JPH07226557A - Electronic circuit and semiconductor device using the same - Google Patents

Abstract

PURPOSE:To eliminate the influence of a bias circuit for changing a DC level, and obtain an output circuit for outputting an high speed output signal whose rise time and fall time are small. CONSTITUTION:The source terminals of a pair of field effect transistors J1, J2 are commonly connected, which are connected with a power supply voltage VSS, through a current source I1. Each of the drain terminals is connected with one end of each of the load resistors RL1, RL2, and connected with output terminals OUT1 and OUT2, respectively. An addition circuit 32 constituted by connecting a capacitor C1 and a resistor R3 in parallel is commonly connected between the other end of each of the load resistors and a ground potential GND. A field effect transistor J3 for adjusting a DC level is connected with the connection part of the addition circuit and the load resistors. Hence the capacitance between the gate and the drain of the transistor J3 for adjusting a DC level is not added to the output signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic circuit of an output portion of an amplifier circuit or a logic circuit, and more particularly, to a drive IC for an optical modulation element which is required to have a variable DC output level and high-speed rising and falling outputs. The present invention also relates to an electronic circuit suitable for an optical modulator including this driving IC and a semiconductor device using the electronic circuit.

[0002]

2. Description of the Related Art An optical fiber and a semiconductor laser are used in a signal transmission system by taking advantage of the characteristics of an optical fiber such as a wide band and low loss which are incomparably larger than that of a metallic wire and the characteristics of a semiconductor laser which is small and capable of high-speed direct modulation. Optical fiber communication systems have been put to practical use. Generally, in an optical fiber communication system, a light intensity modulation / direct detection method is used in which the light intensity of a laser is current-modulated and transmitted, and the receiving side optically-electrically converts and demodulates. An optical fiber communication system using this semiconductor laser is a LAN (local
Application fields are expanding to a network) and data links, and there is a growing demand for larger capacity and ultra high speed. Recently, development of a higher-speed long-distance optical fiber communication system with a digital transmission rate of 10 Gbit / s or more has been advanced. In such a higher-speed long-distance optical fiber communication system, an external modulation method that modulates semiconductor laser light through an optical modulator is used, rather than a direct modulation method that directly drives the semiconductor laser to perform current modulation. This is more suitable for long-distance high-speed optical communication because the wavelength shift of laser light, so-called chirping, is suppressed. As an example of a circuit suitable for high-speed driving that can be used for this external modulation method, for example, Electronics Letters, January 31, 1991.
Sun, Vol. 27, No. 3, pp. 278-280,
"10 Gbit / s bipolar laser driver" (E
LECTRONICS LETTERS 31st Jan.1991 vol.27 No.3 pp278
-280, "10Gbit / s BIPOLAR LASER DRIVER") and the like. FIG. 10 is a block circuit diagram of a driver circuit for driving a laser shown in this paper.
In FIG. 10, reference numeral 10 indicates a driver circuit,
The driver circuit 10 includes an input buffer amplifier A _MP having two input terminals I _NN and I _NP , and emitter-coupled bipolar transistors Q ₁ and Q ₂ whose base inputs are respective outputs of the input buffer amplifier A _MP. , A current mirror circuit C _M1 for flowing a constant current I _MD to the emitter coupling point of the transistors Q ₁ and Q ₂ , and a resistor having one end connected to the collector of the bipolar transistor Q _{1 and} the other end connected to the power supply V _CC. R _D and one end connected to the collector of the bipolar transistor Q _{2 and} the other end connected to the power supply voltage V _CC.
A load resistor _RL connected to the load resistor _RL , an output terminal OUT provided at one end of the load resistor _RL , and a current mirror for flowing a bias current I _DC connected between the output terminal OUT and the collector of the transistor Q _2. And a circuit C _M2 .
In the case of the circuit of this paper, the load resistance R _L is provided to monitor the voltage waveform from the output terminal OUT on the wafer. In actual use, the load resistance R _L is removed and the laser diode is connected. To be done. When this circuit is used for driving a modulation element, the load resistance R _L is set to a resistance value equal to the characteristic impedance of the transmission line connected to the modulation element, and the output signal of the output terminal OUT is transmitted through the transmission line to the electrode of the modulation element. You can connect to.

