JPH07288431A - Differential amplifier circuit - Google Patents

Abstract

PURPOSE:To generate the differential outputs of the equal DC bias voltage and output amplitude so that one external input signal can be inputted and transmitted to a circuit on the next stage by both AC and DC coupling systems. CONSTITUTION:A first output transistor Q2 for generating the differential output at a first amplifier part 2A to input one external input signal IIN and a second output transistor Q3 for generating the differential output at a second amplifier part 2B constituted symmetrically with the first amplifier part 2A are made into a differential pair by connecting their respective emitters through a 9th impedance element RE. Thus, differential outputs Vout3 and Vout4 of the equal DC bias voltage and output amplitude are outputted from the collectors of the first and second output transistors Q2 and Q3.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Industrial Application Conventional Technology (FIG. 4) Problem to be Solved by the Invention (FIGS. 4 and 5) Means for Solving the Problem (FIG. 1) Action (FIG. 1) Example (FIGS. 1 to 3) ) The invention's effect

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential amplifier circuit, and can be applied to, for example, a head amplifier used on the light receiving side of optical communication.

[0003]

2. Description of the Related Art Conventionally, a head amplifier of this type receives a detection signal of a light receiving element for detecting an optical signal that has passed through an optical fiber or the like, converts this detection signal into a current-voltage, amplifies it, and outputs it.

As shown in FIG. 4, the detection current I _IN of the light receiving element P _D for detecting an optical signal is input to the base of the transistor Q ₁ of the transimpedance amplifier circuit 1, and the power is supplied via the emitter and the diode D _1. V _EE .
Further, the detection current I _IN flows into the power source V _EE at one end via the impedance element Z _T and the resistor R ₂ .

The midpoint of the connection between the collector of the transistor Q ₁ and the resistor R _L whose one end is connected to the power supply V _CC is connected to the base of the transistor Q ₂ , and a bias voltage is applied to this base. The emitter of the transistor Q ₂ is connected to the midpoint of the connection between the impedance element Z _T and the resistor R ₂ and outputs the positive phase output V _OUT1 . The collector of the transistor Q ₂ has an impedance element Z whose one end is connected to the power supply V _CC.
It is connected to _X and outputs a reverse phase output V _OUT2 .

[0006]

However, in the transimpedance amplifier circuit 1 having the above configuration, when the detection current I _IN is not input, that is, when there is no signal,
The DC voltage of the positive phase output V _{OUT1 and} the DC voltage of the negative phase output V _OUT2 are different from each other. Further, the positive-phase output V _OUT1 swings downward with the DC voltage when there is no signal as the upper limit. On the other hand, the negative-phase output V _OUT2 swings upward with the DC voltage when there is no signal as the lower limit. Therefore, there is a problem that the method of transmitting the differential output composed of the positive-phase output V _OUT1 and the negative-phase output V _OUT2 to the integrated circuit of the next stage is limited to AC coupling.

That is, in the conventional transimpedance amplifier circuit 1 shown in FIG. 4, when the output voltage amplitude characteristics of the positive phase output V _OUT1 and the negative phase output V _OUT2 are obtained, the power source V _EE
= GND (ground level), the forward voltage of the diode junction is V _F, and the base current of the transistor Q ₁ is ignored, the positive phase output V _OUT1 is

[Equation 1] Required by.

[0008] current I ₂ flowing through the resistor R _2, the following equation

[Equation 2] Required by. The current I ₂ is the same as the transistor Q ₂
Let I _{1 be} the collector current of

[Equation 3] But it is required. From the expressions (2) and (3), the following expression

[Equation 4] Is required.

The negative phase output V _OUT2 is expressed by the following equation.

[Equation 5] Required by. From equation (4), equation (5) is

[Equation 6] Becomes

Here, when there is no signal, that is, when the DC voltage of the positive phase output V _OUT1 when I _IN = 0 is obtained, the following equation is obtained from the equation (1).

