Temperature-compensated bias circuit for power amplifier

This application claims priority under 35 U.S.C. § 119 to Korean patent application number 10-2004-0080840, filed Oct. 11, 2004, which is incorporated by reference along with all other references cited in this application.

1. Field of the Invention

The present invention relates to a power amplifier included in a personal portable communication device such as a cellular phone or a personal digital assistant (PDA), and more particularly, to a temperature-compensated bias circuit for a power amplifier.

2. Description of the Related Art

With the development of electronic technologies, portable electronic apparatuses are efficiently designed and costly effectively manufactured. The portable electronic apparatuses largely include pagers, cellular phones, music players, calculators, laptop computers, and PDAs. The portable electronic apparatuses generally require DC power and one or more batteries are used as an energy source for supplying DC power.

Wireless portable communication terminals such as mobile handsets or cellular phones are becoming compact and light. Accordingly, the size of a battery occupying a considerable portion of the mobile handset is becoming smaller to fit into the mobile handset that is compact and light. In case of the cellular phone, along with smaller terminal and battery, longer talk time is required. Thus, the life of the battery is an important factor in the mobile communication terminals such as mobile handsets or cellular phones.

The temperature in use of these personal wireless communication apparatuses changes according to a change of a season, the operation of an amplifier, or an operation duration time. Maintaining a particular feature of a power amplifier in spite of the change in temperature is another important factor in determining performance of the terminal.

A bias circuit to compensate for a temperature is needed for a superior amplification operation of a power amplifier in an appropriate operation range in spite of the change in temperature. According to a conventional technology, a circuit as shown in FIG. 1 is used for the bias of a power amplifier.

FIG. 1 is a circuit diagram of a bias circuit of a conventional power amplifier. Referring to FIG. 1 , a transistor Q 2 is a simplified form of an amplification end of a power amplifier. A transistor Q 1 is a bias transistor, or a DC buffer transistor, which provides a bias voltage to a base of the transistor Q 2 . Since the transistor Q 1 compensates for insufficient current applied to the transistor Q 2 when a bias voltage V y is directly input to the base of the transistor Q 2 , it is referred to as a DC buffer transistor. In FIG. 1 , a power voltage Vcc is applied to the transistors Q 2 and Q 1 while a reference voltage Vref is applied to a resistor Rref of a bias circuit block 200 . A collector static operational current of the transistor Q 2 is indicated by static operational current I Q .

Prior to the description of the conventional invention, the typical current characteristic of a diode needs to be understood. Those skilled in the art would easily understand that the current characteristic of a typical diode is identical to that according to a base-emitter voltage of a transistor.

FIG. 2 is a graph showing that the characteristic of current according to a voltage between both ends of a diode or the characteristic of current according to the base-emitter voltage of a transistor, with a parameter of temperature. In FIG. 2 , as the temperature increases, a characteristic curve moves to the left so that a diode turn-on voltage V BE (on) decreases. As it is well known, the movement of the curve has a value of about −2mV/° C. When the bias voltage Vbias is constant, the effective base-emitter voltage is that V BE (eff)=Vbias−V BE (on) so that the current increases.

Next, in the temperature compensation operation of the conventional bias circuit block 200 of FIG. 1 , it is assumed that a voltage of a V y node is designed to be 2.6 V by the resistor Rref and two diodes D 1 and D 2 at the room temperature of about 25° C. This means that a value of the resistor Rref is set such that the voltage between both ends of each of the two diodes connected in series becomes 1.3 V.

The voltage between the base-emitter of the transistors Q 1 and Q 2 is 1.3 V like the diodes D 1 and D 2 .

When an operation temperature increases, in the transistors Q 1 and Q 2 , as shown in FIG. 2 , the base-emitter turn-on voltage V BE (on) decreases so that the static operational current I Q increases. However, since the diodes D 1 and D 2 have the same temperature dependency as the transistors Q 1 and Q 2 , the voltage V y decreases accordingly. The decrease of the voltage V y means a decrease in the base-emitter voltage of the transistors Q 1 and Q 2 . Also, since the effective voltage V BE (eff) between the base-emitter voltage of the transistors Q 1 and Q 2 does not change, the static operational current I Q is constant.

