Patent Application
20100244957
1. Field of the Invention
The invention relates to a power circuit for a power amplifier, and more particularly to a power circuit for a power amplifier applied in a communication system.
2. Description of the Related Art
In current communication systems, before a transmission signal is broadcasted through an antenna, the power of the transmission signal has to be amplified by a power amplifier. Among elements of a communication system, a power amplifier consumes a great amount of current from a system power supply when the power amplifier is active. Thus, in such cases, remaining current may not be sufficient for other elements to operate. In efforts to provide sufficient power for all elements to operate when a power amplifier is activated, a communication system requires a system power supply that provides a large amount of total current.
However, for some applications, the total amount of current provided by a system power supply is limited. For example a USB dongle device is limited to a specific power specification of 500 mA (2.5 W). Thus, it is desired to provide a low current power circuit to drive a power amplifier in a low powered device.
An exemplary embodiment of a power circuit for a power amplifier which operates in an inactive period and an active period comprises a power supply unit, a current limiting unit, a storage unit, and a converting unit. The power supply unit provides a first current. The current limiting unit is arranged to process the first current to generate a second current. The storage unit is arranged to provide a storage voltage. The storage unit is charged by the second current during the inactive period and discharged by a third current during the active period. The converting unit provides an active power or a stabilized voltage source to the power amplifier according to the storage voltage, the second current, and the third current during the active period.
An exemplary embodiment of a communication system comprises a power amplifier and a power circuit. The power amplifier operates in an inactive period and an active period. The power amplifier is arranged to receive a transmission signal and amplify a power of the transmission signal. The power circuit is arranged to provide an active power to the power amplifier during the active period. The power circuit comprises a power supply unit, a current limiting unit, a storage unit, and a converting unit. The power supply unit is used to provide a first current. The current limiting unit is arranged to process the first current to generate a second current. The storage unit provides a storage voltage. The storage unit is charged by the second current during the inactive period and discharged by a third current during the active period. The converting unit is arranged to provide the active power to the power amplifier according to the storage voltage, the second current, and the third current during the active period.
An exemplary embodiment of a method for providing power to a power amplifier which operates in an inactive period and an active period is provided. The method comprises the steps of: providing a first current by a system power supply unit; limiting a value of the first current to generate a second current; providing a storage voltage by charging a storage unit by the second current during the inactive period and discharging the storage unit by a third current during the active period; and providing an active power to the power amplifier according to the storage voltage, the second current, and the third current during the active period.
In some embodiments, the step of providing the active power comprises the step of: converting the storage voltage to a fixed driving voltage; providing the second current and the third current to generate a driving current with a first level during the active period; and generating the active power according to the fixed driving voltage and the driving current with the first level during the active period. During the inactive period, the driving current is changed to a second level from the first level, and the second level is lower than the first level.
A detailed description is given in the following embodiments with reference to the accompanying drawings.
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
Power circuits are provided. In an exemplary embodiment of a power circuit in
Because the power amplifier PA alternately operates between the active period and the inactive period, the driving current I_PA, required for the power amplifier PA, changes between a high driving current level and a zero driving current level when the active period and the inactive period are switched. Referring to
When the power amplifier PA operates during the inactive period P_ACTB, since the driving current I_PA provided by the converting unit 12 is at the zero level LVZ, that is the power provided from the converting unit 12 to the power amplifier PA is equal to zero, the converting unit 12 does not require the current I_CL to be provided to the converting unit 12. Referring to
When the power amplifier PA operates during the active period P_ACT, since the converting unit 12 has to generate the driving current I_PA with the high level LVH, that is, the converting unit 12 provides non-zero power to the power amplifier PA, the converting unit 12 requires the current to be input. During the active period, the current I_CL is provided to the converting unit 12, and the capacitor CS is discharged with a current I_CS. Referring to
According to above embodiment, during the active period, since the current provided to the converting unit 12 is obtained by the current I_CL from the current limiting unit 11 and the current I_CS which is generated by discharging of the storage unit 13, the peak value of the current I_VCC from the power supply unit 10 can be reduced. Thus, when the power circuit 1 is applied to a power amplifier in a low powered device with low current supply capabilities, even if the power supply unit 10 of the power current 1 provides low total current, the provided current is sufficient for the power amplifier and other elements within the low powered device to operate.
In some embodiments, the power supply unit 10 can be implemented by a low current supply source, such as a USB power source or a battery. Moreover, the converting unit 12 can be implemented by a DC-DC converter or a buck-boost converter. Please note that the present invention utilize the converting unit 12, such as DC-DC converter or a buck-boost converter with a small capacitor, such as 100 uF, 220 uF, or others depended on the PA current consumption and duty-cycle, to maintain the output voltage on an acceptable voltage without utilizing a storage unit required a large capacitance. It should be appreciated that the present invention provides a communication system with a combination of current limiting unit, a small capacitance storage device, and a converting unit to maintain the stability of power-control for overall communication system. Taking any element of a current limiting unit, a small capacitance storage device, and a converting unit away from the communication system will reduce the performance dramatically or increase the system complexity.
The power circuit 1 of
The communication system 3 receives a signal through the antenna 30. The received signal is amplified by the low noise amplifier 31 and provided to the RF transceiver 32. The RF transceiver 32 processes a radio frequency component of the received signal to generate a receipt signal S_RX. The receipt signal S_RX is then provided to the processor 33 for subsequent signal processes. The processor 33 may provide a transmission signal S_TX to the RF transceiver 32. The RF transceiver 32 processes a radio frequency component of the transmission signal S_TX and provides the processed transmission signal S_TX to the power amplifier PA. The power amplifier PA then amplifies the power of the transmission signal S_TX according to the power provided by the power circuit 3. The transmission signal S_TX with the amplified power is then broadcasted through the antenna 30.
Accordingly, since the storage unit 13 is charged by the current I_CL during the in-active period and the current I_SUM obtained by adding the current I_CL and the current I_CS is provided to the converting unit 12 for the power amplifier PA during the active period, the current I_VCC provided by the power supply unit 10 is sufficient for the power amplifier PA and other elements within the communication system 3, even if the provided current I_VCC is low.
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
