JPH10107553A - Amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an amplifier in which fluctuation in its frequency characteristic is reduced even when the amplitude of an input signal is subject to change. SOLUTION: A trans-impedance amplifier that feeds back an output signal Vc1 of an input transistor(TR) Qin to an input IN via a resistor RF is provided with an internal power supply circuit VRLG consisting of a low-pass filter LPF that receives the output signal Vc1 and of a level shift circuit LS1 that shifts a voltage level of an output of the low-pass filter. An output of the internal power supply circuit VRLG is fed to the collector of the TR Qin via a load resistor RL. Thus, the collector current Ic of the TR Qin is independently of an input current Iin so that the open loop gain of the trans-impedance amplifier is made constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier, and more particularly to an amplifier capable of suppressing an operating point from fluctuating due to fluctuations in the amplitude or DC component of an input current signal.

[0002]

2. Description of the Related Art In a receiver of an optical fiber communication system,
The optical signal carried through the optical fiber is converted into a current signal by a photodiode, and this current signal is subjected to current-voltage conversion by a preamplifier. Further, after the converted voltage signal is amplified by an AGC (Auto Gain Control) amplifier or the like, clock extraction and signal identification reproduction are performed. In general, a transimpedance amplifier having a circuit configuration as shown in FIG. 2 is used as a preamplifier because it has excellent noise characteristics and can operate in a wide band.

In FIG. 2, reference numeral Q _in denotes an input transistor having a common emitter, and the input transistor Q in
The collector of the _in is is connected to the base of the transistor Q _1, is connected to the positive supply voltage V _CC through a load resistor R _L. The emitter of the transistor Q ₁ is, is connected to the anode of the diode D ₁ is connected to the base of the transistor Q _2. The cathode of the diode D ₁ is connected via a feedback resistor R _F is connected to the base of the input transistor Q _in, is connected to the negative supply voltage V _EE through a current source CS _1. The collector of the transistor Q ₂ is connected to the positive supply voltage V _CC, together with the emitter connected to the output terminal OUT, and is connected via a current source CS ₂ to the negative supply voltage V _EE. The input terminal IN, the current signal I _in which the optical signal transmitted by the optical fiber and converted by a photodiode (not shown) is input.

In the transimpedance amplifier configured as described above, the input transistor Q _in and the load resistance R
The output of common emitter amplifier consisting of _L, which lower the input impedance by applying a negative feedback through the feedback resistor R _F. The bandwidth of the transimpedance amplifier is
Generally, it is governed by the pole P _in of the input section. The pole P _in is approximately expressed by the following equation.

[0005]

(Equation 1)

Here, A ₀ is an open loop gain, C _T is a parasitic capacitance of the input section (photodiode capacitance + input capacitance of the transistor), and Z _in is an input impedance. From the equation (1), the band is seen that determined by the parasitic capacitance C _T of the open loop gain A ₀ and the input unit. In the conventional example in which the transimpedance amplifier is constituted by a silicon (Si) bipolar transistor, a characteristic exceeding a band of 10 GHz is realized by reducing the parasitic capacitance by using a transistor having a self-aligned structure.

A transimpedance amplifier of this type is described in, for example, IEE, Proc., Vol. 128 (Dec. 1981), pp. 299-305 (IEE, PROC., Vol. 128 (Dec. 1981), pp.299-30
It is described in 5).

[0008]

In a receiver of an optical fiber communication system, the amplitude of a signal current input to a transimpedance amplifier varies greatly depending on the transmission distance, that is, the length of the optical fiber. For example, at a transmission speed of 10 Gbit / s (Gb / s) and a transmission distance of 10 to 40 k
In an optical fiber communication system having a relatively short distance of m, the signal current I _in input from the photodiode to the preamplifier is used.
Is significantly different from 30 μA to 2 mA. But,
In the above-described conventional technology, no consideration has been given to the deterioration of the frequency characteristic due to the change in the amplitude of the signal current.

Now, consider the case where two types of signal currents having different amplitudes I _in1 and I _in2 (I _in1 <I _in2 ) are input to the transimpedance amplifier of FIG. First, the amplitude I
_{When in1} of the signal current flowing into the input terminal IN of the transimpedance amplifier, the collector current I _c1 flowing to the input transistor Q _in the input current I _in of FIG. 3 - as shown in the collector current I _c characteristics, the following equation It changes around the represented current value.

