JP2573344B2 - Current-voltage conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to, for example, a broadband current used for converting a photoelectric conversion current into a voltage in an optical transmission device.
The present invention relates to a voltage conversion circuit.

2. Description of the Related Art For example, in an optical transmission device using an optical fiber or the like, a transmitted optical signal is converted into an electric signal by a photodetector such as a photodiode and then used for subsequent electric signal processing. . In this case, the output obtained by the photodetector is a very small current. Therefore, in order to facilitate later signal processing, the small current obtained by the photodetector is usually immediately converted to a voltage. The current-voltage conversion circuit that converts this minute current into voltage has low noise and broadband characteristics because it handles very little current and usually contains extremely high frequency components. Is required.

FIGS. 2 and 3 show such a current / voltage conversion circuit.
The circuit shown in the figure is known (IEEE J 20 OURN
AL OF SOLID-STATE CIRCUITS, VOL.SC-21, NO.4, AUG
UST 1986, P530-533) FIG. 2 is a block diagram schematically showing a conventional current / voltage conversion circuit, and FIG. 3 is a circuit diagram showing a detailed circuit example of FIG.

In FIG. 2, reference numeral 1 denotes a transimpedance amplifier circuit, reference numeral 2 denotes a differential amplifier circuit, and reference numeral 3 denotes a reference voltage generation circuit.

The transimpedance amplifier circuit 1 outputs a voltage corresponding to the current applied to the input terminal 1a from an output terminal 1b, and the output terminal 1b is one of two inputs of the differential amplifier circuit 2. Input terminal 2a ₁
It is connected to the. Further, the reference voltage generating circuit section 3
Is for outputting a constant voltage as a reference from the output terminal 3b, the output terminal 3a is connected to the input terminal 2a ₂ is an input of the other of said differential amplifier circuit section 2. Further, the differential amplifier circuit section 2 includes two input terminals 2a ₁ and 2a ₂
, And differentially amplifies the input voltage applied from the _first and _second output terminals 2b1 and 2b2.

As shown in detail in FIG. 3, the transimpedance amplifier circuit section 1 includes a transistor TR ₁ for amplifying a current input from the input terminal 1a.
When a transistor TR ₂ constituting an emitter follower circuit for transmitting the output of the transistor TR ₁ to the next stage of the voltage amplifier circuit, the transistor TR ₃ for voltage amplifying the output of the transistor TR _2, the transistors TR ₃ And a transistor TR ₄ that constitutes an emitter follower circuit for transmitting the output of the transistor to the outside, and furthermore, resistors R ₁ , R ₂ , R ₃ connected to the collector or the emitter of each of these transistors and defining the operation thereof. , R
_4, has a R _6, R _7, so that taking out an output from a connection point between the resistor R ₆ and R _7. The resistance R ₅ that is connected between the base of the emitter and the transistor TR ₁ of the transistor TR ₃ is a feedback resistor for determining the conversion rate of the transimpedance amplifier circuit 1.

Further, the differential amplifier circuit 2 includes a transistor TR ₅ and TR ₆ which constitutes the first stage of the differential amplifier, and a transistor TR ₇ and TR ₈ constituting the differential amplifier of the second stage, Further, a transistor TR constituting the first-stage differential amplifier section
₅ and provided with respective collector resistors R ₈ and R ₉ of the TR _6, further, the common emitter and the respective transistors TR ₇ and TR ₈ constituting the differential amplifying portion of the second stage of transistors TR ₅ and TR ₆ the constant current circuit Ic ₁ connected to the emitter of has a Ic _2, Ic _3, the transistor T
From emitters R ₇ and TR ₈ derived is a differential output.

The reference voltage generating circuit 3 includes two transistors TR ₉ and TR ₁₀ which are diode-connected in series with a common collector and base for temperature compensation, and two resistors R _{10 which} are connected in series with these transistors. and consists R ₁₁ Prefecture, derived is a reference voltage from a connection point of the resistors R ₁₀ and R _11.

A drive voltage Vcc is applied to each of the above circuits from a constant voltage circuit (not shown).

