JP2007221331A - High-frequency amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure a fine CN ratio, even if there is level difference in an input high-frequency signal. <P>SOLUTION: A transistor 42 is fixed biased by fixed bias circuits 44, 56 connected between first and second potential lines 46, 48 which have respectively different potential levels to amplify a high-frequency signal. A transistor 64 is biased by current feedback type bias circuits 66, 68, 70, 72, 74, 76, 78 connected between the first and second potential lines 46, 48, and gain-adjusting means 74, 84, 86 are formed in these current feedback type bias circuits 66, 68, 70, 72, 74, 76, 78 to amplify an output signal of the transistor 42. A transistor 92, biased by current feedback type bias circuits 102, 104, 110, 120 connected between the second potential line 48 and ground potential, amplifies the output signal of the transistor 64. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high-frequency amplifier, and more particularly to a device provided with a plurality of amplification stages.

  The high frequency amplifier may be used for a booster that amplifies a television broadcast signal, for example. An example of this booster is disclosed in Patent Document 1, for example. In the technique of Patent Document 1, a current feedback bias circuit biases the first bipolar transistor amplification stage. A variable attenuator is provided in the current feedback type bias circuit. When changing the amount of attenuation in the variable attenuator, the bias changes at the same time. Further, the output signal of the bipolar transistor amplification stage is amplified by the second bipolar transistor amplification stage. The second bipolar transistor amplification stage is biased by a current feedback bias circuit. A level adjustment circuit is provided in the bias circuit. The two bipolar transistor amplification stages are connected in series between two potential lines.

  In this high-frequency amplifier, the signal level and bias supplied to the first bipolar transistor amplification stage are adjusted by adjusting the variable attenuator. In the second bipolar transistor amplification stage, the level and the bias are adjusted by adjusting the level adjusting circuit. Therefore, in the first and second amplification stages, the bias and the input level can be adjusted to the best state according to the input signal level. Furthermore, since the first and second bipolar transistor amplification stages are connected in series between the first and second potential lines, a large number of distortion characteristics of the first bipolar transistor amplification stage can be obtained. When the current is supplied to the first bipolar transistor amplification stage, the supply current to the second bipolar transistor amplification stage automatically increases, and the distortion characteristics of the second bipolar transistor amplification stage are automatically improved. Conversely, in order to improve the distortion characteristics of the second bipolar transistor amplification stage, when a large amount of current flows through the second bipolar transistor amplification stage, a large amount of current also flows through the first bipolar transistor amplification stage. The distortion characteristics of one bipolar transistor are also improved.

JP 2004-241969 A

  In this high-frequency amplifier, when the input level of the high-frequency signal is high, the level adjustment circuit and the variable attenuator are adjusted to lower the signal level supplied to the first and second bipolar transistors, and the bias is also shallow. And optimal distortion characteristics can be obtained. However, when a high-frequency signal having a high input level and a high-frequency signal having a low level are mixed, a certain amount of current must be continuously supplied to the first and second bipolar transistors. Therefore, when the input high frequency signals are, for example, UHF band television broadcast signals, the arrival direction of radio waves is not always one direction, and the received UHF band television broadcast signals have low levels. The bias becomes deeper than the bias corresponding to the low level, and good C / N cannot be secured. In particular, if the UHF band television broadcast signal with a low level is a terrestrial digital television broadcast signal and has only an input level close to the lowest level that can be received as a digital television broadcast signal, it is important to ensure C / N. It is.

  An object of the present invention is to provide a high-frequency amplifier capable of ensuring a good C / N even if there are level differences among a plurality of high-frequency signals inputted.

