JP5485332B2 - Variable gain amplifier and amplifier circuit - Google Patents

Description

  The present invention relates to a variable gain amplifier and an amplifier circuit.

  Various products are shipped as wide-band variable gain amplifiers that can be used for communication and the like, for example, ADL5331 manufactured by Analog Devices. For example, the ADL 5331 has a wide frequency band of 10 MHz to 1.2 GHz, but the noise characteristics are such that the NF (Noise Figure) is 9 dB.

By the way, the noise characteristic (F) in the receiving unit or the like of the communication apparatus is expressed by the following equation (1) when (n−1) amplifiers are connected in series, that is, when an (n−1) stage amplifier circuit is configured. It is known that the noise characteristics of the amplifier in the previous stage are greatly affected. Note that F _i and G _i (i = 1, 2,..., N−1) are the noise figure and gain at each stage.

"ADL5331 data sheet", [online], May 2009, Analog Devices, Inc., [April 19, 2012 search], Internet <URL: http://www.analog.com/static/imported- files / data_sheets / ADL5331.pdf>

  Usually, in most mobile communication systems, the NF in the receiving unit or the like is stipulated to be 10 dB or less. In order to satisfy this stipulation with a multistage amplifier circuit using a plurality of amplifiers, the NF of the first stage amplifier is 3 dB or less Desired. In this case, the above-mentioned ADL5331 cannot be used.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a variable gain amplifier and an amplifier circuit with improved noise figure.

In order to solve the above problem, the present invention provides a first input terminal, a base connected to the first input terminal, an emitter grounded, and an emitter size corresponding to a desired saturation level of the variable gain amplifier. The determined first transistor, a first capacitor element having one end connected to the collector of the first transistor, one end connected to the other end of the first capacitor element, and the other end connected to the first capacitor A first passive element connected to the base of one transistor; a second passive element having one end connected to the power supply terminal and the other end connected to the collector of the first transistor; connected to the other end of the second passive element, and a second transistor having a collector connected to said power supply terminal, one terminal connected to the emitter of the second transistor, the other end of said first transistor Is connected to the over scan, comprises the third passive element impedance is determined according to the input impedance of the first transistor, and a first output terminal connected to the collector of said first transistor, The first passive element and the first capacitive element are variable gain amplifiers having variable element values.

In the variable gain amplifier described above, the present invention is provided between the third passive element and a base of the first transistor, and one end is connected to the other end of the third passive element. A fourth passive element having the other end connected to the base of the first transistor, a fifth passive element having one end connected to one end of the fourth passive element and the other end grounded The third passive element is connected to the base of the first transistor via the fourth passive element.

  The variable gain amplifier according to the present invention further includes a sixth passive element having one end connected to the emitter of the first transistor and the other end grounded. The emitter is grounded through the sixth passive element.

  The variable gain amplifier according to the present invention further includes a resistance element having one end connected to one end of the third passive element and the other end grounded, wherein the first transistor and the first A field effect transistor is used as the second transistor.

  In the variable gain amplifier described above, the third passive element may be formed of any one of a resistance element, a variable resistance element, and an inductor, or a resistance element, a variable resistance element, One of the inductors is formed by connecting in series.

According to another aspect of the present invention, there is provided the variable gain amplifier described above and an amplifier connected to the preceding stage of the variable gain amplifier, wherein a second input terminal and a base are connected to the second input terminal, and an emitter Is connected to the collector of the third transistor, and the value of the element is fixed. The third transistor has an emitter size determined according to the desired saturation level of the variable gain amplifier. A capacitive element, a seventh passive element having one end connected to the other end of the second capacitive element, the other end connected to the base of the third transistor, and a fixed element value; Is connected to the power supply terminal, the other end is connected to the collector of the third transistor, the base is connected to the other end of the eighth passive element, and the collector is the power supply terminal. Connected to A fourth transistor that has one end connected to the emitter of the fourth transistor, a ninth passive element and the other end is connected to the base of said third transistor, the collector of said third transistor And an amplifier having a second output terminal connected thereto, wherein the amplifier and the variable gain amplifier are connected in series.

  According to the present invention, when the emitter size of the first transistor is increased according to the output level required for the variable gain amplifier, the impedance of the third passive element is set according to the input impedance of the first transistor. By defining, the input impedance of the first transistor connected to the input terminal can be matched with the impedance of the bias circuit including the second transistor and the second and third passive elements. Thereby, a decrease in input impedance of the variable gain amplifier can be suppressed, and the noise figure can be improved.

