Patent Description:
Aspects of the present disclosure relate generally to wireless communications, and, more particularly, to an amplifier with a switchable transformer.

A wireless device includes a transmitter for transmitting signals via one or more antennas. The transmitter may include multiple amplifiers to amplify signals before the signals are transmitted. The amplifiers may include variable gain amplifiers (VGAs), driver amplifiers, and power amplifiers (PAs). A transformer may be used as a load of an amplifier to implement a bandpass filter for amplifying signals within a desired frequency band. A transformer may also be used in the transmitter to convert a differential signal into a single-ended signal, convert a single-ended signal into a differential signal, and/or provide impedance matching.

Attention is drawn to <CIT> describing wideband matching devices. A device may include a primary winding including a first plurality of inductors in series and a first switch coupled to the primary winding and configured to tune the primary winding to a frequency band of a plurality of frequency bands. The device may also include a secondary winding including a second plurality of inductors in series and a second switch coupled to the secondary winding and configured to tune the secondary winding to the frequency band.

Further attention is drawn to <CIT> describing narrow band tunable radio frequency (RF) power amplifiers (PAs) and related methods that provide narrow band tunable gain responses, such as linear gain responses that can be selected for different frequency bands. The narrow band tunable PAs thereby provide out-of-band rejection for different selectable frequency bands so that narrow band filters are not required in the transmit input path for communication devices. The passband location and/or bandwidth for the narrow band gain response can be tuned using different techniques, as desired. The narrow band tunable PAs can also be fabricated using CMOS processing, if desired, so that a CMOS PA integrated circuit is provided.

Attention is also drawn to <CIT> describing a transformer-based impedance matching network that may dynamically change its characteristic impedance by engaging different inductor branches on a primary side and optionally, on the secondary side. A primary side transformer circuit includes a primary inductor and secondary inductor configured to provide impedance matching over a first frequency band. One or more additional inductor branches are switchably coupled to either or both of the primary and secondary inductors to modify the impedance matching characteristics over additional operating frequencies. One or more LC filter branches can be included at the output of the secondary side to filter harmonic frequencies in each of the operating frequency bands.

Attention is further drawn to a paper by <NPL>. The authors of the paper describe dual-power-mode output matching network for a digitally modulated power amplifier (DMPA) to improve low power efficiency is proposed. The matching network incorporates a switched transformer and capacitors. The switched transformer is proposed for tuning its inductance to have two power modes. It is designed to minimize losses due to parasitic components of the switch transistor. The DMPA has a <NUM>-bit resolution to enable a wide digital transmit power control (TPC) range. The peak power is <NUM> dBm with <NUM>% efficiency. The efficiency at <NUM> dBm is improved from <NUM>% to <NUM>% by using the output matching network. Simple static predistortion helps the DMPA reconstruct <NUM>-dBm WCDMA signals at <NUM> with <NUM>% efficiency. The digital TPC range is <NUM> dB.

Further attention is drawn to <CIT> describing that a multi-band amplifier may operate in a first frequency band and a second frequency band. The multi-band amplifier may include a first amplifier, a second amplifier, and a coupler. The coupler may couple a signal, such as a communication signal, to a selected amplifier. In some embodiments, the coupler may include one or more inductive elements to couple the signal to the first or the second amplifier. In some embodiments, the inductive elements may include a balun.

Attention is further drawn to <CIT> describing an unbalanced to balanced antenna matching unit (AMU) capable of operating over a relatively large frequency range by utilizing multiple transformers connected in series, with a set of bypass switches used to control the number of transformers that are "active" in the matching unit at any particular time. Complex impedance matching by the AMU is controlled by a variable capacitor in parallel with the multiple transformers and a variable capacitor in series with the unbalanced input. The parallel variable capacitor may be located on either side of the transformer arrangement. The transformer output may be configured to switch between matching either a low impedance antenna or a high impedance antenna.

The present invention is set forth in the independent claim.

The following presents a simplified summary of one or more implementations in order to provide a basic understanding of such implementations. This summary is not an extensive overview of all contemplated implementations and is intended to neither identify key or critical elements of all implementations nor delineate the scope of any or all implementations. Its sole purpose is to present some concepts of one or more implementations in a simplified form as a prelude to the more detailed description that is presented later.

A first aspect relates to an apparatus such as defined in claim <NUM>.

A second aspect relates to a method for operating an apparatus such as defined in claim <NUM>.

<FIG> shows an example of a system <NUM> in a transmitter according to certain aspects of the present disclosure useful for the understanding of the invention, not corresponding to the claims. The system <NUM> is configured to amplify signals before the signals are transmitted via one or more antennas (not shown) coupled to the transmitter. In one example, the system <NUM> receives intermediate frequency (IF) signals from a previous stage (not shown) that converts baseband signals from a baseband processor into the IF signals. In this example, the system <NUM> amplifies the IF signals and outputs the amplified IF signals to a subsequent stage (not shown) that frequency upconverts the amplified IF signals into radio frequency (RF) signals for transmission. The IF signals may have frequencies in the gigahertz range. In other implementations, the system <NUM> may amplify RF signals.

In certain aspects, the system <NUM> is configured to amplify signals (e.g., IF signals) in multiple frequency bands. The multiple frequency bands may be used for different wireless communication technologies supported by the transmitter or may be used for the same wireless communication technology. In one example, the system <NUM> is configured to amplify signals in a first frequency band and signals in a second frequency band. The first frequency band and the second frequency band may be contiguous or non-contiguous.

In the example in <FIG>, the system <NUM> includes a first amplifier <NUM>, a transformer <NUM>, a second amplifier <NUM>, and a third amplifier <NUM>. In one example, the first amplifier <NUM> is used to amplify signals in both the first frequency band and the second frequency band, the second amplifier <NUM> is used to amplify signals in the first frequency band, and the third amplifier <NUM> is used to amplify signals in the second frequency band. As discussed further below, the transformer <NUM> is used as a load for the first amplifier <NUM> to implement a bandpass filter having a wide passband covering both the first frequency band and the second frequency band.

In this example, the first amplifier <NUM> is a differential amplifier having a differential input and a differential output, in which the differential input includes a first input <NUM> and a second input <NUM>, and the differential output includes a first output <NUM> and a second output <NUM>. The outputs <NUM> and <NUM> of the first amplifier <NUM> are coupled to a primary side of the transformer <NUM> where the transformer <NUM> provides a load for the first amplifier <NUM>. In this example, the first amplifier <NUM> is configured to receive differential signals (e.g., differential IF signals) in both the first frequency band and the second frequency band from the previous stage (not shown) and drive the primary side of the transformer <NUM> based on the received differential signals. An exemplary implementation of the first amplifier <NUM> is discussed below with reference to <FIG>.

The second amplifier <NUM> has a differential input including a first input <NUM> and a second input <NUM>. In the example shown in <FIG>, the system <NUM> includes a first switch <NUM> coupled between the first input <NUM> of the second amplifier <NUM> and a secondary side of the transformer <NUM>, and a second switch <NUM> coupled between the second input <NUM> of the second amplifier <NUM> and the secondary side of the transformer <NUM>. As discussed further below, the second amplifier <NUM> is configured to amplify signals in the first frequency band in a first mode and output the amplified signals in the first frequency band to a subsequent stage (e.g., a first mixer for frequency upconversion to RF).

The third amplifier <NUM> has a differential input including a first input <NUM> and a second input <NUM>. The system <NUM> includes a third switch <NUM> coupled between the first input <NUM> of the third amplifier <NUM> and the secondary side of the transformer <NUM>, and a fourth switch <NUM> coupled between the second input <NUM> of the third amplifier <NUM> and the secondary side of the transformer <NUM>. As discussed further below, the third amplifier <NUM> is configured to amplify signals in the second frequency band in a second mode and output the amplified signals in the second frequency band to a subsequent stage (e.g., a second mixer for frequency upconversion to RF). Thus, in this example, signals in both frequency bands are amplified by the first amplifier <NUM>, signals in the first frequency band are further amplified by the second amplifier <NUM>, and signals in the second frequency band are further amplified by the third amplifier <NUM>.