  A high-frequency amplifier according to an aspect of the present invention includes first to third semiconductor amplification means. The first semiconductor amplifying means amplifies a high-frequency signal, for example, a UHF band television broadcast signal, and is fixedly biased by a fixed bias circuit provided between the first and second potential lines having different potentials. . The second semiconductor amplifying means amplifies the output signal of the first semiconductor amplifying means. The second semiconductor amplification means is biased by a current feedback type bias circuit provided between the first and second potential lines. Gain adjusting means is provided in the current feedback bias circuit. The third semiconductor amplifying means amplifies the output signal of the second semiconductor amplifying means, and is provided between the second potential line and a third potential line having a different potential from the first and second potential lines. The current feedback type bias circuit is biased. Each semiconductor amplifying means can be composed of a bipolar transistor or FET, and the first to third potential lines have potentials that increase in order from the first to the third potential lines, or conversely in order. Is low.

  In the high frequency amplifier configured as described above, since the first semiconductor amplifying means is fixedly biased, even if a low level or a high level is mixed in a plurality of input high frequency signals, a constant level is maintained. Current is flowing. Therefore, the first amplifying means can improve the C / N by appropriately selecting the bias value even if the input high frequency signal has a high level or a low level. . In the second semiconductor amplifying means, the level adjustment and bias adjustment are performed by the gain adjusting means in accordance with the level of the output signal of the first semiconductor amplifying means. The output signal of the second semiconductor amplifying means is amplified by the third semiconductor amplifying means, and the third semiconductor amplifying means is connected between the second potential line and the third potential line. The current flowing through the second potential line is the current flowing through the first and second semiconductor amplification means. Therefore, when the amplification degree in the first and second semiconductor amplification means is large, a current corresponding thereto is supplied to the third semiconductor amplification means, and the amplification degree in the first and second semiconductor amplification means is increased. If it is smaller, a current corresponding thereto is supplied to the third semiconductor amplifying means. Based on this current, a current feedback bias is applied to the third semiconductor amplifying means. Accordingly, since the current corresponding to the first and second amplification states is consumed by the third semiconductor amplifying means, the entire current consumption can be suppressed.

  The gain adjusting means can be provided on the input side or output side of the second semiconductor amplifying means, and the first to third amplifying means can be bipolar transistors or field effect transistors.

  As described above, according to the present invention, since the first semiconductor amplifying means is fixedly biased, a plurality of high-frequency signals having different levels can be input by appropriately setting the bias value. However, good C / N can be obtained, and the current of the third semiconductor amplifying means can be changed according to the operating states of the first and second semiconductor amplifying means, so that power consumption can be suppressed. Can do.

  The high-frequency amplifier according to the first embodiment of the present invention is used in a booster for a television broadcast signal shown in FIG. This booster has two input terminals 2 and 4. The input terminal 2 is supplied with a VHF band television broadcast signal. The input terminal 4 is supplied with a UHF band television broadcast signal. Alternatively, a mixed signal of UHF band and VHF band television broadcast signals is supplied only to the input terminal 4. When a mixed signal is supplied to the input terminal 4, a VHF band television broadcast signal is extracted from the mixed signal by the low-pass filter 6 and supplied to the input switching circuit 8. The low-pass filter 6 has a pass band that allows the VHF band television broadcast signal to pass therethrough. When a VHF band television broadcast signal is supplied to the input terminal 2 and a UHF band television broadcast signal is supplied to the input terminal 4, the input switching circuit 8 receives the VHF band television broadcast signal from the input terminal 2, This is supplied to the low-pass filter 10 having a pass band for passing it.

  The VHF band television broadcast signal is composed of a high frequency VHF band television broadcast signal and a low frequency VHF band television broadcast signal. Among the VHF band television broadcast signals that have passed through the low-pass filter 10, a high-frequency VHF band television broadcast signal is extracted by a band-pass filter 12 having a pass band that passes the high-frequency VHF band broadcast signal. The extracted high frequency VHF band television broadcast signal is attenuated by the variable attenuator 14 and amplified by the high frequency amplifier 16. Unnecessary signal components are removed from the output signal of the high-frequency amplifier 16 by a band-pass filter 18 having a pass band for passing a high-frequency VHF band television broadcast signal.