When the operation temperature decreases, the base-emitter turn-on voltage V BE (on) of in the transistors Q 1 and Q 2 increases so that the static operational current I Q decreases. However, since the diodes D 1 and D 2 have the same temperature dependency as the transistors Q 1 and Q 2 , the voltage V y increases accordingly. The increase of the voltage V y means an increase in the base voltage of the transistors Q 1 and Q 2 . Also, since the effective voltage V BE (eff) between the base-emitter voltage of the transistors Q 1 and Q 2 does not change, the static operational current I Q is constant.

To summarize the above operation, the voltage V y between both ends of each of the diodes D 1 and D 2 tracks the base-emitter turn-on voltage of the transistors Q 1 and Q 2 according to the change in temperature so that the effective voltage V BE (eff) is constantly maintained. Thus, in spite of the change in temperature, the static operational current I Q is contact.

However, practically, when the V y voltage drops to about 2.4 V, the voltage between both ends of the base-emitter of each of the transistors Q 1 and Q 2 automatically decreases to about 1.2 V. However, in this case, the static operational current I Q of the transistor Q 2 increases greater than the size at the room temperature. This is because the sizes of the transistors Q 1 and Q 2 driving a large amount of current are much greater than those of the diodes D 1 and D 2 so that the dependency on temperature is not the same. Thus, it is a problem that the voltage V y must be less than 2.4 V to perform accurate temperature compensation so that the static operational current I Q of the transistor Q 2 is constantly maintained.

When the operation temperature drops lower than the room temperature, the voltage V y increases by the temperature dependency intrinsic to the diodes D 1 and D 2 . When the voltage V y increases to about 2.8 V, the voltage between both ends of the base-emitter of each of the transistors Q 1 and Q 2 automatically increases to about 1.4 V. Accordingly, the static operational current I Q of the transistor Q 2 decreases compared to the current at the room temperature. For the same reason in a case in which the temperature increases, in order to perform accurate temperature compensation by which the static operational current I Q of the transistor Q 2 is constantly maintained, a problem in which the voltage V y must be greater than the static operational current I Q occurs. FIG. 3 is a graph showing the static operational current I Q when the temperature compensation function is insufficient due to the above problem in comparison with the static operational current I Q in an ideal state.

A variety of circuit techniques have been developed to solve a problem in which maintaining the static operational current I Q of the transistor Q 2 constantly by the temperature compensation function based on the temperature dependency of the diodes D 1 and D 2 is difficult. One of the circuit techniques is that the voltage between both ends of each of the diodes D 1 and D 2 connected in series is arbitrarily and appropriately changed according to a change in temperature to provide a more ideal static operational current I Q feature.

Referring to FIG. 4 , one of the conventional techniques having an additional temperature compensation function is described. This circuit includes a bias circuit block 200 and an amplifier block 210 . In the configuration of the circuit, a transistor 226 shows part of an amplification circuit amplifying an RF signal and a transistor 224 is a DC buffer transistor and a resistor R 2 DC-biases a base of the transistor 226 .

The bias circuit block 200 has the same elements as the amplifier block 210 to form a current mirror shape. A transistor 220 and a transistor 222 make mirrored pairs with the transistor 224 and the transistor 226 , respectively, while a resistor R 1 makes a mirrored pair with the resistor R 2 .

A voltage of a node 234 flows from a base of the transistor 220 via the transistor 222 to ground so that a voltage drop is 2V BE . The resistor R 1 is connected to a base node 240 of the transistor 222 . A DC reference voltage Vref is connected to one side of a resistor Rref and current flowing between both ends of the resistor Rref is Iref.

