JP4156539B2 - Variable gain amplifier circuit, IC equipped with the same, wireless communication system - Google Patents

Description

  INDUSTRIAL APPLICABILITY The present invention is capable of controlling a gain used in an integrated circuit, and particularly used in a radio transmission / reception high-frequency integrated circuit. The present invention relates to a communication system.

  Conventionally, in a wireless communication system such as a mobile communication such as a mobile phone, the signal strength of a received signal to be received varies, and changes with movement. Therefore, in order to adjust the strength of the received signal to an optimal level, A variable gain amplifier circuit is used. Such a variable gain amplifier circuit is disclosed in Patent Document 1.

As shown in FIG. 3, the variable gain amplifier circuit includes a first transistor Q1 having an input signal terminal IN1 connected to the base, and a second transistor Q2 having an inverted input signal terminal IN2 connected to the base. A first current source connected to the emitter of the first transistor Q1, a second current source connected to the emitter of the second transistor Q2, the emitter of the first transistor, And an emitter resistor R _E connected between the emitters of the second transistor.

  The variable gain amplifier circuit includes a third transistor Q3 having an emitter connected to the collector of the first transistor Q1 and a collector connected to the output signal terminal OUT1, and a collector of the first transistor Q1. And a fourth transistor Q4 having an emitter connected and a collector connected to a power source, and a first load resistor connected between the collector of the third transistor Q3 and the power source.

  Further, the variable gain amplifier circuit includes a fifth transistor Q5 having an emitter connected to the collector of the second transistor Q2, a collector connected to a power source, and an emitter connected to the collector of the second transistor Q2. Are connected, and the collector is connected to the inverted output signal terminal OUT2. The sixth transistor Q6 has a second load resistor connected between the collector of the sixth transistor Q6 and the power source.

Here, the current value of the first current source and the current value of the second current source are the same in common and expressed as I _0, and the resistance value of the first load resistance and the resistance value of the second load resistance are the same in common. Represented as R _L1 .

A reference voltage V _B1 is applied to the bases of the transistors Q3 and Q6, and a control voltage V _C1 is applied to the bases of the transistors Q4 and Q5. The lower condition than V _C1 is V _B1, while no current flows through the transistor Q4 and transistors Q5, since the current flows through the transistor Q3 and the transistor Q6, the amplified signal is output through the load resistor R _L1 to OUT1, OUT2.

When V _C1 is made larger than V _B1 , current starts to flow through the transistors Q4 and Q5, and the current flowing through the transistors Q3 and Q6 decreases, so that the gain decreases. Gain A _V with respect to the control voltage V _C1 is as shown in the following equation (1).

V _T = kT / q: thermal voltage
k: Boltzmann constant
q: electron unit charge
T: Absolute temperature
JP 58-114614 A (publication date: July 8, 1983)

However, in the conventional configuration, the thermal voltage V _T proportional to the absolute temperature T exists in the gain equation (1). Therefore, the gain of the conventional variable gain amplifier circuit changes with temperature.

In a system that switches between transmission and reception, such as a wireless communication system such as a cellular phone, the time from reception to adjustment of the received signal to an optimum level is limited. Therefore, the following method may be taken as a gain control system of the variable gain amplifier circuit.
(I) Detect the level of the input signal
(II) Calculate how much the level should be changed to achieve the optimum level.
(III) An optimal control voltage value is calculated from the variable level obtained in (II) and the value of Δgain / Δcontrol voltage.
(IV) Set the control voltage value to the value obtained in (III).

When this method is used, the Δ gain / Δ control voltage must always be constant. When the Δ gain / Δ control voltage changes with temperature as in the conventional example, the signal is brought to an optimum level in a short time. This causes a problem that adjustment may not be possible.

  The inventors input a control voltage to a differential amplifier circuit using a current proportional to the square of temperature as a current source, and the output of the differential amplifier circuit is used as a control signal (control voltage) for the variable gain amplifier circuit. By using it, the temperature dependency of Δgain / Δcontrol voltage was prevented and the above problem was solved.

