Apparatus and method for fast phase locked loop (PLL) settling for cellular time-division duplex (TDD) communications systems

A communications device is disclosed that adjusts a target signal to allow a reference phase locked loop (PLL) to lock onto a reference signal that is related to a desired operating frequency in a first mode of operation. The reference PLL locks onto the reference signal when the target signal is calibrated to be proportional to the reference signal. As the communications device transitions between the first mode of operation and a second mode of operation, the communications device performs a shorten calibration cycle on the reference PLL. The reference phase locked loop (PLL) locks onto the reference signal in response to the shorten calibration cycle in the second mode of operation.

BACKGROUND

1. Field of Disclosure

The present disclosure relates generally to a phase locked loop (PLL) and specifically to calibration of a voltage controlled oscillator (VCO) for the cellular phone.

2. Related Art

Cellular phones have evolved from large devices that were only capable of analog voice communications to comparatively smaller devices that are capable of digital voice communications and digital data communications, such as Short Message Service (SMS) for text messaging, email, packet switching for access to the Internet, gaming, Bluetooth, and Multimedia Messaging Service (MMS) to provide some examples. In addition to these capabilities, the cellular phones of today have additional non-communication related capabilities, such as a camera with video recording, an MPEG-1 Audio Layer 3 (MP3) player, and software applications such as a calendar and a phone book, to provide some examples. Even in light of these capabilities, manufacturers of cellular phones are placing even more capabilities into cellular phones and making these more powerful cellular phones smaller.

At the heart of each cellular phone lies a phase locked-loop (PLL). The PLL is responsible for providing an appropriate transmit frequency for the cellular phone prior to commencement of a transmit mode of operation. The PLL is also responsible for providing an appropriate receive frequency for the cellular phone prior to commencement of a receive mode of operation. In order to properly provide the appropriate transmit and/or receive frequency for the cellular phone, a voltage controlled oscillator (VCO) located within the PLL is calibrated to the appropriate transmit and/or receive frequency of the cellular phone. Once the VCO is initially calibrated to be sufficiently proportional to a frequency and/or a phase of a reference frequency, the PLL locks the frequency of the VCO to be proportional to the frequency and/or the phase of the reference frequency to provide the appropriate transmit and/or receive frequency. Often, additional calibration of the VCO following the initial calibration is often required to ensure that the VCO is sufficiently proportional to the frequency and/or the phase of the reference frequency to the appropriate transmit and/or receive frequency. For example, an additional calibration may be required once the cellular phone transitions from the transmit mode of operation to the receive mode of operation and/or from the receive mode of operation to the transmit mode of operation.

Communications standards provide a certain time window for an initial calibration of the VCO. However, in certain communications standards often do not provide sufficient time for the additional calibration, which is typically necessary when the cellular phone transitions from the transmit mode of operation to the receive mode of operation and/or from the receive mode of operation to the transmit mode of operation. As a result, the cellular phone may not be aligned to the appropriate receive frequency when the cellular phone switches from the transmit mode of operation to the receive mode of operation, for example.

Thus, there is a need to calibrate the VCO following the initial calibration when transitioning from the transmit mode of operation to the receive mode of operation and/or from the receive mode of operation to the transmit mode of operation to the appropriate transmit and/or receive frequency of the cellular phone but to do so within the time allotted in the respective communications standard. Further aspects and advantages of the present disclosure will become apparent from the detailed description that follows.

The present disclosure will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.

DETAILED DESCRIPTION OF THE PRESENT DISCLOSURE

Embodiments of this disclosure include three calibration types in which a communications device may calibrate a phase locked loop (PLL). The three calibration types include a full calibration, a fine calibration, and an offset calibration. The full calibration is to be used by the communications device during a first engagement and/or any subsequent engagement of a communication channel by the communications device. The fine calibration is to be used by the communications device when there is short but sufficient time provided for the communications device to transition between modes of operation. Typically, the time provided for the communications device is determined by the communications standard. The fine calibration includes a scaled down version of the full calibration and optionally applying a pre-determined offset to compensate for the transitioning between the modes of operation. The offset calibration is to be used by the communications device when limited time is provided for the communications device to transition between the modes of operation. The offset calibration includes applying a pre-determined offset to compensate for the transitioning between the modes of operation.

