Patent Application
20240250644
In wireless communication devices, a radio frequency (RF) front end module processes modulated RF signals that are received from an antenna or to be transmitted by an antenna. In the transmission path, an RF front end module often has one or more RF power amplifiers that amplify the power of the RF signals to a level suitable for transmission. Ideally, the output level of an RF power amplifier and the input level of the RF power amplifier manifest a linear relationship in the frequency range of the RF signals. In reality, however, the linearity of an RF power amplifier may be undermined due to various factors.
The subject matter disclosed herein relates to thermally-adjustable direct current (DC) bias circuitry for an RF front end module having one or more RF power amplifiers, referred to as RF front end power amplifier module. The DC bias circuitry offers improved RF front end performance. The DC bias circuitry also offers flexibility for circuit designers to adjust the DC control voltage or current applied to RF amplifiers to track the thermal behavior of the RF amplifiers, with minimal RF interference to bias reference device.
In general, in some aspects, the subject matter of the present disclosure can be embodied in a circuit. The circuit includes: an RF amplifier including one or more RF transistors; a DC power source electrically coupled to the RF amplifier; a bias control input that receives a bias control signal from a bias control circuit, where the bias control input is electrically coupled to the DC power source; and a thermal tracking circuit located at a distance from the one or more RF transistors such that RF interference between the one or more RF transistors and the thermal tracking circuit is below a threshold interference during operation of the circuit. The thermal tracking circuit includes one or more heating elements, a DC bias reference device, and a thermal tracking control circuit electrically coupled to the DC power source and to the one or more heating elements. The thermal tracking control circuit generates a thermal tracking control signal that controls a thermal behavior of the one or more heating elements. The one or more heating elements are arranged to heat the DC bias reference device when the one or more heating elements are activated. The DC bias reference device is electrically coupled to the bias control input and configured to modulate a bias voltage of the RF amplifier.
In some implementations, the bias control signal and the thermal tracking control signal are synchronized with a pulse signal.
In some implementations, the one or more heating elements include two or more heating transistors, which may surround the DC bias reference device.
In some implementations, the DC power source is electrically coupled to the RF amplifier via a coupling transistor, which is controlled by the bias control signal.
In some implementations, the DC bias reference device includes a DC bias reference transistor.
In some implementations, the distance is determined based at least on an operating frequency of the RF amplifier, a thermal radiation of the one or more RF transistors, or a size constraint of the circuit.
In some implementations, the bias control circuit is configured to control the DC power source to provide the bias voltage at a predetermined time before the RF amplifier receives an RF signal.
In some aspects, the above-described circuit is included in an apparatus as one of a plurality of amplification stages.
In some aspects, the subject matter of the present disclosure can be embodied in a method for tracking a thermal behavior of an RF amplifier in a circuit. The method includes controlling, via a bias control signal, a DC power source electrically coupled to the RF amplifier. The method includes controlling, via a thermal tracking control signal, the DC power source to supply power to one or more heating elements. The thermal tracking control signal controls a thermal behavior of the one or more heating elements. The method also includes modulating a bias voltage of the RF amplifier based on an output of a DC bias reference device. The one or more heating elements are arranged to heat the DC bias reference device when the one or more heating elements are activated. The DC bias reference device is located at a distance from one or more RF transistors of the RF amplifier such that RF interference between the one or more RF transistors and the DC bias reference device is below a threshold interference during operation of the circuit.
In some implementations, the bias control signal and the thermal tracking control signal are synchronized with a pulse signal.
In some implementations, the one or more heating elements include two or more heating transistors, which may surround the DC bias reference device.
In some implementations, the DC power source is electrically coupled to the RF amplifier via a coupling transistor, which is controlled by the bias control signal.
In some implementations, the DC bias reference device includes a DC bias reference transistor.
In some implementations, the method further includes determining the distance based at least on an operating frequency of the RF amplifier, a thermal radiation of the one or more RF transistors, or a size constraint of the circuit.
In some implementations, the bias control signal controls the DC power source to provide the bias voltage at a predetermined time before the RF amplifier receives an RF signal.
The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of these systems and methods will be apparent from the description and drawings, and from the claims.