  In order to solve the above-described problem, a variable gain amplifier circuit according to the present invention includes an amplifier circuit that changes the gain according to an external input control voltage and outputs an amplified signal obtained by amplifying an input signal with the gain, and a temperature variation And a control voltage adjustment circuit that outputs an adjustment control voltage obtained by adjusting the input control voltage to the amplifier circuit as an input control voltage so as to cancel the fluctuation of the gain due to the above.

  According to the above configuration, the control voltage adjustment circuit is set to output the adjustment control voltage obtained by adjusting the input control voltage to the amplifier circuit as the input control voltage so as to cancel the gain fluctuation due to temperature fluctuation. Thus, the temperature dependence of the amplified signal from the amplifier circuit can be canceled, and an amplified signal having a gain voltage with reduced dependence on temperature fluctuation can be output.

  In the variable gain amplifier circuit, the control voltage adjustment circuit includes a first differential amplifier circuit including a first current source, and the first current source changes a current flowing through the first current source according to a change in absolute temperature. It is preferable to set so as to.

  According to the above configuration, the temperature dependency of the amplified signal from the amplifier circuit can be offset by setting the current flowing through the first current source so as to change in accordance with the change in absolute temperature. It is possible to output an amplified signal having a gain voltage with suppressed characteristics.

  In the variable gain amplifier circuit, the control voltage adjustment circuit includes a first differential amplifier circuit including a first current source, and the current flowing through the first current source is proportional to the square of the absolute temperature. It is desirable that it is set to change.

  According to the above configuration, by setting the current flowing through the first current source so as to change in proportion to the square of the absolute temperature, the temperature dependence of the amplified signal from the amplifier circuit can be offset, and the temperature fluctuation can be reduced. An amplified signal with a gain voltage that avoids the dependency can be output.

  In the variable gain amplifier circuit, the amplifier circuit includes a second differential amplifier circuit including a second current source, and the second current source is set so that a current flowing through the amplifier circuit is proportional to an absolute temperature. May be.

  According to the above configuration, by setting the current flowing through the second current source to be proportional to the absolute temperature, the temperature dependence of the amplified signal from the amplifier circuit can be offset and the dependence on the temperature fluctuation is avoided. An amplification signal of gain voltage can be output.

  In the variable gain amplifier circuit, the amplifier circuit includes a first transistor having an input signal terminal connected to the base, a second transistor having an inverting input signal terminal connected to the base, and the first transistor. A first current source connected to the emitter, a second current source connected to the emitter of the second transistor, an emitter of the first transistor, and an emitter of the second transistor. The emitter is connected to the collector of the first transistor, the emitter is connected to the collector, and the collector is connected to the output signal terminal. The collector is connected to the collector of the first transistor, and the collector is connected to the collector of the first transistor. A fourth transistor connected to the power source, and a first load resistor connected between the collector of the third transistor and the power source A fifth transistor having an emitter connected to the collector of the second transistor and a collector connected to a power supply; an emitter connected to the collector of the second transistor; and a collector connected to an inverted output signal terminal. And a second load resistor connected between the collector of the sixth transistor and a power source, and the control voltage adjustment circuit is based on the control voltage terminal. A seventh transistor connected to a base of the third transistor and a base of the sixth transistor, a reference voltage terminal connected to the base, and a collector commonly connected to the fourth transistor; An eighth transistor connected to a base of the fifth transistor and a base of the fifth transistor; and A third current source connected to the emitter and the emitter of the eighth transistor; a third load resistor connected between the collector of the seventh transistor and VCC; and a collector of the eighth transistor; And a fourth load resistor connected between the VCC and the first current source and the second current source have a characteristic in which the current is proportional to the absolute temperature, By providing the current source with a characteristic that is proportional to the square of the absolute temperature, the current source may have a gain characteristic that does not depend on temperature.

  In order to solve the above-described problems, an IC according to the present invention is characterized by mounting any one of the variable gain amplifier circuits described above. According to the above configuration, by mounting the variable gain amplifier circuit in which the temperature dependence of the amplified signal to be output is reduced, the above configuration is used for mobile communication such as a mobile phone, resulting in temperature fluctuations. Communication failure can be prevented.

