JP2004254071A - Amplifier circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an amplifier circuit in which both a low power supply voltage and a high gain can be satisfied. <P>SOLUTION: A load resistor 2 is connected between a power supply terminal 6 and the output side of a current control means 1 for controlling the output current level depending on the level of a voltage or a current at an input terminal 4. Common joint of the current control means 1 and the load resistor 2 is connected with an output terminal and a constant current source circuit 3 is connected in parallel with the load resistor 2. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an amplifier circuit whose gain design is hardly restricted by a power supply voltage and which can achieve both a low power supply voltage and a high gain, and a parallel feedback type amplifier circuit which can obtain high stability and good noise characteristics. It is.
[0002]
[Prior art]
FIG. 9 is a diagram illustrating a configuration of a conventional amplifier circuit described in Non-Patent Document 1, for example. In the figure, 1 is a current control means, 15 is a bipolar transistor used as a current control means, 2 is a load resistor, 4 is an input terminal, 5 is an output terminal, and 6 is a power supply terminal. The current control means 1 changes the value of the current flowing through the load resistor 2 in proportion to the input value (voltage or current value), and the load resistor 2 generates the output voltage Vout according to the change of the flowing current.
[0003]
FIG. 11 shows the relationship between the current flowing through the current control means 1 and the load resistance 2 when the potential of the output terminal 5 in the amplifier circuit of FIG. 9 is virtually changed from the ground potential to the potential given to the power supply terminal 6. The flowing current value is simultaneously shown as a function of the potential of the output terminal 5. The bias point of this conventional amplifier circuit is such that when the current flowing out through the output terminal 5 is sufficiently small, the current flowing through the current control means 1 and the current flowing through the load resistor 2 when only the bias does not change the input. Determined by the conditions under which the values match.
[0004]
At this time, the potential of the output terminal 5 is obtained from the intersection of the current-voltage characteristic of the current control means 1 when only the bias does not change the input and the current-voltage characteristic of the load resistor 4. Similarly, the output value when the input value becomes the maximum or the minimum is obtained from the intersection of the current-voltage characteristic of the current control means 1 and the current-voltage characteristic of the load resistor 2 in that case, and the width of the output value is obtained. It becomes the maximum output amplitude. The amplifying operation is realized by changing the output value according to the input value. Assuming that the rate of change in the current caused by the current control means 1 due to the change in the input value is B, and the resistance value of the load resistor 2 is R1, The gain G is G = B × R1
It becomes.
[0005]
FIG. 10 is a circuit diagram showing a conventional amplifier circuit and a parallel feedback amplifier circuit configured to include a feedback resistor. 9, reference numeral 150 denotes the conventional amplifier circuit shown in FIG. 9, 200 denotes a feedback resistor, 300 denotes an input terminal, 400 denotes an output terminal, 500 denotes a level shift circuit, 501 denotes a bipolar transistor, 502 denotes a load resistor, and 506 denotes a positive resistance. Power supply terminal.
[0006]
The conventional amplifier circuit 150 amplifies an input voltage. The level shift circuit 500 feeds back the output voltage of the amplifier circuit 150 to the input side of the amplifier circuit 150 via the feedback resistor 200, and applies a DC-like voltage level to the next-stage circuit as an input. Adjust to a suitable value. Since negative feedback is applied to the amplifier circuit 150 by the feedback resistor 200 and the level shift circuit 500, a constant gain can be obtained over a wide frequency band including DC.
[0007]
[Non-Patent Document 1] PR Gray, RG Meyer, translated by Minoru Nagata, "Analog Integrated Circuit Design Technology for Ultra LSI (above)", Baifukan, 1990, p. 158.