[0010]

(Equation 2)

Here, V _CC is a power supply voltage, and V _BE is a base-emitter voltage of the transistor.

Similarly, when the current having the amplitude I _in2 flows into the transimpedance amplifier, the collector current I _c2 flowing through the input transistor Q _in changes around the current value represented by the equation (3). Here, since the amplitude relationship between the two types of signal currents is I _in1 <I _in2 , the amplitude relationship between the collector currents of the input transistor Q _in is I _c1 <I _c2 .

[0013]

(Equation 3)

The open-loop gain A ₀ has a relationship expressed by the following equation (4) with the collector current I _c of the input transistor Q _in . Here, q is the electron charge amount, k is the Boltzmann constant, and T is the junction temperature.

[0015]

(Equation 4)

Therefore, when a signal current having a small amplitude I _in1 is input, the open-loop gain A ₀ is low, and the pole P _in which controls the band is low. For this reason, the band becomes narrow. On the other hand, when a large signal current amplitude I _in2 is input, the higher the open-loop gain A _0, the higher the pole P _in. For this reason, the band is widened. However, the peak occurs in the frequency characteristic of the transimpedance amplifier the pole P _in becomes too high. When the peak occurs, waveform distortion occurs in the output signal, and the optical fiber communication system has a problem that the error rate as a receiver increases.

As described above, in the prior art, there is a problem that the operating point of the circuit fluctuates due to a change in the amplitude of the input signal, the band becomes narrow, and the error rate increases due to waveform distortion.

As will be described later in the sixth embodiment, the DC-coupled amplifier has a problem that the operating point fluctuates due to the fluctuation of the DC component of the input signal, and the gain of the amplifier fluctuates. SUMMARY OF THE INVENTION It is an object of the present invention to provide an amplifier that can suppress a change in frequency characteristics even if the amplitude of an input signal changes.

It is another object of the present invention to provide a preamplifier which can be suitably used for a receiver of an optical fiber communication system, that is, a transimpedance amplifier having a stable operating point with respect to a change in amplitude of an input current signal. .

Still another object of the present invention is to provide an amplifier whose gain is not affected by the DC component of an input signal.

[0021]

In order to achieve the above object, an amplifier according to the present invention comprises an amplifier for feeding an output signal of an amplifier circuit back to an input through at least a resistor.
An internal power supply circuit which receives the output signal as input and provides a bias to the amplifier circuit so that an average value of the output signal is constant with respect to a variation in the amplitude level of the input signal of the amplifier circuit. Is what you do.

In the amplifier, it is preferable that the internal power supply circuit comprises a low-pass filter which receives an output signal of the amplifier circuit as an input, and a level shift circuit which shifts a voltage level of the output of the low-pass filter.

In this case, it is preferable that the low-pass filter has a pass band set lower than a lower limit frequency of the input signal.

The internal power supply circuit may include a high-potential holding circuit that receives an output signal of the amplifier circuit as an input and holds a high potential of the output signal, and a low-potential of the output signal that receives an output signal of the amplifier circuit as an input. Potential holding circuit, and first and second resistors having one ends connected to the outputs of the high potential holding circuit and the low potential holding circuit and the other end connected in common, and the first and second resistors, respectively. And a level shift circuit that is connected to a common connection point of the resistors and applies a bias to the amplifier circuit.

Each of the above amplifiers is preferably a transimpedance amplifier configured to reduce the input impedance by applying a negative feedback to the input of the output of the amplifier circuit via a feedback resistor.

The amplifier according to the present invention comprises at least an amplifier circuit for amplifying an input signal having a DC component, wherein the gain of the amplifier circuit is kept constant based on the DC component detected from the input signal. And an internal power supply circuit for generating a bias for generating the bias.

In this case, it is preferable that the internal power supply circuit comprises a low-pass filter that receives the input signal having the DC component as an input, and a level shift circuit that shifts the voltage level of the output of the low-pass filter.