In the first mode, a controller <NUM> turns on (i.e., closes) the first switch <NUM> and the second switch <NUM>, and turns off (i.e., opens) the third switch <NUM> and the fourth switch <NUM>. Thus, in the first mode, the differential input of the second amplifier <NUM> is coupled to the secondary side of the transformer <NUM> to amplify signals in the first frequency band. In the second mode, the controller <NUM> turns on (i.e., closes) the third switch <NUM> and the fourth switch <NUM>, and turns off (i.e., opens) the first switch <NUM> and the second switch <NUM>. Thus, in the second mode, the differential input of the third amplifier <NUM> is coupled to the secondary side of the transformer <NUM> to amplify signals in the second frequency band. Note that the individual connections between the controller <NUM> and the switches <NUM>, <NUM>, <NUM>, and <NUM> are not shown in <FIG> for ease of illustration.

In the example in <FIG>, the primary side of the transformer <NUM> includes a first inductor <NUM> and a first capacitor <NUM> coupled in parallel between a first terminal <NUM> and a second terminal <NUM> of the transformer <NUM>. The secondary side of the transformer <NUM> includes a second inductor <NUM> and a second capacitor <NUM> coupled in parallel between a third terminal <NUM> and a fourth terminal <NUM> of the transformer <NUM>. The first inductor <NUM> and the second inductor <NUM> are magnetically coupled (i.e., inductively coupled). The magnetic coupling transfers signal power from the primary side to the secondary side of the transformer <NUM>.

In this example, the differential output of the first amplifier <NUM> is coupled to the primary side of the transformer <NUM>. More particularly, the first output <NUM> of the first amplifier <NUM> is coupled to the first terminal <NUM> of the transformer <NUM> and the second output <NUM> of the first amplifier <NUM> is coupled to the second terminal <NUM> of the transformer <NUM>.

In this example, the first switch <NUM> is coupled between the first input <NUM> of the second amplifier <NUM> and the third terminal <NUM> of the transformer <NUM>, and the second switch <NUM> is coupled between the second input <NUM> of the second amplifier <NUM> and the fourth terminal <NUM> of the transformer <NUM>.

In this example, the third switch <NUM> is coupled between the first input <NUM> of the third amplifier <NUM> and the third terminal <NUM> of the transformer <NUM>, and the fourth switch <NUM> is coupled between the second input <NUM> of the third amplifier <NUM> and the fourth terminal <NUM> of the transformer <NUM>.

As discussed above, the first amplifier <NUM> drives the primary side of the transformer <NUM> based on differential signals (e.g., differential IF signals) received at the differential input of the first amplifier <NUM> from the previous stage (not shown). In this regard, <FIG> shows an exemplary implementation of the first amplifier <NUM> according to certain aspects. In this example, the first amplifier <NUM> is a variable gain amplifier.

In the example in <FIG>, the first amplifier <NUM> includes a first set of branches <NUM>-<NUM> to <NUM>-n coupled between the first output <NUM> and ground, and a second set of branches <NUM>-<NUM> to <NUM>-n coupled between the second output <NUM> and ground. Each branch in the first set of branches <NUM>-<NUM> to <NUM>-n includes a respective input transistor <NUM>-<NUM> to <NUM>-n and a respective switch <NUM>-<NUM> to <NUM>-n. In each branch in the first set of branches <NUM>-<NUM> to <NUM>-n, the gate of the respective input transistor <NUM>-<NUM> to <NUM>-n (e.g., NFET) is coupled to the first input <NUM>, and the respective switch <NUM>-<NUM> to <NUM>-n is coupled between the respective input transistor <NUM>-<NUM> to <NUM>-n and the first output <NUM>. Each branch in the second set of branches <NUM>-<NUM> to <NUM>-n includes a respective input transistor <NUM>-<NUM> to <NUM>-n and a respective switch <NUM>-<NUM> to <NUM>-n. In each branch in the second set of branches <NUM>-<NUM> to <NUM>-n, the gate of the respective input transistor <NUM>-<NUM> to <NUM>-n (e.g., NFET) is coupled to the second input <NUM>, and the respective switch <NUM>-<NUM> to <NUM>-n is coupled between the respective input transistor <NUM>-<NUM> to <NUM>-n and the second output <NUM>.

In this example, a gain controller (not shown) controls the gain of the first amplifier <NUM> by controlling the number of the branches <NUM>-<NUM> to <NUM>-n and <NUM>-<NUM> to <NUM>-n that are enabled using control signals C<NUM> to Cn. The larger the number of branches that are enabled, the higher the gain. The gain controller enables a branch by closing the respective switch (e.g., respective one of the switches <NUM>-<NUM> to <NUM>-n and <NUM>-<NUM> to <NUM>-n) and disables a branch by opening the respective switch. In operation, the input transistor in each enabled branch in the first set of branches <NUM>-<NUM> to <NUM>-n drives the first output <NUM> based on the voltage at the first input <NUM>. The input transistor in each enabled branch in the second set of branches <NUM>-<NUM> to <NUM>-n drives the second output <NUM> based on the voltage at the second input <NUM>. Each of the switches <NUM>-<NUM> to <NUM>-n and <NUM>-<NUM> to <NUM>-n may be implemented with an NFET, a PFET, a transmission gate, or another type of switch.

It is to be appreciated that the first amplifier <NUM> is not limited to the exemplary implementation shown in <FIG>.

Returning to <FIG>, the transformer <NUM> implements a bandpass filter that causes the first amplifier <NUM> to amplify signals within a desired passband. The passband is a function of the primary resonance frequency of the transformer <NUM>, the secondary resonance frequency of the transformer <NUM>, and the coupling factor K between the first inductor <NUM> and the second inductor <NUM>. The coupling factor K is a measure of the magnetic coupling between the first inductor <NUM> and the second inductor <NUM>, as discussed further below.

The primary resonance frequency is given by the following: <MAT> where fr<NUM> is the primary resonance frequency, C<NUM> is the capacitance of the first capacitor <NUM>, and L<NUM> is the inductance of the first inductor <NUM>. C<NUM> may also include parasitic capacitance at the outputs <NUM> and <NUM> of the first amplifier <NUM>. As shown in equation (<NUM>), the primary resonance frequency can be set to a desired frequency by choosing the capacitance of the first capacitor <NUM> and the inductance of the first inductor <NUM> accordingly. The secondary resonance frequency is given by the following: <MAT> where fr<NUM> is the secondary resonance frequency, C<NUM> is the capacitance of the second capacitor <NUM>, and L<NUM> is the inductance of the second inductor <NUM>. C<NUM> may also include parasitic capacitance at the inputs <NUM> and <NUM> of the second amplifier <NUM> and/or the inputs <NUM> and <NUM> of the third amplifier <NUM>. As shown in equation (<NUM>), the secondary resonance frequency can be set to a desired frequency by choosing the capacitance of the second capacitor <NUM> and the inductance of the second inductor <NUM> accordingly.

The coupling factor K depends on the overlap between the first inductor <NUM> and the second inductor <NUM>. For example, the first inductor <NUM> and the second inductor <NUM> may be integrated on a chip in which the first inductor <NUM> is implemented with a first planar loop inductor and the second inductor <NUM> is implemented with a second planar loop inductor on the chip. In this example, the first inductor <NUM> and the second inductor <NUM> are formed in different layers of the chip with the first inductor <NUM> overlapping the second inductor <NUM> to magnetically couple the first inductor <NUM> and the second inductor <NUM>. In this example, the coupling factor K is a function of the overlap between the first inductor <NUM> and the second inductor <NUM>, where the coupling factor K is larger for a larger overlap. Thus, the coupling factor K may be set to a desired value by laying out the first inductor <NUM> and the second inductor <NUM> on the chip such that the overlap between the first inductor <NUM> and the second inductor <NUM> corresponds to the desired coupling factor K.

As discussed above, the passband of the transformer <NUM> is a function of the primary resonance frequency, the secondary resonance frequency, and the coupling factor K. In one example, the center frequency of the passband is a function of the primary resonance frequency and the secondary resonance frequency of the transformer <NUM>. In this example, the primary resonance frequency and the secondary resonance frequency may each be set to a frequency approximately equal to the desired center frequency for the passband. As discussed above, the primary resonance frequency is set by the capacitance of the first capacitor <NUM> and the inductance of the first inductor <NUM>, and the secondary resonance frequency is set by the capacitance of the second capacitor <NUM> and the inductance of the second inductor <NUM>.

