JPH0526815Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a high frequency amplifier, and particularly to a high frequency amplifier suitable for a so-called booster that amplifies a television signal before supplying it to a television receiver.

<Prior Art> Conventionally, the above-mentioned high frequency amplifier includes one shown in FIG. 6, for example. This is done from a variable resistor 8 and a resistor 10 in a bias circuit consisting of a resistor 4 connected between the collector and base of the transistor 2 and a resistor 6 connected between the collector and the power supply +Vcc. When adjusting the gain by interposing an attenuator between the collector and the resistor 6 and sliding the arm of the variable resistor 8, the bias of the transistor 2 is also changed at the same time to improve the distortion characteristics. It is something.

There was also something like the one shown in Figure 7. In the bias circuit for the transistor 18 consisting of the bleeder resistors 12, 14 and the emitter resistor 16, the variable resistor 20, the resistors 22, 2
4. An attenuator consisting of capacitors 26 and 28 is connected between the bleeder resistors 12 and 14 and the base of the transistor 18, so that when the variable resistor 20 is slid to adjust the gain, the transistor The bias of No. 18 was also adjusted, and when the amount of attenuation was decreased, the noise figure was improved, and when the amount of attenuation was increased, the distortion characteristics were improved.

<Problems to be solved by the invention> In the high-frequency amplifier shown in Fig. 6, the attenuator is provided on the collector side, so when used in a strong electric field area, a high-level signal is directly transmitted to the base of transistor 2. Since the input signal is input, there is a risk of exceeding the input resistance level of the transistor 2, and the appropriate input level range is narrow, making it difficult to use in areas with strong electric fields.

Also, in the case shown in Fig. 7, since an attenuator is provided on the input side, unlike the case shown in Fig. 6, the problem that the appropriate input level range becomes narrow does not occur.
Moreover, when the amount of attenuation is reduced, the noise figure can be improved, and when the amount of attenuation is increased, the distortion characteristics can be improved. However, since the variable resistor 20 is used as a component of the attenuator, In the signal band, it is affected by the lead inductance and terminal capacitance, and when the input signal is a high frequency higher than VHF, the effect as an attenuator is small, so it is not suitable for use as a wideband high frequency amplifier that amplifies signals from VHF to UHF. The problem was that it could not be used.

<Means for solving the problem> This invention was made in order to solve the above problem, and includes a transistor having a control electrode, an output electrode, and a common electrode, and a connection between the common electrode and a reference potential point. A high frequency amplification section with a first fixed resistor connected between them, a PIN diode connected between the control electrode and the input terminal, and a second fixed resistor connected between the control electrode and the power supply. and a third fixed resistor with one end connected to the input terminal side, the other end of this third fixed resistor is connected to the slider, one end is connected to the reference potential point, and the other end is open. Equipped with a variable resistor. And the PIN diode is
It is connected to the polarity that minimizes the high frequency resistance value when the slider is slid on one end of the variable resistor. Furthermore, the resistance values of the first to third fixed resistors are determined by the control current that causes an output current to flow that improves the noise figure of the transistor when the slider is slid on one end of the variable resistor. is passed through the control electrode, and when the slider is slid on the other end of the variable resistor, the resistance value that causes the control current to flow through the control electrode so that an output current that improves the distortion characteristics of the transistor flows. are selected respectively.

[Effect]

According to this invention, when the slider of the variable resistor is slid onto one end of the variable resistor, the high frequency resistance value of the PIN diode becomes the minimum, and the amount of attenuation becomes the minimum. At this time, the first to third
A fixed resistor causes a control current to flow through the control electrode of the transistor that causes an output current to flow with a good noise figure of the transistor. Therefore, at this time, the high frequency amplifier section operates as a high gain, low noise type high frequency amplifier for weak electric fields. On the other hand, when the slider of the variable resistor is slid toward the other end of the variable resistor, the high frequency resistance value of the PIN diode becomes maximum, and the amount of attenuation becomes maximum. At this time, the first to third fixed resistors together with the PIN diode cause a control current to flow through the control electrode of the transistor, which causes an output current that improves the distortion characteristics of the transistor to flow. Therefore, at this time, the high frequency amplifier section operates as a low gain, low distortion type high frequency amplifier for strong electric fields.

