JPH04361410A - Broad band amplifier device - Google Patents

Abstract

PURPOSE:To obtain the frequency characteristic with excellent gain and noise figure by connecting a gate electrode of a 2nd transistor (TR) to ground in terms of a high frequency and applying a DC bias voltage for deciding the gain to the gate electrode. CONSTITUTION:A gate electrode of a 2nd TR 102 is connected to ground through a capacitor 123 in terms of a high frequency and a bias resistor 111 is connected between a gate electrode and a source electrode of a 1st TR 101. A feedback circuit 151 comprising a feedback resistor 110 and a feedback capacitor 120 is connected between the gate electrode and a drain electrode of the 1st TR 101 and a DC voltage from a gain control power supply 141 is applied to the gate electrode 120 of the 2nd TR 102 via a resistor 112. Thus, the feedback component by a drain-gate feedback capacitance of the 2nd TR is escaped to ground via the gate electrode and the frequency characteristic is improved without giving effect onto the gate electrode of the 1st TR.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wideband amplification device for amplifying high frequency signals.

0002

2. Description of the Related Art In recent years, as broadcasting has become more multi-channel, there has been a strong demand for wider bands and higher frequencies in receiving apparatuses, and there has been a strong demand for wider bands and higher frequencies in the first stage amplifier of the receiving apparatus.

A conventional wideband amplifier is constructed as shown in FIG. A source electrode of the transistor 101 is grounded, and a DC power supply voltage is applied to the drain electrode from a power supply 140 through a choke coil 130. A bias resistor 111 is connected between the gate electrode and the source electrode of the transistor 101, and the transistor 1
A feedback circuit 151 composed of a feedback resistor 110 and a feedback capacitor 120 is connected between the gate electrode and the drain electrode of 01. The signal to be amplified is input from the high frequency signal input terminal 160 to the gate electrode of the transistor 101 via the coupling capacitor 121, and from the drain electrode of the transistor 101 to the coupling capacitor 1.
22 to the high frequency signal output terminal 161.

A part of the signal amplified by the transistor 101 is sent to the transistor 101 via a feedback circuit 151.
Since this returned signal has a phase difference of 180° from the amplified signal, it cancels out the amplified signal.

Therefore, the greater the gain when the feedback circuit 151 is not connected, the greater the decrease in gain when the feedback circuit 151 is connected. Normally, high-frequency amplifiers composed of such field-effect transistors have a gain deviation of "6 [dB/Oct]" with respect to frequency, so the lower the frequency, the greater the gain, and the higher the frequency. The gain decreases accordingly. Therefore, when the feedback circuit 151 is connected, while the gain on the low frequency side is greatly reduced, the decrease in the gain on the high frequency side is small, and as a result, the frequency deviation of the gain is reduced, and broadband characteristics are obtained.

Note that the amount of feedback by the feedback circuit 151 is almost determined by the feedback resistor 110, and the feedback capacitor 120 is normally of a sufficiently large capacity so as not to have frequency characteristics. Further, the resistance value of the feedback resistor 110 is set so that the input/output impedance is approximately equal to 50Ω, which is the characteristic impedance of the transmission path.

[0007]

[Problems to be Solved by the Invention] Such conventional wideband amplifiers have the disadvantage that the amount of feedback increases as the frequency increases due to the feedback capacitance between the drain and gate of the FET, deteriorating the frequency characteristics of gain and noise figure. Was.

SUMMARY OF THE INVENTION An object of the present invention is to provide a wideband amplifier device that can improve frequency characteristics in terms of gain and noise figure.

[0009]

[Means for Solving the Problems] A wideband amplifier according to claim 1 is characterized in that a drain electrode of a first transistor and a second transistor are connected to each other.
A feedback circuit is connected between the gate electrode of the first transistor and the drain electrode of the second transistor, the gate electrode of the second transistor is grounded at high frequency, and the Inputting the amplified signal to the gate electrode of the first transistor, applying a DC bias voltage for determining gain to the gate electrode of the second transistor,
It is characterized in that the output signal is taken out from the drain electrode of the second transistor.

A broadband amplifier according to a second aspect of the present invention includes a dual gate transistor having a first gate electrode and a second gate electrode between a drain electrode and a source electrode, and a first gate electrode of the dual gate transistor. A feedback circuit is connected between the drain electrode of the dual gate transistor and the first gate electrode, and the second gate electrode of the dual gate transistor is grounded at high frequency. A DC bias voltage for gain determination is applied to the second gate electrode of the dual-gate transistor, and an output signal is extracted from the drain electrode of the dual-gate transistor.