The operation of the conventional laser driver circuit 10 thus constructed will be briefly described below. A superimposed current of the modulation signal current i _MD and the bias current I _DC is supplied to the load resistor R _L (which is a laser diode in actual use). The modulation signal current i _MD is input to the input terminals I _NN ,
It is obtained by switching the constant current I _MD in response to the complementary digital signal applied to I _NP and is supplied via the transistor Q ₂ . For example, when “0” is input to the input terminal I _NN (“1” is input to the input terminal I _NP at this time), the output from the input buffer amplifier A _MP input to the base of the transistor Q ₁ . Is “1” and the output from the input buffer amplifier A _MP input to the base of the transistor Q ₂ is “0”,
The constant current I _MD flows through the transistor Q ₁ and the transistor Q ₂
Is turned off, and the bias current I _DC is applied to the load resistance R _L.
Only flows. Conversely, if the "1" is input to the input terminal I _NN (the input terminal I _NP this time "0" is input.), From the input buffer amplifier A _MP that is input to the base of the transistor Q ₁ Output is "0", and the output from the input buffer amplifier A _MP input to the base of the transistor Q ₂ is "1", the transistor Q ₁ is turned off, and the constant current I _MD causes the transistor Q ₂ to flow. A bias current _IDC and a constant current _IMD superposed current flows through the load resistance _RL . That is, the modulation signal current i _MD supplied by the transistor Q ₂ is a signal current that switches between a current value of 0 and I _DC + i _MD . The laser diode oscillates only when a current higher than the threshold current is applied,
Moreover, since the threshold current has a characteristic that it largely fluctuates depending on the temperature, the operation level is adjusted by flowing the bias current I _DC .

Of course, even if the above-mentioned conventional driver circuit configuration is realized by using field effect transistors, the same circuit operation is performed. For example, FIG. 7 shows the basic part of the circuit shown in FIG. 10 extracted and rewritten. In the configuration of FIG. 7, instead of the transistors Q ₁ and Q ₂ shown in FIG. 10, field effect transistors J ₁ and J ₂ are provided, and each block of the current mirror circuits C _M1 and C _M2 is provided as a field effect transistor J.
₄ and J ₃ , and instead of resistors R _D and R _L , resistors R _L1 and R
_They are replaced with _L2 respectively. In this driver circuit 20, the input signal is applied to the input terminals I _NN and I _NP as in FIG. This input signal is appropriately amplified by the input buffer amplifier A _MP and then input to the gate terminals of the field effect transistors J ₁ and J ₂ whose source terminals are common. Field effect transistor J _1, J amplitude of the signal output from the output terminal OUT is amplified by _2, current is adjusted by the gate voltage V _p of the field effect transistor J ₄ for current sources I _MD and the load resistor R _L2 Determined by Furthermore, the DC level of the output signal is determined by the bias current I _DC is adjusted by the gate potential V _b of the field effect transistor J _3. 7 and 10, GND indicates the ground potential and V _CC indicates 4V.

Such a driver circuit 10 or 20 is connected to the load resistance having the characteristic impedance value of the transmission line as described above, and the output signal appearing at the output terminal is converted into an optical modulator using a Mach-Zehnder interferometer, for example. (Less than,
It is called an MZ modulator. ), It can be used as a drive circuit of an external modulation system.

[0006]

However, according to the conventional circuit configuration described above, a circuit for supplying the bias current I _DC for determining the DC level of the output signal, that is, the current mirror circuit C _{M2 in} the case of FIG. Alternatively, the field effect transistor J _{3 in} the case of FIG. 7 is connected to the output terminal OUT. Therefore, the capacitance of the transistor (not shown) forming the current mirror circuit C _M2 or the capacitance between the gate and drain of the field effect transistor J ₃ is added to the output terminal OUT, which deteriorates the high-speed operation of the output signal. ing. Therefore, the conventional circuit configuration is difficult to use in a drive IC of an optical modulation element, an optical modulation device, or the like, which requires a high-speed rising / falling output capable of varying the DC output level.

Therefore, an object of the present invention is to provide an electronic circuit in which a direct current level can be varied and applied to an output signal and the rising and falling times of the output signal are fast, and further, this electronic circuit. Optical modulator driving IC using
And other semiconductor devices.

[0008]

To achieve the above object of the present invention, an electronic circuit according to the present invention comprises a differential amplifier circuit,
In an electronic circuit that includes a level adjustment circuit that adjusts the DC potential of the output terminal of the differential amplifier circuit, and that extracts an output signal from each load resistor of this differential amplifier circuit, the output terminal of at least one load resistor of the differential amplifier circuit It is characterized in that one end of the level adjusting circuit is connected to a terminal different from the above and a voltage source for applying a voltage is connected and arranged to the other end.

In the electronic circuit, one end of the level adjusting circuit is connected to a terminal different from the output terminal of each load resistor of the differential amplifier circuit, or one end of the level adjusting circuit is connected to one load resistor of the differential amplifier circuit. It is also possible to connect to a terminal different from the output terminal and connect the other end of the level adjusting circuit to a terminal different from the output terminal of the other load resistor of the differential amplifier circuit.

In the electronic circuit according to the present invention, a pair of active elements whose one ends are commonly connected, a current source for supplying a constant current to the common connection ends, and complementary input signals are applied to the pair of active elements. Input circuit, a bias circuit that superimposes a DC bias current on the output signal, a voltage source that applies a voltage to the pair of active elements, and a load resistor provided at the other end of each active element. In an electronic circuit that extracts a complementary output from one end of a resistor, a common additional circuit is provided between the other end of each load resistor and the voltage source, and the bias is applied to the connection part between this additional circuit and the other end of each load resistor. It is characterized by connecting and arranging circuits. Alternatively, in the electronic circuit,
An additional circuit may be provided between the other end of one load resistor and the voltage source, and the bias circuit may be connected and arranged at a connection portion between the additional circuit and the other end of the one load resistor.

