JP6611185B2 - Amplifier circuit - Google Patents

Description

  The present invention relates to an amplifier circuit that converts a minute current signal into a voltage signal and amplifies it at the same time.

  In optical communication or the like, an amplifier circuit that receives and amplifies a current generated by a photodiode and converts it into a voltage signal having an amplitude that can be received by a subsequent circuit is required. Depending on the waveform to be received, high linearity is required, so the amplifier circuit needs to be highly linear.

FIG. 12A shows the configuration of an amplifier circuit that receives a single-phase current signal i _in and amplifies a voltage signal. The circuit illustrated in FIG. 12A operates as a transimpedance amplifier (TIA) (see Patent Document 1). In FIG. 12A, A is the amplification factor of the transimpedance amplifier, and Z _T is the transimpedance gain. Since the input current can be extracted by feedback through the feedback resistor R100, a low input impedance can be realized. As an actual amplifier circuit, for example, the circuit shown in FIG. 12B is widely used. This amplifier circuit includes transistors Q100 to Q102, resistors R100 to R103, and a capacitor C100.

In the case of outputting a differential signal, single-phase differential conversion is performed by the circuits shown in FIGS. 13 (A) and 13 (B). The circuit in FIG. 13A converts the single-phase current signal i _in to a differential voltage signal by using the output voltage of the replica circuit 201 of the TIA 200 as the reference voltage supplied to the output buffer circuit 202. (Patent Document 1). The circuit in FIG. 13B uses a low pass filter (LPF) 203 that extracts a DC component from the output of the TIA 200 and supplies this DC component as a reference voltage for the output buffer circuit 202. The single-phase current signal i _in is converted into a differential voltage signal (see Non-Patent Document 1).

  As another configuration of the amplifier circuit, there is also a configuration in which a grounded base amplifier circuit 300 and a grounded emitter amplifier circuit 301 are combined as shown in FIG. 14 (see Non-Patent Document 2).

Japanese Patent Laid-Open No. 2002-76793

T. Takemoto et al., “A 4x 25-to-28Gb / s 4.9mW / Gb / s -9.7dBm High-Sensitivity Optical Receiver Based on 65nm CMOS for Board-to-Board Interconnects”, IEEE ISSCC, Feb.2013 G. Kalogerakis et al., “A Quad 25Gb / s 270mW TIA in 0.13μm BiCMOS with <0.15dB Crosstalk Penalty”, IEEE ISSCC, Feb. 2013

In the field of optical communications, it is necessary to handle high-speed signals. In high-speed signal amplification, fluctuations in power supply voltage become a problem. The quality of the signal is affected by fluctuations in the power supply voltage. As a method for suppressing the influence of shaking, as disclosed in Non-Patent Document 2, there is known a method of performing differentiation using a first-stage amplifier circuit. By performing differentiation with the first-stage amplifier circuit, the second-stage and subsequent amplifier circuits can be operated with a differential signal, and the influence of fluctuations in the power supply voltage can be suppressed. However, the technique disclosed in Non-Patent Document 2 has a problem that the noise caused by the grounded base amplification circuit greatly deteriorates the signal.
The above problem occurs similarly when a grounded gate amplifier circuit is used instead of the grounded base amplifier circuit.

  The present invention has been made to solve the above-described problem, and an object of the present invention is to suppress noise caused by a transistor of a common base amplifier circuit or a common gate amplifier circuit in an amplifier circuit that realizes single-phase differential conversion.

An amplifier circuit according to the present invention includes a first transimpedance amplifier having a positive gain that receives a single-phase current signal and a second transimpedance having a negative gain that receives the current signal. An amplifier, and a differential amplifier that receives the output of the first transimpedance amplifier and the output of the second transimpedance amplifier, and the first transimpedance amplifier is a base ground amplifier circuit or a gate ground. Do from the amplifier Ri, the base grounded amplifier circuit or the input conversion noise current i _eq amplifier circuit composed of said gate grounded amplifier circuit and the second transimpedance amplifier and the differential amplifier, the base grounded amplifier circuit or noise current i _nb of the grounded-gate amplifier circuit, the base-grounded amplifier circuit or the grounded-gate amplifier The load resistance of the road R _B, the base grounded amplifier circuit or transimpedance gain of the grounded-gate amplifier circuit Z _TP, the second transimpedance amplifier transimpedance gain -Z _TN, the base grounded amplifier circuit or the When the input impedance of the grounded-gate amplifier circuit is Z _inb and the input impedance of the second transimpedance amplifier is Z _intia , these parameters are influenced by the noise caused by the transistors of the base-grounded amplifier circuit or the gate-grounded amplifier circuit. It is characterized by satisfying a conditional expression for suppressing the above.