  In order to solve the above problems, a wireless communication system according to the present invention includes the above-described IC. According to the above configuration, since the IC having the variable gain amplifier circuit in which the temperature dependence of the amplified signal to be output is reduced is mounted, the above configuration is used for mobile communication such as a mobile phone, so that the temperature Communication failures due to fluctuations can be prevented.

  As described above, the variable gain amplifier circuit according to the present invention changes the gain according to an external input control voltage and outputs an amplified signal obtained by amplifying an input signal with the gain, and the gain due to temperature fluctuations. And a control voltage adjustment circuit that outputs an adjustment control voltage obtained by adjusting the input control voltage so as to cancel the fluctuation to the amplifier circuit as an input control voltage.

  Therefore, the above configuration can cancel the temperature dependence of the amplified signal from the amplifier circuit by the adjusted adjustment control voltage, and can output the amplified signal of the gain voltage independent of the temperature fluctuation. Therefore, since the above configuration can output an amplified signal that does not depend on temperature fluctuations, when used in a variable gain amplifier circuit in a communication field such as a mobile communication device such as a mobile phone, it has an effect of stabilizing communication.

  An embodiment of the present invention will be described below with reference to FIGS. That is, the embodiment of the variable gain amplifier circuit according to the present invention includes an amplifier circuit 1 similar to the conventional example and a control voltage adjustment circuit 2 as shown in FIG. Note that members having the same functions as those of the conventional variable gain amplifier circuit described in the “Background Art” column are assigned the same reference numerals, and detailed descriptions thereof are omitted.

The amplifier circuit 1 includes input signal terminals IN1 and IN2, transistors Q1 to Q6, constant current sources (second current sources) I ₀ , emitter resistors R _E , load resistors R _L1, and outputs. It is constituted by signal terminals OUT1 and OUT2.

The respective constant current sources I ₀ and an emitter resistor R _E, emitter resistor for each transistor Q1~Q2 constituting the differential amplifier circuit, i.e. has a differential load resistor amplifier circuit, the constant current sources I ₀ Can be set to a high resistance, the gain width of the differential amplifier circuit using the transistors Q1 and Q2 can be increased. In this embodiment, each constant current source I ₀ is different from the conventional one, and details thereof will be described later.

Each of the transistors Q3 to Q6 constitutes a dual differential amplifier circuit. Each load resistor R _L1 is an output load resistor inserted between the collectors of the transistors Q3 to Q6 whose collectors are connected to the output signal terminals OUT1 and OUT2, respectively, and the power supply line VCC.

In such an amplifier circuit 1, the difference between the input signals respectively input to the input signal terminals IN1 and IN2 is caused by the gain adjusted by the control voltages VC2 and VB2 input to the bases of the transistors Q3 and Q6. Amplified amplified signals are output from the output signal terminals OUT1 and OUT2. Note that one of the input signals is usually a reference input signal, and the other is an input signal that requires gain adjustment. Further, the amplified signals from the output signal terminals OUT1 and OUT2 are out of phase with each other, and when only one amplified signal is required, the unnecessary amplified signal side load resistor R _L1 can be omitted.

The control voltage adjusting circuit 2 includes a constant current source (first current source) I ₁ , transistors Q 7 and Q 8, and load resistors R _L2 . The constant current source I ₁ will be described later. A constant current source I ₁ is commonly connected to the emitters of the transistors Q7 and Q8. Each load resistor R _L2 is an output load resistor connected to the collector of each transistor Q7, Q8.

In the control voltage adjusting circuit 2, the input control voltage V _C1 is input to the base of the transistor Q7, and the input control voltage V _B1 is input to the base of the transistor Q8. The adjustment control voltage V _C2 generated by one load resistor R _{L2 at} the collector of the transistor Q7 is connected to the bases of the transistors Q4 and Q5 of the amplifier circuit 1, and at the collector of the transistor Q8 by the other load resistor R _L2. The generated adjustment control voltage V _B2 is connected to the bases of the transistors Q3 and Q6 of the amplifier circuit 1. The gain of the amplifier circuit 1 is controlled by such adjustment control voltages V _C2 and V _B2 .

