JP2011199606A - Amplifier, and radio equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of the linearity of the input/output characteristics of an amplifier.SOLUTION: The amplifier includes a feedback transformer L3 whose both ends on the primary side are connected between the respective output sides of a pair of FET elements Q1, Q2 and which outputs step-down signals for which signals outputted from the FET elements Q1, Q2 are stepped down from both ends on the secondary side, rectifying diodes D1, D2 which are connected in the direction of rectification toward the input side of the FET elements Q1, Q2 between the respective input sides of the FET elements Q1, Q2 and the respective secondary sides of the feedback transformer L3 for outputting the step-down signals having the same phase with that on the input side of the FET elements Q1, Q2, and a bias circuit for supplying a bias voltage or a bias current to the input side of the FET elements Q1, Q2 through the rectifying diodes D1, D2.

Description

  The present invention relates to an amplifier and a wireless device.

  2. Description of the Related Art In recent years, it is known that a high frequency amplifier (hereinafter referred to as an amplifier) used for a wireless device or the like decreases output power (saturated output) and deteriorates input / output characteristics as the frequency of amplification increases.

  As a technique for improving the input / output characteristics of the amplifier, the known technique of Japanese Utility Model Publication No. 63-40700 (Utility Model Reference 1) is applied to improve the input / output characteristics of the amplifier by the rectifying action (effect) of the diode. There is technology. Specifically, in the utility model document 1, in a configuration in which a diode and a high-pass filter are directly connected between the input side of the video amplifier and the ground, a diode is used for a high luminance portion of the video signal. Describes a technique for applying a bias voltage to the diode so that the diode becomes conductive with respect to a low-luminance portion of the video signal.

Japanese Utility Model Publication No. 63-40700

  Generally, when the bias voltage is increased, the gain and output power (saturated output) of the amplifier are increased to some extent. Therefore, by using the technology of Utility Model Document 1, a part of the input power is rectified and a voltage obtained by the rectification effect is added to the bias voltage, so that the larger the input power, the more the bias voltage is applied (applied) Will be). This increases the gain and saturation output of the amplifier.

  As described above, when the frequency is high, more input power is required when the gain and saturation output of the amplifier are low than when the frequency is low. For this reason, the rectification effect of the diode is exhibited, and the input / output characteristics of the amplifier are improved.

  However, even in the case of a low frequency with a high saturation output and good input / output characteristics, a diode rectification effect occurs. For this reason, there was a problem that the linearity of the input / output characteristics deteriorated.

  An object of the present invention is to prevent deterioration in linearity of input / output characteristics of an amplifier.

In order to solve the above problems, an amplifier according to the present invention includes:
At least a pair of amplifying elements connected to perform a push-pull operation;
A transformer for outputting a step-down signal obtained by stepping down a signal output from the amplification element from both ends of the secondary side, with both ends on the primary side connected between the output sides of the pair of amplification elements;
Between each of the input sides of the amplification element and each of the secondary sides of the transformer that outputs the step-down signal in phase with the phase on the input side of the amplification element, toward the input side of the amplification element A rectifying element connected in the direction of rectification;
A bias circuit for supplying a bias voltage or a bias current to the input side of the amplifying element via the rectifying element;
It is characterized by providing.

Furthermore, the amplifier of the present invention includes:
A negative feedback circuit for connecting a secondary side of the transformer and an input side of the amplifying element is provided.

In addition, the wireless device of the present invention,
The amplifier is provided.

  According to the present invention, it is possible to prevent the linearity of the input / output characteristics of the amplifier from deteriorating.

It is a figure which shows the circuit structure of the amplifier in embodiment which concerns on this invention. It is the figure which showed the relationship between a high frequency input voltage and the voltage VGS. It is the figure which showed the relationship when an input / output characteristic is favorable, and when an input / output characteristic deteriorates by correction | amendment. It is the figure which showed the relationship between the gain of an amplification element, and the voltage VGS. It is the figure which showed the input / output characteristic when there are few saturation outputs, and the case where the input / output characteristic improved by correction | amendment. It is a figure which shows the circuit structure of the amplifier in the modification of embodiment which concerns on this invention.