When the operation temperature increases, the base-emitter turn-on voltage V BE (on) of the transistor 222 decreases. However, since current Imir is almost constantly maintained, the voltage of the node 240 is almost constantly maintained. Thus, an effective voltage between the base-emitter of the transistor 222 increases so that collector current of the transistor 222 increases and the voltage of the node 234 drops. When the voltage of the node 234 drops, the voltage of a node 242 drops automatically. Thus, since the effective voltage between the base-emitter of the transistor 226 is constant, a change in the static operational current I Q is restricted.

When the operation temperature decreases, the base-emitter turn-on voltage V BE (on) of the transistor 222 increases. However, since the current Imir is almost constantly maintained, the voltage of the node 240 is almost constantly maintained. Thus, the effective voltage between the base-emitter of the transistor 222 decreases so that the collector current of the transistor 222 decreases and the voltage of the node 234 increases. When the voltage of the node 234 increases, the voltage of a node 242 increases automatically. Thus, since the effective voltage between the base-emitter of the transistor 226 is constant, a change in the static operational current I Q is restricted.

In addition, as a conventional technology to finely adjust a voltage applied to diodes of a bias circuit, U.S. Pat. No. 6,566,954 describes an additional compensation function to a temperature compensation function of a bias circuit in which an active device instead of a resistor is inserted in a transistor amplifying an RF signal.

U.S. Pat. No. 6,452,454 describes a technology of an additional temperature compensation function by additionally providing a plurality of diodes in parallel or current paths in the bias circuit to adjust the amount of current flowing from the reference voltage Vref.

U.S. Pat. No. 6,556,082 describes another circuit technology enabling additional temperature compensation function, which is achieved by adding resistors and adjusting ratio between the resistors.

U.S. Pat. No. 6,424,225 describes a technology in which additional circuits are provided to operate according to a change in temperature so that reference current supplied from the bias circuit can be increased or decreased, thus enabling additional temperature compensation in a wider range.

To solve the above problems, the present invention provides a temperature-compensated bias circuit for a power amplifier having a circuit to compensate for a temperature by controlling a voltage of a bias circuit for the compensation of a temperature of the power amplifier.

According to an aspect of the present invention, a temperature-compensated bias circuit for a power amplifier, in which a first resistor (Rref) connected to a reference voltage is connected to a base terminal of a third transistor (Q 3 ) and an emitter terminal of the third transistor is connected to a first diode (D 1 ), the temperature-compensated bias circuit comprising: a second resistor (R 1 ) connected to the reference voltage; a third resistor (R 2 ) connected to the second resistor in series; a fourth resistor (Rc) having one terminal connected to the reference voltage; a fifth resistor (Re) having one terminal connected to ground; a bias transistor (Q 4 ) having a base terminal connected to a contact point (Vs) between the second resistor and the third resistor, a collector terminal connected to the other terminal of the fourth resistor, and an emitter terminal connected to the other terminal of the fifth resistor; and a sixth resistor (Rf) connected between a collector terminal of the third transistor and a collector terminal of the bias transistor.

According to another aspect of the present invention, a temperature-compensated bias circuit for a power amplifier, in which a first resistor (Rref) connected to a reference voltage is connected to a base terminal of a third transistor (Q 3 ) and an emitter terminal of the third transistor is connected to a first diode (D 1 ), the temperature-compensated bias circuit comprising: a second diode (D 2 ) connected to the reference voltage; a second resistor (R 1 ) connected to the second diode;a third resistor (R 2 ) connected to the second resistor in series; a fourth resistor (Rc) having one terminal connected to the reference voltage; a fifth resistor (Re) having one terminal connected to ground; a bias transistor (Q 4 ) having a base terminal connected to a contact point (Vs) between the second resistor and the third resistor, a collector terminal connected to the other terminal of the fourth resistor, and an emitter terminal connected to the other terminal of the fifth resistor; and a sixth resistor (Rf) connected between a collector terminal of the third transistor and the collector terminal of the bias transistor.

