JPH1075128A - Amplifier and hybrid integrated circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low-noise amplifier capable of amplifying an input signal with a high-gain while correcting an asymmetrical waveform distortion included in itself by amplifying an input signal in two stages by a first and a second transistors. SOLUTION: To the first transistor (FET) 12, a first gate bias part 17 which is a first bias adjustment means and a first bias part 19 which is a first bias setting means are connected. To a second FET 14, a second gate bias part 20 and a second bias part 22 are connected as well. The input signals, including the asymmetrical waveform distortions, are inputted to an input terminal 16. The first FET 12 performs amplification with a high gain, while correcting the low band side of the asymmetrical waveform distortion of the input signals. The second FET 14 performs the amplification with the high gain, while correcting the high band side of the asymmetrical waveform distortion of output signals from the first FET 12 and waveform distortion, while accompanying the nonlinearity or the like of the first and second FETs 12 and 14 themselves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an amplifier suitable for a light receiving unit for an optical CATV, for example, and a hybrid integrated circuit in which the amplifier is mounted on a substrate.

[0002]

2. Description of the Related Art In general, a light receiving section for an optical CATV of this type converts a received optical signal into an electric signal by a photodiode and amplifies the electric signal by a broadband amplifier.

FIG. 8 is a circuit diagram showing an example of a push-pull amplifier 1 used as a conventional broadband amplifier of this kind. This push-pull amplifier 1 has substantially the same characteristics 2
In this method, the transistors 2 and 3 are alternately operated in accordance with the positive and negative of the input signal, and their outputs are combined.
Large output can be obtained.

In addition, by using two transistors 2 and 3 having substantially the same characteristics, distortion of the transistors 1 and 2 themselves can be reduced.

[0005]

However, in such a push-pull amplifier 1, two transistors 2, 2
3, the current is 2 compared to a single amplifier.
Double consumption and large power consumption.

Since the input and output transformers 4 and 5 are required, the weight and cost are increased, and the input transformer 4 needs to be adjusted to distribute the input signals to the transistors 2 and 3. There is a problem that is.

Further, since the amplifier 1 itself can cancel out the mutual distortion by the two transistors 2 and 3, the second-order intermodulation distortion is theoretically zero, but this amplifier 1 has an input to this. There is almost no function of correcting the asymmetric waveform distortion itself included in the input signal to be performed.

Therefore, if the input signal is a broadband high-frequency signal output from, for example, a photodiode having a high output impedance, there is a problem that the waveform distortion can hardly be corrected.

Accordingly, the present invention has been made in view of such circumstances, and an object thereof is to amplify an input signal at a high gain while correcting asymmetric waveform distortion included in the input signal. An object of the present invention is to provide a low noise amplifier.

Another object of the present invention is to easily and accurately adjust a bias point of an amplifier in accordance with a variation in the characteristics of the photodiode even after an external photodiode is mounted on a motherboard. It is another object of the present invention to provide a hybrid integrated circuit capable of amplifying at a high gain while correcting distortion of an output waveform in a wide band.

[0011]

According to the present invention, a first transistor for amplifying an input signal; a second transistor for amplifying an output signal from the first transistor;
First bias setting means for setting a bias point of the first transistor; first bias adjusting means for adjusting a bias point set by the first bias setting means;
A second bias setting means for setting a bias point of the second transistor; and a second bias adjusting means for adjusting a bias point set by the second transistor.

According to the present invention, the input signal is converted into the first and second signals.
, Two-stage amplification can be performed, so that a high gain can be obtained. First, the first-stage transistor performs amplification while mainly correcting the asymmetric waveform distortion of the input signal. Then, the second-stage transistor further corrects the waveform distortion of the input signal. Amplification is performed while correcting distortion such as nonlinear distortion of the second transistor itself.

That is, since the distortion such as the asymmetric waveform distortion of the input signal is corrected by the first and second transistors, for example, in two stages on the low frequency side and the high frequency side, the secondary intermodulation including the asymmetric waveform distortion is performed. Distortion can be significantly and easily reduced over a wide band, and the distortions of the first and second transistors can be mutually offset. In other words, ridges also occur in the waveform distortion due to the frequency characteristics, and these distortions are adjusted by adjusting the bias point to be optimal for correcting the distortion generated in the low frequency side and the distortion generated in the high frequency side. It can be easily reduced over a wide band.

