JP3457877B2 - Current input circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current input circuit, and more particularly to a photocurrent input circuit which has low power consumption, a large input dynamic range, and high speed and is suitable for use in optical communication.

[0002]

2. Description of the Related Art Conventionally, a circuit as shown in FIG. 2 has been used in a photocurrent input circuit. This circuit is disclosed in JP-A-1
No. 18304 (title of the invention: "preamplifier").

In FIG. 2, feedback is applied so that the base (2-24) voltage of the transistor Q21 becomes a forward drop voltage between the base and emitter of the transistor, that is, Vbe, and the photocurrent output from the photodiode P21 is When there is no input, there is no potential difference across the feedback resistor R22, and the output terminal voltage Vo and the base (2-24) voltage of the transistor Q21 have the same potential.

When the photocurrent output from the photodiode P21 flows into the base (2-24) of the transistor Q21, the current multiplied by the current amplification factor, that is, hfe, is the collector (2-25) of the transistor Q21. Flow to. A voltage drop occurs due to the collector current Ic21 flowing through the collector (2-25) and the resistor R21, and the potential of the base (2-25) of the transistor Q22 decreases.
As a result, the emitter (2-2
The emitter current Ie22 flowing in 3) decreases, and the potential of the output voltage Vo decreases. Base of transistor Q21 (2
Since feedback is applied so that the potential of −24) becomes Vbe, a potential difference is generated across the feedback resistor R22, and a current Ir flows. Eventually, the resistor R23 has an emitter current Ie22 from the transistor Q22. And the feedback resistor R
Ir flowing through 22 flows in. The output voltage Vo is determined by these currents and the resistor R23.

When the photocurrent output from the photodiode P21 increases and the voltage drop across the feedback resistor R22 increases, the diode D21 connected in parallel with the feedback resistor R22 becomes conductive and the current flows to the diode D.
This state has the same effect as the amount of feedback is increased, and the current-voltage conversion gain is reduced, and the amplification operation is stabilized without saturating the transistor even when the photocurrent is large.

In FIG. 2, (2-20) is a power supply terminal and (2-21) is a ground (GND) terminal.

[0007]

However, the above conventional circuit has the following problems.

First, when there is no input of the photocurrent output from the photodiode P21, both ends of the resistor R23 are V
from the power supply terminal (2-20) to the collector (2-22) and the emitter (2-2) of the transistor Q22.
The steady current Ie22 continues to flow through 3). This Ie
The current amount of 22 is proportional to the photocurrent Imax at which the transistor of this circuit can operate without being saturated. Imax is expressed by the following equation.

Imax = (Vbe-Vf) / R23 Vf is the cathode-anode voltage of the diode D21. The steady current at this time is expressed by the following equation.

Ie22 = Vbe / R23 Therefore, the current consumption of this circuit during standby becomes large. Further, for the same reason, Imax cannot be set large, which leads to the limitation of the input dynamic range.

The present invention has been made to solve the above problems in the conventional circuit.

[0012]

As shown in FIG. 1, a current input circuit according to a first aspect of the present invention comprises a first transistor (1-9) and a base (1-) of the first transistor.
2) a second transistor (1-10) sharing a base / collector (1-6) with a collector (1-3) of the first transistor and a base, and
A Wilson type current mirror circuit (1-2) composed of a base / collector and a third transistor (1-11) sharing the emitter, and a signal current source (1-1) A current input circuit connected between a power supply terminal (1-16) and a collector of a first transistor of the Wilson current mirror, wherein the current input circuit is an emitter (1-7) of the second transistor of the Wilson current mirror. By connecting the first resistor (1-13) between the ground terminals (1-15) and increasing the transistor size of the second transistor with respect to the first transistor, the signal current source When the input current output from is small, the amount of current flowing through the collector (1-4) of the third transistor is increased, and conversely, from the signal current source. When the input current force is large, by applying compression to the current, by limiting the amount of current flowing through the collector of said third transistor, it is characterized in that it has a large input dynamic range.

A current input circuit according to a second aspect of the present invention is the current input circuit according to the first aspect, further comprising a fourth transistor sharing a base with the third transistor of the Wilson current mirror. A transistor (1-12) is provided, a second resistor (1-14) is connected between the emitter (1-8) of the fourth transistor and the emitter of the third transistor, and By increasing the transistor size of the fourth transistor with respect to the third transistor, the current compression capability is improved and the input dynamic range is further increased.

Furthermore, the current input circuit of the present invention according to claim 3 is the current input circuit according to claim 1 or 2, wherein when the amount of current output from the signal current source is small, In order to suppress the influence of parasitic capacitance, a constant current source (1-17) is connected between the collector of the first transistor and the power supply terminal.

Furthermore, the current input circuit of the present invention according to claim 4 is the current input circuit according to claim 1, 2 or 3, wherein the signal current source (1-1) is an opto-electric conversion device. It is characterized by using a photodiode (1-18) which is an element.