An RF amplifier, such as an RF power amplifier, can operate in various modes depending on wireless communication technologies. In some technologies that utilize Time Division Duplex (TDD), the RF power amplifier is configured to operate in a pulse mode in which the RF power amplifier is turned on and off very rapidly. In particular, for a bipolar junction transistor (BJT)-based RF power amplifier, a bias control circuit can control a DC power source to supply a bias voltage to one or more BJTs (“RF BJTs” or “RF transistors” hereinafter) of the RF power amplifier, thereby controlling the operation of the RF power amplifier. When the RF power amplifier operates in the pulse mode, the bias voltage quickly increases to a relatively high level at the rising edge of a pulse, and quickly drops to a relatively low level at the falling edge of the pulse.
When the RF BJTs are properly biased, the transfer characteristics of the RF BJTs are expected to be linear, and the RF power amplifier is expected to amplify the input RF signals properly. However, because the pulse mode causes rapid in-flow and out-flow of electric currents to and from the RF BJTs, the RF BJTs' temperature can change drastically between two consecutive pulses. The change of temperature can lead to changes of physical properties of the RF BJTs, causing the transfer characteristics of the RF BJTs to shift. As a result, the RF power amplifier can experience degraded linearity, which further leads to degraded communication quality, such as signal distortion and spurious emission.
To mitigate the degraded linearity, an RF front end power amplifier module can use a DC bias reference device (e.g., one or more non-RF transistors) to track the thermal behavior (e.g., heating or cooling) of the RF BJTs. For example, the DC bias reference device can be placed very close to the RF power amplifier such that the temperature change of the RF BJTs is reflected on the DC bias reference device, causing the physical properties of the DC bias reference device to change. The DC bias reference device thus can provide a bias control signal that changes according to the thermal behavior of the RF BJTs so as to modulate the bias voltage. The modulated bias voltage, possibly accompanied by a digital control signal, can compensate the shift of RF BJTs' transfer characteristics and reduce the degradation of linearity.
While the above mechanism can be helpful in tracking the thermal behavior of the RF BJTs, disposing the DC bias reference device close to the RF BJTs can lead to unwanted RF interference between the RF power amplifier and the DC bias reference device. For example, due to the close proximity of the RF power amplifier, the RF emissions from the RF power amplifier transistor can be captured by the DC bias reference device, leading to unwanted RF modulated bias voltage and/or current. Such unwanted bias voltage and/or current can cause signal distortion and RF noise in the RF power amplifier.
In view of the challenges above, implementations of this disclosure provide a thermally adjustable DC bias circuitry that places the DC bias reference device at a distance from the RF power amplifier. Instead of being directly thermally coupled to the RF BJTs, the DC bias reference device is thermally coupled to one or more heating elements configured to emulate the thermal behavior of the RF BJTs. The one or more heating elements generate little or no RF emission. Moreover, the one or more heating elements can be independently controlled by an external control signal to adjust their thermal behaviors. By keeping the distance large enough to avoid interference with the RF power amplifier, the DC bias reference device can still modulate the bias voltage to improve the linearity of the RF power amplifier, with improved RF signal quality and reduced noise within the RF power amplifier.
In the example of
In some implementations, the at least one WWAN with which the at least one base station 120 is associated can be a fifth generation (5G) network among other generations and types of networks. In these implementations, the at least one base station 120 can be a 5G base station that employs orthogonal frequency-division multiplexing (OFDM) and/or non-OFDM and a transmission time interval (TTI) shorter than 1 ms (e.g. 100 or 200 microseconds), to communicate with wireless devices, such as wireless device 110. For example, the at least one base station 120 can take the form of one of several devices, such as a base transceiver station (BTS), a Node-B (NodeB), an evolved NodeB (eNB), a next (fifth) generation (NR) NodeB (gNB), a Home NodeB, a Home eNodeB, a site controller, an access point, a wireless router, a server, router, switch, or other processing entity with a wired or wireless network.