The exemplary embodiments described herein are provided for illustrative purposes, and are not limiting. Other exemplary embodiments are possible, and modifications may be made to the exemplary embodiments within the spirit and scope of the present disclosure. Therefore, the Detailed Description is not meant to limit the present disclosure. Rather, the scope of the present disclosure is defined only in accordance with the following claims and their equivalents.

An Exemplary Communications Device

FIG. 1illustrates a block diagram of a communications device according to an exemplary embodiment of the present disclosure. A communications device100calibrates a reference phase lock loop (PLL)108to provide a target signal156that is sufficiently proportional to a reference signal154. In this situation, the reference PLL108is characterized as being in a locked condition whereby the target signal156essentially tracks the reference signal154. For example, the target signal156essentially tracks a phase of the reference signal154in the locked condition. However, if the target signal156is not sufficiently proportional to the reference signal154, the target signal156does not track the reference signal154. In this situation, the reference PLL108is characterized as being in an unlocked condition.

The communications device100uses the target signal156as a reference signal for a receiver118in a receive mode of operation and as a reference signal for a transmitter116in a transmit mode of operation. In the receive mode of operation, the receiver118is used as a means to receive communications signals from a communications channel. While the transmitter116is used as a means to transmit communications signals onto the communications channel in the transmit mode of operation.

The communications device100calibrates the reference PLL108in either the receive mode of operation or the transmit mode of operation. As to be further discussed below, the communications device100adjusts the calibration of the reference PLL108to cause the reference PLL108enter into the locked condition after switching from the receive mode of operation to the transmit mode of operation and/or from the transmit mode of operation to the receive mode of operation. The communications device100adjusts the calibration of the target signal156within the time allowed by a communications standard such as Second-Generation Wireless Telephone Technology (2G), Third-Generation Wireless Telephone Technology (3G), Long Term Evolution Frequency-Division Duplexing (LTE MD), Long Term Evolution Time-Division Duplexing (LTE TDD), and Time Division Synchronous Code Division Multiple Access (TD-SCDMA) and/or any other suitable communications standard that will be apparent to those skilled in the relevant art(s) without departing from the spirit and scope of the present disclosure.

As shown inFIG. 1, the communications device100includes a reference oscillator102, the reference PLL108, a switching module110, the transmitter116, the receiver118, and a controller module120. The reference oscillator102provides the reference signal154to the reference PLL108. The reference signal154is related to a desired operating frequency of the communications device100. For example, a frequency of the reference signal154may be approximately equal or an integer or fractional multiple of the desired operating frequency of the communications device100. The reference oscillator102includes an oscillator104and an optional scaling module106. The oscillator104provides a reference signal150. The optional scaling module106multiplies and/or divides the reference signal150to generate the reference signal154.

As discussed above, the reference PLL108provides the target signal156that essentially tracks the reference signal154in the locked condition. For example, the reference PLL108causes a frequency and/or a phase of the target signal156to be approximately equal to a frequency and/or a phase of the target signal156. As another example, the reference PLL108causes the phase of the target signal156to be approximately equal to the phase of the target signal156and the frequency of the target signal156to be proportional to, namely an integer or fractional multiple of, the frequency of the target signal156.

The switching module110may provide the target signal156as a transmit reference signal162to the transmitter116in the transmit mode of operation or as a receive reference signal164to the receiver118in the receive mode of operation. The reference PLL108provides a synthesized transmit signal162to the transmitter116that may be used to upconvert, to modulate, and/or to encode signals for transmission onto the communications channel. Similarly, the reference PLL108provides a synthesized receive signal164to the receiver118that may be used to downconvert, to demodulate, and/or to decode signals that are received from the communications channel.

The controller module120calibrates the reference PLL108as the communications device100engages the communications channel in a first mode of operation, such as the receive mode of operation to provide an example, and calibrates the reference PLL108as the communications device100switches from the first mode of operation to a second mode of operation, such as the transmit mode of operation. The controller module120monitors an appropriate tuning signal168of the reference PLL108which is indicative of a difference between the reference signal154and the target signal156. The controller module120adjusts the control signal166during various calibrations, that are to be discussed below.