Further, according to one configuration example of the amplifier circuit of the present invention, when the first transimpedance amplifier is a grounded base amplifier circuit, an output terminal of the grounded base amplifier circuit and one input terminal of the differential amplifier And an emitter follower provided between the two.
Further, according to one configuration example of the amplifier circuit of the present invention, when the first transimpedance amplifier is a grounded base amplifier circuit, the output voltage of the grounded base amplifier circuit is used as the base of the transistor of the grounded base amplifier circuit. And a feedback circuit that feeds back the signal.
In one configuration example of the amplifier circuit of the present invention, the second transimpedance amplifier includes a grounded-emitter amplifier circuit or a grounded-source amplifier circuit that receives the current signal, an input terminal of the second transimpedance amplifier, And at least a feedback resistor inserted between the output terminals.

In addition, one configuration example of the amplifier circuit according to the present invention further includes a signal input terminal of the amplifier circuit to which the current signal is input and an input terminal of the first transimpedance amplifier, and a signal input of the amplifier circuit. And an input impedance adjusting element inserted into at least one of the terminal and the input terminal of the second transimpedance amplifier.
In one configuration example of the amplifier circuit according to the present invention, the input impedance adjusting element is an element composed of only a resistor, an element composed of a series circuit of a transmission line and a resistor, or an inductor and a resistor connected in series. In the circuit, any one of elements obtained by adding capacitance between the connection point of the inductor and the resistor and the ground.
In addition, one configuration example of the amplifier circuit according to the present invention further includes a first amplifier provided between an output terminal of the first transimpedance amplifier and one input terminal of the differential amplifier, and the first amplifier. And a second amplifier having an amplification factor different from that of the first amplifier, which is provided between an output terminal of the transimpedance amplifier of No. 2 and the other input terminal of the differential amplifier. is there.
In one configuration example of the amplifier circuit of the present invention, the differential amplifier is characterized in that the amplification factor on the positive input terminal side is different from the amplification factor on the negative input terminal side.

  According to the present invention, by using a first transimpedance amplifier having a positive amplification factor and a second transimpedance amplifier having a negative amplification factor, each consisting of a grounded base amplification circuit or a grounded gate amplification circuit, Single-phase differential conversion can be realized. Thereby, in this invention, the degradation of the signal quality by the fluctuation | variation of a power supply voltage can be suppressed. Further, according to the present invention, it is possible to suppress noise caused by the transistors of the grounded base amplifier circuit or the grounded gate amplifier circuit, as compared with a conventional amplifier circuit that realizes single-phase differential conversion. Further, in the present invention, since the signal intensity input to each transimpedance amplifier is reduced by shunting, the dynamic range of the amplifier circuit can be improved.

  In the present invention, the signal input terminal of the amplifier circuit to which the current signal is input and the input terminal of the first transimpedance amplifier, and the signal input terminal of the amplifier circuit and the input terminal of the second transimpedance amplifier are provided. By inserting an element for adjusting the input impedance into at least one of the gaps, the input impedance of the amplifier circuit can be set to a desired value.

  In the present invention, the first amplifier is provided between the output terminal of the first transimpedance amplifier and one input terminal of the differential amplifier, and the other of the output terminal of the second transimpedance amplifier and the other of the differential amplifier. When the transimpedance gain of the second transimpedance amplifier is adjusted according to a signal source having a finite impedance by providing a second amplifier having an amplification factor different from that of the first amplifier It is possible to absorb the amplitude difference between the output of the first transimpedance amplifier and the output of the second transimpedance amplifier.

  Further, according to the present invention, by setting the amplification factor on the positive input terminal side and the amplification factor on the negative input terminal side of the differential amplifier to different values, the second difference is obtained according to the signal source having a finite impedance. It is possible to absorb the amplitude difference between the output of the first transimpedance amplifier and the output of the second transimpedance amplifier that occurs when the transimpedance gain of the transimpedance amplifier is adjusted.