1 is a circuit diagram showing a configuration of a variable gain amplifier 1 according to a first embodiment of the present invention. 3 is an equivalent circuit of a bias circuit including a transistor Tr2 in the present embodiment. It is a graph which shows the computer simulation result of the characteristic of the variable gain amplifier 1 in this embodiment. It is a circuit diagram which shows the structure of the variable gain amplifier 2 in 2nd Embodiment. It is a circuit diagram which shows the structure of the variable gain amplifier 3 in 3rd Embodiment. It is a circuit diagram which shows the structure of the variable gain amplifier 4 in 4th Embodiment. It is a circuit diagram which shows the structure of the amplifier circuit 10 in 5th Embodiment.

  Hereinafter, a variable gain amplifier and an amplifier circuit according to an embodiment of the present invention will be described with reference to the drawings.

<First Embodiment>
FIG. 1 is a circuit diagram showing a configuration of a variable gain amplifier 1 according to the first embodiment of the present invention. As shown in FIG. 1, the variable gain amplifier 1 includes an input terminal IN, an output terminal OUT, transistors Tr1 and Tr2, passive elements M1, M2, and M3, and a capacitive element C1.

  The transistor Tr1 has a base connected to the input terminal IN, a collector connected to the output terminal OUT, and an emitter grounded. The emitter size of the transistor Tr1 is determined according to the saturation level (output level) required for the variable gain amplifier 1.

  One end of the capacitive element C1 is connected to the collector of the transistor Tr1, and the other end is connected to one end of the passive element M1. The other end of the passive element M1 is connected to the base of the transistor Tr1. That is, the capacitive element C1 and the passive element M1 form a feedback loop that connects the collector and base of the transistor Tr1. As a result, a signal output from the collector of the transistor Tr1 is fed back to the base of the transistor Tr1 on the input side via the capacitive element C1 and the passive element M1. Further, the capacitance of the capacitive element C1 and the resistance value of the passive element M1 are variable. The gain of amplification by the transistor Tr1 is controlled by determining the feedback amount by changing the value (capacitance, resistance value) of one or both of the capacitive element C1 and the passive element M1.

  The passive element M2 has one end connected to a power supply terminal Bias that supplies a predetermined power supply voltage, and the other end connected to the collector of the transistor Tr1 and the output terminal OUT. The transistor Tr2 has a base connected to the other end of the passive element M2, a collector connected to the power supply terminal Bias, and an emitter connected to one end of the passive element M3. The other end of the passive element M3 is connected to the base of the transistor Tr1 and the input terminal IN. That is, the transistor Tr2 and the passive elements M2 and M3 form a bias circuit (constant current circuit) that applies a bias to the base of the transistor Tr1.

FIG. 2 is an equivalent circuit of a bias circuit including the transistor Tr2 in the present embodiment. In the figure, rbe is the base of the transistor Tr2 - a emitter resistor, gm is the transconductance of the transistor Tr 2, Z1 is the impedance of the passive element M2, Z2 is the impedance of the passive element M3. The voltage Vi corresponds to the voltage at the input terminal IN, the current Ii corresponds to the current at the input terminal IN, and the voltage V1 corresponds to the base-emitter voltage of the transistor Tr2.
The input impedance Zi of the bias circuit in the present embodiment is expressed by the following equation (2).

  Further, the voltage Vi and the current Ii in the formula (1) can be expressed by the following formula (3-1) and the following formula (3-2).

  Substituting equation (3-1) into equation (3-2) yields the following equation (4).

  That is, the input impedance Zi in the equation (2) can be expressed by the following equation (5).

  As can be seen from equation (5), the input impedance Zi of the bias circuit can be changed in proportion to the impedance Z2 of the passive element M3. For this reason, the input impedance of the variable gain amplifier 1 can be easily changed by changing the impedance of the passive element M3.

When the emitter size of the transistor Tr1 is increased according to the output level required for the variable gain amplifier 1, by determining the input impedance Zi of the bias circuit based on the input impedance of the transistor Tr1 and the equation (5), A decrease in input impedance of the variable gain amplifier 1 can be suppressed, and the noise figure can be improved.
That is, in the variable gain amplifier 1 having a variable gain function, the impedance of the passive element M3 is determined according to the input impedance of the transistor Tr1, thereby matching the input impedance of the variable gain amplifier 1 and improving the noise characteristics. can do.

  FIG. 3 is a graph showing a computer simulation result of the characteristics of the variable gain amplifier 1 in the present embodiment. In the figure, the horizontal axis represents frequency and the vertical axis represents gain. The figure shows characteristics when the passive element M1 and the capacitive element C1 are changed. As shown in the figure, the variable gain amplifier 1 has a variable gain function over a wide band.