FIG. 4 is a graph showing characteristics of the above-described conventional current / voltage conversion circuit. In the figure, the horizontal axis represents the input terminal 1a.
Is the input current (I: relative value), and the vertical axis is the output voltage (V: relative value) of the differential amplifier circuit section 2. Further, a solid straight line I in the figure represents a relationship between the input current and the output voltage of the _first output terminal 2b1, and a solid straight line II represents a relationship between the input current and the output voltage of the _second output terminal 2b2. It represents.

Here, in this type of current / voltage conversion circuit, it is required that the value (I ₀ ) of the input current at the point where the above-mentioned straight lines I and II intersect has a constant value. That is, in this type of current / voltage conversion circuit, the information contained in the input current is determined with reference to the input current value (I ₀ ) at the intersection. For example, when the input current exceeds _I0 , it is used as on information, and when it is less than _I0, it is used as off information. Therefore, the value of the I ₀ is various variations, because there arises a possibility that erroneous reading of information.

[Problems to be Solved by the Invention] By the way, in the above-mentioned conventional current-voltage conversion circuit, considering, for example, the case where the environmental temperature changes, the transimpedance amplifier circuit unit 1 and the reference voltage generation circuit unit 3 are not required. depending on the temperature characteristics, the input current, the relationship between the respective first output an output voltage of the terminal 2b ₁ and the second output terminal 2b ₂ of the output voltage changes. The straight lines III and IV represented by the dotted lines in FIG. 4 respectively represent the relationship between the input current and the output voltages of the two output terminals in that case.

As is clear from these straight lines, the aforementioned solid lines (I and
In the case represented by II) is, those input current is coincident and the output voltage and the output voltage of the output terminal 2b ₂ of the output terminal 2b ₁ when I _0, the table with a dotted line (III and IV) would be consistent with the input current I ₁ that is different from the input current I _0, the input current when the output voltage of the two output terminals are matched is different from each other when being. This is because it is practically impossible to match the temperature characteristics of the transimpedance amplifier circuit 1 and the reference voltage generating circuit 3 because the circuit configurations are different from each other.

As a result, this conventional current / voltage conversion circuit has a drawback that the operating point may fluctuate due to a change in environmental temperature or the like.

Considering the case where a large number of current / voltage conversion circuits having the above-described configuration are manufactured, in order for each product to have the same operating point, the absolute value of each element used in each product is required. It is necessary to make the characteristics, for example, the amplification factor, the same, for all the elements used in all the products. However, in general, it is relatively easy to make the characteristics of each element used in one product uniform, that is, to improve the relative accuracy, but the absolute characteristics are all used in all products. It is extremely difficult to uniformly arrange the elements. For this reason, the product yield rate is extremely poor with the configuration as it is, while, for example, when an adjusting mechanism is provided to improve the product yield rate, there is a disadvantage that productivity is significantly reduced.

The present invention has been made under the above-mentioned background,
It is an object of the present invention to provide a current / voltage conversion circuit having a stable operating point, capable of converting a minute current into a voltage with high accuracy, and having excellent productivity.

[Means for Solving the Problems] The present invention solves the above problems by adopting a configuration including the following elements.

A first transimpedance amplifier circuit that outputs a voltage corresponding to the input current;

A second transimpedance amplifier circuit having the same circuit configuration as the first transimpedance amplifier circuit.

A differential amplifier circuit unit having two inputs connected to respective outputs of the first and second transimpedance amplifier circuit units;

The converted current is applied to the input of the first transimpedance amplifier circuit portion, while the reference current is added to the input of the second transimpedance amplifier circuit portion to output the converted current from the output of the differential amplifier circuit portion. Configuration that takes out a voltage corresponding to the difference between the reference current and the reference current.

[Operation] In the configuration described above, the signals applied to the two inputs of the differential amplifier circuit are the outputs from the two transimpedance amplifiers having the same circuit configuration. Therefore, the relationship between the input current of the first transimpedance amplifier circuit section and the output voltage of the differential amplifier circuit section can be obtained simply by improving the ratio accuracy of each element used in these two circuits. It is relatively easy to always keep the intersection of two straight lines constant.

That is, if the ratio accuracy is good, the two transimpedance amplifier circuit units have the same characteristics (characteristics including temperature characteristics). Even if the characteristics fluctuate due to a temperature change, they are the same. Therefore, the two outputs of the differential amplifier circuit section also change symmetrically, and the position of the intersection does not change. The same applies to the problem of variation between products during mass production.