1 is a block diagram showing a configuration of an amplifier circuit according to a first embodiment of the present invention. FIG. 3 is a circuit diagram for analyzing noise generated by the grounded base amplifier circuit in the first embodiment of the present invention. It is a figure which shows the input conversion current noise density of the conventional amplifier circuit and the amplifier circuit which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the amplifier circuit which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the amplifier circuit which concerns on the 3rd Embodiment of this invention. It is a block diagram which shows the other structure of the amplifier circuit which concerns on the 3rd Embodiment of this invention. It is a block diagram which shows the structure of the amplifier circuit which concerns on the 4th Embodiment of this invention. It is a block diagram which shows the structure of the amplifier circuit which concerns on the 5th Embodiment of this invention. It is a block diagram which shows the structure of the amplifier circuit which concerns on the 6th Embodiment of this invention. It is a block diagram which shows the other structure of the amplifier circuit which concerns on the 6th Embodiment of this invention. It is a circuit diagram which shows the structure of the element for input impedance adjustment which concerns on the 7th Embodiment of this invention. It is the block diagram and circuit diagram which show the structure of the conventional amplifier circuit. It is a block diagram which shows the other structure of the conventional amplifier circuit. It is a block diagram which shows the other structure of the conventional amplifier circuit.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an amplifier circuit according to the first embodiment of the present invention. Amplifier circuit 1 of this embodiment has an input current signal i _in single-phase, a transimpedance amplifier (TIA) 2 having a negative gain, common-base amplifier circuit 3 for receiving the current signal i _in And an emitter follower 4 that receives the output of the grounded base amplifier circuit 3 and a differential amplifier 5 that receives the output of the TIA 2 and the output of the emitter follower 4.

The configuration of TIA2 is the same as that shown in FIG. The detailed configuration of the TIA 2 will be described again in an embodiment described later.
The grounded base amplifying circuit 3 is supplied with a constant DC voltage to the base and is grounded in an alternating manner, a current signal i _in is input to the emitter, and a transistor B 1 whose collector is connected to the output terminal of the grounded base amplifying circuit 3. one end connected to a power supply voltage and the other end is composed of the load resistance R _B connected to the output terminal of the common base amplifier circuit 3. Here, the grounded base amplifier circuit 3 operates as a TIA having a positive amplification factor. In actual optical communication, the signal source DA is a photodiode.

The emitter follower 4 has a base to which an output signal of the grounded base amplification circuit 3 is input, an emitter is connected to the output terminal of the emitter follower 4, a collector is connected to the power supply voltage, and one end is an output of the emitter follower 4. It is connected to the terminal, and a emitter resistor R _E other end of which is grounded.

  The output terminal (node X) of the emitter follower 4 is connected to the negative input terminal (inverting input terminal) of the differential amplifier 5, and the output terminal (node Y) of the TIA 2 is connected to the positive input terminal (non-inverting) of the differential amplifier 5. Input terminal).

The current signal i _in is divided into a current i _b input to the grounded base amplification circuit 3 and a current itia input to the _{TIA 2} . The currents i _b and _itia satisfy the following relationship.
i _in = i _b + i _tia (1)
i _tia = i _in × Z _inb / (Z _intia + Z _inb ) (2)
i _b = i _in × Z _intia / (Z _intia + Z _inb ) (3)

Here, Z _intia is the input impedance of the TIA 2, and Z _inb is the input impedance of the grounded base amplification circuit 3. When the transimpedance gain of the common-base amplifier circuit 3 to the transimpedance gain of the Z _TP, TIA 2 and -Z _TN, respectively the output voltage V _outn of the output voltage V _outp, TIA 2 base grounded amplifier circuit 3 is given by the following equation .
V _outp = Z _TP i _b = R _B i _b (4)
V _outn = −Z _TN i _tia (5)

Assuming that the amplification factor of the subsequent differential amplifier 5 is A, the final differential signal output voltage _Vout is as follows. That is, the circuit of FIG. 1 can convert the single-phase current signal i _in into a differential voltage signal.

