JP2004080511A - Differential amplification circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a differential amplification circuit for realizing a small circuit size and low power consumption while the same effect as the conventional case is held. <P>SOLUTION: In the differential amplification circuit, n-type MOS transistors Q1 and Q2 constituting a differential pair are provided, and an input voltage is fed to the MOS transistor Q1. The drain of the MOS transistor Q1 is connected to a negative phase signal output terminal 1, and the drain of the MOS transistor Q2 is connected to a positive phase signal output terminal 2. A coil L1 as an inductive element is connected between the drain of the MOS transistor Q1 and the drain of the MOS transistor Q2. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a differential amplifier circuit for differentially amplifying an input signal, and more particularly to a differential amplifier circuit suitable for a preamplifier for converting a current signal obtained by converting an optical signal into a voltage signal in optical communication.
[0002]
[Prior art]
Conventionally, as a differential amplifier circuit of this type, a preamplifier circuit described in Japanese Patent Application Laid-Open No. 2000-357929, "ISSCC 2001 / SESSION 14 / GIGABIT OPTICAL COMMUNICATIONS II / 14.3 (2001 IEEE International Solid-State Circuit) The optical receiver described in "14.3 A Si Bipolar Laser Diode Driver / Receiver Chip Set for 4-Channel 5Gb / s Parallel Optical Interconnection" announced in "Conference".
[0003]
The preamplifier includes a midpoint potential generating circuit that generates a midpoint potential of the positive-phase output and the negative-phase output of the differential amplifier, and outputs a midpoint potential generated by the midpoint potential generating circuit to a feedback circuit. As a result, feedback is made as a threshold voltage to the negative-phase input terminal of the differential amplifier. For this reason, in this preamplifier, the influence of power supply and temperature fluctuations and process variations (element variations) is canceled, and the difference between the threshold voltage and the 0 level of the input signal can be reduced. It is possible to expand the usable range of the linear region of the differential amplifier circuit, improve large signal characteristics, and reduce distortion characteristics such as pulse width deterioration.
[0004]
On the other hand, the above-mentioned optical receiver includes a control circuit including an adder and an amplifier in order to control a threshold voltage of each differential output of the differential amplifier. The threshold voltage can be controlled.
[0005]
[Problems to be solved by the invention]
However, in the preamplifier and the optical receiver, there is a disadvantage that the scale of a circuit for adjusting or controlling each differential output of the differential amplifier is large, and the power consumption of the circuit is also increased.
SUMMARY OF THE INVENTION An object of the present invention is to provide a differential amplifier circuit having a small circuit size and low power consumption, and capable of realizing the same effects as the conventional one.
[0006]
[Means for Solving the Problems]
In order to solve the above problems and achieve the object of the present invention, the inventions according to claims 1 to 10 are configured as follows.
That is, the invention according to claim 1 includes a differential amplifying means for performing differential amplification of an input signal, and a predetermined amplifying means is provided between a positive-phase signal output terminal and a negative-phase signal output terminal of the differential amplifying means. It is characterized by connecting an inductive element.
[0007]
The invention according to claim 2 further includes a differential amplifier for performing differential amplification of an input signal, wherein an inductive element is provided between a positive-phase signal output terminal and a negative-phase signal output terminal of the differential amplifier. The present invention is characterized in that a predetermined inductive circuit including a capacitive element is connected.
According to a third aspect of the present invention, in the differential amplifier circuit according to the second aspect, the inductive element includes at least two inductive elements, and these inductive elements are connected to a positive-phase signal output terminal of the differential amplifier. The capacitor is connected in series between a negative-phase signal output terminal, and the capacitive element is connected between a common connection part of the inductive element and ground. is there.
[0008]
According to a fourth aspect of the present invention, there is provided a differential amplification unit for performing differential amplification of an input signal,
A microstrip line is connected between a positive-phase signal output terminal and a negative-phase signal output terminal of the differential amplifying means, and any point of the microstrip line is grounded via a capacitive element. It is characterized by the following.
