JP2011176592A - Temperature compensation circuit and power amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a temperature compensation circuit that performs high precision temperature compensation. <P>SOLUTION: A bias circuit 20 is equipped with: a CTAT circuit 30 configured to supply a reference current having negative linear temperature characteristics with respect to an absolute temperature as a base bias current to respective transistors Tr1, Tr2 and Tr3 having positive linear temperature characteristics with respect to the absolute temperature so as to cancel temperature variations in current or voltage of the transistors Tr1, Tr2 and Tr3; and the temperature characteristic compensation circuit 40 configured to compensate deviations between temperature characteristics of the CTAT circuit 30 and temperature characteristics of the transistors Tr1, Tr2 and Tr3. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a temperature compensation circuit and a power amplifier for compensating for a deviation between a temperature characteristic of a power supply circuit and a temperature characteristic of a circuit element.

  The OFDM system (orthogonal frequency division multiplexing) is one of digital modulation systems used in terrestrial digital broadcasting, wireless LAN, power line modems, etc., and enables high-quality communication that is not easily affected by fading and multipath. Has the advantage of Power amplifiers used in this type of digital modulation system are required to have low distortion as well as high output and high efficiency. Generally, a transistor has an input / output characteristic having a linear region in which an output signal increases linearly with an increase in input signal, and a saturation region in which gain compression of the output signal occurs with respect to an increase in input signal. It is known that signal amplification in the saturation region causes distortion of the output signal. In the OFDM method, since a large number of symbols are multiplexed, the transmission signal waveform has a Gaussian distribution, and the PAR (peak-to-average power ratio) tends to increase. For this reason, in the power amplifier used in the OFDM system, the operation output point of a transistor is set to a point backed off by several dB from the saturation output point of the transistor, and the transistor is operated in a region as close to the linear region as possible. Realizes distortion.

  By the way, a power amplifier formed by connecting a plurality of transistors in multiple stages has a temperature characteristic in which the current and voltage of the transistor change according to the temperature. Therefore, in order to keep the gain of the power amplifier constant with respect to the temperature change. For this reason, temperature compensation of the transistor is an important issue. For example, in a transistor with positive temperature characteristics, the current and voltage increase as the temperature rises, so by using a bias power supply with negative temperature characteristics, the temperature change of the current flowing through the transistor is offset by the temperature change of the bias current. It is preferable to design the circuit so that a constant bias current is supplied to the transistor. For example, Japanese Patent Application Laid-Open No. 2004-159213 is known as a document related to this type of temperature compensation technology.

JP 2004-159123 A

  However, in actual circuit design, it is difficult to design a bias power source having a temperature characteristic that completely cancels the temperature change of the current flowing through the transistor with the temperature change of the bias current, and a temperature compensation shift occurs. It is difficult to keep the gain of the power amplifier and P1 dB (1 dB gain compression point) constant with respect to temperature changes.

  Accordingly, an object of the present invention is to propose a temperature compensation circuit capable of realizing highly accurate temperature compensation.

  In order to solve the above problems, a temperature compensation circuit according to the present invention includes a power supply circuit having a temperature compensation function for supplying a current or voltage to a circuit element so as to cancel a temperature change in the current or voltage of the circuit element, and a power supply. A temperature characteristic compensation circuit for compensating for a difference between the temperature characteristic of the circuit and the temperature characteristic of the circuit element is provided. According to such a configuration, it is possible to compensate for a temperature change in the current or voltage supplied from the power supply circuit to the circuit element with high accuracy.

  The temperature characteristic compensation circuit includes one or more temperature compensation resistors, one or more resistance elements that do not have a temperature compensation function, and one or more temperature compensation resistors and one or more that do not have a temperature compensation function. A switch that connects any one of the resistance elements selected in accordance with the temperature to a current path from the power supply to the power supply circuit. Although it is difficult to perform high-precision temperature compensation over a wide temperature range with only a single temperature compensation resistor, one or more temperature compensation resistors and one or more resistance elements that do not have a temperature compensation function can be used. High-precision temperature compensation can be realized by performing temperature compensation using an optimum resistance selected according to temperature.

  The plurality of temperature compensation resistors may include a first temperature compensation resistor having a positive temperature characteristic and a second temperature compensation resistor having a negative temperature characteristic. Thereby, the temperature characteristic of the power supply circuit can be flexibly compensated.