FIG. 2 shows an equivalent circuit diagram of the amplifier circuit 1 of the present embodiment, specifically, a circuit diagram for analyzing noise generated by the grounded base amplifier circuit 3. In the present embodiment, the noise current _inb due to the transistor B1 of the grounded base amplification circuit 3 can be removed. Since a noise current of i _nb flows through the resistor R _B , the small signal voltage V _nX that appears at the node X (the output terminal of the emitter follower 4) according to the noise current i _nb can be expressed by the following equation.
V _nX = −R _B i _nb (7)

In the example of Expression (7), the case where the amplifier circuit subsequent to the grounded base amplifier circuit 3 is an emitter follower 4 having an amplification factor of about 1 is described.
When the output resistance of the signal source DA is sufficiently larger than the input resistance of TIA2, the noise current i _nb generated in the transistor B1 flows into TIA2. The noise current i _nb flowing through the TIA2 is converted into a voltage and output to the node Y (the output terminal of the TIA2). The voltage V _nY that appears at the node Y according to the noise current i _nb is _given by the following equation.
V _nY = −Z _TN i _nb (8)

_Assuming that the amplification factor of the differential amplifier 5 is A as described above, the voltage V _{out, noise} output from the differential amplifier 5 in accordance with the noise current i _nb is expressed by the following equation.
_{V out, noise = A (-Z} TN i nb - (- R B i nb)) = A (R B -Z TN) i nb ·· (9)

Next, the input conversion noise current i _eq is calculated. By dividing the voltage difference between the nodes X and Y caused by the noise current i _nb by the transimpedance gain, the input equivalent noise current can be calculated. Transimpedance gain is obtained by dividing the voltage V _out of _the equation (6) by the current i _in.

Therefore, the input equivalent noise current i _eq is as follows.

In the present embodiment, it is possible to suppress the influence of the noise current i _nb of the grounded base amplifier circuit 3 on the signal. However, in order to obtain such an effect, it is necessary to satisfy the condition i _eq <i _nb . Substituting equation (11) for this condition, the following equation is obtained.

In particular, when R _B = Z _TN , a noise suppression effect is always obtained. If there is frequency dependence, the noise suppression effect can be obtained by considering the band of the signal to be handled and satisfying the above equation (12) in the band. Moreover, even if it is a case where Formula (12) cannot be satisfy | filled in the whole band of the signal used as object, the integrated noise current can be reduced by using the structure of this Embodiment.

The signal input terminal IT of the amplifier circuit 1 and the input terminal of the grounded base amplifier circuit 3 (emitter of the transistor B1) and the input terminal of the TIA2 may be directly connected. It is not always possible to design the input impedance to a desired value. In such a case, as shown in FIG. 1, an input impedance adjusting element Z _incomp1 is inserted between the signal input terminal IT and the input terminal of the grounded base amplifier circuit 3, and the signal input terminals IT and TIA2 are input. An input impedance adjusting element Z _incomp2 may be inserted between the terminals. For example, resistors may be _used as the input impedance adjusting elements Z _incomp1 and Z _incomp2 . The detailed configuration of the input impedance adjusting elements Z _incomp1 and Z _incomp2 will be described again in an embodiment described later.

Even when the input impedance adjusting elements Z _incomp1 and Z _incomp2 are used, it can be seen that noise due to Z _incomp1 and Z _incomp2 is suppressed by the same discussion as above. Even when the signal source DA has a finite impedance, the impedance of the signal source DA viewed from the signal input terminal IT of the amplifier circuit 1 of the present embodiment and the input impedance of the TIA 2 having a negative amplification factor. By setting the ratio of R _B and Z _TN according to the ratio, the same noise suppression effect can be obtained.

  FIG. 3 shows the input equivalent current noise density of the conventional amplifier circuit shown in FIG. 14 and the amplifier circuit 1 of the present embodiment. In FIG. 3, 30 indicates the input converted current noise density of the conventional amplifier circuit, and 31 indicates the input converted current noise density of the amplifier circuit 1 of the present embodiment. According to FIG. 3, it can be seen that noise can be suppressed as compared with the conventional amplifier circuit by using the configuration of the amplifier circuit of the present embodiment.