[0008]
[Problems to be solved by the invention]
In order to operate the conventional amplifier circuit shown in FIG. 9, it is necessary to set the potential of the positive power supply terminal 6 to an appropriate value. For example, if the voltage of the output terminal 5 at the time of bias is Vb and the current value flowing through the current control means 1 at that time is Ib, the potential VR1 of the positive power supply terminal 6 is
VR1 = Vb + Ib × R1
It becomes. Normally, the values of Vb and Ib are selected from the points having the best characteristics in consideration of the frequency characteristics, linearity, withstand voltage and the like of the current control means 1 comprehensively. In addition to this, a high gain can be obtained by increasing the resistance value R1 of the load resistor 2, but for that purpose, the potential of the positive power supply terminal 6 needs to be increased. However, there is a problem in that power consumption increases when the power supply voltage is increased. Further, depending on the environment in which the amplifier circuit is used, a power supply voltage of a necessary magnitude may not be prepared.
[0009]
On the other hand, if an amplifier circuit is designed for a low power supply voltage VR2 (<VR1) in consideration of power consumption and the environment,
R2 = (VR2-Vb) / Ib
Therefore, it is necessary to select the load resistor 2 having the resistance value R2, and a high gain cannot be obtained. That is, there is a problem that the power supply voltage and the gain are in a trade-off relationship, and if one is prioritized, the requirements for the other must be compromised.
[0010]
In addition, when a feedback resistor is added to the conventional amplifier circuit of FIG. 9 to obtain a parallel feedback amplifier circuit as shown in FIG. 10, if a sufficient gain cannot be obtained due to the limitation of the power supply voltage, the gain is obtained. A problem arises in connection with the matching condition of the input impedance of the amplified circuit. Assuming that the gain of the amplifier circuit 150 is G and the resistance value of the feedback resistor 200 is Rf, the input impedance Rin is Rin = Rf / (1 + G).
Given by In order to match the input impedance to the input characteristic impedance when the gain G is small, it may be necessary to use a feedback resistor having a resistance value smaller than necessary to secure a band.
[0011]
However, when the resistance value Rf of the feedback resistor 200 is reduced, the feedback becomes very strong, and the mismatch of the input impedance becomes large in the high frequency region, so that the reflection characteristic at the input terminal is deteriorated. This causes a problem that the stability of the amplifier circuit is impaired. In addition, there is a problem that noise characteristics are poor.
[0012]
The present invention has been made in order to solve these problems, and it is an object of the present invention to provide an amplifier circuit capable of achieving both a low power supply voltage and a high gain and a parallel feedback amplifier circuit having high stability and good noise characteristics. Aim.
[0013]
[Means for Solving the Problems]
The invention according to claim 1 is a current control unit for controlling an output current value according to a value of a voltage or a current input to an input terminal, and a load connected between an output side of the current control unit and a power supply terminal. An amplifier circuit comprising a resistor, wherein a common connection point of the current control means and the load resistor is connected to an output terminal, wherein a constant current source circuit is connected in parallel with the load resistor. .
[0014]
According to a second aspect of the present invention, there is provided an amplifier circuit according to the first aspect, wherein a feedback resistor is connected between the input terminal and the output terminal to form a parallel feedback type.
[0015]
According to a third aspect of the present invention, a level shift circuit is connected to the output terminal of the amplifier circuit of the first aspect, and feedback is provided between an output terminal of the level shift circuit and the input terminal of the amplifier circuit of the first aspect. The amplifier circuit is characterized in that a parallel feedback type is connected by connecting a resistor.
[0016]
According to a fourth aspect of the present invention, there is provided the amplifier circuit according to any one of the first to third aspects, wherein a depletion mode FET is used as a constituent element.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
[First Embodiment]
FIG. 1 is a diagram illustrating an amplifier circuit according to the first embodiment. In the figure, 1 is a current control means, 2 is a load resistor, 3 is a constant current source circuit, 4 is an input terminal, 5 is an output terminal, and 6 is a power supply terminal.