When the input signal is, for example, an output signal from an external photodiode, after attaching this photodiode to the amplifier, the first and second bias points are set to the first and second bias points. By performing readjustment by the bias adjustment means, it is possible to easily readjust the bias point according to the variation in the characteristics of the photodiode. Therefore, it is possible to finely correct the asymmetric waveform distortion caused by the variation in the characteristics of the electronic device in front of the first transistor such as the photodiode.

According to a second aspect of the present invention, the first transistor is set at a bias point for amplifying the input signal with a high gain while correcting the waveform distortion of the input signal. It is characterized in that it is set to a bias point for amplifying with high gain while correcting the waveform distortion of the signal from the transistor and the distortion of the second transistor itself.

According to the present invention, since the bias point of the first transistor is set to the bias point for amplifying the input signal at a high gain while correcting the waveform distortion of the input signal, the waveform of the input signal of the first transistor is set. High gain can be obtained while reducing distortion.

The output from the first transistor is further corrected by the second transistor for waveform distortion of the input signal, and distortion due to the nonlinearity of the first and second transistors themselves is corrected. Therefore, the second-order intermodulation distortion including the asymmetric waveform distortion of the input signal can be significantly reduced over a wide band, and a higher gain can be obtained.

The invention according to claim 3 is characterized in that the first transistor and the second transistor have opposite distortion characteristics.

Since the first and second transistors have distortion characteristics opposite to each other, the mutual reverse distortions can be canceled out and the distortion can be reduced.

According to a fourth aspect of the present invention, the first and second transistors are gallium arsenide (GaAs) field effect transistors or BJTs.

According to the present invention, GaAs FETs (gallium arsenide field effect transistors) and BJTs having excellent wideband high-frequency characteristics and low distortion and low noise characteristics are used as the first and second transistors.
These characteristics can be exhibited also as an amplifier.

According to a fifth aspect of the present invention, the input signal of the first transistor is an electric signal output from the photodiode.

According to the present invention, generally, a high-frequency electric signal is output from a photodiode in a wide band, and this output signal contains an asymmetric waveform distortion. Similarly to the above, correction is performed in two steps by the first and second transistors, so
Second-order intermodulation distortion can be reduced.

Further, the bias points of the first and second transistors are set in advance by the first and second bias setting means to the optimum bias points suitable for the characteristics of the photodiode to be connected. 2 is adjusted by the bias adjusting means.

Moreover, even after the photodiode is connected to the first transistor, the bias points of the first and second transistors are reset by the first and second bias adjusting means in accordance with the variation of the photodiode. Since the adjustment can be performed, the bias points of the first and second transistors can always be adjusted to a desired bias point.

The invention according to claim 6 is characterized in that the first transistor is connected in series to the second transistor via an impedance matching section.

According to this invention, the input signal is amplified in two stages by connecting the first and second transistors in series via the impedance matching section, so that high efficiency and high gain can be obtained. .

The invention according to claim 7 is characterized in that the first and second bias adjusting means are semi-fixed variable resistors.

According to the present invention, since the first and second bias adjusting means are semi-fixed variable resistors, the bias points of the first and second transistors are once adjusted by these bias adjusting means. The adjustment can be performed again according to the variation in the characteristics of the photodiode. That is, the bias points of the first and second transistors can always be set to desired bias points.

In the case of the semi-fixed variable resistor, once adjusted, the resistance value is semi-fixed, so that the resistance value can be prevented from fluctuating due to external force such as vibration.

According to an eighth aspect of the present invention, there is provided a substrate on which a circuit pattern is formed; an amplifier according to any one of the first to sixth aspects mounted on the substrate; And a package having an opening for adjusting the first and second bias adjusting means.

According to the present invention, the amplifier according to any one of claims 1 to 7 is mounted on a substrate and packaged to form a hybrid integrated circuit, which is then mounted on a motherboard. Even later, the first and second bias adjusting means can be adjusted by inserting an adjusting driver or the like from the adjusting operation opening of the package.

Therefore, even after the hybrid integrated circuit and the photodiode are mounted on the motherboard, the desired bias point can always be set by adjusting the first and second bias adjusting means of the amplifier.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In these figures, the same or corresponding parts are denoted by the same reference characters.