[Equation 7] Becomes Similarly, when the DC voltage of the reverse phase output V _OUT2 when there is no signal is obtained, the following equation is obtained from the equation (6).

[Equation 8] Becomes

As a result, the positive phase output V _OUT1 and the negative phase output V _OUT1
It can be seen that the DC voltage when there is no signal is different between _OUT2 and _OUT2 . Further, from the equations (1) and (6), as shown in FIG. 5, the positive phase output V _OUT1 swings downward with 2 V _F as the upper limit, and the negative phase output V _OUT2 is V _CC − (Z _X / R ₂ ) It can be seen that the amplitude swings upward with a lower limit of 2V _F. These two things indicate that the signal transmission method to the next-stage IC is limited to AC coupling.

Further, in the above configuration, for example, when the output amplitude Z _T · I _{IN of the} positive phase output V _OUT1 exceeds 2V _F ,
From equation (1), it can be seen that no output is produced. Therefore, the dynamic range of the positive phase output V _OUT1 is regulated to 2V _F.

The present invention has been made in consideration of the above points, so that one external input signal can be input and can be transmitted to the circuit in the next stage by both AC coupling and DC coupling. Another object of the present invention is to propose a differential amplifier circuit that generates a differential output with uniform output amplitude.

[0014]

In order to solve such a problem, in the present invention, the collector is connected to the first power source V _CC through the first impedance element R _L , and the emitter is the first diode D _1. The first input transistor Q ₁ connected to the second power source V _EE via the base and the base are biased according to the collector voltage of the first input transistor Q ₁ , and the collector connects the second impedance element R _X. It is connected to the first power supply V _CC through, emitter a third impedance element via the R ₂ is connected to the second power supply V _EE and fourth impedance elements first through R _T of the input transistor Q _{A first} amplifier 2A having a first output transistor Q ₂ connected to the base of 1 and a first power supply V _CC with a collector via a fifth impedance element R _L.
A second input transistor Q connected to the second power supply V _EE with the emitter connected through the second diode D _2.
3 , the base is biased according to the collector voltage of the second input transistor Q ₃ , the collector is connected to the first power supply V _CC via the sixth impedance element R _X , and the emitter is the seventh impedance element. _Is connected to the second power supply V _EE via R ₂ and the eighth impedance element R _T
A second amplifier section 2B and a second output transistor Q ₄ which is connected to the second base of the input transistor Q ₃ via the first and second output transistors Q ₂ and Q
_And a ninth impedance element R _E for connecting the _four emitters to each other, the external input signal I _IN is input to the base of the first or second input transistor Q ₁ or Q ₃ , and the differential signal V _OUT3 and V _OUT4 is output from the collectors of the first and second output transistors Q ₂ and Q ₄ .

[0015]

A first output transistor Q ₂ for generating a differential output of the first amplifying section 2A to which one external input signal I _IN is input, and a second output transistor Q ₂ symmetrical to the first amplifying section 2A. The second output transistor Q ₃ for generating the differential output of the amplifying section 2B is connected to the respective emitters via the ninth impedance element R _E to form a differential pair. Differential output V with uniform voltage and output amplitude
_OUT3 and V _OUT4 are the first and second output transistors Q ₂
And from the collector of Q ₃ . As a result, the differential outputs V _OUT3 and V _OUT4 can be transmitted to the integrated circuit in the next stage by both AC coupling and DC coupling.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1 in which parts corresponding to those in FIG. 4 are designated by the same reference numerals, reference numeral 2 denotes a detection current I _IN of the light receiving element P _D which detects an optical signal as a whole, and this detection current I _IN is a current. 1 shows a transimpedance amplifier circuit that converts and amplifies voltage to output a differential output composed of a negative phase output V _OUT3 and a positive phase output V _OUT4 .

The transimpedance amplifier circuit 2 transfers the detected current I _IN to the conventional transimpedance amplifier circuit 1.
To the amplifying section 2A configured in the same manner as the
Output _OUT3 . In addition, the transimpedance amplifier circuit 2 has an amplifier section 2B which is symmetrical to the amplifier section 2A.
More positive phase output V _OUT4 is output.

