Method and apparatus for adjusting transmission power in a two-way device based on battery impedance

A method and apparatus for adjusting transmission power in a portable two-way radio device allows the device to determine an expected battery voltage drop for a subsequent transmit event, based on present transmit power settings and battery impedance, and change the power setting for the subsequent transmit event if the battery voltage is likely to drop below a shutdown threshold at the present power setting or if the expected battery voltage drop will cause the battery voltage to be substantially above the shutdown voltage level and the present power setting is below an optimal level.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to portable electronic devices, and more particularly to portable two-way radio devices that maintain a shut down voltage limit that, if the battery voltage falls below, the portable two-way radio device will shut itself off.

BACKGROUND

Portable electronic devices are typically battery powered, and will cease operating properly when battery voltage drops below a certain voltage level. For many such devices, the only consequence of low battery voltage is that the device can unexpectedly cease operation. In more sophisticated devices, however, more serious consequences can occur. For example, in computing devices, such as tablet devices and mobile phone devices that have computing environments, data can be lost or corrupted if a voltage drop-out event occurs where voltage drops below a level necessary for the circuits in the device to properly function. In some devices that transmit radio signals, unreliable operation of radio circuitry can cause a radio transmission to fall out of a regulated set of parameters and possibly affect signals on nearby frequencies. Some devices can experience significant changes in voltage due to changing electric current demands as components of the device turn on and off. High current demand by a device causes the battery voltage to drop to a point that can damage the cell or cells of the battery, depending on the particular chemistry used in the battery cells. The voltage drop can be modeled as an internal impedance of the battery, and it can change based on a variety of conditions, including battery state of charge, age of the battery, temperature of the battery, and so on.

To avoid the negative effects of voltage drop, it is common to design devices to shut off when the voltage drops below a threshold voltage. This shut off voltage threshold can be selected based on likely conditions, and may include some overhead to account for worse battery conditions. As a result, there is a trade-off; the device is protected from undesired operation at the potential expense of leaving charge capacity in the battery. In addition, it is possible for battery impedance to decrease during operation, such as when a very cold battery is used. Temperature affects battery impedance inversely; as the temperature drops, generally the battery impedance increases. Accordingly, when a cold battery begins to warm, such as due to self-warming from use, its impedance tends to decrease. Thus, setting a fixed shutdown voltage level that is high enough to account for cold batteries likewise can result in not utilizing all the available charge capacity.

Accordingly, there is a need for a method and apparatus that can use more battery charge capacity over the conventional solutions while avoiding shutdown of the device powered by the battery.

DETAILED DESCRIPTION

Embodiments exemplified herein include a method for setting transmission power prior to a transmit event in a portable radio device powered by a battery. The method includes determining a present battery impedance and determining a battery voltage drop that will occur in response to a subsequent transmit event at a present transmission power setting, based on the present battery impedance. The method further includes adjusting the present transmission power setting to an adjusted power setting in response to determining the battery voltage drop, and, subsequent to adjusting the present power setting, the portable radio device transmits at the adjusted power setting.

FIG. 1is a block diagram100of a portable two-way radio device102and associated battery104in accordance with some embodiments. The battery104contains one or more electrochemical cells106which can be connected in series to meet a particular preferred voltage operating range. The cells106can employ any of a variety of electrochemical systems and particular construction which each have their own resulting voltage range and charge capacity. Furthermore, some types of cells106need to be maintained within certain electrical operating parameter ranges. For example, lithium ion cells are often used in portable electronic device systems, and must be operated within a particular voltage range. Causing the cell voltage of a lithium ion cell to fall below an undervoltage limit can result in damage to the cell. In some embodiments, the battery104can contain a fuel gauge108which can track various battery parameters in order to estimate the amount of charge capacity remaining in the cells106. Among the battery parameters that can be tracked are the number of charge and discharge cycles the battery104has experienced and the age of the battery104. The fuel gauge108can also be configured to determine present battery impedance based on observed characteristics, and taking into account factors such as the number of charge/discharge cycles, age, battery chemistry, present charge capacity, and battery temperature. Using such factors a calculation can be determined, or the fuel gauge108can simply use empirically derived test data that has been stored in the fuel gauge108to determine present battery impedance. To assist with determining the present charge capacity and the number of charge/discharge cycles, the fuel gauge uses a sensor such as a coulomb counter110, which sense current into and out of the cells106.