Further, a pair of active elements whose one ends are commonly connected, a current source which supplies a constant current to the common connection ends, and an input circuit which applies a complementary input signal to the pair of active elements.
It consists of a bias circuit that superimposes a DC bias current on the output signal, a voltage source that applies a voltage to the pair of active elements, and a load resistor that is provided at the other end of each active element. In the electronic circuit that takes out the output of
A common capacitance is provided between the other end of each load resistor and the voltage source,
The bias circuit can be connected and arranged in parallel with the capacitor. Alternatively, a capacitance may be provided between the other end of one load resistor and the voltage source, and the bias circuit may be connected and arranged in parallel with the capacitance.

In the electronic circuit, the additional circuit is preferably a parallel circuit of capacitance and resistance or a parallel circuit of capacitance and diode.

Further, in the electronic circuit, it is preferable that each load resistance is equal to the characteristic impedance of the transmission line connected to one end thereof, and as an active element,
A bipolar transistor or a field effect transistor can be used as appropriate.

These electronic circuits can be formed on the same semiconductor substrate to form a semiconductor device, and the semiconductor device is connected and arranged so as to drive an optical modulation element via a transmission line to form an optical modulation device. It is more suitable if it does.

A semiconductor laser, an optical modulation element for ON / OFF modulating the laser light of the semiconductor laser and outputting the same, and at least an input buffer amplifier and an output circuit for driving the optical modulation element by an electric signal through a transmission line. In a light modulator including a driver IC provided therein, a driver I
The output circuit of C can be configured using the electronic circuit described in any one of the above.

[0016]

According to the electronic circuit of the present invention, one end of a level adjusting circuit for adjusting a DC potential is connected to a terminal different from the output terminal of at least one load resistor of the differential amplifier circuit. Therefore, the level adjusting circuit can be separated from the output terminal of the differential amplifier circuit. As a result, the parasitic capacitance of the level adjusting circuit is not added to the output signal terminal, so that the rise and fall times of the output signal are shortened. In the electronic circuit, when one end of the level adjustment circuit is connected to a terminal different from the output terminal of each load resistance of the differential amplification circuit, or one end of the level adjustment circuit is output from one load resistance of the differential amplification circuit. When connecting to a terminal different from the terminal and connecting the other end of the level adjusting circuit to a terminal different from the output terminal of the other load resistor of the differential amplifier circuit, the output signal is speeded up in both cases.

The level adjusting circuit is composed of an additional circuit for varying a voltage level having a diode or a resistor built therein and a bias circuit for superimposing a DC bias current on an output signal of the differential amplifier circuit, or only a bias circuit. In the case of the configuration of the additional circuit and the bias circuit, the DC potential of the output signal can be changed by causing the current of the bias circuit to flow into the additional circuit. On the other hand, when the level adjusting circuit is composed of only the bias circuit, the DC potential of the output signal can be changed by the voltage drop of the bias circuit itself.

Further, according to the electronic circuit of the present invention, the bias circuit for adjusting the DC level is configured to be connected to a terminal different from the output terminal of the load resistor to adjust the bias current. Therefore, the bias circuit can be separated from the output terminal, and the parasitic capacitance of the bias circuit is not added to the output terminal, so that the output signal operates at high speed without being affected by the parasitic capacitance of the bias circuit. The parasitic capacitance of this bias circuit is the capacitance between the collector and the base when it is composed of a bipolar transistor, and the capacitance between the drain and the gate when it is composed of a field effect transistor.

The capacitance forming the additional circuit operates so as to reduce the influence of a resistor or a diode connected in parallel in the high frequency region. Similarly, the capacitance provided between the other end of the load resistor and the voltage source also operates to reduce the influence of the bias circuit connected in parallel in the high frequency region.

Further, in the semiconductor device using the electronic circuit according to the present invention, the characteristics of the active elements of the differential pair configuration are uniform, the characteristics are stable, the parasitic capacitance is reduced, and higher speed operation is possible. If this semiconductor device is used for driving an optical modulator, a small optical modulator that operates at high speed can be realized.

A semiconductor laser, an optical modulation element for ON / OFF modulating the laser light of the semiconductor laser and outputting the same, and at least an input buffer amplifier and an output circuit for driving the optical modulation element by an electric signal through a transmission line. In a light modulator including a driver IC provided therein, a driver I
If the output circuit of C is configured by using the electronic circuit according to any one of the above, the DC level of the output signal can be varied, but the parasitic capacitance of the bias circuit for varying the DC level changes to the output signal. Rising without being added,
An optical output signal with a fast fall time can be obtained.

[0022]

Embodiments of an electronic circuit according to the present invention and a semiconductor device using the same will now be described in detail with reference to the drawings.