In the above example, the bandwidth of the passband (i.e., the width of the passband in frequency) is a function of the coupling factor K. Thus, the passband may be set to a desired bandwidth by setting the coupling factor K accordingly. As discussed above, the coupling factor K may be set by the overlap between the first inductor <NUM> and the second inductor <NUM>.

As discussed above, the first amplifier <NUM> is used to amplify signals in both the first frequency band and the second frequency band. In this regard, the primary resonance frequency, the secondary resonance frequency, and the coupling factor K are chosen to provide the transformer <NUM> with a wide passband covering both the first frequency band and the second frequency band. An example of this is illustrated in <FIG>, which shows an exemplary passband <NUM> of the transformer <NUM>. In this example, the passband <NUM> has a wide bandwidth covering both the first frequency band (labeled "FB1") and the second frequency band (labeled "FB2"). This allows the first amplifier <NUM> to provide high gain for both frequency bands.

In the example shown in <FIG>, the first frequency band spans approximately <NUM> to <NUM> and the second frequency band spans approximately <NUM> to <NUM>. Thus, in this example, the passband <NUM> spans <NUM> to <NUM> to cover both frequency bands. However, it is to be appreciated that the first frequency band and the second frequency band are not limited to the above frequencies.

In some applications, the system <NUM> is used to amplify signals in one of the first frequency band and the second frequency band at a time. For example, in the first mode, the system <NUM> is used to amplify signals in the first frequency band, and, in the second mode, the system <NUM> is used to amplify signals in the second frequency band. In these applications, maintaining a wide passband that covers both frequency bands reduces the power efficiency of the first amplifier <NUM>. This is because only a portion of the wide passband is needed at a time since the first amplifier <NUM> amplifies signals in one of the frequency bands at a time. As a result, the wide passband causes the first amplifier <NUM> to consume power maintaining high gain for the frequency band that is not being used at a given time. The power efficiency is further reduced for the case where the first frequency band and the second frequency band are non-contiguous, as shown in the example in <FIG>. This is because the wide passband covers frequencies in the frequency gap between the first frequency band and the second frequency band which causes the first amplifier <NUM> to consume power providing high gain within the frequency gap.

Aspects of the present disclosure increase the power efficiency of the first amplifier <NUM> by providing a switchable transformer configured to switch between a first passband and a second passband. In one example, the first passband covers the first frequency band and the second passband covers the second frequency band. In this example, each of the first and second passbands has a narrower bandwidth than the wide passband discussed above. In operation, a controller switches the switchable transformer to the first passband when the first frequency band is being used and switches the switchable transformer to the second passband when the second frequency band is being used. Thus, the controller switches the switchable transformer to one of the first and second passbands at a time depending on which of the first and second frequency bands is being used. Since one of the first and second passbands is used at a time and each of the first and second passbands has a narrower bandwidth than the wide passband discussed above, the power consumption of the first amplifier <NUM> is reduced, thereby increasing power efficiency.

<FIG> shows an example of a system <NUM> in a transmitter according to certain aspects of the present disclosure. The system <NUM> is configured to amplify signals before the signals are transmitted via one or more antennas (not shown) coupled to the transmitter. In one example, the system <NUM> receives intermediate frequency (IF) signals from a previous stage (not shown) that converts baseband signals from a baseband processor into the IF signals. In this example, the system <NUM> amplifies the IF signals and outputs the amplified IF signals to a subsequent stage (not shown) that frequency upconverts the amplified IF signals into radio frequency (RF) signals for transmission. In other implementations, the system <NUM> may amplify RF signals.

In certain aspects, the system <NUM> is configured to amplify signals (e.g., IF signals) in multiple frequency bands. The multiple frequency bands may include the first frequency band and the second frequency band discussed above.

In the example in <FIG>, the system <NUM> includes the first amplifier <NUM>, the second amplifier <NUM>, and the third amplifier <NUM> discussed above. The system <NUM> also includes a switchable transformer <NUM> configured to switch between a first passband and a second passband under the control of a controller <NUM>. In one example, the first passband covers the first frequency band and the second passband covers the second frequency band. As discussed further below, the controller <NUM> switches the switchable transformer <NUM> to the first passband in a first mode when the first frequency band is being used and switches the switchable transformer <NUM> to the second passband in a second mode when the second frequency band is being used.

The switchable transformer <NUM> has a primary side, a first secondary side, and a second secondary side. As discussed further below, the first secondary side is used for the first passband and the second secondary side is used for the second passband. In this example, the primary side includes a first switchable inductor <NUM> and a first capacitor <NUM> coupled in parallel with the first switchable inductor <NUM>. The first switchable inductor <NUM> is coupled between a first terminal <NUM> of the switchable transformer <NUM> and a second terminal <NUM> of the switchable transformer <NUM>. The first terminal <NUM> is coupled to the first output <NUM> of the first amplifier <NUM> and the second terminal <NUM> is coupled to the second output <NUM> of the first amplifier <NUM>.

The first switchable inductor <NUM> is configured to switch between a first primary inductance and a second primary inductance where the first primary inductance is used for the first passband and the second primary inductance is used for the second passband. In the example in <FIG>, the first switchable inductor <NUM> includes a first inductor <NUM>, a second inductor <NUM>, a third inductor <NUM>, a fourth inductor <NUM>, and a switching circuit <NUM>. The first inductor <NUM> and the second inductor <NUM> are coupled in series between the first terminal <NUM> and the switching circuit <NUM>, and the third inductor <NUM> and the fourth inductor <NUM> are coupled in series between the second terminal <NUM> and the switching circuit <NUM>. The switching circuit <NUM> is also coupled between the first inductor <NUM> and the second inductor <NUM>, and between the third inductor <NUM> and the fourth inductor <NUM>. The switching circuit <NUM> is also coupled to a bias node <NUM>, which is biased by a DC voltage.

In operation, the switching circuit <NUM> switches the switchable inductor <NUM> between the first primary inductance in the first mode and the second primary inductance in the second mode under the control of the controller <NUM>. In the first mode, the switching circuit <NUM> couples the first inductor <NUM>, the second inductor <NUM>, the third inductor <NUM>, and the fourth inductor <NUM> in series between the first terminal <NUM> and the second terminal <NUM> (and hence between the first output <NUM> and the second output <NUM> of the first amplifier <NUM>). In the first mode, the first primary inductance of the first switchable inductor <NUM> has an inductance equal to the sum of the inductances of the first inductor <NUM>, the second inductor <NUM>, the third inductor <NUM>, and the fourth inductor <NUM>. The switching circuit <NUM> may also couple the bias node <NUM> between the second inductor <NUM> and the third inductor <NUM> in which the bias node provides a common mode voltage for the differential signal at the differential output of the first amplifier <NUM>.

In the second mode, the switching circuit <NUM> couples the first inductor <NUM> and the fourth inductor <NUM> in series between the first terminal <NUM> and the second terminal <NUM> (and hence between the first output <NUM> and the second output <NUM> of the first amplifier <NUM>). In the second mode, the switching circuit <NUM> bypasses the second inductor <NUM> and the third inductor <NUM>. Thus, the second inductor <NUM> and the third inductor <NUM> do not contribute to the inductance of the first switchable inductor <NUM> in the second mode. In the second mode, the second primary inductance of the first switchable inductor <NUM> has an inductance equal to the sum of the inductances of the first inductor <NUM> and the fourth inductor <NUM>. The switching circuit <NUM> may also couple the bias node <NUM> between the first inductor <NUM> and the fourth inductor <NUM>.

In the first mode, the first switchable inductor <NUM> has a first primary resonance given by following: <MAT> where frp1 is the first primary resonance frequency, C<NUM> is the capacitance of the first capacitor <NUM>, and Lp1 is the first primary inductance. C<NUM> may also include parasitic capacitance at the outputs <NUM> and <NUM> of the first amplifier <NUM>. In the second mode, the first switchable inductor <NUM> has a second primary resonance frequency given by the following: <MAT> where frp2 is the second primary resonance frequency and Lp2 is the second primary inductance. Thus, the first switchable inductor <NUM> allows the primary side of the switchable transformer <NUM> to switch between a first primary resonance frequency in the first mode and a second primary resonance frequency in the second mode.