[0018]
FIG. 12 shows the current value flowing through the current control means 1 and the load resistance 2 when the potential of the output terminal 5 is virtually changed from the ground potential to the potential given to the power supply terminal 6 in the amplifier circuit of FIG. And a current value obtained by synthesizing the current flowing through the constant current source circuit 3 as a function of the potential of the output terminal 5.
[0019]
The value of the current flowing through the load resistor 2 increases in proportion to the voltage applied to both ends of the load resistor 2, but the value of the current flowing through the constant current source circuit 3 increases rapidly when a voltage is applied and reaches a certain constant value. At that point, it becomes saturated and becomes almost constant. Therefore, a current-voltage characteristic obtained by combining the load resistor 2 and the current flowing through the constant current source circuit 3 is as shown in FIG. The resistance value of the load resistor 2 is R1, the current saturation value Is of the constant current source circuit 3 is
Is = (VR1-VR2) / R1
And the power supply voltage is VR2. The combined current value I when the current value of the constant current source circuit 3 is saturated is
I = (VR1-Vout) / R1
Therefore, the current-voltage characteristics when the constant current source circuit 3 is removed, the resistance value of the load resistor 2 is R1, and the power supply voltage is VR1 are consistent. Therefore, even if the power supply voltage is set to the lower voltage VR2, a gain of “B × R1” can be obtained, and an amplifier circuit that can achieve both low voltage power supply and high gain can be obtained.
[0020]
At this time, in order to amplify while maintaining the linearity, the fluctuation range of the output voltage Vout needs to be within the voltage range where the current value of the constant current source circuit 3 is saturated. The condition can be satisfied by setting the saturation current value of the circuit 3 appropriately.
[0021]
2 (a) to 2 (f) show an example of the configuration of the current control means 1, in which 11 is an input terminal, 12 is an output terminal, 13 is a ground terminal, 14 is a FET, 15 is a bipolar transistor, 16 Is a series feedback resistor, 17 is a peaking capacitor, and 18 is a cascode connection power supply terminal. The single FET 14 as shown in FIG. 2A or the single bipolar transistor 15 as shown in FIG. Further, as shown in FIGS. 2C and 2D, the FET 14 or the bipolar transistor may have a series feedback resistor 16 or a parallel connection of the series feedback resistor 16 and the peaking capacitor 17. Further, as shown in FIG. 2E, a cascode connection of the FET 14 or the bipolar transistor may be employed. Further, as shown in FIG. 2 (f), the FET 14 can be configured with a gate grounded or a bipolar transistor grounded.
[0022]
3 (a) to 3 (c) show a configuration example of the constant current source circuit 3, in which 31 is a positive terminal, 32 is a negative terminal, 33 is an n-channel depletion mode FET, 34 is a bipolar transistor, Reference numeral 35 denotes a bias resistor, and reference numeral 36 denotes a p-channel depletion mode FET. As shown in FIGS. 3A and 3C, a depletion mode FET can be realized only by coupling a gate and a source. In the case of a bipolar transistor or an enhancement mode FET, it is known that a constant current source circuit can be realized by configuring a circuit as shown in FIG.
[0023]
The present embodiment has an apparently similar configuration to a conventionally known amplifying circuit using only the constant current source circuit 3 as a load as shown in FIG. 13, but the amplifying circuit shown in FIG. In this case, some of the functions of the conventional amplifier circuit shown in FIG. 9, which is the prior art of the amplifier circuit of the present invention, cannot be realized. FIG. 14 shows a constant current value flowing through the current control means 1 when the potential of the output terminal 5 is virtually changed from the ground potential to the potential given to the power supply terminal 6 in the amplifier circuit shown in FIG. The value of the current flowing through the current source circuit 3 (active load) is simultaneously shown as a function of the potential of the output terminal 5. As is apparent from the figure, the output of the present amplifier circuit is rapidly saturated near the ground potential when the current value of the current control means 1 increases, and conversely, when the current value of the current control means 1 decreases, the output of the amplifier circuit becomes the power supply terminal 6. Saturates quickly upon approaching a given potential. As described above, the output characteristic has a strong nonlinearity like a limiter amplifier, and is different from the output characteristic of the conventional linear amplifier circuit shown in FIG. In addition, the current-voltage characteristics of the active load are determined only by the characteristics of the constant current source circuit 3, so that there is no degree of freedom in gain design. Therefore, the amplifier circuit shown in FIG. 13 is functionally different from the conventional amplifier circuit shown in FIG. 9 and the amplifier circuit of the present invention.