<Second Embodiment>
FIG. 4 is a circuit diagram showing a configuration of the variable gain amplifier 2 in the second embodiment. The variable gain amplifier 2 is different from the variable gain amplifier 1 (FIG. 1) in the first embodiment in that the variable gain amplifier 2 includes a passive element M4 and a passive element M5. In the variable gain amplifier 2, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

The passive element M4 is provided between the passive element M3 and the input terminal IN, and one end is connected to the other end of the passive element M3 and the other end is connected to the input terminal IN. That is, in the variable gain amplifier 2, the passive element M3 is connected to the input terminal IN via the passive element M4.
The passive element M5 has one end connected to the other end of the passive element M3 and the other end grounded.

  In the variable gain amplifier 2, the bias circuit is grounded via the passive element M5, whereby the bias applied to the base (and the input terminal IN) of the transistor Tr1 can be stabilized, and the noise characteristics can be further improved. .

<Third Embodiment>
FIG. 5 is a circuit diagram showing a configuration of the variable gain amplifier 3 in the third embodiment. The variable gain amplifier 3 is different from the variable gain amplifier 1 (FIG. 1) in the first embodiment in that the variable gain amplifier 3 includes a passive element M6. In the variable gain amplifier 3, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

The passive element M6 is provided between the emitter of the transistor Tr1 and the ground point, and one end is connected to the emitter of the transistor Tr1 and the other end is grounded. That is, in the variable gain amplifier 3, the emitter of the transistor Tr1 is grounded via the passive element M6.
As a result, it becomes easier to perform noise matching in the high-frequency signal, so that the noise characteristics can be further improved.

  The variable gain amplifier 3 in this embodiment has been described as a configuration in which the passive element M6 is added to the variable gain amplifier 1 in the first embodiment. However, the present invention is not limited to this, and a passive element M6 may be added to the variable gain amplifier 2 in the second embodiment. As a result, the bias applied to the base (and input terminal IN) of the transistor Tr1 can be stabilized, and the noise characteristics of the transistor Tr1 can be further improved.

<Fourth Embodiment>
FIG. 6 is a circuit diagram showing a configuration of the variable gain amplifier 4 in the fourth embodiment. The variable gain amplifier 4 uses a monopolar transistor (field effect transistor) for the transistors Tr1 and Tr2, and includes a resistance element R1. The variable gain amplifier 1 according to the first embodiment (FIG. 1). Is different. In the variable gain amplifier 4, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The resistor element R1 has one end connected to the source of the transistor Tr2 and the other end grounded. In the variable gain amplifier 4, a bias converted into a voltage corresponding to the current flowing through the transistor Tr2 is applied to the gate of the transistor Tr1 via the passive element M3. As a result, the variable gain amplifier 4 can stabilize the bias applied to the gate (and input terminal IN) of the transistor Tr1 as in the variable gain amplifier 2 in the second embodiment, and further improve the noise characteristics. Can do.

<Fifth Embodiment>
FIG. 7 is a circuit diagram showing a configuration of the amplifier circuit 10 according to the fifth embodiment. As shown in FIG. 1, the amplifier circuit 10 includes the variable gain amplifier 1 (FIG. 1) and the amplifier 1A according to the first embodiment. The variable gain amplifier 1 is connected in multiple stages, and the amplifier 1A is connected in the first stage.

  As shown in the figure, the amplifier 1A is variable in that it includes a capacitive element C11 having a fixed capacitance and a passive element M11 having a fixed resistance value instead of the capacitive element C1 and the passive element M1. Different from the gain amplifier 1. That is, the amplifier 1A amplifies the input signal with a predetermined gain. Similarly to the variable gain amplifier 1, the amplifier 1A includes a bias circuit that applies a bias to the gate of the transistor Tr1, and noise characteristics are improved.

  As described above, when a plurality of variable gain amplifiers are arranged in series, the amplifier 1A having a predetermined gain and improved noise characteristics is provided in the first stage, and at least one variable gain amplifier 1 is provided in the subsequent stage. Thus, it is possible to change the gain greatly while having good noise characteristics over a wide frequency band.

  The multi-stage variable gain amplifier that has been used in the receiving unit of communication devices has a large influence on the noise characteristics of the previous circuit, so the noise characteristics are poor and good noise characteristics cannot be obtained at high gain. was there. On the other hand, the variable gain amplifiers of the above-described embodiments have improved noise characteristics by applying a bias according to the input impedance of the transistor Tr1, so that good noise characteristics can be obtained even at high gain. Can do.

  In the present embodiment, the amplifier circuit 10 including the plurality of variable gain amplifiers 1 and the amplifier 1A having a fixed gain is shown. However, instead of the variable gain amplifier 1, a variable gain amplifier 2 or a variable gain amplifier is provided. 3. A variable gain amplifier 4 may be used. Further, as an amplifier having a fixed gain at the first stage, an amplifier having a fixed gain corresponding to the variable gain amplifier 2, the variable gain amplifier 3, and the variable gain amplifier 4 may be used.