Alternatively, in some embodiments a memory112can contain battery information such as the chemistry type used by the cells106, the charge capacity of the cells106, and other information that can be used by a controller116in the portable two-way radio device102in a similar manner as the fuel gauge108to approximate or adjust battery impedance determinations. A thermistor122can additionally provide battery temperature information. The controller116controls one or more radio frequency power amplifiers (RFPA)114of a radio transmitter of the portable two-way radio device102, among other radio components. While the following discussion refers to one transmitter, it will be appreciated by those skilled in the art that a radio device can include multiple transmitters, and that the teachings herein can be applied to multiple transmitters in a radio device. Thus, any reference to “a transmitter” or “the transmitter” is not meant to imply that a radio device contains only one transmitter, or that the embodiments necessarily apply to only one transmitter in a radio device. The controller116can be a microcontroller or microprocessor that executes program code to operate the portable two-way radio and to perform the processes, tasks, and operations described herein, as well as performing conventional two-way radio operations. The controller, and other circuitry in the portable two-way radio device102, can be powered via a power distribution circuit118which provides regulated voltage levels from the battery voltage provided to the portable two-way radio device102by the battery104.

The controller116, among other tasks, controls the transmission power of the transmitter by setting a power setting for the RFPA114. The transmission power setting is adjusted to prevent the battery voltage from dropping below a shutdown voltage threshold. When the RFPA114transmits, it draws a significant current level from the battery104. The difference in current drawn by the portable two-way radio device102between non-transmitting and transmitting states can be an order of magnitude in difference. As a result, the voltage drop during transmit events is significant. The magnitude of the voltage drop between non-transmitting and transmitting states is dependent on the battery impedance and the current drawn by the portable two-way radio device102. However, since the RFPA114transmits at a specified power level, and the battery voltage naturally drops while discharging, the current demand of the RFPA114will increase to maintain the power level corresponding to the power setting. The shutdown threshold is selected as a voltage level of the battery voltage where reliable operation of the portable two-way radio device102is not possible, or the cells106could be damaged, or both. Accordingly, between transmit events, or at least prior to a transmit event, the controller116can determine a voltage drop in battery voltage that will occur in a subsequent transmit event, based on present battery impedance, and adjust the power setting of the RFPA114if necessary. If the power setting is set to an optimum or maximum setting, and the predicted voltage drop will cause the battery voltage to drop below the shutdown threshold, the controller116can reduce the power setting so that the RFPA114will then transmit at a lower power in the subsequent transmit event. Under different circumstances, battery impedance can decrease, such as when a battery is initially very cold, and begins to warm during use, either from self-heating alone or in addition to a change in temperature external to the battery. Accordingly, there can be circumstances where the controller116has reduced the power setting to the RFPA114to avoid excessive voltage drop due to high battery impedance, but as the impedance decreases over time, the controller116can increase the power setting while still maintaining the resulting voltage drop in transmit events above the shutdown threshold level.