That is, the amplifying section 2A includes the impedance element Z _{T in} the configuration of the transimpedance amplifying circuit 1.
Instead of Z _X and Z _X , resistors R _T and R _X are provided, respectively. As a result, Z _T and Z _X in the equation (6) are replaced with R _T and R _X , and the opposite phase is obtained.

[Equation 9] The reverse-phase output V _OUT3 represented by is output from the collector of the transistor Q ₂ .

The amplifier section 2B, instead of the amplifying part transistor Q ₁ of the 2A and symmetrical configuration, Q ₂ and the diode D _1, respectively with these same transistors Q _3, Q ₄ and diode D ₂ is arranged There is. The emitters of the transistors Q ₂ and Q ₄ are connected to each other via a resistor R _E. This allows transistors Q ₂ and Q
₄ is configured as a differential pair.

When the detection current I _IN is input to the transistor Q ₁ , the positive phase output V _OUT1 generated in the emitter of the transistor Q ₂ is transferred to the transistor Q ₄ via the resistor R _E and the resistor R _T in the amplifying section 2B. Given to the base of. In this way, the detection current I _IN is applied to the base of the transistor Q _4.
And the current of opposite phase is given. Therefore, the same as the equation (9)

[Equation 10] The positive-phase output V _OUT4 represented by is output from the collector of the transistor Q ₄ .

In the above structure, the transimpedance amplifier circuit 2 receives the detection current I _IN of the optical signal from the midpoint of the connection between the light receiving element P _D and the external resistor R _IN by AC coupling via the capacitor C. It When there is no signal, that is, I _IN
When = 0, the DC bias voltage of the negative-phase output V _OUT3 is calculated by the following equation from the equation (9) as in the equation (8).

[Equation 11] Becomes Similarly, the DC bias voltage of the positive phase output V _{OUT4 can be calculated} by the following equation from the equation (10).

[Equation 12] Becomes

As a result, the reverse phase output V _OUT3 and the normal phase output V
It can be seen that _OUT4 is biased with the same DC voltage of V _CC- (R _X / R ₂ ) 2V _F , respectively. Next, when the detection current I _IN is input to the base of the transistor Q ₁ , the transistors Q ₂ and Q ₄ are configured as a differential pair, so that as shown in FIG.
_OUT3 and the positive phase output V _OUT4 are DC voltage V _CC − (R _X / R
₂ ) Appears as a signal swinging around 2V _F.

According to the above configuration, one detection current I _IN
And a transistor Q ₂ for generating a differential output of the amplifier 2A, and an amplifier 2 configured symmetrically to the amplifier 2A.
A transistor Q ₄ for generating a differential output of B and a resistor R
By connecting the respective emitters via _E to form a differential pair, differential outputs V _OUT3 and V _OUT4 having a uniform DC bias voltage and output amplitude can be output from the collectors of the transistors Q ₂ and Q _4. . As a result, the differential output V
_OUT3 and V _OUT4 can be transmitted to the integrated circuit of the next stage by both AC coupling and DC coupling.

In the above embodiment, the resistance R _L ,
Regarding the case where the amplifying units 2A and 2B are configured by using R _X , R _T and R ₂ and the DC voltage components generated by the amplifying units 2A and 2B are directly applied to the negative phase output V _OUT3 and the positive phase output V _OUT4 However, the present invention is not limited to this, and as shown in FIG. 3, instead of the resistors R _L , R _X , R _T , and R ₂ , linear or non-linear impedance elements Z _L , Z _X ,
Symmetrical amplifiers 3A and 3 using Z _T and Z ₂ respectively
B from the outside of the amplifying section 3B or the transistor Q
Input the reference voltage V _REF to the base of ₃ and output the negative phase V
_Adjust the DC bias voltage of _OUT5 and positive phase output V _OUT6 ,
The non-uniformity of the DC voltage due to manufacturing error or the like may be removed. Also in this case, the same effect as described above can be obtained.