[0011]

According to the structure of claim 1, since the gate electrode of the second transistor is grounded at high frequency, the feedback component due to the feedback capacitance between the drain and gate of the second transistor is transmitted through the gate electrode of the second transistor. It can escape to ground, does not affect the gate electrode of the first transistor, and improves frequency characteristics.

According to the structure of claim 2, since the second gate electrode of the dual gate transistor is grounded at high frequency, the feedback component due to the feedback capacitance between the drain and gate of the dual gate transistor is transferred to the second gate electrode of the dual gate transistor. Since it can escape to the ground via the electrode, it does not affect the first gate electrode of the dual gate transistor, and the frequency characteristics are improved.

[0013]

Embodiments Hereinafter, embodiments of the present invention will be explained based on FIGS. 1 to 3. Components having the same functions as those in FIG. 4 showing the conventional example will be described with the same reference numerals.

FIG. 1 shows a broadband amplification device according to claim 1. The drain electrode of the first transistor 101 and the source electrode of the second transistor 102 are connected, and the source electrode of the first transistor 101 is grounded 150.
A DC power supply voltage is applied to the drain electrode of the second transistor 102 from a power supply 140 through a choke coil 130. second transistor 1
A bias resistor 111 is connected between the gate electrode and the source electrode of the first transistor 101, and a bias resistor 111 is connected between the gate electrode and the drain electrode of the first transistor 101. includes a feedback resistor 110 and a feedback capacitor 120.
A feedback circuit 151 consisting of the following is connected. Furthermore, a DC voltage is applied to the gate electrode of the second transistor 102 from a gain control power source 141 through a resistor 112.

The signal to be amplified is input to the high frequency signal input terminal 160.
from the transistor 10 via the coupling capacitor 121
The signal is input to the gate electrode of transistor 101 and outputted from the drain electrode of transistor 101 to high frequency signal output terminal 161 via coupling capacitor 122.

The high frequency signal input from the high frequency signal input terminal 160 is amplified by the first transistor 101 and outputted from the high frequency signal output terminal 161 via the second transistor 102, but a part of the output signal is The feedback circuit 151 returns the signal to the gate electrode of the first transistor 101. As a result, as in the conventional example, the gain on the low frequency side is greatly reduced, whereas the gain on the high frequency side is only slightly reduced, resulting in a small frequency deviation of the gain and a wide band characteristic.

The embodiment shown in FIG. 1 differs from the conventional example shown in FIG. 4 in that the first transistor 101 and the second transistor 102 are connected in cascode. The two main effects are as follows.

(1) A feedback component due to the feedback capacitance of the second transistor is released from the gate electrode of the second transistor 102 to ground. (2) The impedance seen from the first transistor 101 on the output side is the mutual conductance (hereinafter referred to as gm
5 of the load impedance.
Since it is smaller than 0Ω, the signal amplitude at point A shown in FIG. 1 is smaller than the signal amplitude at point B shown in the same figure. Therefore, A
The amount of feedback from the point to the gate electrode of the first transistor 101 can be reduced.

For the above reasons, the amount of feedback from point B to the first transistor 101 is smaller than that of the second transistor 102.
can be made much smaller than when not inserted, and can be made less susceptible to feedback capacitance between the drain and gate. As a result, the wideband amplifier shown in FIG. 1 exhibits superior frequency characteristics in terms of gain and noise figure compared to the conventional example.

FIG. 2 shows the results of comparing the frequency characteristics of the gain and noise figure of the broadband amplifier device of the first embodiment shown in FIG. 1 with those of the conventional example. From the same figure, it can be seen that the frequency characteristics of the gain and noise figure of the broadband amplifier device of the first embodiment are significantly improved over the conventional example from around 1 GHz to high frequencies.

In addition, in this embodiment, the power source 140 is “
5V", the gain control power supply 141 becomes "1".
．． The maximum gain can be obtained at 5 V, and the minimum gain at 0 V, and a maximum gain control amount of 30 dB can be obtained at a frequency of 100 MHz.

FIG. 2 shows a broadband amplification device according to claim 2. In FIG. 2, the source electrode of a dual-gate transistor 103 having a first gate electrode G1 and a second gate electrode G2 between the drain electrode and the source electrode is connected to ground 150, and the drain electrode is connected via a choke coil 130. A DC power supply voltage is applied from a power supply 140 . The second gate electrode G2 is connected to the capacitor 123
A bias resistor 111 is connected between the first gate electrode G1 and the source electrode, and a feedback resistor 110 is connected between the first gate electrode and the drain electrode.
A feedback circuit 15 consisting of a feedback capacitor 120 and a feedback capacitor 120.
1 is connected. A DC voltage for gain control is applied to the second gate electrode G2 from a gain control power source 141 through a resistor 112.