System 100 can use multiple channel access functionality, including for example schemes in which the at least one base station 120 and the wireless device 110 are configured to implement the Long Term Evolution wireless communication standard (LTE), LTE Advanced (LTE-A), and/or LTE Multimedia Broadcast Multicast Service (MBMS). In other implementations, the at least one base stations 120 and wireless device 110 are configured to implement UMTS, HSPA, or HSPA+ standards and protocols. Of course, other multiple access schemes and wireless protocols can be utilized. In some examples, one or more such access schemes and wireless protocols can correspond to standards that impose RF power amplifier linearity requirements.
In addition, and as shown in
To communicate with one or both of the at least one base station 120 and the access point 130, the wireless device 110 can include singular or multiple transmitter and receiver components similar or equivalent to one or more of those described in further detail below with reference to
Although
The processor 240 can implement various processing operations of the wireless device 110. For example, the processor 240 can perform signal generation, signal coding, signal analysis, data processing, power control, input/output processing, or any other functionality enabling the wireless device 110 to operate in a communication system, such as system 100 (
The transmitter 210 can be configured to modulate data or other content, filter and amplify outgoing RF signals for transmission by at least one antenna 250A. In some implementations, the transmitter 210 can also be configured to amplify, filter and upconvert baseband or intermediate frequency (IF) signals to RFs signals before such signals are provided to the antenna 250A for transmission. The transmitter 210 can include any suitable structure for generating RF signals for wireless transmission. Additional aspects of the transmitter 210 are described in further detail below with reference to components 212-218 as depicted in
The receiver 220 can be configured to demodulate data or other content received in incoming RF signals by at least one antenna 250B. In some implementations, the receiver 220 can also be configured to amplify, filter and frequency down convert RF signals received via the antenna 250B either to IF or baseband frequency signals prior to conversion to digital form and processing. The receiver 220 can include any suitable structure for processing signals received wirelessly.
Each of the antennas 250A and 250B can include any suitable structure for transmitting and/or receiving wireless RF signals. In some implementations, the antennas 250A and 250B can be implemented by way of a single antenna that can be used for both transmitting and receiving RF signals.
One or multiple transmitters 210, one or multiple receivers 220, and one or multiple antennas 250 could be used in the wireless device 110. For example, in one implementation, device 110 includes at least three transmitters 210 and at least three receivers 220 for communicating via at least a personal area network such as Bluetooth®, a Wi-Fi network such as an IEEE 802.11 based network, and a cellular network. Each transmitter 210 may employ the concepts of the present disclosure. Although shown as separate blocks or components, at least one transmitter 210 and at least one receiver 220 could be combined into a transceiver. Each transceiver may employ the concepts of the present disclosure. Accordingly, rather than showing a separate block for the transmitter 210 and a separate block for the receiver 220 in
The wireless device 110 further includes one or more input/output devices 260. The input/output devices 260 facilitate interaction with a user. Each input/output device 260 includes any suitable structure for providing information to or receiving information from a user, such as a speaker, microphone, keypad, keyboard, display, and/or touch screen.
In addition, the wireless device 110 includes at least one memory 230. The memory 230 stores instructions and data used, generated, and/or collected by the wireless device 110. For example, the memory 230 could store software or firmware instructions executed by the processor(s) 240 and data used to reduce or eliminate interference in incoming signals. Each memory 230 includes any suitable volatile and/or non-volatile storage and retrieval device(s). Any suitable type of memory may be used, such as random access memory (RAM), read only memory (ROM), hard disk, optical disc, subscriber identity module (SIM) card, memory stick, secure digital (SD) memory card, and the like.
In some implementations, the transmitter 210 can include signal processing circuitry 212, modulation circuitry 214, and RF front end circuitry 217. The signal processing circuitry 212 may include one or more circuits that are configured to process signals received as input (e.g. from processor 240). For example, the signal processing circuitry 212 may include a digital-to-analog converter (D/A), which converts a digital input (e.g. a digital signal from processor 240) into an analog signal, which is then provided to a low pass filter, which filters the analog signal and provides the filtered analog signal to the modulation circuitry 214. The modulation circuitry 214, in addition to receiving the filtered analog signal from the signal processing circuitry 212, can, in some implementations, also receive a signal from a local oscillator 216 for modulating or adjusting the frequency of the analog signal, e.g., from a first frequency to a second frequency that is higher than the first frequency. For instance, the modulation circuitry 214 can include a mixer that frequency up-converts the filtered analog signal from a relatively low frequency (e.g. baseband frequency, or an IF that is offset from the baseband frequency) to a relatively high frequency RF signal. Thus, a signal from the local oscillator 216 is used as a carrier signal in transmitter 210. Moreover, as shown in
The RF signal amplified by the power amplifier may be filtered again by at least one additional filter downstream of the power amplifier before being provided as an output of the transmitter 210 to the at least one antenna 250A for wireless transmission. Such filter or filters can alternatively be provided upstream from the power amplifier in which case the output of the power amplifier is provided to the at least one antenna 250A for wireless transmission.