FIG. 1 is a block diagram schematically showing a current / voltage conversion circuit according to a first embodiment of the present invention, and FIG. 5 is a circuit diagram showing a detailed circuit example of FIG. Hereinafter, the first embodiment will be described in detail with reference to these drawings.

This embodiment has a part of the configuration in common with the conventional one shown in FIG. Therefore, in the following description, common portions are denoted by common reference numerals, detailed description thereof will be omitted, and mainly, portions characteristic of the present embodiment will be described in detail.

In FIG. 1, reference numeral 1 denotes a first transimpedance amplifier circuit, reference numeral 2 denotes a differential amplifier circuit, reference numeral 10 denotes a second transimpedance amplifier circuit, and reference numeral 31 denotes a reference current supply. It is a constant current source.

The first transimpedance amplifier circuit section 1 outputs a voltage corresponding to the current applied to the input terminal 1a to an output terminal.
And outputs from the 1b, the output terminal 1b is connected to the input terminal 2a ₁ which is one input of the two inputs of the differential amplifier circuit section 2. Here, the circuit portion composed of the first transimpedance amplifier circuit portion 1 and the differential amplifier circuit portion 2 corresponds to the transimpedance amplifier circuit portion 1 and the differential amplifier circuit portion in the conventional example (FIG. 2). 2 has the same configuration as the circuit portion composed of

Aspect of this embodiment, the differential amplifier circuit portion 2 of the other input terminals 2a _2, the second transimpedance amplifier circuit having a first transimpedance amplifier circuit section 1 the same circuit configuration as the The output terminal 10b of the constant current source 31 is connected to the input terminal 10a of the second transimpedance amplifier
Is connected.

Then, the differential amplifier circuit 2 outputs the differential output from the two output terminals 2b ₁ and 2b ₂ input voltage applied from the two input terminals 2a ₁ and 2a ₂ differentially amplifies Things.

As shown in FIG. 5, the internal circuit configurations of the first transimpedance amplifier circuit section 1, the second transimpedance amplifier circuit section 10, and the differential amplifier circuit section 2 are the same as those of the conventional example (third embodiment). Transimpedance amplifier circuit section 1 and differential amplifier circuit section 2 in FIG.
Since the internal circuit configuration is completely the same, detailed description thereof will be omitted.

Further, the constant current source 31 is constituted by a circuit capable of supplying a constant current substantially equal to the current applied to the input of the first transimpedance amplifier circuit unit 1.

FIG. 6 is a graph showing characteristics of the current / voltage conversion circuit according to the first embodiment. In the figure, the horizontal axis is the input current (I: relative value) applied to the input terminal 1a, and the vertical axis is the output voltage (V: relative value) of the differential amplifier circuit section 2.

In the sixth figure, a solid line of the straight line I _A and II _A is, there relationship between each of the input current and the first output an output voltage of the terminal 2b ₁ and the second output terminal 2b ₂ of the output voltage at a specific temperature And the dotted straight lines III _A and IV _A represent the input current and the first output terminal at another specific temperature.
It illustrates a relationship between each of 2b ₁ of the output voltage and a second output terminal 2b ₂ of the output voltage.

As it is apparent from the graph of FIG. 6, the value of the input current at the intersection of the intersection and a straight line III _A and IV _A of the straight line I _A and II _A are the same both an I _0. In other words, the current / voltage conversion circuit of this embodiment can maintain the I ₀ even when the temperature changes.
Does not fluctuate.

Further, when viewed in terms of the variation among products at the time of mass production, when having properties characteristic of a product extracted arbitrarily is represented by a straight line I _A and II _A in glove FIG. 6, further optionally The other products extracted usually have a straight line III _A
It has the characteristics described by IV _A. That is, the I ₀ is never vary among products.

Therefore, according to this embodiment, it is possible to obtain a current-voltage conversion circuit having a stable operating point, capable of converting a minute current into a voltage with high accuracy, and having excellent productivity. .

FIG. 7 is a block diagram showing a configuration of a current / voltage conversion circuit according to a second embodiment of the present invention.

In this embodiment, a constant current source 32 is used in place of the constant current source 31 in the first embodiment, and other configurations are the same as those in the first embodiment.

The constant current source 32 optically couples a constant power light source 321 and a photodiode 322 as a light receiving element, and applies a constant current output from the photodiode 322 to an input of the second transimpedance amplifier circuit unit 10. It was made.