FIG. 1 is an electronic circuit diagram showing the overall configuration of the amplifier 11 according to the first embodiment of the present invention. The amplifier 11 shown in FIG. 1 receives a broadband high-frequency signal output from, for example, a photodiode (not shown) of a light receiving unit for an optical CATV, and amplifies the signal with high gain while correcting asymmetric waveform distortion. The output side of a first GaAs FET (gallium arsenide field effect transistor) 12 for high frequency amplification as a first transistor is connected in series with the input side of a second GaAs FET 14 as a second transistor via an impedance matching section 13. Connect to the broadband 2
It is configured as a stage amplifier.

The first FET 12 has its input side, that is, the gate G side, electrically connected to an input terminal 16 via a coupling capacitor 15. The input terminal 16 has a light receiving portion for optical CATV, for example. The output terminal of a photodiode not connected is connected, and an electric signal of a broadband high frequency (for example, 770 MHz) optically / electrically converted by the photodiode is input to the input terminal 16.

Further, a first gate bias unit 17 as a first bias adjusting means and one end of a first negative feedback unit 18 are connected to the gate G side of the first FET 12, and a first negative feedback is provided. The other end of the section 18 is connected to the drain D side which is the output side of the first FET 12. On the drain D side, a first bias unit 19 serving as first bias setting means is further provided.
Is connected.

Similarly, the second FET 14 also includes a second gate bias unit 20 as a second bias adjusting means,
The second negative feedback unit 21 and the second bias setting unit
, And the output side of the coupling capacitor 23 is connected to the output end 24 of the coupling capacitor 23, respectively.

The first bias section 19 is connected to the first FET 12
Are set to bias points at which asymmetrical waveform distortion of an input signal can be amplified at a high gain while being mainly corrected on, for example, a low frequency side (or a high frequency side).

On the other hand, the second bias section 22 corrects the bias point of the second FET 14 for the asymmetric distortion of the input signal, for example, on the high frequency side (or low frequency side), and also adjusts the first and second bias points. The bias point is set to be able to amplify with a high gain while correcting distortion due to the nonlinearity of the FETs 12 and 14 themselves. In other words, the bias points of the first and second FETs 12 and 14 correct the asymmetric waveform distortion of the input signal in, for example, a wide band on the high frequency side, and also adjust the bias points of the first and second FETs 12 and 14.
The bias point is set to a value that can cancel the asymmetric distortion caused by the non-linearity of No. 14.

FIG. 2 shows the first and second gate bias units 1.
7 shows an example of the configuration of each of the gate bias units 17 and 20. The gate bias units 17 and 20 include, for example, semi-fixed variable resistors 25, respectively.

The resistance value of the semi-fixed variable resistor 25 is increased or decreased by, for example, rotating a small screw-like adjusting rod (not shown) by a driver or the like, so that the first and second FETs are changed.
The bias points of the first and second FETs 12 and 14 are adjusted by controlling the input voltage applied to the gates G of the gates 12 and 14, respectively.

After the resistance value of the semi-fixed variable resistor 25 is adjusted during the adjustment period, it is temporarily fixed to the resistance value, but the resistance value can be adjusted again.

Therefore, the input terminal 16 of the amplifier 11
When an input signal Sa including, for example, the asymmetric waveform distortion shown in FIG.
FET 12 amplifies this input signal Sa with a high gain while correcting, for example, the low-frequency side of the asymmetric waveform distortion,
For example, the signal Sb shown in FIG. 4 is output.

The second FET 14 is connected to the first FET 12
Input from the output signal Sb.
b, for example, on the high frequency side and the first and second FEs
Amplification is performed at a high gain while correcting waveform distortion due to nonlinearity of the T12 and T14 itself, and for example, the output signal S shown in FIG.
c is output from the output terminal 24.

Therefore, according to the amplifier 11, the asymmetric waveform distortion of the input signal Sa from the photodiode or the like can be corrected in a wide band, and the distortion of the first and second FETs 12 and 14 itself is also corrected. Therefore, the secondary intermodulation distortion can be reduced.

In addition, since the asymmetrical waveform distortion of the input signal is corrected in two stages by the first and second FETs 12 and 14, the correction can be facilitated and the correction amount can be increased. Further, since the input signal Sa is amplified in two stages by the first and second FETs 12 and 14, a large gain can be obtained.

Further, the first and second FETs 12 and 14
Operates without flowing current, so that current consumption can be reduced. Further, since the FETs 12 and 14 are excellent in broadband high-frequency characteristics and low distortion and low noise characteristics, the amplifier 11 can also exhibit these characteristics.