The controller module120initially calibrates the reference PLL108to provide the target signal156that is proportional to the frequency and/or the phase of the reference signal154when the communications device100engages the communications channel. During this initial or full calibration, the controller module120executes an extensive calibration cycle to calibrate the reference PLL108such that it locks onto the reference signal154. Typically, this full calibration involves aligning the frequency and/or the phase of the target signal156to be sufficiently proportional to the frequency and/or the phase of the reference signal154such that the reference PLL108may lock onto the reference signal154. The full calibration of the reference PLL108may consume a large quantity of time in order to properly calibrate the target signal156. For example, the TD-SCDMA communications standard allows at most 120 microseconds to perform the full calibration when the communications device100engages the communications channel.

Typically, the controller module120performs the full calibration while the communications device100is operating in the first mode of operation, such as the receive mode of operation to provide an example. However, those skilled in the relevant art(s) will recognize that the controller module120may also perform the full calibration while the communications device100is operating in the transmit mode of operation without departing from the spirit and scope of the present disclosure. Following the initial engagement of the communications device100to the communications channel in the first mode of operation, the communications device100may transition from the first mode of operation to the second mode of operation, such as the transmit mode of operation to provide an example. Ideally, loading of the reference PLL108by the receiver118in the receive mode of operation is substantially similar to loading of the reference PLL108by the transmitter116in the transmit mode of operation. However, in practice, an input impedance of the transmitter synthesizer116differs from an input impedance of the receiver118. This difference between the input impedances of the transmitter116and the receiver118may cause the reference PLL108to enter into the unlocked condition as the communications device100transitions from the first mode of operation to the second mode of operation. In the unlocked condition, the target signal156does not track the reference signal154unless the controller module120performs another calibration of the reference PLL108to cause the reference PLL108to once again lock onto the reference signal154.

However, the controller module120may no longer have sufficient time to perform another full calibration of the reference PLL108when transitioning from the first mode of operation to the second mode of operation. The amount of time the communications device100may take in performing this transition is typically specified by various communications standards. The controller module120must perform this other calibration of the reference PLL108within these specified times which typically are significantly less than time required to perform the full calibration. For example, the TD-SCDMA communications standard requires the communications device100to transition from the transmit mode of operation to the receive mode of operation in approximately 12.5 microseconds; therefore, any calibration of the reference PLL108following a transition from the transmit mode of operation to the receive mode of operation must be done in 12.5 microseconds as compared to 120 microseconds allowed for the full calibration. Thus, a shortened calibration is required for the reference PLL108when transitioning from the first mode of operation to the second mode of operation.

The controller module120may perform the shortened calibration when transitioning from the first mode of operation to the second mode of operation. The shortened calibration allows for a quick adjustment of the target signal156while leaving sufficient time for the reference PLL108to settle to the locked condition. Some of the communications standards provide for a longer duration of time to transition from the first mode of operation to the second mode of operation when compared to other communications standards. For example, the TD-SCDMA communications standard allows 12.5 microseconds to calibrate when transitioning from the transmit mode of operation to the receive mode of operation and the LTE TDD communications standard allows 47 microseconds to calibrate when transitioning between these modes of operations.

The controller module120may perform a fine calibration for those communications standard that specify longer durations of time to transition from the first mode of operation to the second mode of operation and an offset calibration for those communications standard that specify shorter durations of time to transition from the first mode of operation to the second mode of operation. The controller module120performs the offset calibration by adjusting the control signal166by a predetermined amount. In an exemplary embodiment, the predetermined amount represents a pre-known shifting of the control signal166that results from transitioning between the first mode of operation and the second mode of operation. The pre-known shifting of the control signal166may be determined from an initial product evaluation of the communications device100to determine the shift of the control signal166as the communications device transitions.

For example, the controller module120calibrates the reference PLL108to provide the target frequency156at a first frequency in the receive mode of operation during the full calibration. In this example, the target frequency156shifts to a second frequency when the communications device100transitions from the first mode of operation to a second mode of operation. In this example, the controller module120performs the offset calibration to adjust the target frequency156from the second frequency to the first frequency. After adjusting the target signal156by a predetermined amount, the reference PLL108settles to the locked condition within the duration of time specified by the communications standards.