<Effects> As described above, according to this invention, by changing the resistance value of the variable resistor, one high-frequency amplifier can be used as a high-gain, low-distortion type high-frequency amplifier for strong electric fields or a high-gain, low-noise type high-frequency amplifier for weak electric fields. It can be made to work. Therefore, a low-gain, low-distortion high-frequency amplifier for strong electric fields and a high-gain, low-noise high-frequency amplifier for weak electric fields,
There is no need to manufacture each separately, which reduces manufacturing costs and facilitates inventory management.

Moreover, when one high-frequency amplifier is operated as a low-gain, low-distortion type high-frequency amplifier for strong electric fields or a high-gain, low-noise type high-frequency amplifier for weak electric fields, a PIN diode that also operates as an attenuator is provided on the control electrode side of the transistor. This is done by changing the control current of the transistor by changing the resistance value, so the control current can be varied over a wide range, and even when an excessive signal is supplied to the input terminal, the PIN diode By changing the resistance value using a variable resistor, the operating point of this transistor can be changed, and the output signal can be prevented from being distorted, and the level range of the input signal supplied to this high frequency amplifier can be changed. can be expanded. In addition, since the PIN diode is used as an attenuator, unlike the conventional one shown in Figure 7, it is not affected by the lead inductance of the variable resistor or the capacitance between the terminals, and can be used from the VHF band to the UHF band. Television signals can be attenuated over a wide range of frequencies.

<Example> In Fig. 1, numeral 30 is an input terminal;
Broadband television signals from VHF to UHF are provided. This input terminal 30 is connected to the base of a microwave amplification transistor (hereinafter simply referred to as a transistor) 36 via a series circuit of a coupling capacitor 32 and a PIN diode 34. The PIN diode 34 is connected such that its cathode is connected to the input terminal 30 side, and its anode is connected to the base side of the transistor 36. PIN diode 34
The anode of is connected to the +Vcc power supply via a high frequency choke coil 38 and a bleeder resistor 40. Further, the cathode of the PIN diode 34 is connected to the high frequency choke coil 42 and the bleeder resistor 44.
It is connected to the arm of the variable resistor 46 via.
One end a of this variable resistor 46 is grounded, and the other end b
is open. Further, the emitter of the transistor 36 is grounded via an emitter resistor 48. These PIN diodes 34, high frequency choke coils 38, 42, bleeder resistors 40, 4
4. The variable resistor 46 and the emitter resistor 48 are
A bias circuit for the transistor 36 is configured, and a PIN diode 34, high-frequency choke coils 38, 42, bleeder resistors 40, 44, and a variable resistor 46 connect the input terminal 30 to the transistor 36.
This constitutes an attenuator that attenuates the television signal supplied to the base of the system. In addition, 50, 52,
54 and 56 are bypass capacitors.

The collector of the transistor 36 is connected to the load coil 5
8 to the +Vcc power supply. The load coil 58 has an intermediate tap which is connected to the output terminal 6 via a coupling capacitor 60.
Connected to 2. Note that 64 is also a bypass capacitor.

In the high frequency amplifier shown in FIG. 1, by sliding the arm of the variable resistor 46, the PIN diode 34
The current flowing through the bleeder resistors 40 and 44 changes, and the high frequency resistance value of the PIN diode 34 changes, thereby changing the amount of attenuation of the television signal supplied to the transistor 36.
The bias state of transistor 36 also changes. For example, when one end of the arm of the variable resistor 46 is slid to the side a, the current flowing through the PIN diode 34 becomes maximum, the high frequency resistance value of the PIN diode 34 becomes minimum, and the amount of attenuation also becomes minimum. At this time, the current flowing to the base of the transistor 36 becomes small and the collector current also becomes small, but the resistance values of the bleeder resistors 40 and 44 and the emitter resistor 48 are changed so that the collector current that improves the noise figure flows. Resistance value is selected.

Furthermore, when the arm of the variable resistor 46 is slid toward the other end b side, the current flowing through the PIN diode 34 becomes the minimum, the high frequency resistance value of the PIN diode 34 becomes the maximum, and the amount of attenuation also becomes the maximum. At this time, the current flowing to the base of the transistor 36 becomes large, and the collector current also becomes large, but the resistance values of the bleeder resistors 40 and 44 and the emitter resistor 48 are adjusted so that a collector current that improves the distortion characteristics flows. The resistance value of the variable resistor 46 and the resistance value between both ends of the variable resistor 46 are respectively selected.