Further, in the above embodiment, the case where the transimpedance amplifier circuit 2 is constructed by using the NPN type transistors Q _{1 to} Q ₄ has been described, but the present invention is not limited to this, and the PNP type transistor is used. The present invention can be applied to a case where the transimpedance amplifier circuit is configured by using the diodes in the opposite direction to each other.

Further, in the above-mentioned embodiment, the case where the emitters of the input transistors Q ₁ and Q ₃ are connected to the power source V _EE via the respective diodes D ₁ and D ₂ has been described. The present invention is not limited to this, and can also be applied to a case where the emitters of the input transistors are connected to the power supply via a plurality of diodes.

[0028]

As described above, according to the present invention, the first output transistor for generating the differential output of the first amplifying section to which one external input signal is input and the first amplifying section are symmetrical. The second output transistor for generating a differential output of the second amplifying section configured in the above is connected to each emitter through a ninth impedance element to form a differential pair. It is possible to realize a differential amplifier circuit that can output a differential output having a uniform bias voltage and output amplitude from the collectors of the first and second output transistors. As a result, the differential output can be transmitted to the next-stage integrated circuit or the like by both AC coupling and DC coupling.

[Brief description of drawings]

FIG. 1 is a connection diagram of a transimpedance amplifier circuit showing an embodiment of a differential amplifier circuit according to the present invention.

FIG. 2 is a waveform diagram showing that the negative phase output and the positive phase output are biased with the same DC voltage.

FIG. 3 is a connection diagram showing another embodiment.

FIG. 4 is a connection diagram showing a conventional transimpedance amplifier circuit.

FIG. 5 is a waveform diagram for wetting that the negative phase output and the positive phase output are biased with different DC voltages.

[Explanation of symbols]

1, 2, 3 ... Transimpedance amplifier circuit, 2
A, 2B, 3A, 3B ... Amplifying section, P _D ... Light receiving element.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 11, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction content]

As shown in FIG. 4, the detection current I _IN of the light receiving element P _D for detecting an optical signal is input to the base of the transistor Q ₁ of the transimpedance amplifier circuit 1, and the impedance element Z _T and the resistor R ₂ are connected. Power through _VEE
Flow to.

Claims (3)

[Claims] 1. A first input transistor having a collector connected to a first power supply via a first impedance element, an emitter connected to a second power supply via a first diode, and a base connected to the first input transistor. Biased according to the collector voltage of the first input transistor, the collector is connected to the first power source via a second impedance element, and the emitter is connected to the second power source via a third impedance element. A first amplifier having a first output transistor connected to the base of the first input transistor through a fourth impedance element, and a collector having the first output transistor through a fifth impedance element.
Second input transistor connected to the second power supply via the second diode, and the base is biased according to the collector voltage of the second input transistor, and the collector is connected to the second input transistor connected to the second power supply via the second diode. The second input transistor is connected to the first power source via a sixth impedance element, the emitter is connected to the second power source via a seventh impedance element, and the eighth input element is connected to the second input transistor. A second amplifying section having a second output transistor connected to the base of, and a ninth impedance element interconnecting the emitters of the first and second output transistors, and an external input signal The differential signal is input to the base of the first or second input transistor and a differential signal is output from the collectors of the first and second output transistors. Differential amplifier circuit, characterized in that. 2. The first, second, third and fourth impedance elements respectively include the fifth, sixth, seventh and eighth impedance elements.
2. The differential amplifier circuit according to claim 1, wherein the differential amplifier circuit has the same impedance element. 3. When the external input signal is input to the base of the first input transistor, the base of the second input transistor is connected to a third power supply, thereby providing the differential output. Is adjusted, or when the external input signal is input to the base of the second input transistor, the base of the first input transistor is connected to the third power supply. Therefore, the DC voltage component of the differential output is adjusted, and the differential amplifier circuit according to claim 1 or 2.