The fine calibration includes the offset calibration, as discussed above, as well as another adjustment of the target frequency156to compensate for operational conditions, such as temperature to provide an example, of the communications device100. Typically, this other adjustment takes sufficiently less time to perform than the full calibration. After adjusting the target signal156using the fine calibration, the reference PLL108settles to the locked condition within the duration of time specified by the communications standards.

Typically, the offset calibration is less precise than both the full calibration and the fine calibration but requires less time to complete than both the full calibration and the fine calibration. For example, the TD-SCDMA communications standard allows 75 microseconds to calibrate when switching from the receive mode of operation to the transmit mode of operation. The fine calibration may be completed within the 75 microseconds allowed. As a result, the controller module120may select the fine calibration over the offset calibration because the 75 microseconds may be sufficient to complete the fine calibration while providing a more precise calibration than the offset calibration. As another example, the TD-SCDMA communications standard limits the time to calibrate when switching from the transmit mode of operation to the receive mode of operation to 12.5 microseconds. The fine calibration may not be completed within the 12.5 microseconds allowed but the offset calibration may be completed within the 12.5 microseconds. As a result, the controller module120may select the offset calibration over the fine calibration.

An Exemplary Reference PLL

FIG. 2is a block diagram of a reference PLL that may be used in the communications device according to an exemplary embodiment of the present disclosure. A reference PLL200represents a closed-loop feedback control system that generates the target signal156in relation to a frequency and a phase of the reference signal154. In other words, the reference PLL200performs frequency multiplication and/or division, via a negative feedback mechanism, to generate the target signal156in terms of the reference signal154. The reference PLL200may be implemented using a phase/frequency detector (PFD)202, a charge pump204, a loop filter206, a voltage controlled oscillator (VCO)208, an optional integer frequency divider210, an optional dithering module212, and a controller214. The reference PLL200may represent an exemplary embodiment of the reference PLL108.

The PFD202converts a difference between the frequency and/or the phase of the reference signal154and a phase and/or a frequency of a divided feedback signal258into an error signal250. Specifically, the PFD202produces the error signal250by comparing the frequency and/or the phase of the divided feedback signal258and the frequency and/or the phase of the reference signal154to detect for deviations between the reference signal154and the divided feedback signal258. When the phase and the frequency of the error signal250and the phase and the frequency of the divided feedback signal258are substantially equivalent, the reference PLL200is in the locked condition. In the locked condition, the error signal250is proportional to the phase difference between the reference signal154and the divided feedback signal258.

The charge pump204converts the error signal250to a voltage/current domain representation, denoted as a charge pump output252, to control the frequency of the VCO208. When the reference PLL200is the unlocked condition, the charge pump204increases or decreases the charge pump output252based on the error signal250. When the reference PLL200is in the locked condition the error signal250is minimized and the charge pump204maintains the charge pump output252at a substantially fixed value.

The loop filter206may be used to remove undesirable noise from the charge pump output252to generate a tuning signal254. The loop filter206may be implemented as a low pass filter to suppress high frequency components in the charge pump output252to allow a direct current (DC), or near DC, component of the charge pump output252to control the VCO208. The loop filter206also maintains stability of the reference PLL200.

The VCO208is a voltage to frequency converter. Specifically, the VCO208produces the target signal156based upon the tuning signal254and the frequency control signal268. Typically, the controller214adjusts the frequency control signal268until the target signal156is sufficiently related to the reference signal154during the full calibration. For example, the controller214may cycle through different combinations of the frequency control signal268using a searching algorithm, such as a binary search tree algorithm, a recursion algorithm, a Stern-Brocot algorithm and/or any other suitable search that will be apparent to those skilled in the relevant art(s) without departing from the spirit and scope of the present disclosure until the target signal156is sufficiently related to the reference signal154. The tuning signal254is used to further adjust the target signal156until it is approximately equal or an integer or fractional multiple of the reference signal154. In an exemplary embodiment, the frequency control signal268used to coarsely steer the target signal156to be sufficiently related to the reference signal154to allow the VCO208to lock onto the reference signal154by finely steering the target signal156using the tuning signal254.

The optional integer frequency divider210is located in a feedback path of the reference PLL200. The optional integer frequency divider210divides the target signal156by an integer N to provide the divided feedback signal258. The optional integer frequency divider210may adjust the integer N in response to a channel transmission signal262.