  Embodiments according to the present invention will be described below in detail with reference to the accompanying drawings. However, the scope of the invention is not limited to the illustrated examples.

  Embodiments according to the present invention will be described with reference to FIGS. First, a circuit configuration of the amplifier 1 according to the present invention will be described with reference to FIG. The amplifier 1 is a push-pull amplifier that uses an FET as an amplification element that performs a push-pull operation. The amplifier 1 is applied to a wireless device or the like. Hereinafter, the amplifier 1 will be described as an amplifier that amplifies a frequency in a short wave band (1.8 MHz to 50 MHz).

  Specifically, the amplifier 1 includes an input terminal IN, an input matching transformer L1, and DC blocking capacitors C1 and C2 that allow the input signal to pass through and remove (block) the DC component to supply the bias voltage independently. Bias voltage dividing resistors R1, R2, R3, R4, R5, R6 for dividing the bias voltage, rectifying diodes D1, D2, high frequency passing capacitors C3, C4, first and second resistors Amplifying elements FETQ1 and Q2 as an amplifying element, output matching transformer L2, output terminal OUT, bias setting variable resistors VR1 and VR2 for setting a bias voltage, feedback transformer L3, and high-frequency potential are grounded. Bypass capacitors C5, C6, C7 for dropping to a level are provided.

  In the circuit configuration of the amplifier 1 of FIG. 1, bias voltage dividing resistors R1, R2, R3, R4, R5, R6, rectifying diodes D1, D2, and bias setting variable resistors VR1, VR2 are provided in the bias circuit. Equivalent to. The bias setting variable resistors VR1 and VR2 function as adjusting means for adjusting the bias voltage or the bias current supplied to the amplifying elements FETQ1 and Q2.

  The amplifying elements FETQ1 and Q2 are a pair of amplifying elements that perform a push-pull operation. Specifically, when the amplification element FETQ1 operates (performs amplification), the amplification element FETQ2 does not operate, and when the amplification element FETQ2 operates, the amplification element FETQ1 does not operate. In order to increase the gain, the sources of the amplifier elements FETQ1 and Q2 are often grounded. In the case of grounded source, the phase is inverted between the input side and the output side of the amplifier element.

  Both ends of the primary side of the feedback transformer L3 are connected to the output side (drain terminal side) of the amplification elements FETQ1, Q2. On the secondary side of the feedback transformer L3, the secondary side winding has a predetermined turns ratio, and further includes a midpoint tap. The midpoint tap is grounded to the ground level. The feedback transformer L3 steps down the output signals (for example, a voltage waveform A2 described later) of the amplification elements FETQ1, Q2, and outputs a stepped down signal (for example, a voltage waveform A3 described later).

  The secondary side of the feedback transformer L3 is connected to the anode side of the rectifying diode D1 via the high-frequency passing capacitor C3 and to the anode side of the rectifying diode D2 via C4. Therefore, the step-down signal and the input signals of the amplification elements FETQ1 and Q2 are in phase.

  The high-frequency passing capacitors C3 and C4 pass a step-down signal (for example, a voltage waveform A3 described later), and remove a DC component so that the bias voltage does not become a ground level from the midpoint tap of the feedback transformer L3.

In principle, high-frequency currents cancel each other and do not flow between the midpoint tap on the secondary side and the ground level, and the midpoint does not have to be grounded.
However, it is rare that the characteristics of the amplifier elements FETQ1 and Q2 are exactly the same, and it is desirable to ground them from the viewpoint of stabilizing the DC potential.

  Hereinafter, in the present embodiment, it is assumed that a bias voltage (a voltage VGS between the gate terminal and the source terminal) is supplied to the amplification elements FETQ1 and Q2.