According to this, a very small constant current can be obtained relatively easily without using a complicated circuit.

FIG. 8 is a block diagram showing a configuration of a current / voltage conversion circuit according to a third embodiment of the present invention.

This embodiment uses a reference current generator 33 instead of the constant current source 31 in the first embodiment, and the other configuration is the same as that of the first embodiment.

The reference current generator 33 optically couples a light source 331 such as an LD (laser diode) or an LED (light emitting diode) with a photocurrent conversion circuit 332 including a photodiode or the like and outputs the light from the photocurrent conversion circuit 332. The applied reference current is applied to the input of the second transimpedance amplifier circuit section 10.

According to this, for example, it is possible to divert a monitor unit normally provided in an optical signal generation unit (not shown) as the reference current generation unit 33. In this case, if a monitor of the optical signal generating means for generating an optical signal before being applied as an input signal by being photoelectrically converted to the first transimpedance amplifier circuit section 1 is used, the output fluctuation of the optical signal generating means and the like may occur. Some kinds of noise components can be canceled to some extent, and higher precision and lower noise can be achieved.

FIG. 9 is a block diagram showing a configuration of a current / voltage conversion circuit according to a fourth embodiment of the present invention.

In this embodiment, a current that is inversely proportional to a current to be applied to the input of the first transimpedance amplifier circuit unit 1 is used as a reference current instead of the constant current source 31 in the first embodiment. Things. That is, the current to be converted is converted into a current inversely proportional to the current to be converted through the current conversion circuit 34 and is applied to the input of the second transimpedance amplifier circuit section 10. In this case, the current conversion circuit 34 is, for example, a tenth
What is necessary is just to have the characteristic shown by the straight line of the graph of a figure. In FIG. 10, the horizontal axis (i _I ) is the input current, and the vertical axis (i ₀ ) is the output current.

According to this embodiment, a large output voltage can be obtained from the output terminal of the differential amplifier circuit section 2 and a certain noise component can be canceled.
High accuracy and low noise can be achieved.

[Effects of the Invention] As described above in detail, according to the present invention, the two inputs of the differential amplifier circuit section are connected to the outputs of two transimpedance amplifier circuit sections each having the same circuit configuration. A transposed current is applied to one input of the two transimpedance amplifiers, and a reference current is applied to the other input.
The present invention makes it possible to easily prevent a change in the operating point due to a temperature characteristic or a variation between products due to a canceling effect of a variation factor of the two transimpedance amplifier circuits having the same circuit configuration.

[Brief description of the drawings]

1 is a block diagram schematically showing a current / voltage conversion circuit according to a first embodiment of the present invention, FIG. 2 is a block diagram schematically showing a conventional current / voltage conversion circuit, and FIG. 3 is FIG. FIG. 4 is a graph showing characteristics of a conventional current / voltage conversion circuit, FIG. 5 is a circuit diagram showing a detailed circuit example of FIG. 1, and FIG. FIG. 7 is a graph showing the characteristics of the current / voltage conversion circuit according to the first embodiment, FIG. 7 is a block diagram showing the configuration of the current / voltage conversion circuit according to the second embodiment of the present invention, and FIG. FIG. 9 is a block diagram showing a configuration of a current / voltage conversion circuit according to a third embodiment, FIG. 9 is a block diagram showing a configuration of a current / voltage conversion circuit according to a fourth embodiment of the present invention, and FIG. 6 is a graph showing characteristics of the present invention. 1... First transimpedance amplifier circuit section, 2
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Claims (1)

(57) [Claims] A first transimpedance amplifier circuit for receiving a photoelectric conversion current as an input and outputting a voltage corresponding to the input current; and a first transimpedance amplifier having the same circuit configuration as the first transimpedance amplifier circuit. 2 transimpedance amplifier circuit sections, and a differential amplifier circuit section having two inputs connected to respective outputs of the first and second transimpedance amplifier circuit sections, wherein the first transformer The photoelectric conversion current is added to the input of the impedance amplifier circuit section, while the reference current is added to the input of the second transimpedance amplifier circuit, and the photoelectric conversion current and the output are output from the differential amplifier circuit. A current / voltage conversion circuit for extracting a voltage corresponding to a difference from a reference current.