According to another aspect of the present invention, a temperature-compensated bias circuit for a power amplifier, in which a first resistor (Rref) connected to a reference voltage is connected to a base terminal of a third transistor (Q 3 ) and an emitter terminal of the third transistor is connected to a first diode (D 1 ), the temperature-compensated bias circuit comprising: a second resistor (R 1 ) connected to the reference voltage; a third resistor (R 2 ) connected to the second resistor in series; a sixth resistor (Re) having one terminal connected to ground; a bias transistor (Q 4 ) having a base terminal connected to a contact point (Vs) between the second resistor and the third resistor and an emitter terminal connected to the other terminal of the sixth resistor; and a seventh resistor (Rf) connected between a collector terminal of the third transistor Q 3 and a collector terminal of the bias transistor.

According to another aspect of the present invention, a temperature-compensated bias circuit for a power amplifier, in which a first resistor (Rref) connected to a reference voltage is connected to a base terminal of a third transistor (Q 3 ) and an emitter terminal of the third transistor is connected to a first diode (D 1 ), the temperature-compensated bias circuit comprising: a second diode (D 2 ) connected to the reference voltage; a second resistor (R 1 ) connected to the second diode; a third resistor (R 2 ) connected to the second resistor in series; a sixth resistor (Re) having one terminal connected to ground; a bias transistor (Q 4 ) having a base terminal connected to a contact point (Vs) between the second resistor and the third resistor and an emitter terminal connected to the other terminal of the sixth resistor; and a seventh resistor (Rf) connected between a collector terminal of the third transistor Q 3 and a collector terminal of the bias transistor.

The above and other features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a circuit diagram of a conventional bias circuit of a power amplifier;

FIG. 2 is a graph showing the relationship between the base-emitter voltage and the current of a diode or a transistor;

FIG. 3 is a graph showing the result of comparison between the static operational current I Q when the temperature compensation capability is insufficient and the static operational current I Q in an ideal state;

FIG. 4 is a circuit diagram of a conventional bias circuit of a power amplifier having an additional temperature compensation function;

FIG. 5 is a graph showing the static operational current I Q of a bias circuit according to an embodiment of the present invention;

FIG. 6 is a circuit diagram of a temperature-compensated bias circuit for a power amplifier according to an embodiment of the present invention;

FIG. 7 is a circuit diagram of a temperature-compensated bias circuit for a power amplifier according to another embodiment of the present invention;

FIG. 8 is a circuit diagram of a temperature-compensated bias circuit for a power amplifier according to yet another embodiment of the present invention;

FIG. 9 is a circuit diagram of a temperature-compensated bias circuit for a power amplifier according to still yet another embodiment of the present invention; and

FIGS. 10 through 12 are graphs showing the operation modes of the temperature-compensated bias circuit for a power amplifier according to the present invention.

In the present invention, the additional temperature compensation in a wider range is possible, as shown in FIG. 5 , by designing a circuit which operates to absorb reference current when temperature increases and source reference current when temperature decreases.

The present invention includes methods of maintaining a value of the static operational current I Q at the room temperature as shown in a curve shown in FIG. 5 (Mode 1 ), maintaining the value of the static operational current I Q at the highest temperature within a range allowed by the specification (Mode 2 ), and continuously maintaining the value of the static operational current I Q at the lowest temperature within the range allowed by the specification (Mode 3 ).

In Mode 1 , current at a lower/higher temperature with respect to the room temperature is up/down. In Mode 2 , current at a relatively lower temperature with respect to a higher temperature is up. In Mode 3 , current at a relatively higher temperature with respect to a lower temperature is down.

FIG. 6 is a circuit diagram of a temperature-compensated bias circuit for a power amplifier according to an embodiment of the present invention.

In a power amplifier block and a bias circuit block 500 , a first transistor Q 1 performs DC-buffering according to an input signal. The emitter terminal of the first transistor Q 1 is connected to the base terminal of a second transistor Q 2 . A voltage Vcc is applied to the first and second transistors Q 1 and Q 2 . A first resistor Rref receiving a reference voltage Vref and applying a bias voltage is connected to the base terminal of the third transistor Q 3 . A contact point V y between the first resistor Rref and the base terminal of the third transistor Q 3 is connected to the base terminal of the first transistor Q 1 . Also, a first diode D 1 is connected to the emitter terminal of the third transistor Q 3 .