  When the circuit element is a circuit element (for example, a transistor) having a positive temperature characteristic in which current or voltage increases as the temperature rises, the power supply circuit has a negative temperature characteristic in which current or voltage decreases as the temperature rises. A power supply circuit (for example, a CTAT (Complementary To Absolute Temperature) circuit) is preferable. On the other hand, when the circuit element is a circuit element (for example, a diode) having a negative temperature characteristic in which the current or voltage decreases with an increase in temperature, the power supply circuit has a positive temperature at which the current or voltage increases with an increase in temperature. A power supply circuit having characteristics (for example, a PTAT (Proportional To Absolute Temperature) circuit) is preferable.

  According to the present invention, a deviation between the temperature characteristic of the power supply circuit and the temperature characteristic of the circuit element can be compensated with high accuracy.

It is a circuit block diagram of the power amplifier concerning this embodiment. It is a circuit block diagram of the conventional bias circuit. It is a graph which shows the temperature characteristic of the conventional bias circuit. 3 is a graph showing temperature characteristics of a bias circuit according to Example 1. 6 is a graph showing temperature characteristics of a bias circuit according to Example 2. 10 is a graph showing temperature characteristics of a bias circuit according to Example 3.

Embodiments relating to the present invention will be described below with reference to the drawings.
FIG. 1 shows a circuit configuration of a power amplifier 10 according to the present embodiment. The power amplifier 10 is, for example, for linearly amplifying an OFDM radio signal, and is designed to keep the gain and P1 dB constant with respect to temperature changes. The power amplifier 10 includes a plurality of transistors Tr1, Tr2, Tr3 connected in multiple stages, an input matching circuit 32 for impedance matching between the input terminal 31 and the input of the transistor Tr1, an output of the transistor Tr1, and an input of the transistor Tr2. Impedance matching between the stage matching circuit 33 for impedance matching, the stage matching circuit 34 for impedance matching between the output of the transistor Tr2 and the input of the transistor Tr3, and the output terminal 36 for impedance matching. Output matching circuit 35 and a bias circuit 20 that controls the bias point by supplying base bias currents Ib1, Ib2, and Ib3 to the transistors Tr1, Tr2, and Tr3.

  The transistors Tr1, Tr2, and Tr3 are amplifiers for linearly amplifying a radio signal. In this embodiment, a grounded-emitter bipolar transistor having a base terminal as an input terminal and a collector terminal as an output terminal is used. The base terminal B1 of the foremost transistor Tr1 receives a signal from the input terminal 31 via the input matching circuit 32, its emitter terminal E1 is grounded, and its collector terminal C1 is connected to the collector bias power supply Vcc1. Yes. The base terminal B2 of the second stage transistor Tr2 is connected to the collector terminal C1 via the interstage matching circuit 33, its emitter terminal E2 is grounded, and its collector terminal C2 is connected to the collector bias power supply Vcc2. It is connected. The base terminal B3 of the final stage transistor Tr3 is connected to the collector terminal C2 via the interstage matching circuit 34, the emitter terminal E3 is grounded, and the collector terminal C3 is connected to the collector bias power supply Vcc3. In addition, a signal is output to the output terminal 36 via the output matching circuit 35.

  The bias circuit 20 uses a reference current having a negative linear temperature characteristic with respect to the absolute temperature as a base bias current so as to cancel a temperature change in the current or voltage of the transistors Tr1, Tr2, Tr3 having positive linear temperature characteristics with respect to the absolute temperature. As a CTAT circuit 30 to be supplied to each of the transistors Tr1, Tr2 and Tr3, and a temperature characteristic compensation circuit 40 for compensating for a deviation between the temperature characteristics of the CTAT circuit 30 and the temperature characteristics of the transistors Tr1, Tr2 and Tr3. In the temperature characteristic compensation circuit 40, the negative slope of the temperature characteristic of the CTAT circuit 30 and the positive slope of the temperature characteristics of the transistors Tr1, Tr2, Tr3 cancel each other, and a constant base bias current that does not depend on the temperature change becomes a transistor Tr1. , Tr2 and Tr3 are compensated for the temperature characteristics of the CTAT circuit 30. Details of the temperature characteristic compensation circuit 40 will be described later.