The invention according to claim 5 includes a differential amplifying unit that performs differential amplification of an input signal,
A stripline is connected between the positive-phase signal output terminal and the negative-phase signal output terminal of the differential amplifying means, and any point of the stripline is grounded via a capacitive element. It is assumed that.
[0009]
According to a sixth aspect of the present invention, in the differential amplifier circuit according to any one of the first to fifth aspects, the differential amplifying means converts a current signal into a voltage signal by a differential input / output type. Differential amplifying means, a differential input / output type differential amplifying means for amplifying a voltage signal, a differential input / output type differential amplifying means for amplifying a current signal, and a differential input / output type amplifying a power signal It is characterized by being one of the differential amplifying means.
[0010]
According to a seventh aspect of the present invention, in the differential amplifier circuit according to any one of the first to sixth aspects, the differential amplifying means grounds the negative-phase signal input terminal via a capacitive element. It is characterized by doing so.
According to an eighth aspect of the present invention, in the differential amplifier circuit according to any one of the first to seventh aspects, the differential amplifying circuit includes a positive-phase signal input terminal and a negative-phase signal output terminal. The first feedback circuit connects the negative-phase signal input terminal and the positive-phase signal output terminal with the second feedback circuit.
[0011]
According to a ninth aspect of the present invention, in the differential amplifying circuit according to any one of the first to eighth aspects, the differential amplifying means comprises a differential pair of transistors. It is.
According to a tenth aspect of the present invention, in the differential amplifying circuit according to the ninth aspect, the transistor of the differential pair is any one of a field effect transistor and a bipolar transistor. is there.
[0012]
As described above, according to the present invention, the midpoint between the positive-phase signal output and the negative-phase signal output of the differential amplifier means is provided between the positive-phase output terminal and the negative-phase output terminal of the differential amplifier means by an inductive element or the like. A means for generating a potential is provided.
The inductive element acts as an impedance for the input signal of the differential amplifier.
[0013]
For this reason, when the input signal is in a low frequency band from DC, the impedance becomes almost zero, and a short circuit occurs between the positive-phase signal output terminal and the negative-phase signal output terminal of the differential amplifier means, The differential amplification means loses the function of differential amplification. Therefore, the positive-phase output signal and the negative-phase output signal of the differential amplifying means are combined and cancel each other, so that only the combined midpoint potential (offset voltage) is used as the positive-phase output signal and the negative-phase output signal. Is output.
[0014]
On the other hand, when the input signal is in a high frequency band, the impedance becomes almost infinite, and the gap between the positive-phase output terminal and the negative-phase output terminal of the differential amplifier is open, and the differential amplifier Has a function of differential amplification. Therefore, the positive-phase output signal and the negative-phase output signal of the differential amplifier output a differential signal. At this time, since the inductive element is short-circuited in terms of DC, the midpoint potential of the positive-phase output signal and the negative-phase output signal becomes equal. Therefore, the positive-phase output signal and the negative-phase output signal have a common midpoint potential, and the high-frequency components are differential signals having phases opposite to each other.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the configuration of the first embodiment of the differential amplifier circuit of the present invention will be described with reference to FIG.
The differential amplifier circuit according to the first embodiment is applied to a preamplifier used in optical communication, and is a differential input / output type that converts a current signal obtained by converting an optical signal into a voltage signal. is there.
[0016]
For this purpose, as shown in FIG. 1, the differential amplifier circuit includes N-type MOS transistors Q1 and Q2 forming a differential pair. The sources of the MOS transistors Q1 and Q2 are commonly connected, and the common connection is grounded via a resistor R1 functioning as a constant current source. The drains of the MOS transistors Q1 and Q2 are connected to a power supply VCC via load resistors R2 and R3, respectively.
[0017]
A resistor R4 as feedback means is connected between the gate and the drain of the MOS transistor Q1. Further, a photodiode PD is connected between the gate of the MOS transistor Q1 and the power supply VCC.
A resistor R5 as feedback means is connected between the gate and the drain of the MOS transistor Q2. The gate of the MOS transistor Q2 is grounded via the capacitor C1. In this way, when the gate is grounded at a high frequency, the differential amplification operation can be more stabilized.