  As described above, in the present embodiment, single-phase differential conversion is realized by using the TIA 2 having a negative amplification factor and the grounded base amplifier circuit 3. Thereby, in this Embodiment, the degradation of the signal quality by the fluctuation | variation of a power supply voltage can be suppressed. In addition, in this embodiment, noise can be suppressed as compared with a conventional amplifier circuit that realizes single-phase differential conversion. In the present embodiment, the signal intensity input to each TIA (TIA2 and grounded base amplification circuit 3) is reduced by shunting, which can contribute to the improvement of the dynamic range.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 4 is a block diagram showing a configuration of an amplifier circuit according to the second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals. In this embodiment, a specific example of the first embodiment will be described. The signal source (not shown) that outputs the current signal i _in has an impedance sufficiently higher than the combined resistance of the input impedance of the grounded base amplifier circuit 3 and the input impedance of the TIA 2 as described in the first embodiment. A current source such as a photodiode.

Load resistor R _B to determine the gain of the grounded base amplifier circuit 3 may not be pure resistive. For example, an inductor may be provided in parallel with the pure resistor in order to give the peaking characteristic to the frequency characteristic of the amplifier circuit, and a capacitor may be provided in parallel with the pure resistor in order to limit the band.

In the first embodiment, the grounded base amplifier circuit 3 and the emitter follower 4 are configured by bipolar transistors, but may be configured by MOS transistors.
As described in the first embodiment, the input impedance adjusting element Z _incomp1 is inserted between the signal input terminal IT of the amplifier circuit 1 and the input terminal of the grounded base amplifier circuit 3, and the signal input terminals IT and TIA2 are inserted. The input impedance adjusting element Z _incomp2 may be inserted between the input terminal and the input terminal. The input impedance adjusting elements Z _incomp1 and Z _incomp2 are not limited to pure resistance, and may be configured by a network of capacitors and inductors.

  In the present embodiment, the bias current source IS is provided between the signal input terminal IT of the amplifier circuit 1 and the ground, but the current source IS is not an essential component of the present invention. When the current source IS is provided, a device constituting the current source IS may be a MOS transistor or a bipolar transistor. Further, the current flowing through the transistor constituting the current source IS may be controlled from the outside.

In this embodiment, the bias resistor R1 is provided between the signal input terminal IT of the amplifier circuit 1 and the ground, but the resistor R1 is not an essential component of the present invention. When the resistor R1 is provided, the resistance value may be externally controllable. However, if the value of the resistor R1 is small, no current flows through the amplifier circuit 1. Therefore, it is necessary to use the resistor R1 having a resistance value larger than the combined resistance of the input impedance of the base-grounded amplifier circuit 3 and the input impedance of the TIA2. is there.
The configuration of the present embodiment described above can also be applied to the following embodiments.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. FIG. 5 is a block diagram showing a configuration of an amplifier circuit according to the third embodiment of the present invention. The same components as those in FIGS. 1 and 4 are denoted by the same reference numerals. This embodiment describes another specific example of the first embodiment, and describes the configuration of the TIA 2 having a negative amplification factor.

The TIA2 of the present embodiment includes a grounded emitter amplifier circuit that receives the current signal i _in , an emitter follower that receives the output of the grounded emitter amplifier circuit, one end connected to the input terminal of the TIA2, and the other end. The feedback resistor R5 is connected to the output terminal of the TIA2.

The grounded-emitter amplifier circuit includes a transistor M1 whose base is connected to the input terminal of TIA2, a transistor M2 whose base is supplied with a constant bias voltage _Vb , an emitter connected to the collector of the transistor M1, and a power supply voltage at one end. And a resistor R2 having the other end connected to the collector of the transistor M2 and a resistor R3 having one end connected to the emitter of the transistor M1 and the other end grounded.

  The emitter follower of TIA2 has a base connected to the collector of transistor M2, an emitter connected to the output terminal of TIA2, a collector connected to the power supply voltage, one end connected to the output terminal of TIA2, and the other end Is composed of a grounded resistor R4.

  Further, a circuit configuration as shown in FIG. 6 may be used as the configuration of TIA2. 6 includes a transistor M4 having a base connected to the input terminal of the TIA2, a transistor M5 having a base connected to the collector of the transistor M4, an emitter connected to the output terminal of the TIA2, and one end at the power supply voltage. A resistor R6 connected to the collector of the transistor M4 and the base of the transistor M5, one end connected to the emitter of the transistor M4, the other end grounded, and one end to the output terminal of the TIA2. The resistor R8 is connected, the other end is grounded, and the feedback resistor R9 is connected to the input terminal of the TIA2 at one end and the collector of the transistor M4 and the base of the transistor M5 at the other end.