<Embodiment 1> FIG. 1 is a circuit diagram showing an embodiment of an electronic circuit according to the present invention. In FIG. 1, reference numeral 30 indicates an output circuit. The output circuit 30 includes a pair of field effect transistors J ₁ and J ₂ whose source terminals are commonly connected and a pair of field effect transistors J ₁ and J. a load resistor R _L1, R _L2, each of the one end connected to the respective drain terminals of the _two, the addition circuit 32 connected in common to between the other end and the ground potential GND of the load resistors R _L1, R _L2 , A field effect transistor J ₃ for adjusting the direct current level, which is connected to the connection between the additional circuit 32 and the other _ends of the load resistors R _L1 and R _L2 , and field effect transistors J ₁ and J _2.
Current source I ₁ provided between the commonly connected source terminals and the power supply voltage V _SS . In addition, the additional circuit 32
Is composed of a capacitor C ₁ and a resistor R ₃ connected in parallel.

In the output circuit 30 thus constructed, the input signal voltages respectively inputted to the gate terminals G ₁ and G ₂ of the pair of field effect transistors J ₁ and J ₂ forming a differential pair are amplified. And output from the output terminals OUT ₁ and OUT ₂ provided on the respective drain terminals. At this time, the output signal amplitude depends on the current value of the current source I ₁ and the load resistance R
_L1, determined by the value of R _L2, the DC level of the output signal is determined by the resistance value of the resistor R ₃ of the field effect transistor J ₃ of the gate potential V _b by adding the current value adjusting circuit 32. The capacitance C ₁ of the additional circuit 32 is equal to the resistance R ₃
This is for reducing the influence of the above at high frequencies. Further, it goes without saying that the current source I ₁ may be configured using the field effect transistor J ₄ as in the conventional circuit of FIG.

According to the configuration of the output circuit 30, since the gate-drain capacitance of the field effect transistor J ₃ for adjusting the DC level is not added to the output terminals OUT ₁ and OUT ₂ , the rising and rising edges of the output signal waveform. The fall time can be shortened, and the DC level of the output signal can be varied. Although the case where the field effect transistor is used as the active element has been described in the present embodiment, a bipolar transistor may be used, and the output voltage signal or the output current signal can be increased / decreased according to the input voltage or the input current signal. It goes without saying that any active element having a function can be used.

A case where the output circuit 30 is applied to a driver IC of an optical modulator used in an optical modulator will be described below. FIG. 11 is a block diagram showing an outline of the optical modulator. The light modulator 100 is a semiconductor laser 1
10, a light modulation element 120, and a driver IC 130. The optical output of the semiconductor laser 110 is input to the optical modulation element 120, and the optical modulation element 120 is driven by the driver I.
The optical output modulated according to the output electric signal of C130 is output, and this modulated optical output is transmitted over a long distance through the optical fiber 140. The driver IC 130 includes at least an input buffer amplifier 132 and an output circuit 134. The driver IC 130 amplifies a data input signal to an appropriate signal level by the input buffer amplifier 132, then sufficiently amplifies it by the output circuit 134, and outputs it via the transmission line 136. The modulation element 120 is driven.

A driver I of such a light modulation device 100
When the output circuit 30 shown in FIG. 1 is applied to the output circuit 134 forming C, the output circuit 134 and the optical modulator 12
Since the transmission line 136 exists between 0 and 0, the load resistances R _L1 and R _L2 of the output circuit 30 are made equal to the characteristic impedance of the transmission line 136 to reduce reflection between the output circuit and the optical modulator. There is a need to. The value of this load resistance is, for example, 50Ω. By forming the driver IC 130 to which the output circuit 30 is applied on the same semiconductor substrate, the characteristics of the field effect transistors of the differential pair configuration are uniform and stable, the parasitic capacitance is reduced, and higher speed operation becomes possible. Further, as the light modulation element 120, as shown in FIG.
(A) MZ modulator element 121 and (b) shown in FIG.
The electro-absorption modulation element 126 can be preferably used. Note that FIG. 12 is a schematic plan view of the respective light modulation elements as seen from above. In the MZ modulator 121, the light entering from the input section is split into two at the point A, and the voltage applied to the electrodes 122 and 123 causes the optical waveguides 124, 1
The refractive index of 25 changes and the phase changes. When the light modulated at point B is combined again, ON / OFF light whose intensity is modulated due to interference is output. In a normal use state, a DC voltage is applied to one of the electrodes 122 (or 123) and a high frequency signal is applied to the other electrode 123 (or 122). The MZ modulator 121 can change the ON / OFF polarity of light by changing the applied voltage. When the circuit of this embodiment is used, it is possible to adjust the signal level by applying a DC bias to this high frequency signal. On the other hand, the electro-absorption optical modulator 12
6, the optical waveguide 1 is driven by the voltage applied to the electrode 127.
The absorption coefficient of 28 changes, and light can be turned ON / OFF. In the case of the electro-absorption type optical modulator 126, since there is only one electrode portion, the circuit of this embodiment shown in FIG. 1 capable of superimposing a DC bias signal on a high frequency signal is particularly suitable.