Further, the amplifier 11 includes first and second
Of the FETs 12 and 14 can be adjusted by adjusting the semi-fixed variable resistors 25 of the first and second gate bias units 17 and 20. After the adjustment once, the semi-fixed variable resistor 25 can be adjusted again.

Therefore, generally, after a photodiode having a large variation in characteristics is connected to the amplifier 11, readjustment is performed by the semi-fixed variable resistor 25 in accordance with the variation in the characteristics of the photodiode, and the first and second photodiodes are adjusted. FET1
2, 14 bias points can always be adjusted to the optimum bias point.

Further, when the resistance value of the semi-fixed variable resistor 25 is adjusted, the resistance value is semi-fixed, so that the resistance value can be prevented from changing due to external force such as vibration.

FIG. 6 is an enlarged perspective view of a hybrid IC (integrated circuit) 31 according to a second embodiment of the present invention, and FIG. 7 is a plan view thereof. The hybrid IC 31 is an IC in which the amplifier 11 shown in FIG. 1 is mounted on a substrate and sealed in a package 32, and adjusts the first and second semi-fixed variable resistors 25 and 25 shown in FIG. Is formed in the package 32 for the opening 32a.

According to the hybrid IC 31, before mounting a photodiode (not shown) on the motherboard, the bias point suitable for the characteristics of the photodiode has already been adjusted by adjusting each semi-fixed variable resistor 25.

However, since the characteristics of the photodiode generally vary, it may be necessary to adjust the semi-fixed variable resistors 25 again after mounting the photodiode and the hybrid IC 31 on the motherboard. .

Therefore, in this case, the hybrid IC
For example, a semi-fixed variable resistor 25 can be easily, quickly and surely adjusted by inserting a screwdriver or the like into the adjustment opening 32a of the package 32.

[0056]

As described above, the first aspect of the present invention is:
Since the input signal is amplified in two stages by the first and second transistors, a high gain can be obtained. Also, first
After amplifying while mainly correcting the asymmetric waveform distortion of the input signal by the transistor of the stage, the waveform distortion of the input signal is further corrected by the transistor of the second stage,
Amplification is performed while correcting distortion such as non-linear distortion of the first and second transistors themselves.

That is, since the distortion such as the asymmetric waveform distortion of the input signal is corrected by the first and second transistors, for example, in two steps on the low frequency side and the high frequency side, the secondary intermodulation including the asymmetric waveform distortion is performed. Distortion can be significantly and easily reduced over a wide band, and the distortions of the first and second transistors can be mutually offset. In other words, ridges occur due to frequency characteristics in the waveform distortion, and these distortions are adjusted by adjusting the bias point to be optimal for correcting the distortion generated in the low frequency side and the distortion generated in the high frequency side. It can be easily reduced over a wide band.

When the input signal is, for example, an output signal from an external photodiode, the first and second bias points are set to the first and second bias points after the photodiode is attached to the amplifier. By performing readjustment by the bias adjustment means, it is possible to easily readjust the bias point according to the variation in the characteristics of the photodiode. Therefore, it is possible to finely correct the asymmetric waveform distortion caused by the variation in the characteristics of the electronic device in front of the first transistor such as the photodiode.

According to the second aspect of the present invention, the bias point of the first transistor is set to a bias point for amplifying with a high gain while correcting waveform distortion of an input signal. High gain can be obtained while reducing waveform distortion of the signal.

The output from the first transistor is further corrected for the waveform distortion of the input signal by the second transistor, and the distortion due to the nonlinearity of the first and second transistors themselves is corrected. Therefore, the second-order intermodulation distortion including the asymmetric waveform distortion of the input signal can be significantly reduced over a wide band, and a higher gain can be obtained.

According to the third aspect of the present invention, since the first and second transistors have mutually opposite distortion characteristics, mutual inverse distortions can be canceled out and distortion can be reduced.

According to the fourth aspect of the present invention, GaAs FETs (gallium arsenide field effect transistors) and BJTs having excellent wide band high frequency characteristics, low distortion and low noise characteristics are used as the first and second transistors. Therefore, these characteristics can be exhibited also as an amplifier.

According to the fifth aspect of the present invention, generally, a high-frequency electric signal is output from a photodiode in a wide band, and this output signal contains an asymmetric waveform distortion. As in the first aspect, the correction is performed in two stages by the first and second transistors.
Second-order intermodulation distortion can be reduced over a wide band.

