WO2006112669A1

WO2006112669A1 - Temperature compensation bias circuit for the darlington amplifier

Info

Publication number: WO2006112669A1
Application number: PCT/KR2006/001467
Authority: WO
Inventors: Hyung-Mo Yoo; Allen Sweet
Original assignee: Berex Corp
Current assignee: Berex Corp
Priority date: 2005-04-21
Filing date: 2006-04-19
Publication date: 2006-10-26
Anticipated expiration: 2007-10-21
Also published as: KR20050055642A; KR100556192B1

Abstract

The present invention relates to a temperature compensation bias circuit, and more particularly, to a temperature compensation bias circuit of a Darlington amplifier to which a temperature compensation transistor is coupled in order to improve a temperature characteristic. The temperature compensation bias circuit includes a first transistor having a base to which a signal is input and an emitter from which a collector-base current Icel is output, a second transistor having a base to which an output signal from the emitter of the first transistor is input and a collector from which a collector-base current Ice2 is output, a temperature compensation transistor having an input connected to the base of the first transistor for temperature compensation of the first and second transistors, wherein the temperature compensation transistor has two transistors connected in series and having bases to which collector signals are respectively input, a first resistor connected to the emitter of the first transistor, for controlling the flow of a current flowing through the first transistor and performing impedance matching, a second resistor connected to the emitter of the second transistor, for protecting the second transistor upon occurrence of overvoltage and performing output impedance matching, and a bias resistor coupled to both ends of the temperature compensation transistor so that a constant bias voltage is applied to the temperature compensation transistor.

Description

TEMPERATURE COMPENSATION BIAS CIRCUIT FOR THE

DARLINGTON AMPLIFIER

Technical Field

[I] The present invention relates to a temperature compensation bias circuit, and more particularly, to a temperature compensation bias circuit of a Darlington amplifier to which a temperature compensation transistor is coupled in order to improve a temperature characteristic.

Background Art [2] In general, a Darlington amplifier is a complex circuit having two or more transistors connected in series. In this amplifier, two PNP or NPN transistors are combined and connected to one equivalent transistor. [3] The Darlington amplifier has a very high input impedance, a very low output impedance, and a very high current gain accordingly. Therefore, the Darlington amplifier is used for a high-power amplification circuit since it can obtain a very high current amplification factor.

[4] FIG. 1 is a circuit diagram of a Darlington amplifier in the related art.

[5] As shown in FIG. 1, the Darlington amplifier includes two NPN transistors and four resistors. [6] The resistors Rl, R4 serve to divide a voltage. The resistors Rl, R4 have a feedback effect of deciding a bias point and deciding impedance matching, gain, and linearity. [7] The resistor R2 serves to control a current flowing through the NPN transistor Ql and the NPN transistor Q2 and to perform impedance matching. [8] The resistor R3 is connected to an emitter of the NPN transistor Q2. The resistor R3 serves to protect the NPN transistor Q2 upon occurrence of overvoltage and to perform output impedance matching.

[9] The operation of the Darlington amplifier shown in FIG. 1 will be described below.

[10] The NPN transistor Ql has a base to which a signal is input and an emitter connected to a base of the NPN transistor Q2. The NPN transistor Q2 has a collector from which a signal is output.

[I I] Furthermore, the NPN transistor Ql has the base connected to the resistor R4 and has the collector connected to the resistor Rl.

[12] The resistor R2 is connected between an emitter of the NPN transistor Ql and the base of the NPN transistor Q2. The NPN transistor Q2 has an emitter connected to the resistor R3.

[13] In addition, the collector of the NPN transistor Ql is connected to the collector of the NPN transistor Q2. [14] A base-emitter current Ibel flows between the base and the emitter of the NPN transistor Ql through an input signal input to the base of the NPN transistor Ql. A collector-emitter current Icel flows between the collector and the emitter of the NPN transistor Ql. [15] The collector-emitter current Icel is input to the base of the NPN transistor Q2. The collector-emitter current Icel controls only a necessary current amount to flow through the NPN transistor Q2 through the resistor R2. [16] That is, the collector-emitter current Icel controls the base-emitter current Ibe2 of the NPN transistor Q2 to flow and the collector-emitter current Ice2 to flow through the resistor R3. [17] FIG. 2 is a circuit diagram of a temperature compensation bias circuit including the

Darlington amplifier shown in FIG. 1. [18] Referring to FIG. 2, to reduce a current change amount depending on variation in temperature, a temperature compensation resistor is connected to one side of the

Darlington amplifier.