FIG. 8 is an output waveform diagram in the case where the optical modulator is driven by using the circuit of this embodiment as a load. 20G
NRZ (Non-Return to Zero) signal of bit / s, amplitude 1.2V, both rising and falling time 24ps
Input waveform signal of. In this case, the current source I
₁ is composed of a field effect transistor J ₄ as in the conventional example of FIG. The gate width and gate potential of the field effect transistors J _{1 to} J ₄ were adjusted so that the output amplitude was 3.5 V and the DC level was −1 V. 1 for each of the output waveforms in FIG.
The rising and falling times at 0% -90% voltage were 24 ps and 20 ps, respectively. The capacity C ₁
The capacitance value of was 50 pF, and the resistance value of the resistor R ₃ was 5Ω. Here, when the optical modulator is driven by using the conventional circuit configuration of FIG. 7 as a load, the same input waveform signal is input and the electric field is changed so that the output amplitude becomes 3.5V and the DC level becomes -1V. FIG. 9 shows output waveforms when the gate width and the gate potential of the effect transistors J _{1 to} J ₄ are adjusted. In the case of the conventional example, the rise and fall times were 32 ps and 27 ps, respectively. Therefore, it can be seen that the circuit configuration of the present embodiment makes it possible to make the DC level variable and at the same time realize a faster rise and fall time as compared with the conventional case. In the conventional circuit of FIG. 7, the power supply voltage V _CC is set to the ground potential GND and the field effect transistor J
The sources of ₃ and J ₄ are the power supply voltage (negative voltage) V _SS , and FIG.
The output waveform of

FIG. 13 is a layout diagram showing an example of the output circuit 134 portion formed on the driver IC 130. The wiring is an example in the case of using multilayer wiring. The driver IC 130 can be formed using, for example, a well-known compound semiconductor process. The field effect transistor for the current source I ₁ and the field effect transistors J ₁ , J ₂ , and J ₃ are GaAs MESFETs formed on a semi-insulating GaAs substrate and excellent in high frequency and low noise characteristics, and an insulator is sandwiched between them. The capacitance C ₁ of the additional circuit 32 is formed between the two layers of wiring, and the resistors R _L1 , R _L2 , and R ₃ have, for example, WS.
The metal film resistance of iN is used. Eliminate the influence of parasitic inductance of wire bonding
In order to realize a high speed operation of s or more, the chip is flip-chip bonded to the ceramic substrate. A pad having a diameter of 140 μm for connecting the flip chip is arranged on the layout diagram. As the capacitance value of the capacitance C ₁ , 50p
In order to realize about F, in the case of the layout of FIG. 13A, the size is about 400 μm □. FIG. 13B
In the case of the layout of ( ₁₎ , the shape of the capacitor C ₁ is deformed and the GND pad is arranged at the center, and there is an advantage that the circuit area can be made smaller than in the case of the layout of (a).

<Embodiment 2> FIG. 2 is a circuit diagram showing another embodiment of the electronic circuit according to the present invention. Note that, in FIG. 2, the same components as those of the circuit of the first embodiment shown in FIG. 1 are denoted by the same reference numerals for convenience of description, and detailed description thereof will be omitted. That is, the output circuit 40 of this embodiment
Then, instead of the additional circuit 32 shown in FIG. 1, an additional circuit 42 including a capacitor C ₁ and a diode D ₁ connected in parallel is provided.
1 is different from the output circuit 30 shown in FIG. Also in the case of this circuit configuration, as in the first embodiment, since the gate-drain capacitance of the field-effect transistor J ₃ for adjusting the DC level is not added to the output terminals OUT ₁ and OUT ₂ , the rising and rising edges of the output signal waveform The fall time can be shortened, and the DC level can be changed by the gate potential V _b of the field effect transistor J ₃ . In the configuration of the additional circuit 42, the DC level of the output signal is known before the trial manufacture of the IC, and the DC level is finely adjusted in the range of, for example, about 0 to 0.2 V to improve the yield of the IC. Suitable for In addition,
The capacitance C ₁ is for reducing the influence of the diode D ₁ at high frequencies. Similarly to the first embodiment, the circuit of the present embodiment also has the driver IC 1 of the optical modulator 100 shown in FIG.
It can be applied to the output circuit 134 which constitutes 30, and a high-speed output waveform with a rise time and a fall time similar to the case of using the circuit of the first embodiment shown in FIG. 8 can be obtained.