In a temperature-compensated circuit 600 that is a voltage control bias circuit, a contact point V s between voltage dividing resistors R 1 and R 2 is connected to the base of a fourth transistor Q 4 . A collector resistor Rc is connected to the collector of the fourth transistor Q 4 . An emitter resistor Re is connected to the emitter of the fourth transistor Q 4 . A sixth resistor Rf is connected between the collector terminal of the third transistor Q 3 and the collector output terminal of the fourth resistor Q 4 .

The operation of the temperature-compensated bias circuit for a power amplifier configured as shown in FIG. 6 is described based on operation modes 1 , 2 , and 3 according to a change in temperature.

(1) Operation Mode 1 : Supply+Absorption Mode

First, when the temperature of the circuit is high with respect to the room temperature, since a decrease in the turn-on voltage of the second transistor Q 2 is remarkable compared to a decrease in the voltage V y input to the base of the first transistor Q 1 and a voltage V b input to the base of the second transistor Q 2 , the static operational current I Q increases. To restrict the increase in the static operational current I Q at the high temperature, the following operation occurs in the voltage control circuit 600 .

If the contact point voltage Vs between the resistors R 1 and R 2 is constant regardless of the temperature, since the turn-on voltage of the fourth transistor Q 4 decreases, the collector current of the fourth transistor Q 4 increases so that a voltage drop at the collector resistor Rc increases much. The contact point voltage V AUX between the sixth resistor Rf and the collector terminal of the third transistor Q 3 decreases.

Accordingly, as the fourth transistor allows more amount of current to flow in and a BC junction diode of the third transistor Q 3 is operated, the voltages V y and V b decrease, the increase in the static operational current I Q at a high temperature is restricted. That is, when the temperature is relatively higher than the room temperature, the temperature-compensated circuit 600 absorbs part of the reference current Iref.

Second, when the temperature of the circuit is low and the contact point voltage Vs between the resistors R 1 and R 2 is constant, the turn-on voltage of the fourth transistor Q 4 increases and the collector current of the fourth transistor Q 4 decreases so that a voltage drop at the collector resistor Rc decreases. The contact point voltage V AUX between the sixth resistor Rf and the collector terminal of the fourth transistor Q 4 increases.

Accordingly, the current flows into the transistor Q 2 /the diode D 1 through the resistor Rf so that the voltages V x , V y , and Y b increase the increase so that the static operational current I Q at a lower temperature is restricted.

(2) Operation Mode 2 : Supply Mode

The temperature in all ranges in which the circuit operates may be lower than the maximum temperature allowed by the specification. Since the contact point voltage Vs between the resistors R 1 and R 2 is constant at a relatively low temperature, the turn-on voltage of the fourth transistor Q 4 increases and the collector current of the fourth transistor Q 4 decreases. Thus, the contact point voltage V AUX between the sixth resistor Rf and the collector terminal of the third transistor Q 3 increases.

As the temperature decreases, the current flowing into the third transistor Q 3 /the diode D 1 via the resistor R f (I X >0). Accordingly, the voltages V x , V y , and V b increase. Thus, the static operational current I Q to be decreased as the temperature decreases is maintained.

(3) Operation Mode 3 : Absorption Mode

The temperature in all ranges in which the circuit operates may be higher than the minimum temperature allowed by the specification. Since the contact point voltage Vs between the resistors R 1 and R 2 is constant when the temperature is relatively high, the turn-on voltage of the fourth transistor Q 4 decreases and the collector current of the fourth transistor Q 4 increases. Thus, the contact point voltage V AUX between the resistor Rf and the collector terminal of the third transistor Q 3 decreases.

That is, as the temperature increases, the transistor Q 4 allows more amount of current to flow in and the BC junction diode of the third transistor Q 3 operates so that the voltages V y and V b decrease. Thus, the static operational current I Q to be increased as the temperature increases is maintained.