  Here, the operation of the bias circuit 20 will be described. By switching the power supply of the bias circuit 20 on / off, the operation of the transistors Tr1, Tr2, Tr3 can be switched on / off instantaneously. The bias currents Ib1, Ib2, and Ib3 flowing through the transistors Tr1, Tr2, and Tr3 can be turned off by turning off the power supply of the bias circuit 20 with the collector bias power supplies Vcc1, Vcc2, and Vcc3 turned on. If the bias currents Ib1, Ib2, and Ib3 do not flow, the collector currents of the transistors Tr1, Tr2, and Tr3 hardly flow, so that the transistors Tr1, Tr2, and Tr3 are almost turned off. However, if the collector bias power supplies Vcc1, Vcc2, and Vcc3 are also turned off, it takes time for the transistors Tr1, Tr2, and Tr3 to rise. Therefore, the collector bias power supplies Vcc1, Vcc2, and Vcc3 remain turned on. Control power on / off only. That is, by turning on the collector bias power sources Vcc1, Vcc2, and Vcc3, the transistors Tr1, Tr2, and Tr3 are set in a ready state, and the power source of the bias circuit 20 is turned on / off, whereby the operations of the transistors Tr1, Tr2, and Tr3 are performed. To control.

  For convenience of explanation, a circuit configuration for supplying a bias current from a single CTAT circuit 30 to all the transistors Tr1, Tr2, Tr3 is shown. However, a bias current is supplied from a single CTAT circuit to a single transistor. The circuit may be designed to supply. A choke coil Lb1 for preventing the high-frequency bias current Ib1 from flowing back to the bias circuit 20 may be inserted in the bias current path between the bias circuit 20 and the base terminal B1, and the high-frequency collector bias current is used as a collector bias power source. A choke coil Lc1 for preventing reverse flow to Vcc1 may be inserted in a bias current path between the collector bias power supply Vcc1 and the collector terminal C1. Similarly, choke coils Lb2, Lc2, Lb3, and Lc3 may be inserted in the bias current paths of the transistors Tr2 and Tr3.

  The temperature characteristic compensation circuit 40 includes a plurality of temperature compensation resistors 41 and 42 and any one temperature compensation resistor selected according to the temperature from the plurality of temperature compensation resistors 41 and 42 from the power supply Vcc to the CTAT circuit 30. A switch 43 connected to the current path is provided. In this embodiment, as means for selecting any one of the temperature compensation resistors 41 and 42 according to the temperature, the output voltage of the temperature sensor 46 that outputs a voltage corresponding to the temperature is used. A comparator 44 that compares a reference voltage 43 corresponding to a predetermined temperature and outputs a switch switching signal based on the comparison result is illustrated. For example, when the output voltage of the temperature sensor 46 is smaller than the reference voltage 34, the comparator 44 outputs a switch switching signal instructing that the temperature compensation resistor 41 should be selected to the switch 43, and outputs the temperature sensor 46. When the voltage is higher than the reference voltage 34, a switch switching signal instructing that the temperature compensation resistor 42 should be selected is output to the switch 43. The switch 43 selects one temperature compensation resistor from the plurality of temperature compensation resistors 41 and 42 based on the switch switching signal output from the comparator 44, and selects the selected temperature compensation resistor from the power source Vcc to CTAT. Connect to current path to circuit 30.

  For example, when the positive slopes of the temperature characteristics of the transistors Tr1, Tr2, and Tr3 below a predetermined temperature are steep, and the positive slopes of the temperature characteristics of the transistors Tr1, Tr2, and Tr3 above a predetermined temperature are gentle It is necessary to correct the negative slope of the temperature characteristic of the CTAT circuit 30 below the predetermined temperature to a steep slope and to gently correct the negative slope of the temperature characteristic of the CTAT circuit 30 above the predetermined temperature. For this purpose, a temperature compensation resistor 41 having a positive temperature characteristic (for example, a thermistor PTC or a platinum resistance thermometer) whose resistance value increases as the temperature rises is used. It is preferable to use a material having a negative temperature characteristic (for example, the thermistor NTC) in which the resistance value decreases with increasing.