When a signal is input to the input terminal IN, the input signal (for example, a voltage waveform A1 to be described later) includes, for example, a bypass capacitor C6, a bias voltage dividing resistor R3, a rectifying diode D1, a bias voltage dividing resistor R1, Rectified by a rectifying diode D1 in the path of the DC blocking capacitor C1.
A step-down signal (for example, a voltage waveform A3 described later) obtained by amplifying the input signal by the amplifying element FETQ2 and stepping down the output signal by the feedback transformer L3 is used as bias voltage dividing resistors R5 and R1, and a rectifying diode D1. Then, it is rectified by the rectifying diode D1 in the path of the high-frequency passing capacitor C3.
The rectifying action caused by the step-down signal (hereinafter referred to as rectifying action) limits the rectifying action by the input signal because the direction of the current is opposite to the rectifying action caused by the input signal.

  The rectifying diodes D1 and D2 limit the rectifying action or execute the rectifying action based on the step-down signal. When the rectifying action is limited or executed by the rectifying diodes D1 and D2, the bias voltage or the bias current is adjusted based on the rectified output at the time of limitation or at the time of execution. The rectified output refers to the amount of voltage change caused by the current flowing through the rectifying diodes D1 and D2. For example, when the rectifying action is performed by the rectifying diode D1 and the high-frequency current I1 flows through the rectifying diode, the high-frequency current I1 flows, thereby causing a potential difference between A32 and B32. This potential difference voltage corresponds to the rectified output. On the other hand, when no current flows through the rectifying diodes D1 and D2, the rectified output is zero.

  Next, the operation of the amplifier 1 shown in FIG. 1 will be described. Hereinafter, the operation of the amplifier 1 when the frequency to be amplified is high (for example, about 50 MHz) and when it is low (for example, about 1.8 MHz) will be described. First, the operation of the amplifier 1 when the frequency to be amplified is low will be described.

Generally, when the frequency to be amplified is low, the amplitude of the input voltage is smaller than when the frequency to be amplified is high. For example, as shown in FIG. 1, the voltage waveform A1 of the input voltage when the frequency to be amplified is low has a smaller amplitude than the voltage waveform A4 of the input voltage when the frequency to be amplified is high.
Hereinafter, the operation of the amplifier 1 when the voltage waveform A1 of the input voltage indicating the negative phase is input will be described.

  When the voltage waveform A1 appears on the secondary side of the input matching transformer L1, the voltage waveform A1 is applied to the gate terminal of the amplification element FETQ1, and the voltage waveform A2 having the opposite phase to the voltage waveform A1 appears at the drain terminal.

  A voltage waveform A3 having a phase opposite to that of the voltage waveform A2 appears below the midpoint tap on the secondary side of the feedback transformer L3. That is, the voltage waveforms A1 and A3 are in phase. Here, since the target output of the amplifier 1 is constant regardless of the gain difference depending on the frequency, the voltage waveform A3 is constant regardless of the frequency if the output is the same.

  In this case, since the voltage waveform A1 is a signal indicating a negative phase, the high-frequency current I1 flows in the direction shown in FIG. Further, since the voltage waveform A3 is also a signal indicating a negative phase, the high-frequency current I2 flows in the direction shown in FIG. Then, the high-frequency currents I1 and I2 flow in directions that cancel each other. In this case, since the amplitude of the voltage waveform A1 is smaller than that of the voltage waveform A4, the rate of reduction of the current component of the high-frequency current I1 is larger than when the frequency is high, and the rectifying diode D1 limits the rectifying action. Will be. That is, the rectifying action by the rectifying diode D1 is weakened. At this time, if the current components of the high-frequency currents I1 and I2 are substantially the same, the high-frequency currents I1 and I2 cancel each other, so that the rectified output of the rectifying diode D1 hardly occurs (substantially becomes zero). In this case, since the rectified output of the rectifying diode D1 hardly occurs, the voltage V obtained by dividing the voltage + B is applied (supplied) to the amplifying element FETQ1 as the voltage VGS via the rectifying diode D1. Thereby, the rise (raising) of the voltage VGS can be suppressed.