Figure 2 shows the relationship between frequency and gain when the arm of the variable resistor 46 is slid to one end a to minimize attenuation, and to the other end b to maximize attenuation. show. As is clear from this, when the arm of the variable resistor 46 is slid to the other end b, one end a
UHF frequency range (470M
Approximately 8 dB greater attenuation can be obtained over the entire range (from Hz to 770 MHz). This is because when a variable resistor 20 is used as an attenuator like the one shown in FIG. This is because they are not affected by this kind of influence. Of course, VHF frequency range (90MHz ~
Similar attenuation can be obtained over the entire range (222MHz).

Comparing the distortion characteristics when the arm of the variable resistor 46 is immediately slid at one end a and the distortion characteristics when the arm of the variable resistor 46 is slid toward the other end b are shown in FIGS. 3 and 4. It will look like the figure. In other words, Figures 3 and 4 show the intermodulation distortion measured at each measurement frequency of 615MHz and 625MHz, and both show the signal strength.
105dBμ is taken as 0dB. As you can see from these figures, 615MHz x 3 - 625MHz x 2 = 595MHz,
At any point of 625MHz x 3 - 615MHz = 645MHz,
When the arm of the variable resistor 46 is slid toward the other end b side,
The intermodulation distortion was improved by about 10 dB compared to when one end of the arm of the variable resistor 46 was slid to the side a, and
615MHz x 2 - 625MHz x 2 = 605MHz, 625MHz x
When the arm of the variable resistor 46 was slid to the other end b side at any point of 2-615MHz=635MHz, the intermodulation distortion was improved by about 25 dB compared to the case where one end was slid to the a side.

FIG. 5 shows the noise figure characteristics of the transistor 36 alone. When one end of the arm of the variable resistor 46 is slid to side a, the noise figure becomes approximately 1 dB, and the arm of the variable resistor 46 is moved to the other end to side b. approx. than when sliding
It has been improved by 1.4dB. Note that the actual noise figure is a value obtained by adding the amount of attenuation caused by the PIN diode 34 at that time to the value shown in FIG.

Putting these together, for example, at a frequency of 620 MHz, when one end of the arm of the variable resistor 46 is slid to the side a, the gain is 13.25 dB (MKR1 in Figure 2), the noise figure is 1.1 dB, and the distortion characteristic is -36 dB ( The output is 105dBμ), which is sufficient for a high-gain, low-noise high-frequency amplifier. Furthermore, when the arm of the variable resistor 46 is slid to the other end b side at the same frequency as above, the gain is
6dB (MKR2 in Fig. 2), the noise figure is 10.6dB, and the distortion characteristics are -62dB (output 105dBμ), which are sufficient characteristics as a low gain, high output high frequency amplifier. Therefore, by simply adjusting the variable resistor 46, one amplifier can be used as a high-gain, low-noise high-frequency amplifier for weak electric field regions and a low-gain, high-output high-frequency amplifier for strong electric field regions.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an embodiment of the high frequency amplifier according to this invention, Fig. 2 is a diagram showing the gain characteristics of the embodiment, and Fig. 3 shows the arm of the variable resistor of the embodiment.
A diagram showing two-signal distortion characteristics in a state where it is slid to the side,
Fig. 4 is a diagram showing two-signal distortion characteristics in a state where the arm of the variable resistor of the same embodiment is slid to the other end b side, Fig. 5 is a diagram showing the noise figure characteristics of the same embodiment, and Fig. 6 is a circuit diagram of one example of a conventional high frequency amplifier, and FIG. 7 is a circuit diagram of another conventional high frequency amplifier. 34...PIN diode, 36...transistor (high frequency amplification section), 46...variable resistor.

Claims (1)

[Scope of utility model registration request] A high frequency amplification section including a transistor having a control electrode, an output electrode, and a common electrode, and a first fixed resistor connected between the common electrode and a reference potential point, and between the control electrode and the input terminal. connected to
a PIN diode, a second fixed resistor connected between the control electrode and the power supply, a third fixed resistor whose one end is connected to the input terminal side, and the third fixed resistor. a variable resistor whose other end is connected to the slider, one end is connected to the reference potential point, and the other end is open, the PIN diode;
When the slider is slid on one end of the variable resistor, the high frequency resistance is connected to the polarity that minimizes it, and the resistance values of the first to third fixed resistors are set to the polarity of the variable resistor. When the slider is slid on one end side, a control current is passed through the control electrode so that an output current that improves the noise figure of the transistor flows, and the other end side of the variable resistor is connected to the above control current. A high frequency amplifier in which a resistance value for flowing the control current to the control electrode is selected so that an output current that improves the distortion characteristics of the transistor flows when the slider is slid.