The first secondary side of the switchable transformer <NUM> includes a second switchable inductor <NUM> and a second capacitor <NUM> coupled in parallel with the second switchable inductor <NUM>. The second switchable inductor <NUM> is coupled between a third terminal <NUM> of the switchable transformer <NUM> and a fourth terminal <NUM> of the switchable transformer <NUM>. The third terminal <NUM> is coupled to the first input <NUM> of the second amplifier <NUM> (e.g., via one or more metal lines, a transmission line, or a combination thereof) and the fourth terminal <NUM> is coupled to the second input <NUM> of the second amplifier <NUM> (e.g., via one or more metal lines, a transmission line, or a combination thereof). The second switchable inductor <NUM> is magnetically coupled to the first switchable inductor <NUM> by a coupling factor K<NUM> which may depend on the overlap between the second switchable inductor <NUM> and the first switchable inductor <NUM>.

The second switchable inductor <NUM> includes a fifth inductor <NUM>, a sixth inductor <NUM>, and a switch <NUM> coupled between the fifth inductor <NUM> and the sixth inductor <NUM>. In the first mode, the controller <NUM> closes the switch <NUM>. Thus, in the first mode, the second switchable inductor <NUM> has an inductance given by the sum of the inductances of the fifth inductor <NUM> and the sixth inductor <NUM>. In the second mode, the controller <NUM> opens the switch <NUM>, which decouples the fifth inductor <NUM> and the sixth inductor <NUM>. This effectively disables the second switchable inductor <NUM>.

In the example shown in <FIG>, the switch <NUM> is located at the center of the second switchable inductor <NUM>, which acts as a virtual ground for a differential signal at the second switchable inductor <NUM>. In this example, locating the switch <NUM> at the virtual ground significantly reduces the impact that the parasitic capacitance of the switch <NUM> has on the differential signal. However, it is to be appreciated that the present disclosure is not limited to this example. In other implementations, the switch <NUM> may be placed in another location in the second switchable inductor <NUM>, as discussed further below.

In the first mode, the second switchable inductor <NUM> has a first secondary resonance frequency given by the following: <MAT> where frs1 is the first secondary resonance frequency, C<NUM> is the capacitance of the second capacitor <NUM>, and L<NUM> is the inductance of the second switchable inductor <NUM>. C<NUM> may also include parasitic capacitance at the inputs <NUM> and <NUM> of the second amplifier <NUM>.

The second secondary side of the switchable transformer <NUM> includes a third switchable inductor <NUM> and a third capacitor <NUM> coupled in parallel with the third switchable inductor <NUM>. The third switchable inductor <NUM> is coupled between a fifth terminal <NUM> of the switchable transformer <NUM> and a sixth terminal <NUM> of the switchable transformer <NUM>. The fifth terminal <NUM> is coupled to the first input <NUM> of the third amplifier <NUM> (e.g., via one or more metal lines, a transmission line, or a combination thereof) and the sixth terminal <NUM> is coupled to the second input <NUM> of the third amplifier <NUM> (e.g., via one or more metal lines, a transmission line, or a combination thereof). The third switchable inductor <NUM> is magnetically coupled to the first switchable inductor <NUM> by a coupling factor K<NUM> which may depend on the overlap between the third switchable inductor <NUM> and the first switchable inductor <NUM>.

The third switchable inductor <NUM> includes a seventh inductor <NUM>, an eighth inductor <NUM>, and a switch <NUM> coupled between the seventh inductor <NUM> and the eighth inductor <NUM>. In the first mode, the controller <NUM> opens the switch <NUM> which decouples the seventh inductor <NUM> and the eighth inductor <NUM>. This effectively disables the third switchable inductor <NUM>. In the second mode, the controller <NUM> closes the switch <NUM>. Thus, in the second mode, the third switchable inductor <NUM> has an inductance given by the sum of the inductances of the seventh inductor <NUM> and the eighth inductor <NUM>.

In the example shown in <FIG>, the switch <NUM> is located at the center of the third switchable inductor <NUM>, which acts as a virtual ground for a differential signal at the third switchable inductor <NUM>. In this example, locating the switch <NUM> at the virtual ground significantly reduces the impact that the parasitic capacitance of the switch <NUM> has on the differential signal. However, it is to be appreciated that the present disclosure is not limited to this example. In other implementations, the switch <NUM> may be placed in another location in the third switchable inductor <NUM>, as discussed further below.

In the second mode, the third switchable inductor <NUM> has a second secondary resonance frequency given by the following: <MAT> where frs2 is the second secondary resonance frequency, C<NUM> is the capacitance of the third capacitor <NUM>, and L<NUM> is the inductance of the third switchable inductor <NUM>. C<NUM> may also include parasitic capacitance at the inputs <NUM> and <NUM> of the third amplifier <NUM>.

As discussed above, the controller <NUM> switches the switchable transformer <NUM> to the first mode when the first frequency band is being used. In the first mode, the switchable transformer <NUM> has a first passband that is a function of the first primary resonance frp1 given in equation (<NUM>), the first secondary resonance frequency frs1 given in equation (<NUM>), and the first coupling factor K<NUM> discussed above. In certain aspects, the first passband is configured to cover the first frequency band by setting the first primary resonance frp1, the first secondary resonance frequency frs1, and the first coupling factor K<NUM> accordingly. An example of the first passband <NUM> is shown in <FIG>. In this example, the first passband <NUM> covers the first frequency band (labeled "FB1") and therefore provides high gain for the first frequency band. In addition, the first passband <NUM> has a narrower bandwidth than the wide passband <NUM> shown in <FIG>, and therefore reduces power consumption of the first amplifier <NUM>.

In the second mode, the switchable transformer <NUM> has a second passband that is a function of the second primary resonance frp2 given in equation (<NUM>), the second secondary resonance frequency frs2 given in equation (<NUM>), and the second coupling factor K<NUM> discussed above. In certain aspects, the second passband is configured to cover the second frequency band by setting the second primary resonance frp2, the second secondary resonance frequency frs2, and the second coupling factor K<NUM> accordingly. An example of the second passband <NUM> is shown in <FIG>. In this example, the second passband <NUM> covers the second frequency band (labeled "FB2") and therefore provides high gain for the second frequency band. In addition, the second passband <NUM> has a narrower bandwidth than the wide passband <NUM> shown in <FIG>, and therefore reduces power consumption of the first amplifier <NUM>.

Each of the capacitors <NUM>, <NUM>, and <NUM> may be implemented with a variable capacitor (shown in the example in <FIG>) or a fixed capacitor. For example, the first capacitor <NUM> may be implemented with a variable capacitor to finely tune the resonance frequency of the primary side of the switchable transformer <NUM> (e.g., to compensate for process-voltage-temperature (PVT) variation). Similarly, the second capacitor <NUM> may be implemented with a variable capacitor to finely tune the resonance frequency of the first secondary side of the switchable transformer <NUM> (e.g., to compensate for PVT variation), and the third capacitor <NUM> may be implemented with a variable capacitor to finely tune the resonance frequency of the second secondary side of the switchable transformer <NUM> (e.g., to compensate for PVT variation).

In some implementations, the inputs <NUM> and <NUM> of the second amplifier <NUM> may be DC biased through a center tap of the second switchable inductor <NUM>. In other implementations, the inputs <NUM> and <NUM> of the second amplifier <NUM> may be DC biased by a separate DC bias voltage source (not shown) (e.g., for the case where the inputs <NUM> and <NUM> of the second amplifier <NUM> are coupled to the switchable transformer <NUM> via long transmission lines). In this example, the system <NUM> may include coupling capacitors between the inputs <NUM> and <NUM> of the second amplifier <NUM> and the switchable transformer <NUM> to isolate the DC bias voltage at the inputs <NUM> and <NUM> of the second amplifier <NUM> from the switchable transformer <NUM>. In this regard, <FIG> shows an example of a first coupling capacitor <NUM> coupled between the first input <NUM> of the second amplifier <NUM> and the third terminal <NUM> of the switchable transformer <NUM>, and a second coupling capacitor <NUM> coupled between the second input <NUM> of the second amplifier <NUM> and the fourth terminal <NUM> of the switchable transformer <NUM>.

