a processor, controller, or other entity to open and close selected switches of the transistors switches S1-Sn. When a switch is closed, it connects its associated capacitor to the second terminal604. For example, if the switch S2is closed by its associated CC control line, the capacitor C2is connected between the first terminal602and the second terminal604. The capacitors that are associated with closed switches combine to form a total capacitance between the first terminal602and the second terminal604. For example, the capacitors associated with closed switches combine in a parallel combination to determine the total capacitance. Thus, it is possible to vary the capacitance provided by the variable capacitor600by opening and closing the appropriate switches. By varying or setting the capacitance value of the variable capacitor600, it is possible to tune the operation of the matching circuits400and500shown inFIG. 4andFIG. 5.

FIG. 7shows an exemplary embodiment of a tunable loadline apparatus700configured for improved efficiency and reduced circuit area. For example, the apparatus700is suitable for use as the tunable loadline200shown inFIG. 2or the tunable loadline300shown inFIG. 3. In an aspect, the apparatus700is implemented by one or more modules configured to provide the functions as described herein. For example, in an aspect, each module comprises hardware and/or hardware executing software.

The apparatus700comprises a first module comprising means (702) for generating an amplified signal having a selected power level, which in an aspect comprises the amplifier110.

The apparatus700comprises a second module comprising means (704) for loading the amplified signal to generate a first output signal having a first power level at a first output terminal; the means for loading configured to convert the selected power level to the first power level, which in an aspect comprises the first impedance network202.

The apparatus700comprises a third module comprising means (706) for selectively loading the amplified signal to generate a second output signal having a second power level at a second output terminal; the means for selectively loading configured to combine with the means for loading to load the amplified signal to convert the selected power level to the second power level, which in an aspect comprises the second impedance network204.

Those of skill in the art would understand that information and signals may be represented or processed using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. It is further noted that transistor types and technologies may be substituted, rearranged or otherwise modified to achieve the same results. For example, circuits shown utilizing PMOS transistors may be modified to use NMOS transistors and vice versa. Thus, the amplifiers disclosed herein may be realized using a variety of transistor types and technologies and are not limited to those transistor types and technologies illustrated in the Drawings. For example, transistors types such as BJT, GaAs, MOSFET or any other transistor technology may be used.