In order to determine the voltage drop in battery voltage for a subsequent transmit event, the controller116can use the present battery impedance and the current that will be drawn, based on a present power setting and the present battery voltage. The controller116can also determine an expected change in voltage drop based on battery factors such as chemistry type used by the cells106, present temperature of the battery104, age of the battery104, and so on. One way the controller116can determine the present battery impedance is by reading an impedance value from the fuel gauge108, assuming the battery104contains a fuel gauge108that determines battery impedance. Alternatively, the controller116can operate an auxiliary component120of the portable two-way radio102that has a known or determinable current demand. The auxiliary component120can be part of any other subsystem in the portable two-way radio device102that has a known or determinable current demand. Alternatively, the auxiliary component120can be a dedicated circuit operated by the controller116for the purpose of determining battery impedance. The controller116first determines the present battery voltage without the auxiliary component120activated (or deactivated), and then activates (or deactivates) the auxiliary component120and determines the battery voltage with the auxiliary component120activated (or deactivated) to determine a voltage differential in the battery voltage. The determined voltage differential is divided by the current change through the auxiliary component120when it was activated or deactivated. The ratio of voltage to current is an impedance, and reflects the present battery impedance, which can be used to then determine an expected voltage drop in a subsequent transmit event. The controller116can use additional information to modify or refine the impedance determination, such as information in the memory112of the battery104, as well as temperature information that may be available, such as by a thermistor122. Chemistry type, battery age, and present temperature all affect the discharge profile of the battery voltage and can thus be used to predict voltage drop during a transmit event. Once the controller116has determined the voltage drop that will occur in a subsequent transmit event, the controller116can adjust the power setting of the RFPA114, if necessary, for a subsequent transmit event. The controller116can periodically determine expected voltage drop at regular intervals or according to some other schedule. Furthermore, the controller116can provide an indication to the user of the portable two-way radio device if the transmit power is being reduced. The indication can be a visual alert, an audio alert (e.g. a “beep”), or both, so that the user knows the portable two-way radio device102is operating at less than optimal power. Furthermore, the ability of the controller116to adjust transmit power can be selectable by the user, allowing either power adjusting operation or conventional operation.

FIG. 2is a series of graph charts200,202showing variations in battery voltage versus time in response to variations in current sourced from a battery in accordance with some embodiments. The variations are the result of activating or deactivating an auxiliary component of the portable two-way radio to determine present battery impedance. In the first variation200, battery voltage204and current206are charted; in the second variation202battery voltage212and current214are charted. In the first variation200, during time207, the auxiliary component is activated, causing current206to increase by a current differential210, which causes a corresponding voltage drop208. The ratio of the voltage drop208to the current differential210indicates present battery impedance. In the second variation202, the auxiliary component is deactivated during time215, producing a current decrease differential218and a corresponding voltage increase differential216. Again, the ratio of voltage differential216to current differential218indicates present battery impedance. Either of these variations can be used by, for example, controller116ofFIG. 1to determine present battery impedance. The method of changing current demand by a known amount and then observing the resulting voltage change is especially well suited for portable two-way radio devices that only have a positive and negative contact interface with the battery, and are therefore unable to obtain any other information about the battery.

FIG. 3is a graph chart300of the battery voltage302and current303versus time, including transmit events306,310and adjustments in power setting based on battery impedance in accordance with some embodiments. The chart300further shows a shutdown voltage threshold304which, if the battery voltage302drops below this shutdown threshold304, it will cause the portable two-way radio device to shut down (e.g. turn off until the battery is recharged or replaced). During transmit event306, the battery voltage302remains above the shutdown threshold. At time308the portable two-way radio device determines the battery impedance and determines that at a subsequent transmit event310, at the present power setting, the voltage will drop to level312. In this example, since the battery voltage would drop below the shutdown threshold304at the power settings as set at time308, the controller reduces the power setting based on the expected voltage drop, taking into account changes in current to maintain constant power, the discharge profile of the battery at the present state of charge and temperature, the present impedance of the battery, and so on. At the adjusted power setting, then, the battery voltage only drops to level314, staying above the shutdown threshold. It should be noted that the charted battery voltage shown here is not meant to represent an actual case, rather it is meant to more clearly illustrate the embodiments being discussed. As can be seen the current303is larger during transmit event306than during transmit event310. The method represented byFIG. 3can be repeated until the power setting reaches a minimum setting and cannot be set lower, with the controller periodically determining impedance to determine voltage drop and then whether or not a further adjustment is necessary.

FIG. 4is a graph chart400showing battery voltage402, battery impedance404, and current401versus time, including transmit events406,414resulting from adjustments in response to battery impedance404decreasing over time in accordance with some embodiments, such as when a cold battery warms up. Initially the power setting that controls the transmit power level has already been reduced as the battery impedance404is high. At time405the portable two-way radio device determines that at the present power setting (which is less than optimal) will cause a battery voltage drop to level408, which is below the shutdown threshold403, during transmit event406. Accordingly the controller further reduces the power setting so that the battery voltage only drops to level410, which is above the shutdown threshold403.