Further, the amplifier circuit may be a common-emitter amplifier circuit, and the output voltage of the internal power supply circuit may be applied to the emitter of the common-emitter amplifier circuit via a resistor.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of an amplifier according to the present invention is an amplifier which feeds back an output signal of an amplifier circuit to an input via a resistor. In this configuration, an internal power supply circuit that applies a bias to the amplifier circuit so that the average value of the output signal is constant is provided.

The amplifier according to the present invention thus configured detects the amplitude of the input current signal by extracting the DC component from the output of the amplifier circuit, and newly detects the operating point of the amplifier circuit so that the operating point is always at the same position. Controls the amplifier circuit. As a result, the open loop gain of the amplifier circuit is kept constant, and even if the amplitude of the input signal changes, fluctuations in the frequency characteristics can be suppressed. An amplifier having such characteristics is suitable for a transimpedance amplifier used for a preamplifier constituting a receiver of an optical fiber communication system. The internal power supply circuit may include a low-pass filter that receives an output signal of the amplifier circuit and a level shift circuit that receives the output of the low-pass filter and applies a bias to the amplifier circuit.

According to another preferred embodiment of the amplifier according to the present invention, there is provided an amplifier having at least a common-emitter amplifier circuit for amplifying an input signal having a DC component. An internal power supply circuit for generating a bias for keeping the gain of the amplifier circuit constant based on the detected DC component is provided. The amplifier thus configured can keep the gain constant without being affected by the fluctuation of the DC component of the input signal.
It is suitable for use when a common-emitter amplifier and another amplifier must be DC-coupled to be integrated on the same semiconductor chip.

[0032]

Next, a more specific embodiment of the amplifier according to the present invention will be described in detail with reference to the accompanying drawings.

<Embodiment 1> FIG. 1 is a circuit diagram showing a first embodiment of an amplifier according to the present invention, in which a transimpedance amplifier is formed. In FIG. 1, the same components as those shown in the conventional example of FIG. 2 are denoted by the same reference numerals for convenience of description, and detailed description thereof will be omitted. That is, the present embodiment is different in that the load resistance _RL is not connected to the power supply voltage V _CC but is connected to a newly provided internal power supply circuit VRLG. An internal power supply circuit VRLG is constituted by a low pass filter LPF and level shift circuit LS _1.
Transimpedance amplifier of the present embodiment, for example when used in a relatively short distance transmission system transmission distance 10~40km at a transmission rate 10Gb / s, the magnitude of the input signal current I _in to the transimpedance amplifier 30μA
２2 mA. As an example, the power supply voltage V _CC =
5 V, negative power supply voltage V _EE = -3.5 V, the cut-off frequency of the low-pass filter is about 30 kHz, the bandwidth of the transimpedance amplifier is about 10 GHz, and the input impedance is about 30 to 40 Ω.

The operation of the internal power supply circuit VRLG will be described below. Now, consider a case where a signal current having an amplitude of I _in1 is input to the transimpedance amplifier of this embodiment. At this time, the output signal V _c1 emitter grounded amplifier circuit which consists of the input transistor Q _in is mainly a voltage value represented by the following formula (5), a feedback resistor R _F of the resistance value and the input signal current I _in1
, That is, the amplitude of R _F · I _in1 . Therefore, by setting the pass band of the low-pass filter LPF lower than the lower limit frequency of the input signal, the output voltage of the low-pass filter LPF becomes V _c1 .

[0035]

(Equation 5)

Here, assuming that the voltage shift amount of the level shift circuit LS ₁ is V _A , the output V of the internal power supply circuit VRLG is
_RL is represented by the following equation (6).

[0037]

(Equation 6)

That is, the output V of the internal power supply circuit VRLG
_RL changes according to the amplitude of the input current I _in1 . As a result, the collector current I flowing through the input transistor Q _in
c changes around the collector current value I _c1 represented by the following equation (7).

[0039]

(Equation 7)

As can be seen from equation (7), the collector current I _c1 of the input transistor Q _in does not depend on the amplitude of the input current I _in1 . Thus, the input current I _in of FIG. 4 - as shown in the collector current I _c characteristics, the amplitude of the input current I _in is changed from I _in1 to I _in2, average value of the collector current I _c of the input transistor Q _in Does not change. Therefore, the open-loop gain of the transimpedance amplifier does not change, and the pole P _in that controls the band does not change. Therefore, it is possible to realize a transimpedance amplifier the amplitude of the input signal I _in is suppressed to a small variation of the frequency characteristics vary.