Also, the bias points of the first and second transistors are set in advance by the first and second bias setting means to the optimum bias points suitable for the characteristics of the photodiode to be connected. 2 is adjusted by the bias adjusting means.

Further, even after the photodiode is connected to the first transistor, the bias points of the first and second transistors are reset by the first and second bias adjusting means in accordance with the variation of the photodiode. Since the adjustment can be performed, the bias points of the first and second transistors can always be adjusted to a desired bias point.

According to the sixth aspect of the present invention, the first and second transistors are connected in series via the impedance matching section to amplify the input signal in two stages, so that high efficiency and high gain are obtained. be able to.

According to the seventh aspect of the present invention, since the first and second bias adjusting means are semi-fixed variable resistors, the bias points of the first and second transistors are once adjusted by these bias adjusting means. After that, adjustment can be performed again according to the variation in the characteristics of the photodiode. That is, the bias points of the first and second transistors can always be set to desired bias points.

In the case of the semi-fixed variable resistor, once adjusted, the resistance value is semi-fixed, so that the resistance value can be prevented from fluctuating due to external force such as vibration.

According to an eighth aspect of the present invention, the amplifier according to any one of the first to seventh aspects is mounted on a substrate and packaged to form a hybrid integrated circuit. Even after mounting on
The first and second bias adjusting means can be adjusted by inserting an adjusting driver or the like from the adjusting opening of the package.

Therefore, even after the hybrid integrated circuit and the photodiode are mounted on the motherboard, the desired bias point can always be set by adjusting the first and second bias adjusting means of the amplifier.

[Brief description of the drawings]

FIG. 1 is an electronic circuit diagram of an amplifier according to a first embodiment of the present invention.

FIG. 2 is an enlarged electronic circuit diagram of a main part of FIG. 1;

FIG. 3 is a waveform diagram of an input signal input to the embodiment shown in FIG. 1;

FIG. 4 is a waveform chart of an output signal of a first FET of the embodiment shown in FIG. 1;

FIG. 5 is a waveform chart of an output signal of a second FET of the embodiment shown in FIG. 1;

FIG. 6 shows a hybrid I according to a second embodiment of the present invention.
The perspective view of C.

FIG. 7 is a plan view of FIG. 6;

FIG. 8 is an electronic circuit diagram of a conventional push-pull amplifier.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Amplifier 12 1st GaAsFET (1st transistor) 13 Impedance matching part 14 2nd GaAsFET (2nd transistor) 17 1st gate bias part (1st bias adjustment means) 19 1st bias part ( (First bias setting means) 20 second gate bias section (second bias adjusting means) 22 second bias section (second bias setting means) 25 semi-fixed variable resistor 31 hybrid IC 32 package 32a bias Adjustment opening

Claims (8)

[Claims] A first transistor for amplifying an input signal; and a second transistor for amplifying an output signal from the first transistor.
A first bias setting means for setting a bias point of the first transistor; a first bias adjusting means for adjusting a bias point set by the first bias setting means; An amplifier, comprising: second bias setting means for setting a bias point; and second bias adjusting means for adjusting a bias point set by a second transistor. 2. The first transistor is set at a bias point for amplifying an input signal with a high gain while correcting waveform distortion of the input signal, and the second transistor is configured to output a signal from the first transistor. The amplifier according to claim 1, wherein the bias point is set to amplify at a high gain while correcting the waveform distortion and the distortion of the second transistor itself. 3. The amplifier according to claim 1, wherein the first transistor and the second transistor have opposite distortion characteristics. 4. The amplifier according to claim 1, wherein the first and second transistors are gallium arsenide (GaAs) field effect transistors or BJTs. 5. The amplifier according to claim 1, wherein the input signal of the first transistor is an electric signal output from a photodiode. 6. The amplifier according to claim 1, wherein the first transistor is connected in series to the second transistor via an impedance matching unit. 7. The method according to claim 1, wherein said first and second bias adjusting means are semi-fixed variable resistors.
An amplifier according to any one of the preceding claims. 8. A substrate on which a circuit pattern is formed; an amplifier according to claim 1 mounted on the substrate; and a first and a second while accommodating the substrate on which the amplifier is mounted. A package having an opening for adjusting the bias adjusting means.