Similarly to the case of FIG. 5, the transistor M4 and the resistors R6 and R7 constitute a grounded emitter amplifier circuit, and the transistor M5 and the resistor R8 constitute an emitter follower.
In the configuration of TIA2 shown in FIG. 6, the position of the feedback resistor is different from that in FIG. 5, but even when the TIA2 having the configuration shown in FIG. 6 is used, the effect described in the first embodiment can be obtained. Can do.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. FIG. 7 is a block diagram showing the configuration of an amplifier circuit according to the fourth embodiment of the present invention. The same components as those in FIGS. 1 and 4 to 6 are denoted by the same reference numerals. In this embodiment, another specific example of the first embodiment will be described. A MOS transistor is used instead of a bipolar transistor.

Amplifier circuit 1 of this embodiment has an input current signal i _in, negative and TIA2a having an amplification factor, and grounded-gate amplifier circuit 3a for receiving the current signal i _in, the output of TIA2a and grounded-gate amplifier It comprises a differential amplifier 5 that receives the output of the circuit 3a.

The TIA 2a includes a grounded source amplifier circuit that receives the current signal i _in and a current feedback circuit to the input unit. Source amplifier circuit has a gate connected to an input terminal of TIA2a, the MOS transistor M6 whose source is grounded, the bias voltage V _b3 is supplied to the gate, a drain connected to the output terminal of TIA2a, source transistor M6 And a resistor R10 having one end connected to the power supply voltage and the other end connected to the output terminal of the TIA 2a.

Current feedback circuit includes a MOS transistor M8 having a gate connected to the output terminal of TIA2a, bias voltage V _b2 is supplied to the gate, the source of the MOS transistor M9 which are connected to the drain of the transistor M8, one end to the supply voltage A resistor R11 having the other end connected to the drain of the transistor M9, one end connected to the input terminal of the TIA2a, and the other end connected to the source of the transistor M8, an input impedance adjusting element Z _incomp2 , and one end Is connected to the input terminal of the TIA 2a and the other end of the current source IS1 is grounded. Note that Z _incomp2 in FIG. 7 is an element for adjusting the input impedance, and also functions as a feedback resistor.

Grounded-gate amplifier circuit 3a provided in place of the grounded base amplifier circuit, the gate bias voltage V _b1 is AC grounded is supplied to the source current signal i _in is input, a drain of the grounded-gate amplifier circuit 3a composed of the transistors B3 connected to the output terminal, one terminal connected to the power supply voltage, the other end connected to the output terminal of the grounded-gate amplifier circuit 3a and the load resistor R _B. The common-gate amplifier circuit 3a operates as a TIA having a positive amplification factor.

An input impedance adjusting element Z _incomp1 is inserted between the signal input terminal IT of the amplifier circuit 1 and the input terminal of the _common- gate amplifier circuit 3a (source of the transistor B3). _Incomp1 may be omitted, and the signal input terminal IT may be directly connected to the input terminal of the _common- gate amplifier circuit 3a.

  The output terminal of the grounded gate amplification circuit 3a is connected to the positive input terminal (non-inverting input terminal) of the differential amplifier 5, and the output terminal of the TIA 2a is connected to the negative input terminal (inverting input terminal) of the differential amplifier 5. The

  Thus, also in this embodiment using a MOS transistor instead of a bipolar transistor, noise due to the transistor B3 of the common-gate amplifier circuit 3a can be suppressed, and the same effect as in the first embodiment can be obtained. .

[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be described. FIG. 8 is a block diagram showing a configuration of an amplifier circuit according to the fifth embodiment of the present invention. The same reference numerals are given to the same configurations as those in FIGS. 1 and 4 to 6. In the present embodiment, another configuration example of the grounded base amplifier circuit will be described.

Amplifier circuit 1 of this embodiment has an input current signal i _in a TIA2b having a negative gain, and grounded base amplifier circuit 3b for receiving the current signal i _in, the base-grounded amplifier circuit 3b outputs of And the differential amplifier 5 having the output of the TIA 2b and the output of the emitter follower 4 as inputs.