[0023] The signal to be amplified is input to the high frequency signal input terminal 160.
from the drain electrode to the first gate electrode G1 via the coupling capacitor 121, and from the drain electrode to the coupling capacitor 12.
2 to the high frequency signal output terminal 161.

A part of the output signal is returned to the first gate electrode G1 by the feedback circuit 151, and as a result, the gain on the low frequency side is greatly reduced as in the conventional example, but the gain on the high frequency side is reduced. is small, resulting in a small gain frequency deviation and a wideband characteristic.

The second embodiment shown in FIG. 2 differs from the conventional example shown in FIG. 4 in that a dual-gate transistor 103 is used instead of the transistor 101, and this difference in configuration is the main difference. The effects are the following two points.

(1) A feedback component due to the feedback capacitance between the drain and the second gate is released from the second gate electrode G2 to the ground. (2) Since the signal amplitude in the channel section between the first gate G1 and the second gate G2 is smaller than the signal amplitude at the drain electrode, the amount of feedback between the channel section and the first gate G1 can be reduced. .

For the above reasons, the amount of feedback from the drain of the dual gate transistor 103 to the first gate G1 can be made much smaller than in the conventional example. As a result, it exhibits better frequency characteristics than the conventional example in terms of gain and noise figure.

In this embodiment, the power source 140 is “
5V", the gain control power supply 141 becomes "1".
．． The maximum gain can be obtained at "5 V" and the minimum gain can be obtained at "0 V", and a maximum gain control amount of 25 dB at a frequency of 100 MHz can be obtained.

The circuits of the above embodiments can also be integrated on a semiconductor substrate.

[0030]

In the broadband amplification device according to claim 1, the drain electrode of the first transistor and the source electrode of the second transistor are connected, and the gate electrode of the first transistor and the drain electrode of the second transistor are connected to each other. Since a feedback circuit is connected between the electrode and the gate electrode of the second transistor is grounded at high frequency, the feedback component due to the feedback capacitance between the drain and gate of the second transistor is released to the ground through the gate electrode of the second transistor. Therefore, the frequency characteristics can be improved without affecting the gate electrode of the first transistor.

A broadband amplifier according to a second aspect of the present invention includes a dual gate transistor having a first gate electrode and a second gate electrode between a drain electrode and a source electrode, and a first gate electrode of the dual gate transistor. A feedback circuit was connected between the drain electrode of the dual-gate transistor and the first gate electrode, and the second gate electrode of the dual-gate transistor was grounded at high frequency. Since the feedback component due to the feedback capacitance can be released to the ground through the second gate electrode, the frequency characteristics can be improved without affecting the first gate electrode.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a wideband amplification device according to claim 1.

FIG. 2 is a frequency characteristic diagram of the same device and a conventional product.

FIG. 3 is a configuration diagram of a wideband amplification device according to claim 2.

FIG. 4 is a configuration diagram of a conventional wideband amplifier device.

[Explanation of symbols]

101 First transistor 102 Second transistor 141 Gain control power supply 151 Feedback circuit 160 High frequency signal input terminal 161 High frequency signal output terminal 103 Dual gate transistor G1
First gate G2 Second gate 150 Ground

Claims (2)

[Claims] 1. Connecting a drain electrode of a first transistor and a source electrode of a second transistor, and connecting a feedback circuit between a gate electrode of the first transistor and a drain electrode of the second transistor, The gate electrode of the second transistor is grounded at high frequency, the amplified signal is input to the gate electrode of the first transistor, a DC bias voltage for gain determination is applied to the gate electrode of the second transistor, and the second A broadband amplifier that extracts an output signal from the drain electrode of a transistor. [Claim 2] A first electrode between the drain electrode and the source electrode.
a dual gate transistor having a gate electrode and a second gate electrode; a signal to be amplified is input to the first gate electrode of the dual gate transistor; A feedback circuit is connected to the dual gate transistor, the second gate electrode of the dual gate transistor is grounded at high frequency, a DC bias voltage for gain determination is applied to the second gate electrode of the dual gate transistor, and the drain of the dual gate transistor is connected to the feedback circuit. A wideband amplifier that extracts output signals from electrodes.