The optional dithering module212allows the reference PLL200to dither the divide value over time between two or more integer values to obtain an effective time averaged fractional division factor. More specifically, the optional dithering module212selects between the two or more integer values for each iteration of the reference PLL200in response to a division code260, so that on average, a fractional division factor can be represented. The optional dithering module212generates the division code260in response to the divide ratio control signal262.

The controller module214calibrates the reference PLL200in one of the full calibration, the fine calibration, and/or the offset calibration. The controller module214illustrates an exemplary implementation of the full calibration, the fine calibration, and/or the offset calibration that were discussed above. The controller module214initially calibrates the reference PLL200to provide the target signal156that is proportional to the frequency and/or the phase of the reference signal154when a communications device, such as the communications device100to provide an example, engages a communications channel.

The controller module214may provide the channel transmission signal262that causes the optional dithering module212to provide the divide ratio control signal262that corresponds to the communications channel. The controller module214provides a first value for the frequency control signal268to cause the VCO208to provide the target signal156at a first frequency. The controller module214monitors the tuning signal254once the target signal156has reached the first frequency. The controller module214compares the tuning signal254to a predetermined tuning signal to determine whether the reference PLL200is in the locked condition. The predetermined tuning signal represents a pre-known tuning signal that is presented within the reference PLL200when the reference PLL200is the locked condition. For example, the pre-known tuning signal may represent a DC voltage when the reference PLL200is the locked condition. The controller module214compares a magnitude of a difference between the tuning signal254and the pre-known tuning signal to a locking threshold. When magnitude of the difference is less than or equal to the locking threshold, the target signal156is sufficiently related to the reference signal154. In this situation, the reference PLL200enters in the locked condition to track the reference signal154.

However, when the magnitude of the difference is greater than the locking threshold, the target signal156is not sufficiently related to the reference signal154. In this situation, the reference PLL200is in the unlocked condition. The controller module214then provides a second value for the frequency control signal268to cause the VCO208to provide the target signal156at a second frequency. The controller module214determines whether the second frequency causes the reference PLL200to enter into the locked condition. If not, the controller module214continues to adjust the frequency control signal268until the VCO208enters into the locked condition. However, this example is not limiting, those skilled in the relevant art(s) will recognize that other methods may be used in tuning the reference PLL200so that the reference PLL200enters into the locked condition.

After receiving communications signals from the communications channel in the receive mode of operation, the communications device may transition from the receive mode of operation to the transmit mode of operation. After transmitting communications signal onto the communications channel, the communications device may transition from the transmit mode of operation back to the receive mode of operation or engage another communications channel. As discussed above, the controller module214may calibrate the reference PLL200using the fine calibration, and/or the offset calibration while the communications device is transitioning between these modes of operation. Typically, selection of the fine calibration and or the offset calibration is based on the communications standard in which the communications device is operating.

For example, as shown inFIG. 3, the communications device may be operating in the LTE TDD standard. When the communications device transitions from the receive mode of operation to the transmit mode of operation, the LTE TDD standard allows 71.3 microseconds for the controller module214to calibrate the VCO208so that the reference PLL200locks onto the reference signal154. In this situation, the controller module214selects the fine calibration when the communications device is transitioning from the receive mode of operation to the transmit mode of operation.

As another example, also shown inFIG. 3, the communications device may be operating in the TD-SCDMA standard. When the communications device transitions from the transmit mode of operation to the receive mode of operation, the TD-SCDMA standard allows 12.5 microseconds for the controller module214to calibrate the VCO208so that the reference PLL200locks onto the reference signal154. In this situation, the controller module214selects the offset calibration when the communications device is transitioning from the transmit mode of operation to the receive mode of operation because the LTE TDD standard provides sufficient time to complete the offset calibration but not sufficient time to complete the fine calibration.

The controller module214performs the offset calibration by adjusting the target signal156by the predetermined amount that relates to a shifting of the target signal156that results from transitioning between modes of operation. Typically, the predetermined amount represents a predetermined voltage and/or current that is coupled onto the tuning signal254and/or shifting of the VCO tuning elements. This predetermined voltage, current, and/or VCO tuning elements shift the target signal156to accommodate for the difference that results from transitioning between modes of operation. After adjusting the target signal156by the predetermined amount, the reference PLL200settles to the locked condition within the duration of time specified by the communications standards.