In some implementations, the inputs <NUM> and <NUM> of the third amplifier <NUM> may be DC biased through a center tap of the third switchable inductor <NUM>. In other implementations, the inputs <NUM> and <NUM> of the third amplifier <NUM> may be DC biased by a separate DC bias voltage source (not shown) (e.g., for the case where the inputs <NUM> and <NUM> of the third amplifier <NUM> are coupled to the switchable transformer <NUM> via long transmission lines). In this example, the system <NUM> may include coupling capacitors between the inputs <NUM> and <NUM> of the third amplifier <NUM> and the switchable transformer <NUM> to isolate the DC bias voltage at the inputs <NUM> and <NUM> of the third amplifier <NUM> from the switchable transformer <NUM>. In this regard, <FIG> shows an example of a third coupling capacitor <NUM> coupled between the first input <NUM> of the third amplifier <NUM> and the fifth terminal <NUM> of the switchable transformer <NUM>, and a fourth coupling capacitor <NUM> coupled between the second input <NUM> of the third amplifier <NUM> and the sixth terminal <NUM> of the switchable transformer <NUM>.

<FIG> shows another exemplary implementation of the second switchable inductor <NUM> and the third switchable inductor <NUM>. In this example, the second switchable inductor <NUM> includes an inductor <NUM>, a first switch <NUM>-<NUM> coupled between the inductor <NUM> and the third terminal <NUM> and a second switch <NUM>-<NUM> coupled between the inductor <NUM> and the fourth terminal <NUM>. In the first mode, the controller <NUM> closes the switches <NUM>-<NUM> and <NUM>-<NUM> and, in the second mode, the controller <NUM> opens the switches <NUM>-<NUM> and <NUM>-<NUM>. However, it is to be appreciated that the second switchable inductor <NUM> is not limited to the exemplary implementations shown in <FIG> and <FIG>. In general, the second switchable inductor <NUM> includes at least one inductor and at least one switch coupled in series with the at least one inductor in which the second switchable inductor <NUM> is enabled when the at least one switch is closed and disabled with the at least one switch is open. In the examples in <FIG> and <FIG>, the second capacitor <NUM> is coupled in parallel with the at least one inductor and the at least one switch.

In this example, the third switchable inductor <NUM> includes an inductor <NUM>, a first switch <NUM>-<NUM> coupled between the inductor <NUM> and the fifth terminal <NUM> and a second switch <NUM>-<NUM> coupled between the inductor <NUM> and the sixth terminal <NUM>. In the first mode, the controller <NUM> opens the switches <NUM>-<NUM> and <NUM>-<NUM> and, in the second mode, the controller <NUM> closes the switches <NUM>-<NUM> and <NUM>-<NUM>. However, it is to be appreciated that the third switchable inductor <NUM> is not limited to the exemplary implementations shown in <FIG> and <FIG>. In general, the third switchable inductor <NUM> includes at least one inductor and at least one switch coupled in series with the at least one inductor in which the third switchable inductor <NUM> is enabled when the at least one switch is closed and disabled with the at least one switch is open. In the examples in <FIG> and <FIG>, the third capacitor <NUM> is coupled in parallel with the at least one inductor and the at least one switch.

<FIG> shows an exemplary implementation of the switching circuit <NUM>. In this example, the switching circuit <NUM> includes a first switch <NUM> coupled between the second inductor <NUM> and the bias node <NUM>, and a second switch <NUM> coupled between the third inductor <NUM> and the bias node <NUM>. The switching circuit <NUM> also includes a third switch <NUM> coupled between the first inductor <NUM> and the bias node, and a fourth switch <NUM> coupled between the fourth inductor <NUM> and the bias node <NUM>.

In the first mode, the controller <NUM> closes the first switch <NUM> and the second switch <NUM>, and opens the third switch <NUM> and the fourth switch <NUM>. As a result, the first inductor <NUM>, the second inductor <NUM>, the third inductor <NUM>, and the fourth inductor <NUM> coupled in series between the first terminal <NUM> and the second terminal <NUM>. In this mode, the primary side has the first primary inductance discussed above which is equal to the sum of the inductances of the first inductor <NUM>, the second inductor <NUM>, the third inductor <NUM>, and the fourth inductor <NUM>.

In the second mode, the controller <NUM> opens the first switch <NUM> and the second switch <NUM>, and closes the third switch <NUM> and the fourth switch <NUM>. As a result, the first inductor <NUM> and the fourth inductor <NUM> are coupled in series between the first terminal <NUM> and the second terminal <NUM>. In this mode, the primary side has the second primary inductance discussed above which is equal to the sum of the inductances of the first inductor <NUM> and the fourth inductor <NUM>.

In the example shown in <FIG>, the switches <NUM>, <NUM>, <NUM>, and <NUM> are located adjacent to the center of the first switchable inductor <NUM>, which acts as a virtual ground for a differential signal at the first switchable inductor <NUM>. In this example, locating the switches <NUM>, <NUM>, <NUM>, and <NUM> adjacent to the virtual ground significantly reduces the impact that the parasitic capacitances of the switches <NUM>, <NUM>, <NUM>, and <NUM> have on the differential signal.

It is to be appreciated that the switching circuit <NUM> is not limited to the exemplary implementation shown in <FIG>. In this regard, it is to be appreciated that the exemplary functions of the switching circuit <NUM> discussed above may be realized using other arrangements of switches.

It is also to be appreciated that the first switchable inductor <NUM> is not limited to the exemplary implementation shown in <FIG>. In this regard, it is to be appreciated that the first switchable inductor <NUM> may be implemented with other arrangements of two or more inductors and one or more switches configured to switch the first switchable inductor <NUM> between the first primary inductance and the second primary inductance. In general, the first switchable inductor <NUM> may include at least one first inductor (e.g., inductors <NUM> and <NUM>), at least one second inductor (e.g., inductors <NUM> and <NUM>) coupled in series with the at least one first inductor, and at least one switch (e.g., switches <NUM> and <NUM>) coupled in parallel with the at least one second inductor. In general, the first switchable inductor <NUM> may be switched to the first primary inductance by opening the at least one switch, in which the first primary inductance is equal to the sum of the inductances of the at least one first inductor and the at least one second inductor. The first switchable inductor <NUM> may be switched to the second primary inductance by closing the at least one switch, in which the second primary inductance is equal to the inductance of the at least one first inductor. In this case, the at least one second inductor is bypassed. In general, the first capacitor <NUM> is coupled in parallel with the at least one first inductor and the at least one second inductor.

<FIG> shows a top view of an example of an inductor <NUM> that may be used to implement the first inductor <NUM>, the second inductor <NUM>, the third inductor <NUM>, and the fourth inductor <NUM>. However, it is to be appreciated that the present disclosure is not limited to this example, and that the first inductor <NUM>, the second inductor <NUM>, the third inductor <NUM>, and the fourth inductor <NUM> may be implemented with another inductor.

In this example, the inductor <NUM> is a planar spiral inductor integrated on a chip. The inductor <NUM> may be formed from a first metal layer on the chip using photolithography and/or another fabrication technique. The different portions of the inductor <NUM> corresponding to the first inductor <NUM>, the second inductor <NUM>, the third inductor <NUM>, and the fourth inductor <NUM> are labeled in <FIG> according to certain aspects. In the example in <FIG>, ends <NUM> and <NUM> of the inductor <NUM> are coupled by a bridge <NUM> (shown in <FIG>) that crosses over portion <NUM> of the inductor <NUM>. The bridge <NUM> is formed from a different metal layer than the first metal layer discussed above, and allows one portion of the inductor <NUM> to cross over another portion of the inductor <NUM> for the example where the inductor <NUM> is a spiral inductor. Each end <NUM> and <NUM> of the inductor <NUM> may be coupled to the bridge <NUM> by a respective via (not shown). It is to be appreciated that, in some implementations, the bridge <NUM> may cross under portion <NUM> of the inductor <NUM>. Similarly, ends <NUM> and <NUM> of the inductor <NUM> are coupled by a bridge <NUM> (shown in <FIG>) that crosses over portion <NUM> of the inductor <NUM>.