  Similarly, a low-frequency VHF band television broadcast signal out of the VHF band television broadcast signal that has passed through the low-pass filter 10 is extracted by a band-pass filter 20 having a pass band that passes the low-frequency filter, and the variable attenuator 22 attenuates the amount of attenuation. Are adjusted and amplified by the high-frequency amplifier 24. An unnecessary signal component is removed from the output signal to the high-frequency amplifier 24 by a band-pass filter 26 having a pass band for passing a low-frequency VHF band television broadcast signal.

  The output signals (amplified high and low frequency VHF band television broadcast signals) of the bandpass filters 18 and 26 from which unnecessary signal components have been removed are passed through the VHF band high frequency and low frequency television broadcast signals. It is supplied to a low-pass filter 30 having a pass band and synthesized.

  The UHF band television broadcast signal or mixed signal supplied to the input terminal 4 is supplied to a high-pass filter 32 having a pass band that allows the UHF band television broadcast signal to pass therethrough. A UHF band television broadcast signal is output from the high pass filter 32. The UHF band television broadcast signal is a mixture of an analog television broadcast signal and a digital television broadcast signal, an analog television broadcast signal only, or a digital television broadcast signal only. In any case, the UHF band television broadcast signal is a plurality of waves, and there is a level difference among them.

  The output signal of the high pass filter 32 is supplied to the high frequency amplifier 34 through the variable attenuator 33, amplified by the high frequency amplifier 34, and supplied to the high pass filter 36. The high pass filter 36 has a pass band that allows the UHF band television broadcast signal to pass through, and removes unnecessary signal components from the output signal of the amplifier 34. The output band of the high pass filter 36 (amplified UHF band television broadcast signal) and the output signal of the low pass filter 30 (amplified VHF band television broadcast signal) pass the UHF band television broadcast signal. And is supplied to the output terminal 40.

  As shown in FIG. 1, the high-frequency amplifier 34 includes first semiconductor amplifying means, for example, an NPN-type bipolar transistor 42. The bipolar transistor 42 has a control electrode such as a base, a common electrode such as an emitter, and an output electrode such as a collector. The base is connected to a first potential line 46 having a potential of, for example, + Vcc via a resistor 44. The emitter is connected to the second potential line 48. The potential of the second potential line 48 is lower than the potential of the first potential line 46. The collector is connected to the first potential line 46 via a low-pass filter 54 having a pass band for passing a UHF band television broadcast signal constituted by inductors 50a and 50b and capacitors 52a and 52b, and an inductor 56. Yes. Thereby, the transistor 42 is fixedly biased. In other words, the resistor 44 and the inductor 56 constitute a fixed bias circuit. The inductor 56 is a load. This fixed bias circuit always gives a constant bias to the transistor 42. Even if there is a level difference between the levels of a plurality of high frequency signals supplied from the variable attenuator 33 to the base of the transistor 42 via the capacitor 58, the bias is set to a predetermined C / N with the lowest level high frequency signal. It is set to a value that can be secured. The variable attenuator 33 is controlled so that the amount of attenuation increases when there is a fairly high level of the input high frequency signal. The collector of the transistor 42 is connected to a reference potential, for example, a ground potential in an alternating manner by a capacitor 60. Reference numerals 62a and 62b indicate bypass capacitors.

  The high-frequency amplifier 34 includes second semiconductor amplifying means, for example, an NPN bipolar transistor 64, the collector of which is connected to the first potential line 46 through an inductor 66, and the emitter of the second amplifier through a resistor 68. Are connected to the potential line 48. Between the first potential line 46 and the second potential line 48, a resistor 70, an inductor 72, a variable resistor 74, a resistor 76, and a resistor 78 are connected in series from the first potential line 46 side. It is connected. The arm of the variable resistor 74 is connected to the base of the transistor 64. These, the resistor 68, and the inductor 66 constitute a current feedback type bias circuit, and the bias changes by adjusting the position of the arm of the variable resistor 74. The inductor 66 is a load.