The fine calibration includes the offset calibration, as discussed above, as well as another adjustment of the target frequency156to compensate for operational conditions, such as temperature and/or power supply to provide an example, of the communications device. The controller module214adjusts the target signal156by the predetermined amount in a substantially similar manner as the offset calibration. The controller module214additionally adjusts the target signal156to compensate for the operational conditions. Typically, this operational adjustment may be characterized as being similar to the full calibration, but scaled down. The controller module214provides a predetermined number of different values for the frequency control signal268to cause the VCO208to provide the target signal156at different frequencies. In an exemplary embodiment, the predetermined number of different values represents two different combinations of the searching algorithm. However, this example is not limiting, those skilled in the relevant art(s) will recognize that the predetermined number of different values may represent any suitable number of different combinations of the searching algorithm so long as the fine calibration is completed within the time allotted by the communications standard without departing from the spirit and scope of the present disclosure.

An Exemplary Calibration Requirement Table for Different Communications Standards

FIG. 3is a table that represents each type of calibration that may be used by the communications device for different communications standards according to an exemplary embodiment of the present disclosure.FIG. 3includes exemplary communications standards in which a communications device, such as the communications device100to provide an example may operate in; however, those skilled in the relevant art(s) will recognize that the communications device may operate in accordance with other communications standards without departing from the spirit and scope of the present disclosure.

For each communications standard,FIG. 3depicts the time allowed by each respective communications standard for a controller module, such as the controller module120or the controller module214to provide some examples, to calibrate a reference PLL, such as the reference PLL108or the reference PLL200to provide some examples. For example,FIG. 3depicts that the TD-SCDMA communications standard allows 200 microseconds for the controller module to properly calibrate the reference PLL when the communications device engages a communications channel. The 200 microseconds provided by the TD-SCDMA communications standard may be sufficient to perform the full calibration. However, the calibration period for the transition from the receive mode of operation to the transmit mode of operation provided by the TD-SCDMA is 75 microseconds. The 75 microseconds may be sufficient to perform the fine calibration but not sufficient to perform the full calibration. Further, the calibration period for the transition from the transmit mode of operation to the receive mode of operation provided by the TD-SCDMA is 12.5 microseconds. The 12.5 microseconds may be sufficient to perform the offset calibration but not sufficient to perform the full calibration and/or the fine calibration.

An Exemplary Voltage Controlled Oscillator (VCO)

FIG. 4Illustrates a Block Diagram of an Exemplary Voltage Controlled oscillator (VCO) that may be used in the communications device according to an exemplary embodiment of the present disclosure. A controller module, such as the controller module120or the controller module214to provide some examples, calibrates a VCO400in one of the full calibration, the fine calibration, and/or the offset calibration to provide target outputs452.1and452.2. The target outputs452.1and452.2represent an exemplary embodiment of the target output156. The VCO400includes a fine frequency component402and a course frequency component404which operate in conjunction with each other to provide the target signal156.

The fine frequency component402includes a first fine capacitor406.1, a second fine capacitor406.2, and a varactor diode408. As shown inFIG. 4, the tuning signal254is applied to the varactor diode408. The varactor diode408represents a variable capacitance whose capacitance is a function of the tuning signal254. The first fine capacitor406.1and the second fine capacitor406.2are coupled to the varactor diode408to isolate the tuning signal254from the course frequency component404. Typically, the first fine capacitor406.1and the second fine capacitor406.2represent large capacitors when compared to the varactor diode408such that a capacitance of the fine frequency component402is dominated by the varactor diode408.

The coarse frequency component404includes transistor switches410.1through410.n, first capacitors412.1through412.n, second capacitors414.1through414.n, a first inductor416.1and a second inductor416.2. The switches410.1through410.ncause their corresponding first capacitors412.1through412.nand second capacitors414.1through414.nto contribute to a capacitance of the coarse frequency component404when activated by a corresponding frequency control signal450.1through450.n. The frequency control signals450.1through450.nrepresent an exemplary embodiment of the frequency control signal268. In other words, the first capacitors412.1through412.nand second capacitors414.1through414.nare switched in and out of the coarse frequency component404by their corresponding switches410.1through410.n. In an exemplary embodiment, the coarse frequency component404may include first capacitors412.1through412.8and second capacitors414.1through414.8. Those capacitors that are switched in the course frequency component404contribute to the capacitance of the course frequency component404while those capacitors that are switched out of the course frequency component404do not. The first inductor416.1, the second inductor416.2, and the first capacitors412.1through412.nand the second capacitors414.1through414.nthat are switched in the course frequency component404are configured and arranged to form a resonant circuit.