In this example, the switching circuit <NUM> (not shown in <FIG>) is coupled between locations <NUM> and <NUM> of the inductor <NUM>, and between locations <NUM> and <NUM> of the inductor <NUM>. Location <NUM> corresponds to the terminal of the first inductor <NUM> coupled to the second inductor <NUM>, and location <NUM> corresponds to the terminal of the fourth inductor <NUM> coupled to the third inductor <NUM>. In the second mode, the switching circuit <NUM> couples the inductor <NUM> to the bias node <NUM> (not shown in <FIG>) at locations <NUM> and <NUM>. In this case, the inductance of the first switchable inductor <NUM> is approximately equal to the sum of the inductances of the first inductor <NUM> and the fourth inductor <NUM>.

Location <NUM> corresponds to the terminal of the second inductor <NUM> coupled to the switching circuit <NUM>, and location <NUM> corresponds to the terminal of the third inductor <NUM> coupled to the switching circuit <NUM>. In this example, locations <NUM> and <NUM> of the inductor <NUM> correspond to two ends of the inductor <NUM> separated by a gap. In the first mode, the switching circuit <NUM> couples the inductor <NUM> to the bias node <NUM> at locations <NUM> and <NUM>. In this case, the inductance of the first switchable inductor <NUM> is approximately equal to the sum of the inductances of the first inductor <NUM>, the second inductor <NUM>, the third inductor <NUM>, and the fourth inductor <NUM>.

<FIG> shows a top view of an example of an inductor <NUM> that may be used to implement the fifth inductor <NUM> and the sixth inductor <NUM>. However, it is to be appreciated that the present disclosure is not limited to this example, and that the fifth inductor <NUM> and the sixth inductor <NUM> may be implemented with another inductor.

In this example, the inductor <NUM> is a planar spiral inductor integrated on a chip. The inductor <NUM> may be formed from a second metal layer on the chip using photolithography and/or another fabrication technique. The different portions of the inductor <NUM> corresponding to the fifth inductor <NUM> and the sixth inductor <NUM> are labeled in <FIG> according to certain aspects. In the example in <FIG>, ends <NUM> and <NUM> of the inductor <NUM> are coupled by a bridge <NUM> (shown in <FIG>) that crosses over portion <NUM> of the inductor <NUM>. The bridge <NUM> is formed from a different metal layer than the second metal layer discussed above, and allows one portion of the inductor <NUM> to cross over another portion of the inductor <NUM> for the example where the inductor <NUM> is a spiral inductor. Each end <NUM> and <NUM> of the inductor <NUM> may be coupled to the bridge <NUM> by a respective via (not shown). It is to be appreciated that, in some implementations, the bridge <NUM> may cross under portion <NUM> of the inductor <NUM>.

In this example, the switch <NUM> (not shown in <FIG>) is coupled between locations <NUM> and <NUM> of the inductor <NUM>. Location <NUM> corresponds to the terminal of the sixth inductor <NUM> coupled to the switch <NUM>, and location <NUM> corresponds to the terminal of the fifth inductor <NUM> coupled to the switch <NUM>. The controller <NUM> (not shown in <FIG>) turns on the switch <NUM> in the first mode and turns off the switch <NUM> in the second mode.

<FIG> shows a top view of an example of an inductor <NUM> that may be used to implement the seventh inductor <NUM> and the eighth inductor <NUM>. However, it is to be appreciated that the present disclosure is not limited to this example, and that the seventh inductor <NUM> and the eighth inductor <NUM> may be implemented with another inductor.

In this example, the inductor <NUM> is a planar loop inductor. The inductor <NUM> may be formed from a third metal layer on the chip using photolithography and/or another fabrication technique. The different portions of the inductor <NUM> corresponding to the seventh inductor <NUM> and the eighth inductor <NUM> are labeled in <FIG> according to certain aspects.

In this example, the switch <NUM> (not shown in <FIG>) is coupled between locations <NUM> and <NUM> of the inductor <NUM>. Location <NUM> corresponds to the terminal of the seventh inductor <NUM> coupled to the switch <NUM>, and location <NUM> corresponds to the terminal of the eighth inductor <NUM> coupled to the switch <NUM>. The controller <NUM> (not shown in <FIG>) turns off the switch <NUM> in the first mode and turns on the switch <NUM> in the second mode.

<FIG> shows a top view of the inductors <NUM>, <NUM>, and <NUM> according to certain aspects. In this example, the inductor <NUM> overlaps the inductor <NUM> to provide magnetic coupling of the inductors <NUM> and <NUM>, and the inductor <NUM> overlaps the inductor <NUM> to provide magnetic coupling of the inductors <NUM> and <NUM>. The overlapping of the inductors <NUM>, <NUM>, and <NUM> is possible since the inductors <NUM>, <NUM>, and <NUM> are formed from different metal layers on the chip. More particularly, the inductor <NUM> is formed from the first metal layer of the chip, the inductor <NUM> is formed from the second metal layer of the chip, and the inductor <NUM> is formed from the third metal layer of the chip. In the example in <FIG>, the inductor <NUM> is located below the inductor <NUM>, and the inductor <NUM> is located above the inductor <NUM>. However, it is to be appreciated that the present disclosure is not limited to this example. In another implementation, the inductor <NUM> may be located above the inductor <NUM>, and the inductor <NUM> may be located below the inductor <NUM>.

The degree of overlap between the inductor <NUM> and the inductor <NUM> determines the coupling factor K<NUM> between the primary side and the first secondary side of the switchable transformer <NUM>. Thus, in this example, a desired coupling factor K<NUM> between the primary side and the first secondary side can be achieved by laying out the inductors <NUM> and <NUM> such that the overlap between the inductors <NUM> and <NUM> corresponds to the desired coupling factor K<NUM>.

Similarly, the degree of overlap between the inductor <NUM> and the inductor <NUM> determines the coupling factor K<NUM> between the primary side and the second secondary side of the switchable transformer <NUM>. Thus, in this example, a desired coupling factor K<NUM> between the primary side and the second secondary side can be achieved by laying out the inductors <NUM> and <NUM> such that the overlap between the inductors <NUM> and <NUM> corresponds to the desired coupling factor K<NUM>.

It is to be appreciated that the terms "first metal layer," "second metal layer," and "third metal layer" are used herein as a convenient way of distinguishing between the different metal layers used to form the inductors <NUM>, <NUM>, and <NUM>. In certain aspects, the first metal layer, the second metal, and the third metal layer may include the top three metal layers of a chip to minimize parasitic capacitances. However, it is to be appreciated that the first metal layer, the second metal layer, and the third metal layer are not limited to this example.

<FIG> shows an example of a system <NUM> in a transmitter according to certain aspects. The system <NUM> includes the exemplary system <NUM> illustrated in any one of <FIG>. The system <NUM> also includes a first transformer <NUM>, a second transformer <NUM>, a first mixer <NUM>, a third transformer <NUM>, and a second mixer <NUM>.

In the example in <FIG>, the primary side of the first transformer <NUM> includes a first inductor <NUM> and a capacitor <NUM> coupled in parallel between ground and a first terminal <NUM> of the first transformer <NUM>. The secondary side of the first transformer <NUM> includes a second inductor <NUM> and a resistor <NUM> coupled in parallel between a second terminal <NUM> and a third terminal <NUM> of the first transformer <NUM>. The first inductor <NUM> and the second inductor <NUM> are magnetically coupled (i.e., inductively coupled).

In this example, the first terminal <NUM> of the first transformer <NUM> is coupled to a previous stage (not shown) of the transmitter. The previous stage may receive a baseband signal (e.g. from a baseband processor), convert the baseband signal into an IF signal, and input the IF signal to the first terminal <NUM> of the first transformer <NUM>. The differential input of the first amplifier <NUM> is coupled to the secondary side of the first transformer <NUM>. More particularly, the second terminal <NUM> of the first transformer <NUM> is coupled to the first input <NUM> of the first amplifier <NUM> and the third terminal <NUM> of the first transformer <NUM> is coupled to the second input <NUM> of the first amplifier <NUM>. The first amplifier <NUM> may have parasitic capacitance at the inputs <NUM> and <NUM> in which the resonance frequency at the secondary side of the first transformer <NUM> is determined by the inductance of the second inductor <NUM> and the parasitic capacitance.