[0018]
The drain of the MOS transistor Q1 is connected to the negative-phase signal output terminal 1, and the drain of the MOS transistor Q2 is connected to the positive-phase signal output terminal 2. Further, a coil (inductor) L1, which is an inductive element, is connected between the drain of the MOS transistor Q1 and the drain of the MOS transistor Q2.
Here, the coil L1 forms a midpoint potential generating circuit that generates a midpoint potential between the drain voltage of the MOS transistor Q1 and the drain voltage of the MOS transistor Q2.
[0019]
A power supply line connecting the load resistors R2, R3 and the power supply VCC is grounded via a capacitor C2. As a result, the noise of the power supply VCC is removed, and the load resistors R2 and R3 are grounded at a high frequency to maintain the isolation of the circuit.
In the differential amplifier circuit configured as above, the gate of the MOS transistor Q1 functions as a positive-phase signal input terminal, and its drain functions as a negative-phase signal output terminal. Further, the gate of the MOS transistor Q2 functions as a negative-phase signal input terminal, and its drain functions as a positive-phase signal output terminal.
[0020]
Next, an outline of the operation of the first embodiment having the above configuration will be described.
Now, when an optical signal is input to the light receiving element PD, the optical signal is converted into a current signal. The current signal flows into a common connection between the MOS transistor Q1 and the resistor R4, and is converted into a voltage signal by the resistor R4. The converted voltage signal becomes the input voltage Vin of the MOS transistor Q1 (see FIG. 3A), and is amplified by the MOS transistor Q1.
[0021]
On the other hand, the MOS transistor Q2 has its gate grounded at a high frequency by a capacitor C1 and is connected to a resistor R1 which is a current source common to the MOS transistor Q1. Therefore, the MOS transistor Q2 performs the same operation as that in which an input signal having a phase opposite to that of the MOS transistor Q1 is input, and performs an inversion operation on the MOS transistor Q1.
[0022]
As a result, output voltages Vout1 and Vout2 are generated at the negative-phase signal output terminal 1 and the positive-phase signal output terminal 2, respectively, and the output voltages Vout1 and Vout2 have phases opposite to each other (see FIG. 3B). .
Next, the details of the input / output operation in the first embodiment will be described.
The first embodiment is characterized in that a coil L1 which is an inductive element is connected between the drain of the MOS transistor Q1 and the drain of the MOS transistor Q2.
[0023]
Therefore, for comparison with the operation when the coil L1 is connected, the input / output operation when the coil L1 is not connected will be described with reference to FIG.
In this case, the input voltage Vin of the MOS transistor Q1 is, for example, as shown in FIG. As shown in FIG. 2B, the output voltage Vout1 of the negative-phase signal output terminal 1 and the output voltage Vout2 of the positive-phase signal output terminal 2 exist around the drain voltages of the MOS transistors Q1 and Q2, respectively. . Therefore, the output voltage Vout1 and the output voltage Vout2 do not cross the midpoint potential between the drain voltage of the MOS transistor Q1 and the drain voltage of the MOS transistor Q2, as shown in FIG.
[0024]
Next, a case where the coil L1 is connected between the drain of the MOS transistor Q1 and the drain of the MOS transistor Q2 will be described.
When the coil L1 is connected as described above, the coil L1 acts as the impedance Z with respect to the input voltage Vin shown in FIG. The value of the impedance Z can be expressed by the following equation, where L1 is the inductance of the coil L1 and f is the frequency of the input voltage Vin.
[0025]
Z = 2πf × L1 (1)
As a result, when the input voltage Vin is in a band (region) where the frequency is lower than DC, the impedance Z becomes substantially zero, and the drains of the MOS transistors Q1 and Q2 are short-circuited by the coil L1. Q2 loses the function of differential amplification. For this reason, the output voltages Vout1 and Vout2 of the MOS transistors Q1 and Q2 of the differential pair are combined and cancel each other, and only the combined midpoint potential (offset voltage) is output as the output voltages Vout1 and Vout2. You.