  The output of the low-pass filter 54 is supplied to the connection point between the variable resistor 74 and the resistor 76 via the DC blocking capacitor 80, and this output is supplied to the base of the transistor 64 via the resistor 76 and the capacitor 82. Has been. The connection point between the variable resistor 74 and the inductor 72 is connected to the ground potential through the resistor 84 and the capacitor 86, and the resistor 76, the variable resistor 74, and the resistor 84 are grounded in an alternating manner. The emitter of the transistor 64 is connected to the ground potential via the capacitor 88 and is grounded in an alternating manner. Accordingly, by adjusting the arm of the variable resistor 74, the output level of the low-pass filter 54 supplied to the transistor 64 is also adjusted. That is, the current feedback type bias circuit incorporates gain adjusting means. Note that when the position of the arm of the variable resistor 74 is adjusted to the A side shown in FIG. 1 so that the bias becomes deep, the level of the high-frequency signal supplied to the transistor 64 increases and the bias becomes shallow. When the position of the arm of the device 74 is adjusted to the B side, the level of the high frequency signal supplied to the transistor 64 decreases. Reference numeral 90 denotes a bypass capacitor.

  The high frequency amplifier 34 also includes third semiconductor amplification means, for example, an NPN bipolar transistor 92. The output signal of the transistor 64 is supplied to the base of the transistor 92 via a low-pass filter 98 having a pass band for passing a UHF band television broadcast signal composed of an inductor 94 and capacitors 96a and 96b and a DC blocking capacitor 100. ing. The transistor 92 is biased by a current feedback type bias circuit. In this bias circuit, a resistor 102 is connected between a base and a third potential line, for example, a ground potential, and the base is further connected to a second potential line 48 via a resistor 104 and a high-frequency blocking coil 106. Has been. The high frequency blocking coil 106 and the capacitor 108 constitute a high frequency blocking filter. The emitter of the transistor 92 is connected to the ground potential through a parallel circuit of a resistor 110 and a capacitor 112. The collector is composed of an inductor 114 and capacitors 116a and 116b, and is connected to a high-pass filter 36 shown in FIG. 2 via a low-pass filter 118 having a pass band for allowing UHF band television broadcast signals to pass through. The collector is connected to the second potential line 48 via the low-pass filter 118, the inductor 120, and the high-frequency blocking coil 106. That is, this bias circuit is connected between the second potential line 48 and the ground potential. Reference numeral 122 denotes a bypass capacitor.

  Considering the first potential line 46 and the ground potential as a reference, the amplification stage composed of the transistors 42 and 64 and the amplification stage composed of the transistor 92 are connected in series via the second potential line 48. .

  In the high frequency amplifier 34 configured as described above, since a fixed bias is applied to the transistor 42, even in a signal having a low level and a poor C / N ratio among UHF band television broadcast signals supplied to the transistor 42. A certain C / N can be secured. The amplified output signal from the transistor 42 is amplified by the transistor 64. By adjusting the variable resistor 74 provided in the current feedback bias circuit of the transistor 64, the bias state of the transistor 64 and the transistor The gain at 64 can be adjusted. In addition, since a fixed bias is applied to the transistor 42, if there is a signal with a high signal level supplied to the transistor 64, the variable resistor 74 is adjusted to the B side to reduce the gain and bias. Therefore, unnecessary current does not need to flow through the transistor 64. Further, since the current from the transistors 42 and 64 flows to the transistor 92 via the second potential line 48, for example, when the level of the input high-frequency signal is high and it is not necessary to greatly amplify, the transistor 64 And the current flowing through the transistor 92 is also reduced. As a result, power consumption can be suppressed.