At a subsequent time412, and after the battery impedance has dropped significantly, another determination is made that at the present power setting (e.g. as set prior to transmission event406) the battery voltage will drop to level416in subsequent transmission event414, which is significantly above the shut down threshold403. As a result, the portable two-way radio device can increase the power setting to increase transmission power such that the battery voltage falls to level418during transmission event414, which is still above the shutdown threshold level403, but lower than level416which would have occurred with the lower power setting. Accordingly, the current401during transmission event406is less than the current during transmission event414as the power setting is increased for transmission event414over that of transmission event406. Thus, the portable two-way radio device can adjust the power setting in order to increase the transmission power and take advantage of a decreasing battery impedance, possibly even returning to an optimum power level.

FIG. 5is a graph chart500of battery voltage502showing dynamic adjustment of power setting during a transmit event506where the power setting is also adjusted before the transmit event in response to the battery impedance in accordance with some embodiments. Prior to transmit event506it can be assumed that the power setting for the transmitter of the portable two-way radio device has been lowered based on battery impedance and the resulting voltage drop due to shutdown threshold504. However, while at the start of transmit event506the current512increases to power the RFPA to the set power level, and the battery voltage is above the shutdown threshold504. The battery voltage502continues to drop, and would continue to drop along level508, which falls below the shutdown threshold504. To prevent the battery voltage502from falling below the shutdown threshold504, the portable two-way radio device begins to decrease the power setting at time509. Accordingly, after time509, the current512begins to fall until the end of transmit event506, where the current then resumes the same level it was at prior to transmit event506. By dynamically adjusting the power setting during the transmit event (i.e. while transmitting), and hence lowering the current demand512after time509in the present example, the battery voltage remains at level510, which is above the shutdown threshold504. Similarly, when the battery impedance is decreasing during a transmit event, the portable two-way radio device can increase the power setting during a transmit event so long as the battery voltage remains above the shutdown threshold.

FIG. 6shows a flow chart diagram of a method600of adjusting transmit power based on battery impedance before the onset of a transmit event in accordance with some embodiments. Thus, at the start602of the method600, the portable two-way radio device is powered on and operational. At some point, the portable two-way radio device is triggered to determine an expected voltage drop in battery voltage for a subsequent transmit event at the present power setting in step604. The expected voltage drop can be determined by first determining the present battery impedance, which can include reading the battery impedance from a fuel gauge or equivalent circuit device in the battery, as well as determining the battery impedance exclusively by the portable two-way radio device by measuring the voltage differential in response to a known current differential. Once the expected voltage drop is determined, the expected level during a subsequent transmit event can be determined based on the present battery voltage. The method then, in step606, determines whether the present power setting will cause the battery voltage to drop below the shutdown threshold level. If yes, then in step610the method600reduces the power setting to a level that will not cause the battery voltage to drop below the shutdown threshold level in the subsequent transmit event. The method can then proceed to step612where the portable two-way radio device transmits at the reduced power setting. Alternatively, if prior to step612occurring a sufficient period of time passes, the method can return from step610to step604.

If, in step606, it is determined that at the present power setting the battery voltage is not likely to drop below the shutdown threshold level, the method600can proceed to step608where the method600determines whether the present power setting is less than an optimal power setting. The power setting can be less than an optimal, or maximum power setting if the power setting had previously been lowered due to high battery impedance, but at the present time the battery impedance may have reduced due to, for example, an increase in battery temperature in a previously cold battery. Accordingly, if the present power setting is less than optimal, and the expected voltage drop at the present power setting will keep the battery voltage sufficiently above the shutdown voltage threshold, then the method600can proceed to step614and increase the power setting so that, in the subsequent transmit event, the transmitter will transmit at a higher power, in step616, than if the present power setting (as of the time of performing step608) are used in the subsequent transmit event. If, in step608, it is determining that the present power setting is already at the optimal level, or if the present power setting is less than the optimal setting, but can't be increased, the method600proceeds to step620, leaving the present power setting unmodified for the subsequent transmit event in step620. In some embodiments, while transmitting in the subsequent transmit event in either of steps612,616,620, the method600can dynamically adjust the power setting of the transmitter while transmitting in step618to prevent the battery voltage from dropping below the shutdown threshold level, assuming the power setting can be reduced any further. The final power setting after the subsequent transmit event finishes can then be used as the present power setting for the next iteration of method600as the method returns from step618to process604.