Then, in the present embodiment, the constant current source I _0, the output current of the constant current source I ₀ is proportional to the absolute temperature T, the constant current source I ₁ is constant-current source output current I ₁ is the absolute temperature T Is set to be proportional to the square of.

Next, the operation of the variable gain amplifier circuit according to the present invention will be described. First, the reference voltage V _B1 is applied to the base of the transistor Q8, and the comparison voltage V _C1 is applied to the base of the transistor Q7 as the input control voltage.

Since the base voltages of the transistors Q4 and Q5 are V _C2 and the base voltages of the transistors Q3 and Q6 are V _B2 ,
The relationship among V _C1 , V _B1 , V _C2 and V _B2 is as shown in the following equation (2).

Since the V _C2 -V _B2 is applied to the base of the transistor Q4, Q5 and Q3, Q6, the more the gain equation conventional example (1), the gain A _V of the variable gain amplifier circuit of FIG. 1 is the following formula (3)

Here, since I ₀ is proportional to the absolute temperature T and I ₁ is proportional to the square of the absolute temperature T, I ₀ = αT, I ₁ = βT ² (α, β: arbitrary constant) (4)
Can be represented as the gain A _V, at the following equation (5),

It can be expressed.

As is apparent from the equation (5), a constant current source I _0, which in proportion to the variation of the absolute temperature T of the current value, and, at least of the constant current source I ₁ was proportional to the square of the absolute temperature T of the current value by using one, the influence of the gain a _V thermal voltage proportional to the absolute temperature T is the temperature dependency of the gain a _V of the variable gain amplifier circuit according to the present invention shown being offset in Figure 1 is reduced. More preferably, the constant current source I _0, which in proportion to the variation of the absolute temperature T of the current value, and, by using both the constant current source I ₁ which is proportional to the square of the absolute temperature T of the current value, the absolute temperature effect of the gain a _V of the thermal voltage proportional to T is be more reliably canceled out, the temperature dependence of the gain a _V of the variable gain amplifier circuit according to the present invention shown in FIG. 1 can be avoided.

  Therefore, the variable gain amplifier circuit can be suitably used in a communication field such as a mobile communication such as a mobile phone that needs to quickly adjust the gain of a received signal whose strength changes variously, and can stabilize communication. .

Next, FIG. 2 shows an embodiment for producing a constant current source I ₁ that is proportional to the square of the absolute temperature. First, the constant current source I ₁ includes constant current sources I _A and I _B and transistors QA to QD. The constant current source I _A is a constant current source whose output current is proportional to the absolute temperature T, while the constant current source I _B is a constant current source whose output current does not depend on temperature.

The constant current source I _A is connected between the power supply line VCC and the collector of the transistor QA. The base of transistor QA is connected to its collector. The emitter of the transistor QA is connected to the collector of the transistor QB. The base of transistor QB is connected to its collector. The emitter of transistor QB is connected to ground. The collector of the transistor QC is connected to the power supply line VCC. The base of the transistor QC is connected to the collector and base of the transistor QA. The emitter of the transistor QC is connected to one terminal of the constant current source I _B. The other terminal of the constant current source I _B is connected to ground. The collector of the transistor QD is connected to the emitters of the transistors Q7 and Q8. The base of the transistor QD is connected to the emitter of the transistor QC. The emitter of the transistor QC is grounded.

In such a constant current source I ₁ , the base emitter voltage of the transistor QA is V _{BE (QA)} , the collector current is I _{C (QA)} , the base emitter voltage of the transistor QB is V _{BE (QB)} , and the collector current is I _{C (QB)} , the base emitter voltage of the transistor QC is V _{BE (QC)} , the collector current is I _{C (QC)} , the base emitter voltage of the transistor QD is V _{BE (QD)} , and the collector current is I _{C (QC)} ,
V _{BE (QA)} + V _{BE (QB)} = V _{BE (QC)} + V _{BE (QD)}
From I _{C (QA)} I _{C (QB)} = I _{C (QC)} I _{C (QD)}
And
I _A = I _{C (QA)} = I _{C (QB)} , I _B = I _{C (QC)} , I _out = I _{C (QD)}
So,
I _out = I _A ² / I _B = (6)
It becomes.