Here, the internal power supply circuit V used in this embodiment is
A specific configuration example of the low-pass filter LPF and level shift circuit LS ₁ constituting the RLG shown in FIG. The low-pass filter can be composed of a resistor R _LPF and a capacitor C _LPF . The pass band of the low-pass filter LPF needs to be set lower than the lower limit frequency of the input signal. 10-4 described above
Assuming a relatively short distance transmission system of 0 km,
Since the cutoff frequency of the low-pass filter is about 30 kHz, the resistance R _LPF = 1 kΩ and the capacitance C _LPF = about 5 nF. Note that when the value of the capacitance C _LPF is very large and it is difficult to mount it on a semiconductor chip, an external capacitance may be used. The level shift circuit LS _1, as shown in FIG. 8, the transistors Q ₁₁ and Q ₂₁ is provided between the power supply voltage V _CC and V _EE, resistors R _11, diode D _11, D _21, D
₃₁ comprises current sources CS ₁₁ and CS ₂₁ . The output voltage V _out to the input voltage V _in of the level shift circuit LS _1, that is, the output voltage V _RL of the internal power supply circuit VRLG
Is represented by the following equation. Therefore, the output voltage of the level shift circuit LS ₁ is level-shifted voltage V _BE amount than the input voltage V _in.

[0042]

(Equation 8)

<Embodiment 2> FIG. 5 is a circuit diagram showing a second embodiment of the amplifier according to the present invention, in which a transimpedance amplifier is formed. In FIG. 5, the same components as those shown in the first embodiment of FIG. 1 are denoted by the same reference numerals for convenience of description, and detailed description thereof will be omitted. That is, in this embodiment, the output signal V _{c1 of the} transimpedance amplifier is supplied to the low-pass filter of the internal power supply circuit VDLG via the emitter follower EF _{1 including} the transistor Q ₃ and the current source CS ₃ provided between the power supply voltages V _CC and V _EE. The difference from the first embodiment is that the input is made to the LPF. When the output voltage V _c1 of the input transistor Q _in is configured to be inputted to the low pass filter LPF through the emitter follower can reduce the load of the low-pass filter LPF as seen from the collector of the transistor Q _in. However, the low-pass filter L
Input potential of the PF is by the emitter follower EF _1, voltage V
To decrease only _BE, it is necessary to set the shift amount of the level shift circuit LS ₂ to V _A + V _BE. Specifically, when using the same configuration as the level shift circuit LS ₁ shown in FIG. 8, may be adjusted number of diodes connected in series between the base of the emitter and the transistor Q ₂₁ of the transistor Q _11. In the case of the circuit configuration of the present embodiment, four diode series circuits may be used.

The transimpedance amplifier of the present embodiment having such a configuration, as in the first embodiment, the operating point even amplitude and variation of the input signal I _in is stabilized, have a smaller characteristic frequency variation doing.

<Embodiment 3> FIG. 6 is a circuit diagram showing a third embodiment of the amplifier according to the present invention, in which a transimpedance amplifier using a cascode circuit is formed. 6, the same components as those shown in the second embodiment of FIG. 5 are denoted by the same reference numerals for convenience of description, and detailed description thereof will be omitted. That is, a point that insert a cascode transistor Q _cas between the input transistor Q _in the load resistor R _L in the present embodiment, the diode D ₁ and the current source CS ₁ along with it
The difference from the second embodiment is that a diode _D51 is inserted between them.

As described above, the cascode transistor _Qcas
Is inserted, the input transistor Q _in
, The bandwidth of the transimpedance amplifier can be improved.

[0047] Also in this embodiment, as in the first embodiment, also the operating point is stabilized and fluctuation amplitude of the input signal I _in is, can be obtained transimpedance amplifier having a low characteristic frequency variation Of course.