TIA2b has its emitter grounded amplifier circuit which receives the current signal i _in an emitter follower which receives the output of the emitter amplifier circuit, one end connected to an input terminal of TIA2b, the other end to the output terminal of TIA2b The feedback resistor R5 is connected. The grounded emitter amplifier circuit includes a transistor M1 and resistors R2 and R3. The emitter follower of the TIA 2b includes a transistor M3 and a resistor R4.

In the grounded base amplifier circuit 3b, a current signal i _in is input to the emitter, the collector is connected to the output terminal of the grounded base amplifier circuit 3b, one end is connected to the power supply voltage, and the other end is connected to the base grounded amplifier circuit. 3b and the load resistance R _B connected to the output terminal of, and a feedback circuit 6 for the feedback to the base of transistor B1 the output voltage of the base-grounded amplifier circuit 3b in amplification factor beta. In this case, the amplification factor β of the feedback circuit 6 normally takes a negative value (β <0).

  Thus, also in the present embodiment in which the feedback circuit is provided in the grounded base amplifier circuit 3b, noise due to the transistor B1 of the grounded base amplifier circuit 3b can be suppressed, and the same effect as in the first embodiment can be obtained. Can do.

[Sixth Embodiment]
Next, a sixth embodiment of the present invention will be described. FIG. 9 is a block diagram showing the configuration of an amplifier circuit according to the sixth embodiment of the present invention. The same components as those in FIGS. 1, 4 to 6 and 8 are denoted by the same reference numerals. . In this embodiment, a case where the signal source has a finite impedance will be described.

If the signal source DA has a finite impedance, noise current i _nb generated by transistor B1 grounded base amplifier circuit 3 is shunted to the current i _nt flowing current i _ns and TIA2 flowing into the source DA. The shunt ratio at this time depends on the impedance R _S of the signal source DA and the input impedance Z _{int of the} TIA 2 having a negative amplification factor. Therefore, the current i _nt flowing into the TIA 2 can be expressed as the following equation.
i _nt = i _nb (R _s ) / (Z _int + R _s ) (13)

  That is, by adjusting the transimpedance gain of the TIA 2 having a negative amplification factor, noise generated in the transistor B1 of the base-grounded amplifier circuit 3 can be appropriately suppressed, and the same effect as that of the first embodiment can be obtained. Can be obtained.

  At this time, an amplitude difference may occur between the node X (the output terminal of the emitter follower 4) and the node Y (the output terminal of the TIA2), but in order to absorb the amplitude difference, the single-phase amplifier 7 having different amplification factors from each other. , 8 may be inserted. The amplification factors of the amplifiers 7 and 8 may be set so that, for example, the overall common-mode rejection ratio of the amplifier circuit 1 of FIG. 9 is maximized. The present embodiment is applicable to each of the first to fifth embodiments.

  Further, in order to absorb the amplitude difference between the node X and the node Y due to the adjustment of the transimpedance gain of the TIA 2, the positive input terminal and the negative input terminal of the differential amplifier 5 in the configuration of the amplifier circuit shown in FIG. A difference in amplification factor may be provided between the two. Therefore, it is possible to use a method of changing the driving force by changing the size or number of input transistors of the differential amplifier 5 between the positive input terminal side and the negative input terminal side. The amplification factors on the positive input terminal side and the negative input terminal side of the differential amplifier 5 may be set so that, for example, the overall common-mode rejection ratio of the amplifier circuit 1 in FIG. 10 is maximized.

[Seventh Embodiment]
Next, a seventh embodiment of the present invention will be described. In the present embodiment, specific examples of the input impedance adjusting elements Z _incomp1 and Z _incomp2 described in the first to _sixth embodiments will be described. FIG. 11A shows a configuration in which the input impedance adjusting element Z _incomp1 is configured by only the resistor R. FIG.

In the example of FIG. 11B, the input impedance adjusting element Z _incomp1 is composed of a transmission line TL and a resistor R inserted in series between the input terminal and the output terminal. The configuration of FIG. 11B is effective when the signal is high speed and the distance from the signal input terminal IT to the TIA of the amplifier circuit is long.

In the example of FIG. 11C, the input impedance adjusting element Z _incomp1 includes an inductor L and a resistor R inserted in series between the input terminal and the output terminal, a connection point between the inductor L and the resistor R, and the ground. And a capacitor C inserted therebetween. In this configuration, it is difficult to see the parasitic capacitance by the inductor L, and the characteristics can be adjusted by the capacitance C.