[19] Furthermore, to compensate for a reduction in a voltage of the temperature compensation resistor connected to the Darlington amplifier, a supply voltage higher than a voltage necessary for the operation of the Darlington amplifier is applied. [20] FIG. 3 is a graph illustrating voltage-current change curve in the Darlington amplifier of FIG. 1. [21]

Disclosure of Invention

Technical Problem

[22] From FIG. 3, it can be seen that the Darlington amplifier is designed to operate at a voltage of 5 V, and when a temperature is changed from a normal temperature (25⁰C) at which a voltage of 5V is applied to -3O⁰C or 85⁰C, the rate of current change reduces by 12% and increases by 43%.

[23] This is caused by a semiconductor characteristic in which the band gap of the NPN transistor Ql and the NPN transistor Q2 is increased at -3O⁰C, but is reduced at +85⁰C.

[24] At -3O⁰C, the band gap of the NPN transistor Ql and the NPN transistor Q2 is increased. Therefore, in order for the same current to be supplied from the Darlington amplifier, it is necessary to increase an external voltage.

[25] However, as the external voltage is constant, a current flowing through the

Darlington amplifier is decreased. It results in a degraded characteristic in which Radio Frequency (RF) characteristics at normal temperature, such as gain, power, and linearity, are not properly obtained. [26] In other words, as a temperature is lowered, an amount of current reduction is increased. This results in a degraded characteristic. [27] At 85⁰C, the band gap of the NPN transistor Ql and the NPN transistor Q2 is reduced. Therefore, in order for the same current to be supplied from the Darlington amplifier, it is necessary to decrease an external voltage. [28] However, as the external voltage is constant, a current flowing through the

Darlington amplifier is increased. It results in a degraded characteristic in which the

RF characteristics at normal temperature, such as gain, power, and linearity, are not properly obtained. [29] That is, In other words, as a temperature is increased, an amount of current reduction is increased. This results in a degraded characteristic. [30] Therefore, if the band gap is varied depending on changed in temperature, a transistor turn-on voltage is changed and a current flowing through the transistor is changed accordingly. [31] That is, at a low-temperature state, the band gap of the semiconductor is increased and the turn-on voltage of the transistor rises. However, a bias voltage decided by

R1/R4 of the Darlington amplifier shown in FIG. 1 is decreased. [32] In contrast, at a high- temperature state, the band gap of the semiconductor is decreased. Accordingly, the bias voltage decided by R1/R4 of the Darlington amplifier shown in FIG. 1 is increased. [33] From the above, it can be seen that variation in current and variation in temperature have the exponential relationship. [34] FIG. 4 is a curve showing the voltage and current variation relationship when an external resistor of 16Ω is added to the Darlington amplifier of FIG. 1 and a voltage is raised from 5V to 6V. [35] From FIG. 4, it can be seen that about 14% of current is reduced when a voltage of

6V, which is higher than a driving voltage (5V) of the Darlington amplifier, is applied and a Darlington driving voltage of 6V is applied at -3O⁰C compared with normal temperature (25⁰C) in order to compensate for a voltage reduction occurring due to the addition of the external resistor in the temperature compensation bias circuit in which the external resistor is added to the Darlington amplifier of FIG. 2 and about 14% of current is increased at 85⁰C. [36] FIG. 5 is a graph illustrating power loss at the temperature compensation bias circuit employing the external resistor. [37] The power loss refers to loss occurring due to the flow of a current in the temperature compensation resistor shown in FIG. 2. From FIG. 5, it can be seen that power loss of 19% occurs at normal temperature (25⁰C) when a voltage is 6V, power loss of 17% occurs at -3O⁰C, and power loss of 23% occurs at -85⁰C. [38] However, in the prior art Darlington amplifier and the temperature compensation bias circuit using the same, an amount of current change is very great depending on variation in temperature. Therefore, it is necessary to add an external resistor, etc. in order to solve the problem.

[39] Furthermore, the prior art Darlington amplifier and the temperature compensation bias circuit using the same are problematic in that a voltage higher than an operating voltage in order to drive the Darlington amplifier must be applied due to the addition of the external resistor, etc., an overall system efficiency is low because of a voltage consumed at the external resistor, etc., and additional power loss is caused due to the external resistor, etc.

[40]

Technical Solution

[41] Accordingly, the present invention has been made in view of the above problems occurring in the prior art, and it is an object of the present invention to provide a temperature compensation bias circuit of a Darlington amplifier, in which it can perform temperature compensation through the combination of a temperature compensation transistor or diode without adding an external resistor to the Darlington amplifier or applying a voltage higher than a driving voltage.