<Third Embodiment> FIG. 3 is a circuit diagram showing still another embodiment of the electronic circuit according to the present invention. Note that, in FIG. 3, the same components as those of the circuit of the first embodiment shown in FIG. 1 are denoted by the same reference numerals for convenience of description, and detailed description thereof will be omitted. That is, in the output circuit 50 of the present embodiment, the additional circuit 52 including the resistor R ₃ and the capacitor C ₁ connected in parallel has the load resistor whose one end is connected to one field effect transistor J ₂ forming a differential pair. It differs from the output circuit 30 shown in FIG. 1 in that it is connected only to the other end of R _L2 . Also in the case of the present embodiment, as in the first embodiment, since the gate-drain capacitance of the field effect transistor J ₃ for DC level adjustment is not added to the output terminals OUT ₁ and OUT ₂ , the rise of the output signal waveform, The fall time can be shortened, and the DC level can be changed by the gate potential V _b of the transistor J ₃ . In the output circuit 50 including such an additional circuit 52, the other field effect transistor J ₁ forming the differential pair is used.
This is suitable when the value of the load resistance R _L1 connected to is fixed to, for example, 50Ω and the output terminal OUT ₁ is used for monitor output. The capacitor C ₁ is for reducing the influence of the resistor R ₃ at high frequencies. Of course, also in the case of the present embodiment, as in the case of the first embodiment, the output circuit 134 which constitutes the driver IC 130 of the optical modulation device 100 shown in FIG.
It is possible to obtain a high-speed output waveform with a rise time and a fall time similar to the case of using the circuit of the first embodiment shown in FIG.

<Embodiment 4> FIG. 4 is a circuit diagram showing another embodiment of the electronic circuit according to the present invention. Note that, in FIG. 4, the same components as those of the circuit of the third embodiment shown in FIG. 3 are denoted by the same reference numerals for convenience of description, and detailed description thereof will be omitted. That is, in the output circuit 60 of this embodiment, an additional circuit 62 including a capacitor C ₁ and a diode D ₁ connected in parallel is used instead of the additional circuit 52 shown in FIG. 3 is different from the output circuit 50 of FIG. Also in the case of this circuit configuration, similarly to the third embodiment, since the gate-drain capacitance of the field effect transistor J ₃ for adjusting the DC level is not added to the output terminals OUT ₁ and OUT ₂ , the rising and rising edges of the output signal waveform. The fall time can be shortened, and the DC level can be changed by the gate potential V _b of the field effect transistor J ₃ . In the configuration of the additional circuit 62, the DC level of the output signal is known before the trial manufacture of the IC, and the DC level is finely adjusted in the range of, for example, about 0 to 0.2 V to obtain the IC.
It is suitable for improving the yield. Further, the output circuit 60 including such an additional circuit 62 is
Similar to the third embodiment, when the value of the load resistance R _L1 connected to the other field effect transistor J ₁ forming the differential pair is fixed to 50Ω and the output terminal OUT ₁ is used for monitor output. Is effective for. The capacitance C ₁ is for reducing the influence of the diode D ₁ at high frequencies. Similarly to the first embodiment, the circuit of the present embodiment can be applied to the output circuit 134 that constitutes the driver IC 130 of the optical modulator 100 shown in FIG. 11, and the case of using the circuit of the first embodiment shown in FIG. It is possible to obtain a high-speed output waveform with the same rise and fall times.

<Embodiment 5> FIG. 5 is a circuit diagram showing still another embodiment of the electronic circuit according to the present invention. Note that, in FIG. 5, the same components as those of the circuit of the first embodiment shown in FIG. 1 are denoted by the same reference numerals for convenience of description, and detailed description thereof will be omitted. That is, in the output circuit 70 of the present embodiment, the other _ends of the load resistors R _L1 and R _L2 and the ground potential GN are connected.
1 is different from the output circuit 30 shown in FIG. 1 in that a capacitance C ₁ is provided between the capacitance C ₁ and D and a field effect transistor J ₃ for adjusting a DC level is connected in parallel with the capacitance C ₁ . The output circuit 70 amplifies the signals input to the field effect transistors J ₁ and J ₂ and outputs the amplified signals from the output terminals OUT ₁ and OUT ₂ . At this time, the amplitude of the output signal is determined by the current value of the current source I _{1 and} the values of the load resistors R _L1 and R _L2 . The DC level of the output signal is determined by the current value of the current source I ₁ and the gate potential V _b of the field effect transistor J ₃ . Capacity C
₁ is for reducing the influence of the field effect transistor J ₃ at high frequencies. With this circuit configuration, the gate-drain capacitance of the field-effect transistor J ₃ for adjusting the DC level is not added to the output terminals OUT ₁ and OUT ₂ , so that the rise and fall times of the output signal waveform can be shortened. In addition, the DC level can be changed by the gate potential V _b of the transistor J ₃ .
This circuit configuration is characterized in that the DC level adjustment is made by the field effect transistor J _{3 as} compared with the circuit configurations shown in FIGS.
It is one of the points that can be realized. Also, this circuit configuration
Similar to the circuits of the embodiments shown in FIGS. 2 and 4, it is effective when the DC level of the output is known before the trial manufacture of the IC. Further, the circuit of the present embodiment is similar to that of the first embodiment, as shown in FIG.
8 can be applied to the output circuit 134 which constitutes the driver IC 130 of the optical modulator 100 shown in FIG.
It is possible to obtain a high-speed output waveform with a rise time and a fall time similar to the case of using the circuit of FIG.