[0026]
On the other hand, when the input voltage Vin is in a high frequency band, the impedance Z becomes almost infinite, the drain between the MOS transistors Q1 and Q2 is open, and the MOS transistors Q1 and Q2 have a function of differential amplification. Will have. Therefore, the output voltages Vout1 and Vout2 of the MOS transistors Q1 and Q2 of the differential pair output a differential signal. At this time, since the coil L1 is DC short-circuited, the midpoint potential (the DC voltage including the offset voltage) of the output voltage Vout1 and the output voltage Vout2 becomes equal. Therefore, as shown in FIG. 3B, the output voltage Vout1 and the output voltage Vout2 have the same drain potential of the MOS transistor Q1 and the middle potential of the drain potential of the MOS transistor Q2, and the high-frequency components are opposite to each other. It becomes a phase differential signal.
[0027]
As described above, according to the first embodiment, the coil L1 is connected between the drain of the MOS transistor Q1 and the drain of the MOS transistor Q2. Therefore, while the circuit scale is small and the circuit consumes low power, the same effect as the conventional one (expansion of the usable range of the linear region of the differential amplifier circuit, improvement of large signal characteristics, distortion such as pulse width deterioration, etc.) is obtained. Characteristics reduction) can be realized.
[0028]
Further, in the first embodiment, the number of constituent elements can be significantly reduced as compared with the related art. For this reason, an input signal can be applied to a high-frequency band signal (high bit rate signal) without affecting the input signal, and can be applied to a high-frequency band input signal.
Next, a configuration of a differential amplifier circuit according to a second embodiment of the present invention will be described with reference to FIG.
[0029]
In the first embodiment shown in FIG. 1, the coil L1 is used as the inductive element. However, when the high-frequency characteristics of the coil L1 are deteriorated (when the Q value is small), the coil L11 cannot function as an inductive element, and the impedance in the high-frequency band is reduced to reduce the MOS transistor. Q1 and Q2 may not be able to perform differential amplification.
[0030]
Therefore, in the second embodiment, the coil L1 shown in FIG. 1 is replaced with an inductive circuit 3 as shown in FIG. Since the configuration of the other parts of the second embodiment is basically the same as that of the first embodiment, the same components are denoted by the same reference numerals, and the description thereof will be omitted. Will be described only.
As shown in FIG. 4, the inductive circuit 3 is a circuit in which coils L11 to L13, which are inductive elements, and capacitors C11, C12, which are capacitive elements, are combined.
[0031]
More specifically, coils L11 to L13 are connected in series between the drain of the MOS transistor Q1 and the drain of the MOS transistor Q2. The common connection between the coil L11 and the coil L12 is grounded via the capacitor C11, and the common connection between the coil L12 and the coil L13 is grounded via the capacitor C12.
[0032]
Here, it is preferable that the coils L11 and L13 have excellent high frequency characteristics (Q value). With this configuration, when the input voltage is in the high frequency band, isolation (electrical insulation) is ensured by the coil L11 and the capacitor C11 at the drain of the MOS transistor Q1, and is isolated by the coil L13 and the capacitor C12 at the drain of the MOS transistor Q2. Is secured. As a result, a good differential output signal can be obtained in a high frequency band.
[0033]
Further, in the low frequency band, since the impedance of the capacitors C11 and C12 is large, the output voltages Vout1 and Vout2 have the same potential as in the first embodiment.
As described above, according to the second embodiment, the inductive circuit 3 is provided between the drain of the MOS transistor Q1 and the drain of the MOS transistor Q2. Therefore, the same effect as in the first embodiment can be obtained.
[0034]
In the above embodiment, the inductive element is formed by the coil L1, or the inductive circuit 3 is formed by a combination of the coils L11 to L13 and the capacitors C11 and C12.
However, in the present invention, a microstrip line or a strip line may be used instead, and any point thereof may be grounded via a capacitive element (capacitor).
[0035]
Here, the microstrip line is one of distributed constant circuits in a microwave integrated circuit, and has a structure in which a ground conductor is arranged on the lower surface of a dielectric substrate and a center conductor is arranged on the upper surface.