[42] To achieve the above object, according to an aspect of the present invention, there is provided a temperature compensation bias circuit of a Darlington amplifier, including a first transistor having a base to which a signal is input and an emitter from which a collector-base current Icel is output, a second transistor having a base to which an output signal from the emitter of the first transistor is input and a collector from which a collector-base current Ice2 is output, a temperature compensation transistor having an input connected to the base of the first transistor for temperature compensation of the first and second transistors, wherein the temperature compensation transistor has two transistors connected in series and having bases to which collector signals are respectively input, a first resistor connected to the emitter of the first transistor, for controlling the flow of a current flowing through the first transistor and performing impedance matching, a second resistor connected to the emitter of the second transistor, for protecting the second transistor upon occurrence of overvoltage and performing output impedance matching, and a bias resistor coupled to both ends of the temperature compensation transistor so that a constant bias voltage is applied to the temperature compensation transistor.

[43] The preset invention can construct a temperature compensation bias circuit without using an additional component in order to compensate for a temperature of the Darlington amplifier and using a voltage higher than a voltage necessary to drive the Darlington amplifier. Accordingly, the preset invention is advantageous in that it can obtain a temperature compensation effect that is twice better than that in the related art.

Brief Description of the Drawings

[44] FIG. 1 is a circuit diagram of a Darlington amplifier in the related art;

[45] FIG. 2 is a circuit diagram of a temperature compensation application circuit in the related art;

[46] FIG. 3 is a graph illustrating a voltage-current change curve in the related art;

[47] FIG. 4 is a graph illustrating the other voltage-current change curve depending on the addition of a temperature compensation resistor in the related art. [48] FIG. 5 is a graph illustrating power loss of a temperature compensation bias circuit in the related art; [49] FIG. 6 is a circuit diagram of a Darlington amplifier according to the present invention; [50] FIG. 7 is a detailed circuit diagram of a temperature compensation application circuit shown in FIG. 6; and [51] FIG. 8 is a graph illustrating a voltage-current change curve according to the present invention. [52]

Best Mode for Carrying Out the Invention [53] The present invention will now be described in detail in connection with preferred embodiments with reference to the accompanying drawings. [54] FIG. 6 is a circuit diagram of a Darlington amplifier according to the present invention. [55] Referring to FIG. 6, the Darlington amplifier includes a first transistor 610, a second transistor 620, a temperature compensation transistor 630, a first resistor 640, a second resistor 650, and a bias resistor 660. [56] The first transistor 610 has a base to which a signal is input and an emitter connected to a base of the second transistor 620. [57] The second transistor 620 has the base connected to the emitter of the first transistor

610 and has a collector-emitter current set to flow through the second resistor 650. [58] The temperature compensation transistor 630 includes two transistors coupled in series. The two transistors have bases to which collector signals are input and serve as a diode. At this time, a current is set to flow through the bias resistor 660. [59] In the present embodiment, it has been described that the number of transistors constituting the temperature compensation transistor 630 is two corresponding to the number of the first transistor 610 and the second transistor 620. However, the temperature compensation bias circuit may be constructed such that the number of the first transistor 610 and the second transistor 620 is identical to that of the temperature compensation transistor 630.

[60] Meanwhile, in the present embodiment, it has been described that transistors connected in series are used in order to perform temperature compensation. However, the transistors may be replaced with diodes connected in series in order to perform temperature compensation.

[61] The first resistor 640 is connected to the emitter of the first transistor 610, and it serves to control a current and perform impedance matching.

[62] The second resistor 650 is connected to the emitter of the second transistor 620, and it serves to protect the second transistor 620 from overvoltage and perform output impedance matching.

[63] The bias resistor 660 is connected to both ends of the temperature compensation transistor 630 and serves to apply a constant bias voltage to the temperature compensation transistor 630.

[64] The operation of the Darlington amplifier constructed as shown in FIG. 6 will be described below.

[65] The output terminal is applied with a voltage Vcc. In a state where a predetermined voltage is kept by the bias resistor 660 of the input signal terminal, the base of the first transistor 610 is applied with a signal. The base-emitter current Ibel flows between the based and emitter of the first transistor 610 and the collector-emitter current Icel flows between the collector and the emitter of the first transistor 610.

[66] In addition, the first resistor connected to the emitter of the first transistor 610 controls the collector-emitter current Icel.

[67] The collector-emitter current Icel of the first transistor 610 is input to the base of the second transistor 620 and controls a current flowing through the second transistor 620.

[68] That is, as the collector-emitter current Icel of the first transistor 610 is input to the base of the second transistor 620, the base-emitter current Ibe2 flows between the base and emitter of the second transistor 620 and the collector-emitter current Ice2 flows through the second resistor 650 between the collector and emitter of the second transistor 620.

[69] Meanwhile, as the output terminal is applied with the voltage Vcc, the voltage is also applied to the temperature compensation transistor 630 connected to the bias resistor 660 of the input terminal and a current flows through the bias resistor 660.