  Here, the configuration of the conventional bias circuit will be described with reference to FIGS. The conventional bias circuit 31 includes a CTAT circuit 30 composed of a transistor having a base-emitter connected, and a bias resistor 32 connected between the power supply Vcc and the CTAT circuit 30. The CTAT circuit 30 is a bandgap reference voltage circuit that generates a DC reference voltage that is reasonably stable with respect to temperature. Such a bandgap reference voltage circuit utilizes the characteristics of a bipolar transistor that generates a substantially constant base-emitter voltage. In a silicon transistor, the base-emitter voltage is 0.5V to 0.8V. Is in range. Since the voltage generated at the base and emitter of the transistor has a negative temperature coefficient, the CTAT circuit 30 is a power supply circuit using the voltage generated at the base and emitter of the transistor. The output voltage Vout is determined by the voltage drop between the emitters. The output voltage Vout can be adjusted by adjusting the bias resistor 32. Further, since the base-emitter voltage has a negative temperature coefficient, the output voltage Vout also has a negative temperature coefficient. As shown in FIG. 3, the temperature characteristic 100 of the output voltage Vout is determined by the temperature characteristic of the bias resistor 32, and the temperature change is almost constant at any temperature. Accordingly, if the temperature characteristic of the amplifier that receives the bias current supplied from the bias circuit 31 changes depending on the temperature, the temperature change of the bias current supplied to the amplifier is changed by the temperature characteristic 100 of the output voltage Vout of the bias circuit 31. Makes it difficult to compensate completely, and the bias current varies depending on the temperature. On the other hand, according to the bias circuit 20 according to the present embodiment, any one temperature compensation resistor selected according to the temperature from the plurality of temperature compensation resistors 41 and 42 is connected from the power source Vcc to the CTAT circuit 30. By switching and connecting to the current path, temperature changes in the currents or voltages of the transistors Tr1, Tr2, and Tr3 are offset, and constant bias currents Ib1, Ib2, and Ib3 that are independent of temperature are supplied to the transistors Tr1, Tr2, and Tr3. Can do.

  In the present embodiment, a plurality of temperature compensation resistors are not essential, and any one or more temperature compensation resistors may be replaced with a resistance element (a resistance element having no temperature compensation function). In other words, the temperature characteristic compensation circuit 40 includes one or a plurality of temperature compensation resistors and one or a plurality of resistance elements not having a temperature compensation function, and has one or a plurality of temperature compensation resistors and a temperature compensation function. Any one selected from one or a plurality of resistive elements that do not have may be connected to the current path from the power supply Vcc to the CTAT circuit 30.

  The temperature characteristic compensation circuit 40 according to the first embodiment uses the thermistor PTC as the temperature compensation resistor 41 and the thermistor NTC as the temperature compensation resistor 42. The thermistor PTC has a temperature characteristic in which the resistance value increases as the temperature rises, and the thermistor NTC has a temperature characteristic in which the resistance value decreases as the temperature rises. The reference voltage 45 is, for example, a voltage corresponding to the absolute temperature T0. The comparator 44 compares the reference voltage 45 with the output voltage of the temperature sensor 36, and if the absolute temperature is less than T0, the temperature is A switch switching signal that instructs switching connection to the compensation resistor 41 is output to the switch 43. When the absolute temperature is equal to or higher than T0, a switch switching signal that instructs switching connection to the temperature compensation resistor 42 is output to the switch 43. Output to. Since the resistance value of the thermistor PTC increases as the temperature rises, if the switch 43 is switched to the temperature compensation resistor 41 below the absolute temperature T0, the bias current flowing through the CTAT circuit 30 having negative temperature characteristics is limited, and the CTAT circuit The negative slope of the temperature characteristic of 30 becomes steep. As shown in FIG. 4, at an absolute temperature T0 or lower, the temperature characteristic 210 of the CTAT circuit 30 connected to the temperature characteristic compensation circuit 40 has a voltage and current higher than the temperature characteristic 100 of the CTAT circuit not connected to the temperature characteristic compensation circuit 40. The decrease becomes steep. On the other hand, since the resistance value of the thermistor NTC decreases as the temperature rises, if the switch 43 is switched to the temperature compensation resistor 42 at an absolute temperature T0 or higher, the decrease in the bias current flowing through the CTAT circuit 30 having negative temperature characteristics is alleviated. As a result, the negative slope of the temperature characteristic of the CTAT circuit 30 becomes gentle. As shown in FIG. 4, at the absolute temperature T0 or higher, the temperature characteristic 220 of the CTAT circuit 30 connected to the temperature characteristic compensation circuit 40 has a voltage and current higher than the temperature characteristic 100 of the CTAT circuit not connected to the temperature characteristic compensation circuit 40. The decrease will be moderate. According to the temperature characteristic compensation circuit 40 according to the first embodiment, the transistor Tr1, the positive slope of the temperature characteristic below the absolute temperature T0 is a steep slope, and the positive slope of the temperature characteristic above the absolute temperature T0 is gentle. Constant bias currents Ib1, Ib2, and Ib3 having no temperature dependency can be supplied to Tr2 and Tr3. Since the platinum resistance thermometer has a temperature characteristic that the resistance value increases as the temperature rises, a platinum resistance thermometer is used as the temperature compensation resistor 41 and a thermistor NTC is used as the temperature compensation resistor 42. Even in this case, similar effects can be obtained.