The strip line also has a structure basically similar to that of the microstrip line.
[0036]
The differential amplifier circuit of the above embodiment is applied to a preamplifier used in optical communication, and is a differential input / output type that converts a current signal obtained by converting an optical signal into a voltage signal. It was taken.
However, in addition to the above, the differential amplifier circuit of the present invention includes a differential input / output type differential amplifier circuit for amplifying a voltage signal, a differential input / output type differential amplifier circuit for amplifying a current signal, and power Of course, the present invention can be applied to a differential input / output type differential amplifier circuit for amplifying a signal.
[0037]
Further, in the above embodiment, the MOS transistors Q1 and Q2 are used as the transistors of the differential pair.
However, in addition to MOS transistors as transistors of the differential pair, bipolar transistors, MESFETs (metal-semiconductor field-effect transistors), and MISFETs (metal insulator semiconductor field effectors that use a good field effector) may be used.
[0038]
【The invention's effect】
As described above, according to the present invention, it is possible to realize the same effect as the conventional one while having a small circuit scale and low power consumption.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a first embodiment of the present invention.
FIG. 2 is a waveform diagram of each section for explaining an input / output operation when no coil is provided in the circuit of FIG. 1;
FIG. 3 is a waveform diagram of each section for explaining an input / output operation when a coil is provided in the circuit of FIG. 1;
FIG. 4 is a circuit diagram showing a configuration of a second embodiment of the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 negative phase signal output terminal, 2 positive phase signal output terminal, 3 inductive circuit, Q1, Q2 MOS transistor, L1 coil, C1, C2 capacitor, L11 to L13 coil, C11, C12 capacitor, R1 Resistance for constant current source , R2, R3
Load resistance, R4, R5 Feedback resistance

Claims (10)

A differential amplification means for performing differential amplification of the input signal,
A differential amplifier circuit, wherein a predetermined inductive element is connected between a positive-phase signal output terminal and a negative-phase signal output terminal of the differential amplifier. A differential amplification means for performing differential amplification of the input signal,
A predetermined inductive circuit comprising an inductive element and a capacitive element is connected between a positive-phase signal output terminal and a negative-phase signal output terminal of the differential amplifying means. Amplifier circuit. The inductive element comprises at least two elements, and these inductive elements are connected in series between a positive-phase signal output terminal and a negative-phase signal output terminal of the differential amplifying means; The differential amplifier circuit according to claim 2, wherein the element is connected between a common connection portion of the inductive element and ground. A differential amplification means for performing differential amplification of the input signal,
A microstrip line is connected between a positive-phase signal output terminal and a negative-phase signal output terminal of the differential amplifying means, and any point of the microstrip line is grounded via a capacitive element. A differential amplifier circuit. A differential amplification means for performing differential amplification of the input signal,
A stripline is connected between the positive-phase signal output terminal and the negative-phase signal output terminal of the differential amplifying means, and any point of the stripline is grounded via a capacitive element. Differential amplifier circuit. The differential amplifier includes a differential input / output type differential amplifier that converts a current signal into a voltage signal, a differential input / output type differential amplifier that amplifies a voltage signal, and a differential input / output type that amplifies a current signal. 6. An output type differential amplifying means and a differential input / output type differential amplifying means for amplifying a power signal. Differential amplifier circuit. 7. The differential amplifier circuit according to claim 1, wherein said differential amplifier has an anti-phase signal input terminal grounded via a capacitive element. The differential amplifier connects the positive-phase signal input terminal and the negative-phase signal output terminal by a first feedback circuit, and connects the negative-phase signal input terminal and the positive-phase signal output terminal by a second feedback circuit. The differential amplifier circuit according to any one of claims 1 to 7, wherein the differential amplifier circuit is configured as described above. 9. The differential amplifier circuit according to claim 1, wherein said differential amplifier comprises a differential pair of transistors. The differential amplifier circuit according to claim 9, wherein the transistor of the differential pair is any one of a field effect transistor and a bipolar transistor.

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