[0024]
FIG. 4 is a diagram showing one example of the first embodiment. In this embodiment, the constant current source circuit 3 is realized by using the depletion mode FET 33. As described above, in the case of the depletion mode FET, the constant current source circuit 3 can be realized with a simple configuration in which the gate and the source are coupled. The advantage is that the increase can be kept to a minimum.
[0025]
[Second embodiment]
FIG. 5 is a diagram illustrating an amplifier circuit according to the second embodiment. In the figure, 100 denotes the amplifier circuit of the first embodiment, 200 denotes a feedback resistor, 300 denotes an input terminal, 400 denotes an output terminal, and 500 denotes a level shift circuit. The amplifier circuit 100 amplifies the input signal, and the level shift circuit 500 feeds back the output signal of the amplifier circuit 100 to the input of the amplifier circuit 100 via the feedback resistor 200 and provides the output signal to the next-stage circuit as an input. Adjust the DC voltage level to an appropriate value.
[0026]
Therefore, negative feedback is applied to the amplifier circuit 100 by the feedback resistor 200 and the level shift circuit 500, and a parallel feedback amplifier circuit having a constant gain over a wide frequency band including DC can be obtained. As described above, since the amplifier circuit 100 can achieve both low power supply voltage and high gain, it is not necessary to lower the resistance value of the feedback resistor 200 more than necessary to secure a band.
[0027]
Further, even under a constant power supply voltage value, the resistance value of the load resistor 2 in the amplifier circuit 100 can be freely set within a certain fixed range by adjusting the saturation current value of the constant current source circuit 3. Therefore, the value of the input impedance can be set so that a good matching state can be realized. Therefore, the reflection characteristics of the input can maintain good characteristics within the band, so that the stability of the amplifier circuit is not impaired. In addition, since high gain can be secured, there is an advantage that good noise characteristics can be obtained.
[0028]
FIG. 6 is a diagram showing a first example of the second embodiment. In the figure, 501 is a bipolar transistor, 502 is a load resistor, and 506 is a positive power supply terminal. Since the present embodiment is a parallel feedback type amplifier circuit using the amplifier circuit of the first embodiment, as is clear from the above description, the amplifier circuit has high stability and low noise characteristics. .
[0029]
FIG. 7 is a diagram showing a second example of the second embodiment. Although the level shift circuit does not exist in the figure, the level shift circuit 500 may be omitted when the output of the amplifier circuit 100 has the same voltage level as its own input or the input of the next-stage circuit. This is because they use what they can do. Since the present embodiment is also a parallel feedback type amplifier circuit using the amplifier circuit of the first embodiment, it is an amplifier circuit having high stability and low noise characteristics as apparent from the above description. .
[0030]
FIG. 8 is a diagram showing a third example of the second embodiment. In the figure, 503 denotes an FET for the level shift circuit 500, 504 denotes a diode for the level shift circuit 500, 506 denotes a positive power supply terminal, and 507 denotes a negative power supply terminal. Since the present embodiment is also a parallel feedback type amplifier circuit using the amplifier circuit of the first embodiment, it is an amplifier circuit having high stability and low noise characteristics as apparent from the above description. . In the present embodiment, the constant current source circuit 3 is realized by using the depletion mode FET 33, and the constant current source circuit can be realized with a simple configuration in which the gate and the source are coupled. There is an advantage that an increase in the circuit scale when implementing the invention can be minimized.