<Embodiment 6> FIG. 6 is a circuit diagram showing another embodiment of the electronic circuit according to the present invention. In FIG. 6, the same components as those of the circuit of the fifth embodiment shown in FIG. 5 are designated by the same reference numerals for convenience of description, and detailed description thereof will be omitted. That is, in the output circuit 80 of this embodiment, the capacitance C ₁ is provided only between the other end of the load resistor _{RL 2} whose one end is connected to one of the field effect transistors J ₂ forming the differential pair and the ground potential GND. , A field effect transistor J for adjusting the direct current level in parallel with the capacitance C ₁ .
₃ is different from the output circuit 70 shown in FIG. The operation of the output circuit 80 is similar to that of the circuit of the fifth embodiment, but the value of the load resistance R _L1 connected to the other field effect transistor J ₁ forming the differential pair is set to, for example, 50Ω.
It is more suitable when the output terminal OUT ₁ is fixed to the output terminal and used for monitor output. Also in this output circuit 80, since the gate-drain capacitance of the field effect transistor J ₃ for adjusting the DC level is not added to the output terminals OUT ₁ and OUT ₂ , the rise and fall times of the output signal waveform are accelerated. In addition, the DC level can be changed by the gate potential V _b of the transistor J ₃ . The capacitor C ₁ is for reducing the influence of the field effect transistor J ₃ at high frequencies. Similarly to the first embodiment, the circuit of the present embodiment also includes the output circuit 1 that constitutes the driver IC 130 of the optical modulator 100 shown in FIG.
34, and a high-speed output waveform with a rise and fall time similar to the case of using the circuit of the first embodiment shown in FIG. 8 can be obtained.

The preferred embodiment of the present invention has been described above. However, the present invention is not limited to the above embodiment, and for example, a field effect transistor can be replaced with a bipolar transistor, which deviates from the spirit of the present invention. It goes without saying that various design changes can be made within the range not covered.

[0036]

When the output circuit configuration of the electronic circuit according to the present invention is used, the parasitic capacitance of the transistor for adjusting the direct current level is not added to the output signal terminal. For this reason,
It is possible to obtain an output signal with a fast rise and fall time and to change the DC level.

If the electronic circuit according to the present invention is formed on the same semiconductor substrate, the characteristics of the differential pair transistors forming the output circuit are uniform and stable, the parasitic capacitance is reduced, and higher speed operation becomes possible. Furthermore, if this semiconductor device is applied to an output circuit of a driver IC that drives a light modulation element,
It is possible to realize an optical modulator having an optical output waveform with a fast rise and fall time.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing another embodiment of the electronic circuit according to the present invention.

FIG. 3 is a circuit diagram showing still another embodiment of the electronic circuit according to the present invention.

FIG. 4 is a circuit diagram showing another embodiment of the electronic circuit according to the present invention.

FIG. 5 is a circuit diagram showing still another embodiment of the electronic circuit according to the present invention.

FIG. 6 is a circuit diagram showing another embodiment of the electronic circuit according to the present invention.

FIG. 7 is a circuit diagram showing a conventional example of a laser driver circuit having a field effect transistor configuration.

8 is a diagram showing an output waveform when the electronic circuit according to the present invention of FIG. 1 is used in a driver circuit of a light modulation element.

9 is a diagram showing an output waveform when the conventional circuit of FIG. 7 is used for a driver circuit of an optical modulator.

FIG. 10 is a circuit diagram showing a conventional example of a laser driver circuit having a bipolar transistor configuration.

FIG. 11 is a block diagram showing a schematic configuration of an optical modulator to which an electronic circuit according to the present invention is applied.

FIG. 12 is a diagram showing an example of a light modulation element that can be driven by an electronic circuit according to the present invention, (a) is a schematic plan view of a light modulation element using a Mach-Zehnder interferometer, and (b) is an electroabsorption type. It is a schematic plan view of a light modulation element.

FIG. 13 is a diagram showing a layout example when the electronic circuit according to the present invention in FIG. 1 is formed on a semiconductor substrate for a driver IC of a light modulation device.