The VCO400may include an oscillator core formed by the transistors418.1and418.2, and a biasing current source420.

The controller module provides various frequency control signal450.1through450.nto switch various first capacitors412.1through412.nand various second capacitors414.1through414.nin and out of the coarse frequency component404during the full calibration. The various frequency control signals450.1through450.nare determined in accordance with the searching algorithm. The switching in and out of the first capacitors412.1through412.nand the second capacitors414.1through414.nin this manner adjusts a frequency of the target outputs452.1and452.2. Typically, the frequency of the target outputs452.1and452.2is inversely related to the capacitance of the coarse frequency component404. The controller module continuously switches the first capacitors412.1through412.nand the second capacitors414.1through414.nin accordance with the searching algorithm until the target outputs452.1and452.2are sufficiently related to the reference signal154to allow the VCO400to lock onto the reference signal154by finely adjusting the capacitance of the fine frequency component402using the tuning signal254.

The controller module adjusts the capacitance of the fine frequency component402and/or adjusts frequency control signals450.1through450.nby the predetermined amount during the offset calibration.

The controller module adjusts the capacitance of the fine frequency component402by the predetermined amount and adjusts the frequency control signals450.1through450.nby enabling a scaled down version of the full calibration cycle to adjust the capacitance of the coarse frequency component404during the fine calibration.

An Exemplary Operational Control Flow of the Communication Device

FIG. 5is a flowchart of exemplary operational steps of the communications device according to an exemplary embodiment of the present disclosure. The present disclosure is not limited to this operational description. Rather, it will be apparent to persons skilled in the relevant art(s) from the teachings herein that other operational control flows are within the scope and spirit of the present disclosure. The following discussion describes the steps inFIG. 5.

At step510, the operational control flow determines a communications channel from among a plurality of communications channels that is to be used by a communications device to transmit and/or receive a communications signal.

At step520, the operational control flow performs the full calibration to calibrate the communications device for the communications channel. Specifically, the operational control flow adjusts a reference PLL, such as the reference PLL108or the reference PLL200to provide some examples, within the communications device to lock onto a reference signal, such as reference signal154to provide an example.

At step530, the operational control flow receives the communications signal from step510from the communications channel from step510and/or transmits the communications signal from step510onto the communications channel from step510.

At step540, the operational control flows determines whether the communications device is to select another communications channel from among the plurality of communications channels or to transition from the receive mode of operation to the transmit mode of operation or from the transmit mode of operation to the receive mode of operation. For example, the operational control flow determines whether the communications device is to subsequently transmit another communications onto the communications channel from step510after receiving the communications signal from step510from the communications channel from step510. As another example, the operational control flow determines whether the communications device is to subsequently receive another communications from the communications channel from step510after transmit the communications signal from step510onto the communications channel from step510.

The operational control flow proceeds to step550to transition between these modes of operation or reverts back to step510to select another communications channel.

At step540, the operational control flow determines whether the communications device is to transition between the modes of operation of step530. If so, the operational control flow proceeds to step550, otherwise, the operational control reverts to step510to determine another communications signal.

At step550, the operational control flow determines the operation transition time allowed by a communications standard. For example, the operational control flow transitions from the transmit mode of operation to the receive mode of operation while operating in the TD-SCDMA communications standard. In this example, the operational control flow determines the transition time allowed by the TD-SCDMA communications standard to transition from the transmit mode of operation to the receive mode of operation which is approximately 12.5 microseconds.

At step560, the operational control flow determines whether the communications standard provides sufficient time to calibrate the communications device using the fine calibration. If so, the operational control flow proceeds to step570. Otherwise, the operational control flow proceeds to step580.

At step570, the operational control flow performs the fine calibration then reverts to step540.

At step580, the operational control flow performs the offset calibration then reverts to step540.

CONCLUSION