  Here, with reference to FIG. 2 and FIG. 3, the effect when the increase in the voltage VGS is suppressed when the frequency is low (when the rectifying action by the diode is weak) will be described. First, FIG. 2 will be described. FIG. 2 is a diagram showing the characteristics of the voltage VGS with respect to the high frequency input voltage. The horizontal axis of FIG. 2 shows the high frequency input voltage (voltage generated by the high frequency input power: corresponding to the voltage waveform A1). The vertical axis represents the voltage VGS. As shown in FIG. 2, the voltage VGS exhibits a characteristic that increases from the threshold value V1 of the high-frequency input voltage.

  Here, if the increase in the voltage VGS can be suppressed, the value at which the voltage VGS increases toward the higher side of the high-frequency input voltage can be shifted to the threshold value V2 by the arrow in FIG. If the value at which the voltage VGS increases can be shifted to the threshold value V2, for example, when the value indicated by V21 in FIG. 2 is a high-frequency input voltage, the voltage VGS does not increase and becomes a constant value. Thereby, it is possible to prevent the input / output characteristics (see FIG. 3 described later) from becoming nonlinear.

  FIG. 3 is a diagram showing the relationship between the case where the input / output characteristics are good and the case where the input / output characteristics deteriorate due to correction (raising). The vertical axis represents the output power of the amplifier, and the horizontal axis represents the input power of the amplifier. A11 shows the input / output characteristics when the increase in the voltage VGS is suppressed (when the rectifying action by the diode is weak). A12 shows the input / output characteristics when the rectifying action by the diode is strong. The broken lines in the figure indicate ideal input / output characteristics.

  As shown in A11, the input / output characteristic when the rectification action by the diode is weak shows a linear characteristic. On the other hand, as indicated by A12, the input / output characteristics when the rectifying action by the diode is strong shows nonlinear characteristics. For example, when the target output power is 100 W, the output power of 100 W can be obtained with the input power of 3 W if the input / output characteristics are A11. However, when the input / output characteristics are A12, the input power of 3 W exceeds the target output power of 100 W. For this reason, when the rectifying action by the diode is increased when the frequency is low, there is a problem that it is difficult to optimize the input power.

  A12 becomes non-linear because the gain of the amplifying element increases and the output power increases as the voltage VGS increases. Here, the relationship between the voltage VGS and the gain of the amplifying element will be described with reference to FIG. As shown in FIG. 4, when the voltage VGS exceeds the threshold value Vth, the gain of the amplifying element increases and then decreases. For example, if the voltage VGS increases within a predetermined region (in a region where the gain of the amplifying element increases), the gain of the amplifying element increases. As the gain of the amplifying element increases, the output power also increases. For this reason, when the voltage VGS rises when the frequency is low, the output power rises, resulting in a nonlinear input / output characteristic as indicated by A12 in FIG. In this case, distortion occurs in the output power.

  On the other hand, if the increase in voltage VGS can be suppressed, the gain of the amplifying element does not increase. That is, since the gain of the amplifying element can be made constant, the output power does not increase.

  In the amplifier 1 shown in FIG. 1, the increase in the voltage VGS can be suppressed as described above. For this reason, the input / output characteristics can be kept linear as shown by A11 in FIG. 3, and distortion of the output power can be prevented.

  Returning to FIG. 1, the operation of the amplifier 1 when the frequency to be amplified is high will be described. Hereinafter, the operation of the amplifier 1 when the voltage waveform A4 of the input voltage indicating the negative phase is input will be described.

  When the voltage waveform A4 appears on the secondary side of the input matching transformer L1, the voltage waveform A4 is applied to the gate terminal of the amplifying element FETQ1, and the voltage waveform A2 having a phase opposite to that of the voltage waveform A4 is applied to the drain terminal. (Similar to waveform A2) appears.