<Embodiment 4> FIG. 7 is a circuit diagram showing a fourth embodiment of the amplifier according to the present invention, in which a double feedback transimpedance amplifier is formed. In FIG. 7, the same components as those shown in the second embodiment of FIG. 5 are denoted by the same reference numerals for convenience of description, and detailed description thereof will be omitted. That is, in this embodiment, the base of the transistor Q ₁ is connected to the power supply voltage V _CC via the resistor R _1, and the emitter of the input transistor Q _in is connected via a series circuit of the feedback resistor R _F2 and the feedback capacitor C _F2. And the input transistor Q
that the emitter of _in is grounded through a resistor R _E1, that the connection point of the collector and the load resistance R _L of the input transistor Q _in is connected to the base of the transistor Q _4, the emitter of the transistor Q ₄ is transistor via the resistor R ₂ is connected to the base of Q ₅ is connected to the emitter of the transistor Q _5, the resistance R with the emitter of the transistor Q ₅ is connected to the base of the input transistor Q _in via the feedback resistor R _{F1 3} through a point which is grounded, the transistor Q _4, that the collectors of Q ₅ is connected to the base of the transistor Q _1, and the transistor Q _1, that no diode D ₁ is between the current source CS ₁ This is different from the second embodiment.

The double feedback transimpedance amplifier is composed of a current feedback by a resistor R _F1 , a resistor R _F2 and a capacitor C
_This is a transimpedance amplifier having voltage feedback by _F2 . Since the input impedance can be reduced by the current feedback, the band can be widened. Further, by compensating for the phase delay by the voltage feedback, it is possible to prevent a peak from occurring in the frequency characteristic of the transimpedance. A conventional double feedback transimpedance amplifier having such a characteristic is described in IEE, Journal of Solid State Circuits, Vol. 29 (December, 1994), pp. 1577 to 1582, (IEEE Journal of Solid-State Circuit
s, Vol. 29 (Dec., 1994), pp. 1577-1582), and a description thereof is omitted here.

[0050] In this embodiment, the conventional dual-feedback transimpedance amplifier, the output voltage V _c3 of the input transistor Q _in the same manner as in the second embodiment the internal power supply circuit VRLG inputted via the emitter follower EF ₁ And the output voltage V _RL is applied to the load resistance R _L.

[0051] Also in this embodiment, as in the second embodiment, also the operating point is stabilized and fluctuation amplitude of the input signal I _in is, obtain a dual feedback type transimpedance amplifier having a low characteristic frequency variation be able to.

<Embodiment 5> FIG. 9 is a circuit diagram showing a fifth embodiment of the amplifier according to the present invention, in which a transimpedance amplifier is formed. In FIG. 9, the same components as those shown in the second embodiment of FIG. 5 are denoted by the same reference numerals for convenience of description, and detailed description thereof will be omitted. That is, in the present embodiment, the high-potential holding circuit TH, the low-potential holding circuit BH, the resistors R _A1 and R _A2
And the internal power supply circuit VRLG from the level shift circuit LS ₂
Is different from the second embodiment in that

The output signal V _c1 of the input transistor Q _in is
Via the emitter follower EF _1, it is input to the high-potential holding circuit TH and the low potential holding circuit BH. High potential holding circuit T
H holds the high potential of the output signal V _c1 , and the low potential holding circuit BH holds and outputs the low potential of the output signal V _c1 . When the resistance value of the resistor R _A1 and R _A2 are set to be the same, the potential of the signal input to the level shift circuit LS ₂ is a just middle potential of the high potential and the low potential of the output signal V _c1. That is, the same effect as obtained through the low-pass filter can be obtained. Therefore, even with the configuration of the present embodiment, a transimpedance amplifier having a stable frequency characteristic without changing the operating point with respect to the amplitude fluctuation of the input signal Iin can be obtained as _in the previous embodiments.