  The temperature characteristic compensation circuit 40 according to the second embodiment uses a platinum resistance thermometer as the temperature compensation resistor 41, and replaces the temperature compensation resistor 42 with a resistor element (for example, a chip resistor element, a metal film). Resistive element) is used. The temperature characteristic 210 of the CTAT circuit 30 below the absolute temperature T0 is similar to the first embodiment in that the voltage and current decrease more rapidly than the temperature characteristic 100 of the CTAT circuit not connected to the temperature characteristic compensation circuit 40. On the other hand, since the temperature characteristic of the resistor is the same as that of the conventional bias resistor 32, the temperature characteristic 230 of the CTAT circuit 30 at the absolute temperature T0 or higher is transferred to the temperature characteristic compensation circuit 40 as shown in FIG. This is the same as the temperature characteristic 100 of the CTAT circuit that is not connected. According to the temperature characteristic compensation circuit 40 according to the second embodiment, the transistor Tr1, the positive slope of the temperature characteristic below the absolute temperature T0 is a steep slope, and the positive slope of the temperature characteristic above the absolute temperature T0 is normal. Constant bias currents Ib1, Ib2, and Ib3 having no temperature dependency can be supplied to Tr2 and Tr3. Similar effects can be obtained by using a thermistor PTC as the temperature compensation resistor 41 and using a resistance element having no temperature compensation function instead of the temperature compensation resistor 42.

  The temperature characteristic compensation circuit 40 according to the third embodiment uses a resistance element (for example, a chip resistance element or a metal film resistance element) that does not have a temperature compensation function instead of the temperature compensation resistor 41, and the thermistor NTC as the temperature compensation resistor 42. Is used. The temperature characteristic 220 of the CTAT circuit 30 at the absolute temperature T0 or higher is similar to the temperature characteristic 100 of the CTAT circuit not connected to the temperature characteristic compensation circuit 40, as in the first embodiment. On the other hand, since the temperature characteristic of the resistor is the same as that of the conventional bias resistor 32, the temperature characteristic 240 of the CTAT circuit 30 below the absolute temperature T0 is transferred to the temperature characteristic compensation circuit 40 as shown in FIG. This is the same as the temperature characteristic 100 of the CTAT circuit that is not connected. According to the temperature characteristic compensation circuit 40 according to the third embodiment, the transistor Tr1, the positive slope of the temperature characteristic below the absolute temperature T0 is normal, and the positive slope of the temperature characteristic above the absolute temperature T0 is gradual. Constant bias currents Ib1, Ib2, and Ib3 having no temperature dependency can be supplied to Tr2 and Tr3.

  In the first to third embodiments, the CTAT circuit 30 is illustrated as a bias power source that supplies the bias currents Ib1, Ib2, and Ib3 to the transistors Tr1, Tr2, and Tr3 having positive temperature characteristics. However, the present invention is not limited to this. For example, a PTAT circuit may be used as a bias power source that supplies bias currents Ib1, Ib2, and Ib3 to transistors Tr1, Tr2, and Tr3 having negative temperature characteristics. In the first to third embodiments, the bias circuit 20 of the power amplifier 10 is illustrated as an application example of the temperature characteristic compensation circuit 40, but may be applied to a temperature compensation circuit for a reference voltage, a temperature sensor, or the like.

  The present invention can be applied to a bias circuit of a power amplifier, a temperature compensation circuit for a reference voltage, a temperature sensor, or the like.

DESCRIPTION OF SYMBOLS 10 ... Power amplifier 20 ... Bias circuit 30 ... CTAT circuit 40 ... Temperature characteristic compensation circuit 41, 42 ... Temperature compensation resistor 43 ... Switch 44 ... Comparator 45 ... Reference voltage 46 ... Temperature sensor Tr1, Tr2, Tr3 ... Transistor

Claims (3)

A power supply circuit having a temperature compensation function for supplying a current or voltage to the circuit element so as to cancel a temperature change in the current or voltage of the circuit element;
A temperature characteristic compensation circuit for compensating for a deviation between the temperature characteristic of the power supply circuit and the temperature characteristic of the circuit element;
A temperature compensation circuit comprising: The temperature compensation circuit according to claim 1,
The temperature characteristic compensation circuit includes one or more temperature compensation resistors, one or more resistance elements that do not have a temperature compensation function, and one or more temperature compensation resistors and one that does not have the temperature compensation function. A temperature compensation circuit comprising: a switch that connects any one selected from one or a plurality of resistance elements according to temperature to a current path from a power supply to the power supply circuit.   A power amplifier comprising the temperature compensation circuit according to claim 1.

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