Here, since I _A is proportional to absolute temperature and I _B does not depend on temperature, in the constant current source I ₁ , the transistors QA and QB connected in series to each other in two stages are connected to the constant current source I _A. By connecting in series, I _out of the constant current source I ₁ is proportional to the square of the absolute temperature T.

Therefore, if I _out in FIG. 2 is used as I ₁ in FIG. 1, a variable gain amplifier circuit having no temperature dependence can be realized. _A constant current source proportional to the absolute temperature, such as the constant current source I ₀ in FIG. 1 or the constant current source I _{A in} FIG. 2, can be realized by using a band gap current source that is a known technique.

  Since such a variable gain amplifier circuit according to the present invention can be mainly composed of a semiconductor such as a transistor, it can be easily integrated into an IC. Such a miniaturized circuit is a wireless communication device such as a mobile phone. Can be easily installed in the system.

  In the above embodiment, an example in which an npn transistor is used for each of the transistors Q1 to Q8 has been described. However, a pnp transistor or FET may be used, or a combination thereof may be used. Good.

  The variable gain amplifier circuit of the present invention, an IC equipped with the variable gain amplifier circuit, and a wireless communication system equipped with the variable gain amplifier circuit can output an amplified signal having a gain characteristic with reduced dependence on temperature fluctuations. Therefore, the present invention can be applied to applications in the communication field such as mobile communication such as a mobile phone that is often used outdoors, where communication failure due to temperature fluctuation is likely to occur.

1 is a circuit diagram showing an embodiment of a variable gain amplifier circuit of the present invention. FIG. 2 is a circuit diagram of an embodiment of the constant current source I ₁ of FIG. It is a circuit diagram of a variable gain amplifier circuit, showing the prior art.

Explanation of symbols

1 amplifier circuit 2 control voltage adjustment circuit I _0, I ₁ constant current source Q1~Q8 transistor R _L1, R _L2 load resistor R _E emitter resistor

Claims (3)

An amplifier circuit that changes the gain by an external input control voltage and outputs an amplified signal obtained by amplifying the input signal by the gain;
In the variable gain amplifier circuit, characterized in that it and a control voltage adjustment circuit for outputting to the amplifier circuit adjusting control voltage to adjust the entering-force control voltage as an input control voltage,
The amplifier circuit is
A first transistor having an input signal terminal connected to the base;
A second transistor having an inverting input signal terminal connected to the base;
A first current source connected to the emitter of the first transistor;
A second current source connected to the emitter of the second transistor;
An emitter resistor connected between the emitter of the first transistor and the emitter of the second transistor;
A third transistor having an emitter connected to the collector of the first transistor and a collector connected to an output signal terminal;
A fourth transistor having an emitter connected to the collector of the first transistor and a collector connected to a power source;
A first load resistor connected between the collector of the third transistor and a power source;
A fifth transistor having an emitter connected to the collector of the second transistor and a collector connected to a power source;
A sixth transistor having an emitter connected to the collector of the second transistor and a collector connected to an inverted output signal terminal;
A second load resistor connected between the collector of the sixth transistor and a power source,
The control voltage adjustment circuit is
A seventh transistor having a control voltage terminal connected to the base and a collector commonly connected to the base of the third transistor and the base of the sixth transistor;
An eighth transistor having a reference voltage terminal connected to the base and a collector connected in common to the base of the fourth transistor and the base of the fifth transistor;
A third current source connected to the emitter of the seventh transistor and the emitter of the eighth transistor;
A third load resistor connected between the collector of the seventh transistor and VCC;
A fourth load resistor connected between the collector of the eighth transistor and VCC;
By having the characteristic that the current of the first current source and the current of the second current source are proportional to absolute temperature, and the characteristic of the current of the third current source being proportional to the square of absolute temperature,
A variable gain amplifier circuit having a gain characteristic independent of temperature . An IC comprising the variable gain amplifier circuit according to claim 1 . A wireless communication system comprising the IC according to claim 2 .

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