Here, a specific configuration example of the high potential holding circuit TH and the low potential holding circuit BH is shown in FIG. As shown in the figure, the high potential holding circuit TH includes a transistor Q _TH and a capacitor C _TH , and the low potential holding circuit BH includes a diode _{DB H} and a capacitor C _BH . High potential holding circuit TH
And when the input signal V _in2 low potential holding circuit BH rises, the transistor Q _TH is rendered conductive, the diode D _BH becomes non-conductive, capacitor C _TH is high potential value V of the input signal V _in2
It is charged to a potential lower by V _BE than _{in2 (H)} . on the other hand,
When the input signal _Vin2 falls, the transistor Q
_TH is nonconductive, the diode D _BH becomes conductive, the capacitor C _BH is discharged to a potential higher by V _BE than the low potential value V _in2 input signal V _{in2 (L).} Therefore, application of the output signal of the high potential hold circuit TH and the low potential holding circuit BH to the resistor R _A1 and R _A2, the output potential V _out2 is expressed by the following equation.

[0055]

(Equation 9)

From the above equation (9), it can be seen that as the output potential _Vout2 , a potential in the center of the input signal _Vin2 , that is, an average value can be obtained.

<Embodiment 6> FIG. 12 is a circuit diagram showing a sixth embodiment of the amplifier according to the present invention, in which a DC-coupled common-emitter amplifier is formed. Although the embodiments described so far are cases where the present invention is applied to a transimpedance amplifier, this embodiment is a case where the present invention is applied to a common-emitter amplifier shown in FIG. When an input signal is applied to a common-emitter amplifier through a capacitor, the DC component of the input signal is not transmitted to the common-emitter amplifier,
When a common-emitter amplifier is DC-coupled to another amplifier, a problem arises that the operating point fluctuates due to the fluctuation of the DC component of the input signal and the gain fluctuates. For example, when a common-emitter amplifier and another amplifier are integrated on the same semiconductor chip, it is difficult to form a large-capacity capacitive element on a semiconductor substrate, and thus DC coupling is often used.

Now, consider a case where the input signal S _in is applied by DC coupling to the common emitter amplifier of FIG. Here, the DC component of the input signal S _in is assumed to be V _in . Gain A ₁ in this case the amplifier is expressed by the following equation.

[0059]

(Equation 10)

[0060] On the other hand, the collector current I _c of the input transistor Q _in is expressed by the following equation.

[0061]

[Equation 11]

[0062] Here, V _E is the ground potential, or bias circuit but or a generated potentials by (not shown), conventionally, what between the DC component V _in the input signal and the potential V _E There was no correlation. Therefore, the DC component V of the input signal
When _in changes, the collector current I _c is changed, the gain A ₁ of the amplifier is disadvantageously changed. This problem,
This can be avoided by applying the present invention. Hereinafter, FIG.
The case where the present invention is applied to a common-emitter amplifier will be described with reference to FIG.

[0063] circuit configuration of this embodiment shown in FIG. 12, a low-pass filter LPF which receives the signal S _in, V _E generator VEG is provided comprising a level shift circuit LS ₃ Prefecture, V _E generator VEG Output _VE to input transistor Q
that are applied to the resistor R _E connected to the emitter of _in is different from the conventional example shown in FIG. 11. In the amplifier of the present embodiment configured as described above, the level shift circuit L
If the level shift amount of S ₃ and V _B, V _E generating circuit VE
The output V _E of G is given by the following expression.

[0064]

(Equation 12)

[0065] Therefore, the collector current I _c of the input transistor Q _in is expressed by the following equation.

[0066]

(Equation 13)

Here, for example, a level shift amount V _B using a level shift circuit LS ₃ composed of a transistor Q ₆ , a diode D ₇₁ and a current source CS ₄ as shown in FIG.
Is selected to be -2V _BE , the collector current I _c is I _c = V _BE /
Next R _E, becomes independent of the DC component V _in the input signal. Thus, the gain of the amplifier of this embodiment also regardless of fluctuation of the DC component V _in the input signal, it is possible to keep constant.

[0068] Here, an example is shown consisting of a low-pass filter and level shift circuit as V _E generating circuit,
High potential holding circuit as in the embodiment shown in FIG. 9, the low potential holding circuit, the same effect can be obtained even with the resistance and the level shift circuit to constitute a V _E generation circuit.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the spirit of the present invention. It is. For example, in each of the above embodiments, the example in which the present invention is applied to a transimpedance amplifier using a bipolar transistor or a DC-coupled common emitter amplifier has been described.
It is needless to say that the present invention can be applied to a similar configuration using an FET, HEMT, or the like.