[70] If the voltage Vcc is applied to the first transistor 610 and the second transistor 620 and the turn-on voltage is changed at a low-temperature or high-temperature state, the turn-on voltage of the temperature compensation transistor 630 connected to the bias resistor of the input terminal is also changed. [71] That is, the base of the first transistor 610 is applied with a constant voltage regardless of variation in temperature and the base of the second transistor 620 connected to the emitter of the first transistor 610 is also applied with a constant voltage.

[72] Variation in an amount of current flowing through the first transistor 610 and the second transistor 620 constituting the Darlington amplifier 600 is also kept constant regardless of low temperature or high temperature.

[73] At this time, the voltage Vcc and a current flow through the temperature compensation transistor 630, which is connected to the bias resistor 660 of the input terminal, in proportion to a voltage and current flowing through the Darlington amplifier 600.

[74] That is, a temperature depending on the operation of the first transistor 610 and the second transistor 620 of the Darlington amplifier 600 is compensated for in a state where the temperature compensation transistor 630 connected to the bias resistor 660 of the input terminal is optimal.

[75] The transistor element of the temperature compensation transistor 630 can perform temperature compensation by controlling the bias voltage within an available temperature range.

[76] Therefore, the temperature compensation transistor 630 connected to the bias resistor 660 of the input terminal causes a current flowing through the Darlington amplifier 600 of the first transistor 610 and the second transistor 620 to be the same regardless of variation in temperature. As a result, RF characteristics, such as RF gain, RF power, and RF linearity, are not influenced by variation in temperature.

[77] FIG. 7 is a detailed circuit diagram of the temperature compensation application circuit shown in FIG. 6.

[78] As shown in FIG. 7, a temperature compensation resistor that drops the supply voltage Vcc at an output terminal of a Monolithic Microwave IC (MMIC) circuit including the Darlington amplifier 600 of FIG. 6 is removed, and temperature compensation is performed by the operation of the temperature compensation transistor within the MMIC circuit. Therefore, unnecessary power consumption can be saved and a temperature compensation effect can be doubled.

[79] FIG. 8 is a graph illustrating voltage-current variation depending on the operation of the temperature compensation bias circuit of the Darlington amplifier shown in FIGS. 6 and 7.

[80] From FIG. 8, it can be seen that in a Darlington amplifier designed to operate at 5V, about 10% of a current change amount is generated at 3.5V versus -3O⁰C and about 13% of a current change amount is generated at 85⁰C.

[81] It can also be seen that in a state where a voltage of up to 5 V is applied, about of 7% of a reduced current change amount is kept constant at -3O⁰C, about of 7% of an increased current change amount is kept constant at 85O⁰C, and a current change amount between -3O⁰C and 85⁰C is improved within a range of about +/-10% at +/- 30%.

[82] Therefore, there is an effect in that a temperature compensation effect can be doubled using the temperature compensation transistor without applying an unnecessary high voltage of the Darlington amplifier.

[83]

Industrial Applicability

[84] As described above, the preset invention constructs a temperature compensation bias circuit without using an additional component in order to compensate for a temperature of the Darlington amplifier and using a voltage higher than a voltage necessary to drive the Darlington amplifier. Accordingly, the preset invention is advantageous in that it can obtain a temperature compensation effect that is twice better than that in the related art.

[85] While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.

Claims

[1] A temperature compensation bias circuit of a Darlington amplifier, comprising: a first transistor having a base to which a signal is input and an emitter from which a collector-base current Icel is output; a second transistor having a base to which an output signal from the emitter of the first transistor is input and a collector from which a collector-base current Ice2 is output; a temperature compensation transistor having an input connected to the base of the first transistor for temperature compensation of the first and second transistors, wherein the temperature compensation transistor has two transistors connected in series and having bases to which collector signals are respectively input; a first resistor connected to the emitter of the first transistor, for controlling the flow of a current flowing through the first transistor and performing impedance matching; a second resistor connected to the emitter of the second transistor, for protecting the second transistor upon occurrence of overvoltage and performing output impedance matching; and a bias resistor coupled to both ends of the temperature compensation transistor so that a constant bias voltage is applied to the temperature compensation transistor.

[2] The temperature compensation bias circuit of claim 1, wherein temperature compensation resistor is removed that generates a drop of a supply voltage at an output terminal of a MMIC circuit including the first transistor and the second transistor, temperature compensation is performed by the operation of the temperature compensation transistor.

[3] The temperature compensation bias circuit of claim 1 or 2, wherein the temperature compensation transistor is replaceable with temperature compensation diodes connected in series.