In general the method600ofFIG. 6can be characterized as a method of adjusting current demand for a high current event in an electronic device powered by a battery. The method includes determining a present battery impedance, and determining a battery voltage drop that will occur in response to a high current operation in a subsequent high current event at a present current setting, based on the present battery impedance. The electronic device can then commence adjusting the present current setting to an adjusted current setting in response to determining the battery voltage drop, based on a shutdown voltage threshold level. Subsequent to adjusting the present current setting, the electronic device can then perform the high current process at the adjusted current setting.

FIG. 7shows a flow chart diagram of a method700of determining expected battery voltage drop by a portable two-way radio device in accordance with some embodiments. The entire method700can be performed as part of step604ofFIG. 6. At the start702the portable two-way radio device is operational and has determined that it is time to perform method700. In the present method700the portable two-way radio device acquires battery data from the battery in step704. The battery data, or battery parameters can include the present battery impedance, as provided by a fuel gauge in the battery. Other battery parameters can include an indication of chemistry type, discharge profile data, battery temperature, temperature coefficients that indicate how battery impedance changes with temperature, battery age, battery cycle life, and so on. In step706the portable two-way radio device can determine and/or adjust a battery impedance determination. If the present impedance is tracked and determined by a fuel gauge in the battery, then step706can be skipped. Otherwise, the portable two-way radio device can, based on the battery parameters, determine a nominal impedance and adjust it based on battery parameters provided in step704. In step708, the portable two-way radio device determines what current will be required at the present power setting. Since power is the product of voltage and current, the present battery voltage is used as a starting point. Dividing the present battery power setting by the present battery voltage will yield the current necessary to achieve that power. Then a voltage drop can be determined by multiplying the current needed to produce the power by the present battery impedance. However, the resulting voltage drop results in a higher current demand to meet the required transmission power. As a result, an iterative process can be used to converge the voltage and current required for the present power setting. Alternatively, the method can use only one iteration, assuming the voltage drop produced by one iteration is a sufficient approximation, and that dynamic adjustment of power setting will prevent the battery voltage from falling below the shutdown threshold. Once the expected voltage drop has been determined, the method700ends at710.

FIG. 8shows a flow chart diagram of a method800of determining expected battery voltage drop by a portable two-way radio device in accordance with some embodiments. As with the method700ofFIG. 7, method800can be substantially performed in step604of method600inFIG. 6. Method800is an active determination of battery impedance performed by the portable two-way radio device, and can be used, for example, when no battery information is available to the portable two-way radio device. At the start802, the portable two-way radio device is operational and has been triggered, or otherwise determined that the expected voltage drop needs to be determined. In step804the portable two-way radio device determines the present battery voltage, and then adjusts the current demand of the portable two-way radio device by changing the operational state of an auxiliary component. That is, the auxiliary component can be turned on (increasing current demand of the portable two-way radio device), or shut off (reducing current demand by the portable two-way radio device), or adjusted in some other way to change the current demand by a known or determinable amount. In step806the portable two-way radio device determines the voltage differential produced in the battery voltage by changing the operational state of the auxiliary component. That is, the change in battery voltage resulting from changing the operational state of the auxiliary component. In step808the present battery impedance is then determined as a ratio of the voltage differential divided by the change in current resulting from changing the operational state of the auxiliary component. In the end810, the method800can then determine an expected voltage drop based on the present power setting using the determined present battery impedance, as in method700ofFIG. 7. Either an estimate can be used or an iterative calculation can be performed to determine the expected voltage drop for a constant power setting. Thereafter, the portable two-way radio device can determine, as in method600ofFIG. 6, whether to adjust the present power setting.

The various exemplary embodiments taught and suggested herein provide the benefit of allowing a battery powered electronic device, such as a portable two-way radio device, that has occasional relatively high level electric current events, to adjust the current demand to avoid having the battery voltage drop below a shutdown threshold level, thereby extending the operational capacity that can be provided by the battery. Furthermore, under some circumstances, it provides an increase in the amount of current that can be drawn from the battery when the battery impedance decreases.