  As shown in FIG. 3, the high-frequency amplifier 34 a according to the second embodiment of the present invention is configured to perform gain adjustment on the collector side of the transistor 64 and to apply a current feedback bias to the transistor 64. . That is, the base of the transistor 64 is connected to the second potential line 48 via the resistor 78 as in the first embodiment, and the emitter is connected to the second potential line 48 via the resistor 68. In addition, the capacitor 88 is connected to the ground potential. The base of the transistor 64 is connected to the collector of the transistor 64 via the resistor 70a and the inductor 56a. The collector is connected to the first potential line 46 via a resistor 76a, a variable resistor 74a, an inductor 72a, and a resistor 70a. The arm of the variable resistor 74 a is connected to the collector of the transistor 64. The connection point between the variable resistor 74a and the inductor 72a is grounded via a series circuit of a resistor 84a and a capacitor 86a. As a result, the collector of the transistor 64 is grounded in an AC manner via the resistor 76a, the variable resistor 74a, the resistor 84a, and the capacitor 86a.

  With this configuration, the level of the output signal from the collector of the transistor 64 is adjusted and the bias of the transistor 64 is adjusted by operating the arm of the variable resistor 74a. As in the first embodiment, this adjustment is performed by moving the arm of the variable resistor 74a to the A side shown in FIG. 3 and increasing the bias to attenuate the output signal from the transistor 64 by the variable resistor 74a or the like. The amount is reduced. When the arm of the variable resistor 74a is moved to the B side to reduce the bias, the amount of attenuation of the output signal from the transistor 64 by the variable resistor 74a and the like increases. In this way, after amplification by the transistor 64, the signal is attenuated by the variable resistor 74a or the like, so that distortion of the output signal can be reduced, and the UHF band television signal is a terrestrial digital television broadcast signal. It is advantageous if there is a difference in input level.

  In the above embodiment, an NPN bipolar transistor is used for each of the transistors 42, 64, and 92. However, instead of this, a PNP bipolar transistor can be used, or an FET (field effect transistor) can be used. it can. For example, when a PNP bipolar transistor is used, the potential of the first potential line 46 is the lowest, the potential of the second potential line 48 is the next lowest, and the ground potential as the third potential line can be the highest. . In the first embodiment, the resistor 70 and the inductor 72 are provided. However, either one may be omitted depending on circumstances. The capacitor 88 can also be omitted. A resistor may be used in place of the inductors 56, 66, and 120.

1 is a circuit diagram of a high-frequency amplifier according to a first embodiment of the present invention. It is a block diagram of the booster using the high frequency amplifier of FIG. It is a circuit diagram of the high frequency amplifier of the 2nd Embodiment of this invention.

Explanation of symbols

42 transistor (first amplification means)
44 Resistor (fixed bias circuit)
46 First potential line 48 Second potential line 56 Inductor (fixed bias circuit)
64 transistors (second amplification means)
66 72 inductor (current feedback bias circuit)
68 70 76 78 Resistor (Current feedback bias circuit)
74 Variable resistor (current feedback bias circuit, gain adjustment means)
84 Resistor (gain adjustment means)
92 transistor (third amplification means)
102 104 110 Resistor (current feedback bias circuit)
120 inductor (current feedback bias circuit)

Claims (5)

A first semiconductor amplifying means which is fixedly biased by a fixed bias circuit provided between first and second potential lines of different potentials and amplifies a high frequency signal;
Biased by a current feedback bias circuit provided between the first and second potential lines, gain adjusting means is provided in the current feedback bias circuit, and the output signal of the first semiconductor amplifying means is amplified. Two semiconductor amplifying means;
Biased by a current feedback bias circuit provided between the second potential line and a third potential line having a different potential from the first and second potential lines, the output signal of the second semiconductor amplifying means is A third semiconductor amplification means for amplifying,
A high-frequency amplifier provided.   2. The high frequency amplifier according to claim 1, wherein the gain adjusting means is provided on an input side of the second semiconductor amplifying means.   2. The high frequency amplifier according to claim 1, wherein the gain adjusting means is provided on the output side of the second semiconductor amplifying means.   2. The high frequency amplifier according to claim 1, wherein the first to third amplifying means are bipolar transistors.   2. The high frequency amplifier according to claim 1, wherein the first to third amplifying means are field effect transistors.

Images