The RF power amplifier 310_1 can be, e.g., a class A, B, or C power amplifier, or an RF power amplifier of other types. As shown in
The power amplifier 310_1 is electrically coupled to the DC bias circuit 320A, which provides the power amplifier 310_1 with a DC bias voltage such that the one or more RF transistors Q1 are properly biased. As shown in
The bias control circuit 323 can have, e.g., control logic that implements communication protocols according to the RF signal at the input 391. Based on the communication protocols, a the bias control circuit 323 can generate a bias control signal Iref1 and input the bias control signal Iref1 to the DC bias circuit 320A to control when and how much to apply the DC bias voltage. For example, when the RF power amplifier 310_1 operates in the pulse mode, the bias control signal Iref1 can assert shortly before the RF signal reaches the input 391, thereby activating, via components such as a coupling transistor Q3 and a capacitor C3, the RF power amplifier 310_1 when the RF signal reaches the RF power amplifier 310_1. Similarly, the bias control signal Iref1 can drop at a predetermined time, such that the RF power amplifier 310_1 deactivates according to a predetermined duty cycle of the pulse.
The proximity of the reference device 330 (in particular, Q2) to the one or more RF transistors Q1 can help reduce the unwanted impact on the linearity of the RF power amplifier 310_1 due to drastic and frequent temperature changes of the one or more RF transistors Q1. This can be achieved, e.g., by placing the DC bias reference device 330 close to the one or more RF transistors Q1 through to track the thermal behaviors of Q1 in order to modulate the DC bias voltage or current.
As shown in
While ideally thermal coupling Q1 with Q2 in
At the outset, the DC bias circuit 420A of the RF front end power amplifier module 400A is similar to the DC bias circuit 320A in
The RF front end power amplifier module 400A has a DC bias reference device 430. Similar to the DC bias reference device 330 in
Compared with the position of the DC bias reference device 330, the relatively large distance between the DC bias reference device 430 and the RF power amplifier 410_1 can make the thermal coupling between the two weak and non-detectable. Therefore, in order for the DC bias reference device 430 to track the thermal behavior of the one or more RF transistors Q1, the RF front end power amplifier module 400A implements a thermal tracking circuit 450 that emulates the thermal behavior of the one or more RF transistors Q1. By placing the DC bias reference device 430 very close to the thermal tracking circuit 450, the temperature changes on the thermal tracking circuit 450 are reflected on Q2 via thermal coupling. As such, the DC bias reference device 430 can still track, though indirectly, the thermal behavior of the one or more RF transistors Q1. Furthermore, the thermal tracking can be readily and independently adjusted via the bias control signal Iref2 to a level that produces desired dynamic linearity performances.
The thermal tracking circuit 450 has one or more heating elements 440, such as transistors Q5. The collector of each transistor Q5 receives a DC voltage from a DC power source 441. The base of each transistor Q5 is biased, via components such as resistor R2, with a DC bias voltage from a DC power source 451. The thermal tracking circuit 450 receives a thermal tracking control signal Iref2 from a thermal tracking control circuit 453, which can be integrated with the thermal tracking circuit 450 or can be external to thermal tracking circuit 450. The thermal tracking control signal Iref2, which can be an analog signal in some implementations, modulates, via transistor Q6, the DC bias voltage applied on the base of transistors Q5. The thermal tracking circuit 450 can also include components such as one or more transistors Q7 and/or one or more capacitors C6.