[0031]
【The invention's effect】
As described above, the amplifier circuit of the present invention can easily realize an amplifier circuit that can achieve both low power supply voltage and high gain by adding the constant current source circuit in parallel with the load resistance. In addition, the amplifier circuit of the parallel feedback type can set the value of the input impedance so that a good matching state can be realized, and the input reflection characteristics can maintain good characteristics within the band, so that the stable Sex is not impaired. In addition, since high gain can be secured, good noise characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram of an amplifier circuit according to a first embodiment.
FIGS. 2A to 2F are specific circuit diagrams of current control means of the amplifier circuit of FIG.
FIGS. 3A to 3C are specific circuit diagrams of a constant current source circuit of the amplifier circuit of FIG. 1;
FIG. 4 is a specific circuit diagram of one embodiment of the amplifier circuit of FIG. 1;
FIG. 5 is a block diagram of a parallel feedback amplifier circuit according to a second embodiment;
FIG. 6 is a specific circuit diagram of a first embodiment of the parallel feedback amplifier circuit of FIG. 5;
FIG. 7 is a specific circuit diagram of a second embodiment of the parallel feedback amplifier circuit of FIG. 5;
FIG. 8 is a specific circuit diagram of a third embodiment of the parallel feedback type amplifier circuit of FIG. 5;
FIG. 9 is a specific circuit diagram of a conventional amplifier circuit.
FIG. 10 is a specific circuit diagram of a conventional parallel feedback type amplifier circuit including a conventional amplifier circuit.
FIG. 11 is a diagram illustrating the operation of a conventional amplifier circuit.
FIG. 12 is a diagram illustrating the operation of the amplifier circuit of the present invention.
FIG. 13 is a block diagram of a conventional amplifier circuit using only a constant current source circuit as a load.
FIG. 14 is a diagram illustrating the operation of a conventional amplifier circuit having only a constant current source circuit as a load.
[Explanation of symbols]
1: current control means, 11: input terminal of current control means, 12: output terminal of current control means, 13 ground terminal of current control means, 14: FET for current control means, 15: bipolar transistor for current control means , 16: series feedback resistor, 17: peaking capacitor, 18: cascode connection power terminal 2: load resistor 3: constant current source circuit, 31: positive terminal of constant current source circuit, 32: negative terminal of constant current source circuit Terminal, 33: n-channel depletion mode FET for constant current source circuit, 34: bipolar transistor for constant current source circuit, 35: load resistance, 36: p-channel depletion mode FET for constant current source circuit
4: input terminal 5: output terminal 6: power supply terminal 100: amplifier circuit of the present invention, 150: conventional amplifier circuit, 200: feedback resistor, 300: input terminal of an amplifier circuit of a parallel feedback type, 400: parallel feedback type Output terminals of the amplifying circuit: 500: level shift circuit: 501: bipolar transistor for level shift circuit, 502: load resistor for level shift circuit, 503: FET for level shift circuit, 504: diode for level shift circuit, 506: Positive power supply terminal, 507: Negative power supply terminal

Claims (4)

Current control means for controlling an output current value in accordance with a voltage or current value input to an input terminal; and a load resistor connected between an output side of the current control means and a power supply terminal; And a constant current source circuit connected in parallel with the load resistor in an amplifier circuit having a common connection point of the load resistor and an output terminal. 2. An amplifier circuit according to claim 1, wherein a feedback resistor is connected between said input terminal and said output terminal of said amplifier circuit to form a parallel feedback type. A parallel feedback type wherein a level shift circuit is connected to the output terminal of the amplifier circuit according to claim 1, and a feedback resistor is connected between an output terminal of the level shift circuit and the input terminal of the amplifier circuit according to claim 1. An amplifier circuit, characterized in that: The amplifier circuit according to any one of claims 1, 2 or 3,
An amplifier circuit comprising a depletion mode FET as a constituent element.

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