  As in the case where the frequency is low, a voltage waveform A3 having a phase opposite to that of the voltage waveform A2 appears below the midpoint tap on the secondary side of the feedback transformer L3. That is, the voltage waveforms A1 and A3 are in phase. Since the target output of the amplifier 1 is constant regardless of the gain difference depending on the frequency, the voltage waveform A3 is constant regardless of the frequency if the output is the same.

  In this case, as in the case where the frequency is low, the high-frequency currents I1 and I2 flow in directions that cancel each other. However, since the voltage waveform A4 has a larger amplitude than the voltage waveform A1, the rate at which the current component of the high-frequency current I1 decreases is smaller than when the frequency is low. That is, the rectifying action by the rectifying diode D1 is stronger than when the frequency is low. Specifically, a current corresponding to a value obtained by subtracting I2 from the high-frequency current I1 flows through the rectifying diode D1, and a voltage corresponding to a potential difference between A2 and B2 is generated by the current. In this case, the voltage of the potential difference between A2 and B2 becomes the rectified output of the rectifying diode D1. The voltage of the potential difference between A2 and B2 is added (raised) to the voltage V, and the raised voltage V is applied (supplied) to the FET element Q1 through the rectifying diode D1 as the voltage VGS. (That is, the raised voltage VGS is supplied to the FET element Q1). At this time, if the raised voltage VGS is a value within a predetermined region (see FIG. 4), the gain of the amplifying element increases and the output power also increases.

  Next, with reference to FIG. 5, the effect when the voltage VGS is raised when the frequency is high (when the rectifying action by the diode is strong) will be described. FIG. 5 is a diagram showing the input / output characteristics when the saturation output is small and the case where the input / output characteristics are improved by correction (raising). A13 shows the input / output characteristics when the rectifying action by the diode is weak. A14 shows the input / output characteristics when the rectifying action of the diode is strong.

  As shown in A13, the input / output characteristics when the rectification action by the diode is weak shows non-linear characteristics. On the other hand, as indicated by A14, the input / output characteristics when the rectifying action by the diode is strong shows linear characteristics. For example, when the target output power is 100 W, the input power of 3 A is sufficient for the input / output characteristics of A14, but the input power of 6 W is required for the input / output characteristics of A13. For this reason, when the rectifying action by the diode is weakened when the frequency is high, there is a problem that a large input power is required as compared with the case where the rectifying action is strong.

  As described with reference to FIG. 4, when the voltage VGS increases within a predetermined region, the gain of the amplifying element increases, and the output power also increases as the gain of the amplifying element increases. In the amplifier 1 shown in FIG. 1, the voltage VGS can be raised (raised) as described above. For this reason, the input / output characteristics are linear as shown by A14 in FIG. 5, and the occurrence of distortion of the output power can be prevented.

  In the present embodiment, the case where the voltage waveforms A1 and A4 indicating the negative phase appear has been described, but the case where the voltage waveforms A5 and A8 indicating the positive phase appear also is similar to the above. Operation is performed.

  As described above, according to the present embodiment, when the frequency is high or low, the input / output characteristics of the amplifier can be made linear, so that the input / output characteristics of the amplifier can be prevented from deteriorating. For example, when the frequency is low, the input / output characteristics of the amplifier can be kept linear by keeping the voltage VGS constant. When the frequency is high, the input / output characteristics of the amplifier can be made linear by raising the voltage VGS. For this reason, generation | occurrence | production of distortion of output electric power can be prevented.