Another function of the present invention is to constantly maintain the static operational current of a power amplifier regardless a change in the reference voltage Vref. The reference voltage Vref is an item included in the specification of a typical cellular phone and variation thereof to a degree is allowed. When the reference voltage Vref increases or decreases, the operational characteristic of the circuit shown in FIG. 6 is as follows.

First, when the reference voltage Vref increases, the contact point voltage Vs increases so that an increase in the voltage V y is prevented.

Second, when the reference voltage Vref decreases, the contact point voltage Vs decreases so that, since the circuit operates like a low temperature-compensated bias circuit, a decrease in the voltage V y is prevented.

Thus, the change of the characteristic of the power amplifier is reduced regardless of the increase and decrease of the reference voltage Vref.

FIG. 7 is a circuit diagram of a temperature-compensated bias circuit for a power amplifier according to another embodiment of the present invention. Referring to FIG. 7 , in a temperature-compensated circuit 700 , as a diode D 2 is added at a front or rear end of the voltage dividing resistor R 1 at the temperature-compensated circuit 600 of FIG. 6 , the voltage Vs changes according to the temperature. The voltages V x and V y are changed so that the compensation of a temperature becomes smooth.

Thus, In the circuit 700 shown in FIG. 7 , the voltage Vs increases at a high temperature so that the voltage V y is further decreased. The voltage Vs decreases at a low temperature so that the voltage V y is further increased.

FIG. 8 is a circuit diagram of a temperature-compensated bias circuit for a power amplifier according to yet another embodiment of the present invention. Referring to FIG. 8 , a temperature-compensated circuit 800 , in which the collector resistor Rc is removed from the temperature-compensated circuit 600 in FIG. 6 , can perform temperature compensation only by the absorption of current by the fourth transistor Q 4 . The operation principle of the temperature-compensated circuit 800 is the same as that of the operation mode 3 of FIG. 6 (Absorption Mode).

FIG. 9 is a circuit diagram of a temperature-compensated bias circuit for a power amplifier according to still yet another embodiment of the present invention. Referring to FIG. 9 , a temperature-compensated circuit 900 , in which the diode D 2 is added at the front or read end of the voltage dividing resistor R 1 in the temperature-compensated circuit 700 in FIG. 7 , the voltage Vs changes according to the temperature. The voltages V x and V y are changed so that the compensation of a temperature becomes smooth. The operation principle of the temperature-compensated circuit 900 is the same as that of the operation mode 3 of FIG. 7 (Absorption Mode)

FIGS. 10 through 12 are graphs showing the operation modes of the temperature-compensated bias circuit for a power amplifier according to the present invention.

FIGS. 10A and 10B are graphs showing changes in the I Q and V y according to a change in temperature in the operation mode 1 (supply+absorption mode), respectively.

FIGS. 11A and 11B are graphs showing changes in the I Q and V y according to a change in temperature in the operation mode 2 (supply mode), respectively.

FIGS. 12A and 12B are graphs showing changes in the I Q and V y according to a change in temperature in the operation mode 3 (absorption mode), respectively.

While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

As described above, according to the temperature-compensated bias circuit according to the present invention, in spite of a change in temperature, the static operation current of the power amplifier is maintained at the room temperature (Mode 1 ), the value of the static operational current I Q at the highest temperature is maintained within a range allowed by the specification (Mode 2 ), and the value of the static operational current I Q at the lowest temperature is constantly maintained within the range allowed by the specification (Mode 3 ). Thus, the linearity of the power amplifier is maintained and unnecessary power consumption due to the power amplifier is prevented.

Furthermore, a portable wireless communication apparatus having the power amplifier according to the present invention can maintain the optimal communication quality regardless of a surrounding temperature and have a longer talk time.

The embodiments of the present invention have been described above for purposes of illustrating the present invention. It is not intended to be exhaustive or to limit the invention to the precise form described. Many modifications and variations are possible in light of the teaching above. Accordingly, the scope of the invention is defined by the appended claims.