In FIG. 11 (A) ~ FIG 11 (C), but shows the configuration of the element Z _InComp1, configuration of the element Z _InComp2 is the same as element Z _InComp1.
The locations where the elements Z _incomp1 and Z _incomp2 are inserted are as described in the first to sixth embodiments. _Further, only the element Z _incomp1 may be provided, or only the element Z _incomp2 may be provided.

  The present invention can be applied to a transimpedance amplifier.

DESCRIPTION OF SYMBOLS 1 ... Amplification circuit 2, 2a, 2b ... Transimpedance amplifier, 3, 3b ... Grounded base amplification circuit, 3a ... Grounded gate amplification circuit, 4 ... Emitter follower, 5 ... Differential amplifier, 6 ... Feedback circuit, 7, 8 ... amplifier, DA ... signal source, IS, IS1 ... current source, B1 to B3, M1 to M9 ... _{transistors, R, R B, R E} , R1~R11 ... _resistors, Z incomp1, Z incomp2 ... for input impedance adjustment Element, TL ... transmission line, L ... inductor, C ... capacitance.

Claims (8)

A first transimpedance amplifier having a positive gain and having a single-phase current signal as input;
A second transimpedance amplifier having a negative amplification factor that receives the current signal;
A differential amplifier having the output of the first transimpedance amplifier and the output of the second transimpedance amplifier as inputs;
The first transimpedance amplifier, Ri Do from the base-grounded amplifier circuit or grounded-gate amplifier circuit,
The input equivalent noise current of the amplifier circuit composed of the grounded base amplifier circuit or the grounded gate amplifier circuit, the second transimpedance amplifier, and the differential amplifier is i _eq , and the grounded base amplifier circuit or the grounded gate amplifier circuit The noise current is i _nb , the load resistance of the grounded base amplifier circuit or the grounded gate amplifier circuit is R _B , the transimpedance gain of the grounded base amplifier circuit or the grounded gate amplifier circuit is Z _TP , and the second transimpedance amplifier When the transimpedance gain of −Z _TN , the input impedance of the grounded base amplifier circuit or the grounded gate amplifier circuit is Z _inb , and the input impedance of the second transimpedance amplifier is Z _intia ,

An amplifier circuit characterized by satisfying The amplifier circuit according to claim 1,
Further, when the first transimpedance amplifier is a grounded base amplifier circuit, an emitter follower provided between the output terminal of the grounded base amplifier circuit and one input terminal of the differential amplifier is provided. A characteristic amplification circuit. The amplifier circuit according to claim 1 or 2,
And a feedback circuit that feeds back an output voltage of the grounded base amplifier circuit to a base of a transistor of the grounded base amplifier circuit when the first transimpedance amplifier is a grounded base amplifier circuit. circuit. The amplifier circuit according to any one of claims 1 to 3,
The second transimpedance amplifier is:
A grounded-emitter amplifier circuit or a grounded-source amplifier circuit that receives the current signal; and
An amplifier circuit comprising at least a feedback resistor inserted between an input terminal and an output terminal of the second transimpedance amplifier. The amplifier circuit according to any one of claims 1 to 4,
Further, between the signal input terminal of the amplifier circuit to which the current signal is input and the input terminal of the first transimpedance amplifier, and the signal input terminal of the amplifier circuit and the input terminal of the second transimpedance amplifier; An amplifier circuit comprising an input impedance adjusting element inserted into at least one of the terminals. The amplifier circuit according to claim 5, wherein
The element for adjusting the input impedance is an element consisting of only a resistor, an element consisting of a series circuit of a transmission line and a resistor, or a circuit where an inductor and a resistor are connected in series. An amplifying circuit, wherein the amplifying circuit is any one of elements added with a ground. The amplifier circuit according to any one of claims 1 to 6,
A first amplifier provided between an output terminal of the first transimpedance amplifier and one input terminal of the differential amplifier;
And a second amplifier having an amplification factor different from that of the first amplifier, which is provided between an output terminal of the second transimpedance amplifier and the other input terminal of the differential amplifier. Amplification circuit. The amplifier circuit according to any one of claims 1 to 6,
In the differential amplifier, an amplification factor on the positive input terminal side and an amplification factor on the negative input terminal side are different.

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