[0070]

As described above, according to the present invention,
Even if the amplitude of the input signal changes, the operating point of the amplifier can be prevented from changing. This makes it possible to obtain a transimpedance amplifier capable of minimizing fluctuations in frequency characteristics.

In the case of a DC-coupled amplifier, it is possible to obtain an amplifier in which the fluctuation of the gain is suppressed even if the DC component of the input signal fluctuates.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing a conventional transimpedance amplifier.

FIG. 3 is a characteristic diagram schematically showing an I _in -I _c characteristic of the amplifier of FIG. 2;

FIG. 4 is a characteristic diagram schematically showing an I _in -I _c characteristic of the amplifier of FIG. 1;

FIG. 5 is a circuit diagram showing a second embodiment of the amplifier according to the present invention.

FIG. 6 is a circuit diagram showing a third embodiment of the amplifier according to the present invention.

FIG. 7 is a circuit diagram showing a fourth embodiment of the amplifier according to the present invention.

FIG. 8 is a circuit diagram showing an example of an internal power supply circuit used in the amplifier of FIG.

FIG. 9 is a circuit diagram showing a fifth embodiment of the amplifier according to the present invention.

10 is a circuit diagram showing an example of a high potential holding circuit and a low potential holding circuit used in the amplifier of FIG.

FIG. 11 is a circuit diagram showing a conventional example of an amplifier having a common emitter amplifier circuit using DC coupling.

FIG. 12 is a circuit diagram showing a sixth embodiment of the amplifier according to the present invention.

FIG. 13 is a circuit diagram showing an example of a level shift circuit used in the amplifier of FIG.

[Explanation of symbols]

Q _in ... input _{transistor, R L, R F, R} A1, R A2 ... resistance, VRLG ... internal power supply circuit, LPF ... low pass _{filter, LS 1, LS 2, LS} 3 ... level shift circuit, EF ₁ ...
Emitter follower, TH: high potential holding circuit, BH: low potential holding circuit.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H04B 10/04 10/06 (72) Inventor Ryoji Takeyari 1-280 Higashi-Koigabo, Kokubunji-shi, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (72 Inventor Katsuyoshi Washio 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (8)

[Claims] An amplifier that feeds back an output signal of an amplifier circuit to an input via at least a resistor, receives the output signal as an input, and receives an average value of the output signal with respect to a fluctuation in an amplitude level of the input signal of the amplifier circuit. An amplifier provided with an internal power supply circuit for applying a bias to the amplifier circuit so as to make constant. 2. The amplifier according to claim 1, wherein said internal power supply circuit comprises a low-pass filter to which an output signal of said amplifier circuit is input, and a level shift circuit for shifting a voltage level of an output of said low-pass filter. 3. The amplifier according to claim 2, wherein said low-pass filter has a pass band set lower than a lower limit frequency of said input signal. 4. A high-potential holding circuit for receiving an output signal of the amplifying circuit as an input and holding a high potential of the output signal, and a low-potential of the output signal receiving an output signal of the amplifying circuit as an input. Potential holding circuit, and first and second resistors having one ends connected to the outputs of the high potential holding circuit and the low potential holding circuit and the other end connected in common, and the first and second resistors, respectively. 2. The amplifier according to claim 1, further comprising: a level shift circuit connected to a common connection point of said resistors and biasing said amplifier circuit. 5. The transimpedance amplifier according to claim 1, wherein the amplifier is configured to reduce the input impedance by applying a negative feedback to the input of the output of the amplification circuit via a feedback resistor. The amplifier according to the paragraph. 6. An amplifier having at least an amplifier circuit for amplifying an input signal having a DC component, wherein a bias for maintaining a constant gain of the amplifier circuit is generated based on the DC component detected from the input signal. An amplifier having an internal power supply circuit. 7. The amplifier according to claim 6, wherein said internal power supply circuit comprises a low-pass filter which receives said input signal having said DC component as an input, and a level shift circuit which shifts a voltage level of an output of said low-pass filter. . 8. The amplifier according to claim 7, wherein said amplifier circuit is a common-emitter amplifier circuit, and an output voltage of said internal power supply circuit is applied to an emitter of said common-emitter amplifier circuit via a resistor.