In this example, the first transformer <NUM> is configured to have a passband covering the first frequency band and the second frequency band so that signals in both frequency bands are passed to the first amplifier <NUM>. In this regard, the inductances of the first and second inductors <NUM> and <NUM>, the capacitance of the capacitor <NUM>, and the coupling factor K between the first and second inductors <NUM> and <NUM> are chosen to achieve a passband covering the first and second frequency bands. The resistor <NUM> may be used for de-Qing at the differential input of the first amplifier <NUM>. In this example, the first transformer <NUM> may also be configured to convert a single-ended IF signal received at the first terminal <NUM> into a differential IF signal at the second and third terminals <NUM> and <NUM>.

In the example in <FIG>, the primary side of the second transformer <NUM> includes a first inductor <NUM> and a first capacitor <NUM> coupled in parallel between a first terminal <NUM> of the second transformer <NUM> and a second terminal <NUM> of the second transformer <NUM>. The secondary side of the second transformer <NUM> includes a second inductor <NUM> and a second capacitor <NUM> coupled in parallel between a third terminal <NUM> and a fourth terminal <NUM> of the second transformer <NUM>. The first inductor <NUM> and the second inductor <NUM> are magnetically coupled (i.e., inductively coupled).

In this example, the second amplifier <NUM> has a differential output including a first output <NUM> coupled to the first terminal <NUM> of the second transformer <NUM>, and a second output <NUM> coupled to the second terminal <NUM> of the second transformer <NUM>. The third terminal <NUM> and the fourth terminal <NUM> of the second transformer <NUM> are coupled to the first mixer <NUM>.

In this example, the second transformer <NUM> is configured to have a passband covering the first frequency band so that second amplifier <NUM> amplifies signals in the first frequency band. In this regard, the inductances of the first and second inductors <NUM> and <NUM>, the capacitances of the first and second capacitors <NUM> and <NUM>, and the coupling factor K between the first and second inductors <NUM> and <NUM> are chosen to achieve a passband covering the first frequency band.

The first mixer <NUM> is configured to receive the amplified signal in the first frequency band from the second transformer <NUM> and frequency upconvert the signal into an RF signal for transmission. The first mixer <NUM> may upconvert the signal by mixing the signal with a first local oscillator signal.

In the example in <FIG>, the primary side of the third transformer <NUM> includes a first inductor <NUM> and a first capacitor <NUM> coupled in parallel between a first terminal <NUM> of the third transformer <NUM> and a second terminal <NUM> of the third transformer <NUM>. The secondary side of the third transformer <NUM> includes a second inductor <NUM> and a second capacitor <NUM> coupled in parallel between a third terminal <NUM> and a fourth terminal <NUM> of the third transformer <NUM>. The first inductor <NUM> and the second inductor <NUM> are magnetically coupled (i.e., inductively coupled).

In this example, the third amplifier <NUM> has a differential output including a first output <NUM> coupled to the first terminal <NUM> of the third transformer <NUM>, and a second output <NUM> coupled to the second terminal <NUM> of the third transformer <NUM>. The third terminal <NUM> and the fourth terminal <NUM> of the third transformer <NUM> are coupled to the second mixer <NUM>.

In this example, the third transformer <NUM> is configured to have a passband covering the second frequency band so that third amplifier <NUM> amplifies signals in the second frequency band. In this regard, the inductances of the first and second inductors <NUM> and <NUM>, the capacitances of the first and second capacitors <NUM> and <NUM>, and the coupling factor K between the first and second inductors <NUM> and <NUM> are chosen to achieve a passband covering the second frequency band.

The second mixer <NUM> is configured to receive the amplified signal in the second frequency band from the third transformer <NUM> and frequency upconvert the signal into an RF signal for transmission. The second mixer <NUM> may upconvert the signal by mixing the signal with a second local oscillator signal.

Each of the capacitors <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> may be implemented with a variable capacitor (shown in the example in <FIG>) or a fixed capacitor.

<FIG> shows an example in which the transmitter includes a power amplifier <NUM> and an antenna <NUM>. The input of the power amplifier <NUM> is coupled to the output of the first mixer <NUM> and the output of the power amplifier <NUM> is coupled to the antenna <NUM>. The input of the first mixer <NUM> is coupled to the second transformer <NUM> shown in <FIG>. In operation, the power amplifier <NUM> is configured to receive the RF signal output by the first mixer <NUM>, amplify the RF signal, and output the amplified RF signal to the antenna <NUM> for transmission. It is to be appreciated that the transmitter may include one or more additional components between the first mixer <NUM> and the antenna <NUM> not shown in <FIG>.

<FIG> shows an example in which the transmitter includes a splitter <NUM>, an antenna array <NUM> including multiple antennas <NUM>-<NUM> to <NUM>-n, and multiple transmit chains <NUM>-<NUM> to <NUM>-n according to certain aspects. The splitter <NUM> has an input coupled to the output of the first mixer <NUM> and multiple outputs. Each transmit chain <NUM>-<NUM> to <NUM>-n is coupled between a respective one of the outputs of the splitter <NUM> and a respective one of the antennas <NUM>-<NUM> to <NUM>-n.

In this example, each of the transmit chains <NUM>-<NUM> to <NUM>-n includes a respective phase shifter <NUM>-<NUM> to <NUM>-n and a respective power amplifier <NUM>-<NUM> to <NUM>-n. In each transmit chain <NUM>-<NUM> to <NUM>-n, the input of the respective phase shifter <NUM>-<NUM> to <NUM>-n is coupled to the respective output of the splitter <NUM>, the input of the respective power amplifier <NUM>-<NUM> to <NUM>-n is coupled to the output of the respective phase shifter <NUM>-<NUM> to <NUM>-n, and the output of the respective power amplifier <NUM>-<NUM> to <NUM>-n is coupled to the respective antenna <NUM>-<NUM> to <NUM>-n. Each phase shifter <NUM>-<NUM> to <NUM>-n is configured to shift the phase of the respective RF signal by a respective phase. Each power amplifier <NUM>-<NUM> to <NUM>-n is configured to amplify the signal from the respective phase shifter <NUM>-<NUM> to <NUM>-n and output the amplified signal to the respective antenna <NUM>-<NUM> to <NUM>-n for transmission. In operation, a beamformer (not shown) controls the phases of the phase shifters <NUM>-<NUM> to <NUM>-n to achieve a desired transmit beam direction for the antenna array <NUM> using beamforming.

<FIG> shows an example in which the transmitter includes a power amplifier <NUM> and an antenna <NUM>. The input of the power amplifier <NUM> is coupled to the output of the second mixer <NUM> and the output of the power amplifier <NUM> is coupled to the antenna <NUM>. The input of the second mixer <NUM> is coupled to the third transformer <NUM> shown in <FIG>. In operation, the power amplifier <NUM> is configured to receive the RF signal output by the second mixer <NUM>, amplify the RF signal, and output the amplified RF signal to the antenna <NUM> for transmission. It is to be appreciated that the transmitter may include one or more additional components between the second mixer <NUM> and the antenna <NUM> not shown in <FIG>.

<FIG> shows an example in which the transmitter includes a splitter <NUM>, an antenna array <NUM> including multiple antennas <NUM>-<NUM> to <NUM>-n, and multiple transmit chains <NUM>-<NUM> to <NUM>-n according to certain aspects. The splitter <NUM> has an input coupled to the output of the second mixer <NUM> and multiple outputs. Each transmit chain <NUM>-<NUM> to <NUM>-n is coupled between a respective one of the outputs of the splitter <NUM> and a respective one of the antennas <NUM>-<NUM> to <NUM>-n.

<FIG> is a diagram of an environment <NUM> that includes an electronic device <NUM> that includes a wireless transceiver <NUM>. The wireless transceiver <NUM> may include the any one or more of the systems illustrated in <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>. In the environment <NUM>, the electronic device <NUM> communicates with a base station <NUM> through a wireless link <NUM>. As shown, the electronic device <NUM> is depicted as a smart phone. However, the electronic device <NUM> may be implemented as any suitable computing or other electronic device, such as a cellular base station, broadband router, access point, cellular or mobile phone, gaming device, navigation device, media device, laptop computer, desktop computer, tablet computer, server computer, network-attached storage (NAS) device, smart appliance, vehicle-based communication system, Internet of Things (IoT) device, sensor or security device, asset tracker, and so forth.