As discussed previously, the thermal tracking circuit 450 simulates the thermal behavior of the one or more RF transistors Q1. To this end, the thermal tracking control circuit 453 can control the thermal tracking control signal Iref1, to be synchronized with the bias control signal Iref1. For example, both the bias control signal Iref2 and the thermal tracking control signal Iref2 can be synchronized with a pulse signal. The pulse signal can serve as a trigger signal, which asserts at a predetermined time before an incoming RF signal reaches the RF front end power amplifier module 400A. As such, when the bias control signal Iref1 modulates the DC bias voltage on the one or more RF transistors Q1 to activate Q1 (e.g., cause Q1 to heat up) or deactivate Q1 (e.g., cause Q1 to cool down), the thermal tracking control signal Iref2 contemporaneously modulates the DC bias voltage on the heating elements 440 to activate or deactivate the transistors Q5. Because the one or more DC bias reference transistors Q2 are located very close to (e.g., surrounded by or sandwiched by) the heating elements 440, the temperature changes on the heating elements 440 are reflected on the one or more DC bias reference transistors Q2 via thermal coupling. As such, the transfer characteristic of Q2 shifts according to the heating and cooling of the one or more RF transistors Q1, even if there is no detectable thermal coupling directly between Q2 and Q1. Similar to the mechanism described with reference to
The thermal tracking mechanism described with reference to
The thermal tracking mechanism described with reference to
While the RF front end power amplifier modules 400A and 400B use transistors Q5 as heating elements 440, other types of circuit components, such as resistors, can be used in other implementations, so long as the heating elements can be configured with similar thermal reactions to the thermal tracking control signal Iref2.
In addition, while the DC power sources 421, 441, and 451 are illustrated as separate instances and can vary in their output DC voltage, the DC power sources 421, 441, and 451 can be implemented as a single DC power source with the same output DC voltage. In some implementations, the DC power sources 421, 441, and 451 can include power pins that receive power from external power sources.
Furthermore, with respect to circuit components such as R0, R1, R2, C1, C3, C5, C6, Q3, Q6, and Q7, some implementations can have more or fewer instances of these components. For example, while
Additionally, while
At 502, the method 500 involves controlling, via a bias control signal, a DC power source electrically coupled to the RF amplifier. The controlling of the DC power source can be similar to the controlling of the DC power source 421 via the thermal tracking control signal Iref1, as described with reference to
At 504, the method 500 involves controlling, via a thermal tracking control signal, the DC power source to supply power to the one or more heating elements. In some implementations, the thermal tracking control signal controls a thermal behavior of the one or more heating elements, similar to the controlling of the thermal behavior of the heating elements 440 via the thermal tracking control signal Iref2, as described with reference to
At 506, the method 500 involves modulating a bias voltage of the RF amplifier based on an output of a DC bias reference device. In some implementations, the one or more heating elements are arranged to heat the DC bias reference device when the one or more heating elements are activated. Also, the DC bias reference device is located at a distance from one or more RF transistors of the RF amplifier such that RF interference between the one or more RF transistors and the DC bias reference device is below a threshold interference during operation of the circuit. The modulation of the bias voltage of the RF amplifier can be similar to the modulation of the bias voltage of the RF power amplifier 410_1, as described with reference to
While features described above are primarily implemented by wireless devices, these features can likewise be implemented by access nodes, base stations, or other types fixed or portable wireless communication equipment and/or infrastructure. For example, a base station in communication with a cellular phone can have RF front end circuitry that implements the above-described features with respect to thermally adjustable DC bias circuit.
While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular implementations of particular inventions. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially be claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.
Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system modules and components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.
In addition, techniques, systems, subsystems, and methods described and illustrated in the various implementations as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.
For purposes of this document, a connection may be a direct connection or an indirect connection (e.g., via one or more other parts). In some cases, when an element is referred to as being connected or coupled to another element, the element may be directly connected to the other element or indirectly connected to the other element via intervening elements. When an element is referred to as being directly connected to another element, then there are no intervening elements between the element and the other element. Two devices are “in communication” if they are directly or indirectly connected so that they can communicate electronic signals between them.
Particular implementations of the subject matter have been described. Other implementations are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results.