  Further, in the present embodiment, the operation of the amplifier 1 has been described for the case where the frequency is low and the case where the frequency is high. However, depending on the characteristics of the amplifier 1, the gain and saturation output of the amplifier 1 are reduced when the frequency is low. In this case, the gain and saturation output of the amplifier 1 may decrease in some frequency intervals, or the gain and saturation output of the amplifier 1 may vary depending on the ambient temperature. Even in such a case, the amplifier 1 adjusts the voltage VGS (bias voltage) based on the step-down signal (for example, the voltage waveform A3) opposite in phase to the output signal (for example, the voltage waveform A2). Therefore, the linearity of the input / output characteristics can be improved and the distortion can be reduced.

(Modification)
A modification of the embodiment will be described with reference to FIG. Hereinafter, the same reference numerals are given to the same parts as those in the embodiment, and the detailed description thereof is used, and different parts will be described below.

  As shown in FIG. 3, in the amplifier 1A, the secondary side of the feedback transformer L3 is branched, and the branched path is connected to one end of the DC blocking capacitor C1 via the feedback amount adjusting resistor R7. Further, the secondary side of the feedback transformer L3 is branched, and the branched path is connected to one end of the DC blocking capacitor C2 via the feedback amount adjusting resistor R8. That is, a negative feedback circuit that connects the secondary side of the feedback transformer L3 to the input side (gate terminal side) of the amplifying elements FETQ1, Q2 is configured.

  Here, for example, it is assumed that a voltage waveform A1 indicating a negative phase appears at the terminal A33. In this case, as in FIG. 1, a voltage waveform A2 having a phase opposite to that of the voltage waveform A1 appears at the drain terminal of the FET element Q1. A voltage waveform A21 appears above the midpoint tap on the secondary side of the feedback transformer. In this case, the voltage waveform A1 and the voltage waveform A21 are voltages having opposite phases. Therefore, the distortion component included in the voltage waveform A21 can be canceled (reduced) by feeding back the voltage waveform A21 via the feedback transformer L3 and the feedback amount adjustment resistor R7. Thereby, distortion of the output signal of the amplifier 1A can be reduced.

  Further, even when the voltage waveform A6 indicating the positive phase appears at the terminal A34, the distortion component included in the voltage waveform A22 can be canceled, and the distortion of the output signal of the amplifier 1A can be reduced.

  As described above, according to the present modification, the secondary side of the feedback transformer L3 is branched, and the branched path is connected to one end of the DC blocking capacitors C1 and C2 via the feedback adjustment resistors R7 and R8. Distortion of the output signal of the amplifier 1A can be reduced.

  Further, with the configuration of the amplifier 1A shown in FIG. 6, it is not necessary to prepare another feedback transformer L3 as a negative feedback circuit, so that space saving and cost reduction can be achieved.

  In addition, the detailed structure and detailed operation of the amplifiers 1 and 1A in the present embodiment can be changed as appropriate without departing from the spirit of the present invention.

1, 1A Amplifier C1, C2 DC blocking capacitor C3, C4 High frequency passing capacitor C5, C6, C7 Bypass capacitor D1, D2 Rectifying diode Q1, Q2 Amplifying element FET
IN input terminal L1 Input matching transformer L2 Output matching transformer L3 Feedback transformer OUT Output terminals R1, R2, R3, R4, R5, R6 Bias voltage dividing resistor VR1, VR2 Bias setting variable resistor VGS Bias voltage

Claims (3)

At least a pair of amplifying elements connected to perform a push-pull operation;
A transformer for outputting a step-down signal obtained by stepping down a signal output from the amplification element from both ends of the secondary side, with both ends on the primary side connected between the output sides of the pair of amplification elements;
Between each of the input sides of the amplification element and each of the secondary sides of the transformer that outputs the step-down signal in phase with the phase on the input side of the amplification element, toward the input side of the amplification element A rectifying element connected in the direction of rectification;
A bias circuit for supplying a bias voltage or a bias current to the input side of the amplifying element via the rectifying element;
An amplifier comprising:   The amplifier according to claim 1, further comprising a negative feedback circuit that connects a secondary side of the transformer and an input side of the amplifying element. A wireless device comprising the amplifier according to claim 1.

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