The base station <NUM> communicates with the electronic device <NUM> via the wireless link <NUM>, which may be implemented as any suitable type of wireless link. Although depicted as a base station tower of a cellular radio network, the base station <NUM> may represent or be implemented as another device, such as a satellite, terrestrial broadcast tower, access point, peer to peer device, mesh network node, fiber optic line, another electronic device generally as described above, and so forth. Hence, the electronic device <NUM> may communicate with the base station <NUM> or another device via a wired connection, a wireless connection, or a combination thereof. The wireless link <NUM> can include a downlink of data or control information communicated from the base station <NUM> to the electronic device <NUM> and an uplink of other data or control information communicated from the electronic device <NUM> to the base station <NUM>. The wireless link <NUM> may be implemented using any suitable communication protocol or standard, such as 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE, 3GPP NR <NUM>), IEEE <NUM>, IEEE <NUM>, Bluetooth™, and so forth.

The electronic device <NUM> includes a processor <NUM> and a memory <NUM>. The memory <NUM> may be or form a portion of a computer readable storage medium. The processor <NUM> may include any type of processor, such as an application processor or a multi-core processor, that is configured to execute processor-executable instructions (e.g., code) stored by the memory <NUM>. The memory <NUM> may include any suitable type of data storage media, such as volatile memory (e.g., random access memory (RAM)), nonvolatile memory (e.g., Flash memory), optical media, magnetic media (e.g., disk or tape), and so forth. In the context of this disclosure, the memory <NUM> is implemented to store instructions <NUM>, data <NUM>, and other information of the electronic device <NUM>, and thus when configured as or part of a computer readable storage medium, the memory <NUM> does not include transitory propagating signals or carrier waves.

The electronic device <NUM> may also include input/output (I/O) ports <NUM>. The I/O ports <NUM> enable data exchanges or interaction with other devices, networks, or users or between components of the device.

The electronic device <NUM> may further include a signal processor (SP) <NUM> (e.g., such as a digital signal processor (DSP)). The signal processor <NUM> may function similar to the processor and may be capable executing instructions and/or processing information in conjunction with the memory <NUM>.

For communication purposes, the electronic device <NUM> also includes a modem <NUM>, the wireless transceiver <NUM>, and one or more antennas (e.g., the antenna <NUM>, the antenna <NUM>, the antenna array <NUM> and/or the antenna array <NUM>). The wireless transceiver <NUM> provides connectivity to respective networks and other electronic devices connected therewith using RF wireless signals. The wireless transceiver <NUM> may facilitate communication over any suitable type of wireless network, such as a wireless local area network (LAN) (WLAN), a peer to peer (P2P) network, a mesh network, a cellular network, a wireless wide area network (WWAN), a navigational network (e.g., the Global Positioning System (GPS) of North America or another Global Navigation Satellite System (GNSS)), and/or a wireless personal area network (WPAN).

The controller <NUM> may be implemented with a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete hardware components (e.g., logic gates), or any combination thereof designed to perform the functions described herein. A processor may perform the functions described herein by executing software comprising code for performing the functions. The software may be stored on a computer-readable storage medium, such as a RAM, a ROM, an EEPROM, an optical disk, and/or a magnetic disk.

<FIG> illustrates a method <NUM> for operating an apparatus according to certain aspects. The apparatus includes a first amplifier (e.g., first amplifier <NUM>), and a transformer (e.g., switchable transformer <NUM>) including a first switchable inductor (e.g., first switchable inductor <NUM>) coupled to the first amplifier, a second switchable inductor (e.g., second switchable inductor <NUM>) magnetically coupled to the first switchable inductor, and a third switchable inductor (e.g., third switchable inductor <NUM>) magnetically coupled to the first switchable inductor.

At block <NUM>, in a first mode, the first switchable inductor is switched to a first inductance. For example, the first switchable inductor may be switched to the first inductance by the switching circuit <NUM>.

At block <NUM>, in the first mode, the second switchable inductor is enabled. For example, the second switchable inductor may be enabled by closing the switch <NUM>. In this example, the switch <NUM> may be closed by the controller <NUM>.

At block <NUM>, in the,first mode, the third switchable inductor is disabled. For example, the third switchable inductor may be disabled by opening the switch <NUM>. In this example, the switch <NUM> may be opened by the controller <NUM>.

At block <NUM>, in a second mode, the first switchable inductor is switched to a second inductance. For example, the first switchable inductor may be switched to the second inductance by the switching circuit <NUM>.

At block <NUM>, in the second mode, the second switchable inductor is disabled. For example, the second switchable inductor may be disabled by opening the switch <NUM>. In this example, the switch <NUM> may be opened by the controller <NUM>.

At block <NUM>, in the second mode, the third switchable inductor is enabled. For example, the third switchable inductor may be enabled by closing the switch <NUM>. In this example, the switch <NUM> may be closed by the controller <NUM>.

It is to be appreciated that the present disclosure is not limited to the exemplary terminology used above to describe aspects of the present disclosure. For example, an inductor of a transformer may also be referred to as a winding or another term. Also, it is to be appreciated that an inductor may be referred to as a coil even in cases where the inductor is not physically implemented with a coil. It is also to be appreciated that magnetic coupling may also be referred to as inductive coupling or another term.

It is to be appreciated that any of the switches discussed above may be implemented with one or more n-type field effect transistors (NFETs), one or more p-type field effect transistors (PFETs), a transmission gate, or another type of switch. For an example of a switch implemented with an NFET, the switch is turned on by applying a high voltage (e.g., supply voltage) to the gate of the NFET and turned off by applying a low voltage (e.g., ground) to the gate of the NFET. For an example of a switch implemented with a PFET, the switch is turned off by applying a high voltage (e.g., supply voltage) to the gate of the PFET and turned on by applying a low voltage (e.g., ground) to the gate of the PFET.

The term "coupled" is used herein to refer to the direct or indirect electrical coupling between two structures. It is also to be appreciated that the term "ground" may refer to a DC ground or an AC ground, and thus the term "ground" covers both possibilities. It is also to be appreciated that an "inductor" may include multiple inductors coupled in series. It is also to be appreciated than an "input" may be a single-ended input, a differential input, or one of two inputs of a differential input, and an "output" may be a single-ended output, a differential output, or one of two outputs of a differential output.

Claim 1:
An apparatus, comprising:
a first amplifier (<NUM>) having a first output (<NUM>) and a second output (<NUM>),
wherein the first amplifier is configured to amplify input signals in at least a first frequency band and a second frequency band;
a transformer (<NUM>) comprising:
a first switchable inductor (<NUM>) coupled between the first output and the second output;
a first capacitor (<NUM>) coupled in parallel with the first switchable inductor;
a second switchable inductor (<NUM>) magnetically coupled to the first switchable inductor, wherein the second switchable inductor comprises at least one first inductor (<NUM>, <NUM>) and at least one first switch (<NUM>) coupled in series with the at least one inductor;
a second capacitor (<NUM>) coupled in parallel with the second switchable inductor;
a third switchable inductor (<NUM>) magnetically coupled to the first switchable inductor, wherein the third switchable inductor comprises at least one second inductor (<NUM>, <NUM>) and at least one second switch (<NUM>) coupled in series with the at least one second inductor; and
a third capacitor (<NUM>) coupled in parallel with the third switchable inductor; and
a controller (<NUM>) configured to:
in a first mode, switch the first switchable inductor to a first inductance, enable the second switchable inductor using the at least one first switch, and disable the third switchable inductor using the at least one second switch; and
in a second mode, switch the first switchable inductor to a second inductance, disable the second switchable inductor using the at least one first switch, and enable the third switchable inductor using the at least one second switch;
wherein in the first mode, the first switchable inductor, the first capacitor (<NUM>), the second capacitor (<NUM>), and the second switchable inductor together form a first bandpass filter configured to cover the first frequency band, and wherein in the second mode, the first switchable inductor, the first capacitor (<NUM>), the third capacitor (<NUM>),
and the third switchable inductor together form a second bandpass filter configured to cover the second frequency band.