[Explanation of symbols]

10, 20 ... Output circuit 30, 40, 50, 60 ... Output circuit 32, 42, 52, 62 ... Additional circuit 70, 80 ... Output circuit 100 ... Optical modulator 110 ... Semiconductor laser 120 ... Optical modulator 130 ... Driver IC 132 ... Input buffer amplifier 140 ... Optical fiber A _MP ... Amplifier C _M1 , C _M2 ... Current mirror circuit C ₁ ... Capacitance D ₁ ... Diode I ₁ ... Current source J ₁ , J ₂ , J ₃ , J ₄ ... Field effect transistor R ₃ ... resistor R _L1, R _L2 ... load resistor V _CC ... supply voltage (positive potential) V _SS ... power supply voltage (negative potential)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H03K 5/02 L 17/04 A 9184-5J 17/60 17/687 19/0185 8839-5J H03K 19/00 101 B

Claims (17)

[Claims] 1. An electronic circuit comprising a differential amplifier circuit and a level adjusting circuit for adjusting a DC potential of an output terminal of the differential amplifier circuit, wherein an output signal is taken out from each load resistance of the differential amplifier circuit. An electronic circuit, wherein one end of a level adjusting circuit is connected to a terminal different from the output terminal of at least one load resistor of an amplifier circuit, and a voltage source for applying a voltage is connected and arranged to the other end. 2. The electronic circuit according to claim 1, wherein one end of the level adjusting circuit is connected to a terminal different from the output terminal of each load resistor of the differential amplifier circuit. 3. One end of the level adjusting circuit is connected to a terminal different from the output terminal of one load resistor of the differential amplifier circuit, and the other end of the level adjusting circuit is connected to the output terminal of the other load resistor of the differential amplifier circuit. The connection is made to different terminals.
The electronic circuit according to. 4. A pair of active elements, one ends of which are commonly connected,
A current source that supplies a constant current to this common connection terminal, an input circuit that applies a complementary input signal to a pair of active elements, a bias circuit that superimposes a DC bias current on the output signal, and a pair of active elements In an electronic circuit that consists of a voltage source that applies a voltage and a load resistor that is provided at the other end of each active element, and that outputs complementary output from one end of each load resistor, between the other end of each load resistor and the voltage source. An electronic circuit in which a common additional circuit is provided, and the bias circuit is connected and arranged at a connection portion between the additional circuit and the other end of each load resistor. 5. A pair of active elements, one ends of which are commonly connected,
A current source that supplies a constant current to this common connection terminal, an input circuit that applies a complementary input signal to a pair of active elements, a bias circuit that superimposes a DC bias current on the output signal, and a pair of active elements In an electronic circuit that consists of a voltage source that applies a voltage and a load resistor provided at the other end of each active element, and that outputs complementary outputs from one end of each load resistor, the other end of one load resistor and the voltage source An electronic circuit characterized in that an additional circuit is provided in between, and the bias circuit is connected and arranged at a connection portion between the additional circuit and the other end of the one load resistor. 6. A pair of active elements, one ends of which are commonly connected,
A current source that supplies a constant current to this common connection terminal, an input circuit that applies a complementary input signal to a pair of active elements, a bias circuit that superimposes a DC bias current on the output signal, and a pair of active elements In an electronic circuit that consists of a voltage source that applies a voltage and a load resistor that is provided at the other end of each active element, and that outputs complementary output from one end of each load resistor, between the other end of each load resistor and the voltage source. An electronic circuit characterized in that a common capacitor is provided in the capacitor, and the bias circuit is connected and arranged in parallel with the capacitor. 7. A pair of active elements, one ends of which are commonly connected,
A current source that supplies a constant current to this common connection terminal, an input circuit that applies a complementary input signal to a pair of active elements, a bias circuit that superimposes a DC bias current on the output signal, and a pair of active elements In an electronic circuit that consists of a voltage source that applies a voltage and a load resistor provided at the other end of each active element, and that outputs complementary outputs from one end of each load resistor, the other end of one load resistor and the voltage source An electronic circuit characterized in that a capacitor is provided between the capacitors and a bias circuit is connected in parallel with the capacitor. 8. The electronic circuit according to claim 4, wherein the additional circuit is a parallel circuit of a capacitor and a resistor. 9. The electronic circuit according to claim 4, wherein the additional circuit is a parallel circuit of a capacitor and a diode. 10. The electronic circuit according to claim 1, wherein each load resistance is equal to a characteristic impedance of a transmission line connected to one end of each load resistance. 11. The electronic circuit according to claim 4, wherein the active element is a bipolar transistor whose collector-emitter current is controlled according to a base input signal. 12. The electronic circuit according to claim 4, wherein the active element is a field effect transistor in which a drain-source current is controlled according to a gate input signal. 13. The electronic circuit according to claim 11, wherein one end of the commonly connected active elements is an emitter terminal of a bipolar transistor and the other end is a collector terminal. 14. The electronic circuit according to claim 12, wherein one end of the commonly connected active elements is a source terminal of the field effect transistor, and the other end thereof is a drain terminal. 15. A semiconductor device having the electronic circuit according to claim 1 formed on the same semiconductor substrate. 16. The semiconductor device according to claim 15,
An optical modulation device, which is connected and arranged so as to drive an optical modulation element via a transmission line. 17. A semiconductor laser, and an optical modulator for ON / OFF modulating the laser light of the semiconductor laser and outputting the modulated laser light.
15. An optical modulator including at least an input buffer amplifier for driving the optical modulator with an electric signal via a transmission line and a driver IC including an output circuit, wherein the output circuit of the driver IC is any one of claims 1 to 14. An optical modulator comprising the electronic circuit according to claim 1.