In addition, you may make it use a variable resistance element or a variable inductor for the passive element M1 in each above-mentioned embodiment. Alternatively, the passive element M1 may be configured by connecting a plurality of variable resistance elements or variable inductors in series, or connecting a variable resistance element or variable inductor and a resistance element or inductor in series. .
Moreover, you may make it use any of a resistive element, a variable resistive element, an inductor, and a variable inductor for the passive elements M2-M6 in each above-mentioned embodiment. Alternatively, passive elements M2 to M6 may be configured by connecting any one or all of a resistance element, a variable resistance element, and an inductor in series.

The first to sixth passive elements described in the present invention correspond to the passive elements M1 to M6 in the embodiment. The first capacitive element described in the present invention corresponds to the capacitive element C1 in the embodiment. The first and second transistors described in the present invention correspond to the transistors Tr1 and Tr2 in the embodiment. The first input terminal and the first output terminal in the present invention correspond to the input terminal and the output terminal of the variable gain amplifier in the embodiment.
The seventh, eighth, and ninth passive elements described in the present invention correspond to the passive elements M11, M2, and M3 included in the amplifier 1A in the fifth embodiment. The second capacitive element described in the invention corresponds to the capacitive element C11 included in the amplifier 1A in the fifth embodiment. The third and fourth transistors described in the present invention correspond to the transistors Tr1 and Tr2 included in the amplifier 1A in the fifth embodiment. The second input terminal and the second output terminal described in the present invention correspond to the input terminal IN and the output terminal OUT included in the amplifier 1A in the fifth embodiment.

  INDUSTRIAL APPLICABILITY The present invention is suitable for an amplifier circuit in a communication apparatus that is required to amplify a received signal with low power over a wide frequency band, and good noise characteristics can be obtained.

1, 2, 3, 4 ... Variable gain amplifier 1A ... Amplifier 10 ... Amplifier circuit Bias ... Power supply terminal C1, C11 ... Capacitance element M1, M2, M3, M4, M5, M6, M11 ... Passive element IN ... Input terminal OUT ... Output terminal R1... Resistance element Tr1, Tr2.

Claims (6)

A first input terminal;
A first transistor having a base connected to the first input terminal, an emitter grounded, and an emitter size determined according to a desired saturation level of the variable gain amplifier;
A first capacitive element having one end connected to the collector of the first transistor;
A first passive element having one end connected to the other end of the first capacitor and the other end connected to the base of the first transistor;
A second passive element having one end connected to the power supply terminal and the other end connected to the collector of the first transistor;
A second transistor having a base connected to the other end of the second passive element and a collector connected to the power supply terminal;
A third passive element having one end connected to the emitter of the second transistor, the other end connected to the base of the first transistor, and an impedance determined according to the input impedance of the first transistor;
A first output terminal connected to the collector of the first transistor;
A variable gain amplifier, wherein the first passive element and the first capacitive element have variable element values. The variable gain amplifier according to claim 1, wherein
Provided between the third passive element and the base of the first transistor, with one end connected to the other end of the third passive element and the other end connected to the base of the first transistor. A fourth passive element,
A fifth passive element having one end connected to one end of the fourth passive element and the other end grounded;
The third passive element is connected to a base of the first transistor through the fourth passive element. A variable gain amplifier, wherein: A variable gain amplifier according to claim 1 or claim 2,
A sixth passive element having one end connected to the emitter of the first transistor and the other end grounded;
The variable gain amplifier, wherein an emitter of the first transistor is grounded via the sixth passive element. The variable gain amplifier according to claim 1, wherein
A resistance element having one end connected to one end of the third passive element and the other end grounded;
A field effect transistor is used for the first transistor and the second transistor. A variable gain amplifier, wherein: A variable gain amplifier according to any one of claims 1 to 4,
The third passive element is
A variable gain amplifier formed by any one of a resistance element, a variable resistance element, and an inductor, or formed by connecting a plurality of resistance elements, variable resistance elements, and inductors in series. . A variable gain amplifier according to any one of claims 1 to 5,
An amplifier connected in front of the variable gain amplifier,
A second input terminal;
A third transistor having a base connected to the second input terminal, an emitter grounded, and an emitter size determined according to a desired saturation level of the variable gain amplifier;
A second capacitive element having one end connected to the collector of the third transistor and having a fixed element value;
A seventh passive element having one end connected to the other end of the second capacitive element, the other end connected to the base of the third transistor, and a fixed element value;
An eighth passive element having one end connected to the power supply terminal and the other end connected to the collector of the third transistor;
A fourth transistor having a base connected to the other end of the eighth passive element and a collector connected to the power supply terminal;
A ninth passive element having one end connected to the emitter of the fourth transistor and the other end connected to the base of the third transistor;
An amplifier comprising: a second output terminal connected to the collector of the third transistor;
Comprising
The amplifier circuit and the variable gain amplifier are connected in series.

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