That is, as shown in the circuit configuration diagram of FIG. 1, in the current input circuit of the present invention, in order to solve the above problems, the circuit configuration is changed from the conventional circuit configuration to the current mirror configuration. The Wilson type current mirror (1-2) was used for the modification, especially for the reason described below. Furthermore, for the first transistor (1-9) forming the Wilson current mirror, the second transistor (1-10) is used.
Of the third transistor (1-11) to the fourth transistor (1-1
The transistor size in 2) was increased. Further, the first resistor (1-13) is connected between the emitter (1-7) of the second transistor and the ground (GND) terminal (1-15),
A second resistor (1-14) was connected between the emitter of the fourth transistor (1-8) and the emitter of the third transistor. Furthermore, the collector (1-3) of the first transistor
Constant current source (1-17) between the power supply terminal (1-16) and
Connected. The direction in which this constant current flows is from the power supply terminal to the collector of the first transistor.

By adopting the above-mentioned current mirror structure, almost no current flows in each transistor when the current (photocurrent) output from the signal current source (photodiode) does not flow. As a result, current consumption during standby can be suppressed. Then, the first transistor connected to the emitter of the second transistor and the emitter of the fourth transistor,
When the current (photocurrent) output from the signal current source (photodiode) becomes large due to the change in the resistance and the second resistance and the transistor size, the current is logarithmically compressed,
Even if a large current is input, voltage conversion can be performed without saturation of the transistor. Also, the introduction of the Wilson current mirror as a current mirror is
This is because the influence of the parasitic capacitance of the first transistor is reduced, and the addition of a constant current source is also intended to reduce the influence of the parasitic capacitance by causing a current to flow through each transistor.
As a result, even when the current (photocurrent) output from the signal current source (photodiode) is very small, the current (photocurrent) is transmitted to the subsequent stage without being impaired by the parasitic capacitance. Further, by supplying a constant current to each transistor, it is possible to cope with a high-speed signal current. The addition of this constant current source increases the current consumption during standby, but at the same input dynamic range, it is much smaller than the conventional circuit system.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 is a circuit configuration diagram of a photocurrent input circuit according to an embodiment of the present invention.

In FIG. 3, the photocurrent output from the photodiode P31 flows to the collector (3-3) of the transistor Q31. At this time, the collector current flowing through the collector (3-3) of the transistor Q31 is Ic31, the current flowing through the collector (3-10) of the transistor Q32 is Ic32, and the emitter (3-7) -GND (3
-15) Connect a resistor R31 between
If the size of the transistor Q32 is set to n times (6 times in the embodiment shown in FIG. 3), the following formula is established.

Ln (Ic31 / Ic32) = q / KT
(Ic32 · R31) -ln (n) q: elementary charge amount = 1.60219 × 10 ⁻¹⁹ [C] T: absolute temperature [K] K: Boltzmann constant = 1.38062 × 10 ⁻³⁴ [J /
K] From the above equation, when the photocurrent output from the photodiode P31 is small, it is amplified by about n times, and the transistor Q
32 as a collector current Ic32. On the other hand, when the photocurrent is large, the resistor R31 works to limit the current amount of the transistor Q32, and the collector current Ic32 is logarithmically compressed.

As a result, the input dynamic range of photocurrent is increased. Since the Wilson type current mirror (3-2) is used, the transistor Q3
Since the collector (3-3) of 1 is almost fixed to twice Vbe from GND (3-15), the transistor Q3
The influence of the parasitic capacitance between the collector (3-3) and the base (3-10) of 1 can be reduced. As a result, when the photocurrent output from the photodiode P31 is very small, the collector (3-3) / base (3-10) of the transistor Q31.
To reduce the problem that a signal is not transmitted to the subsequent stage due to charging / discharging of the parasitic capacitance between them, or the photocurrent signal flowing when a high-speed optical signal is applied to the photodiode P31 has a blunted waveform due to the parasitic capacitance. You can

In FIG. 3, (3-16) is a power supply terminal, Q33 is a Wilson type current mirror (3-
2) the third transistor, (3-5) is its collector, R33 is its collector resistance, Ic33
Is its collector current and Vo is the output terminal voltage.

(Other Embodiment 1) FIG. 4 is a circuit configuration diagram of a photocurrent input circuit according to another embodiment of the present invention.

The circuit of FIG. 4 has a third transistor Q43 of the Wilson type current mirror (4-2) and a base (4).
-3) Add a fourth transistor Q44 that shares
Moreover, a resistor R is provided between the emitter (4-8) of the transistor Q44 and the emitter (4-10) of the transistor Q43.
42 is connected. Also, the transistor Q43
On the other hand, the size of the transistor Q44 is m times (20 times in the embodiment of FIG. 4). At this time, the transistor Q
Collector current Ic4 flowing through the collector (4-4) of 43
3 and the collector current Ic44 flowing in the collector (4-5) of the transistor Q44 satisfy the following equation.

Ln (Ic43 / Ic44) = q / KT
(Ic44.R42) -ln (m) Ic43 + Ic44 = Ic42 Therefore, the collector current Ic42 logarithmically compressed by the transistor Q42 is further logarithmically compressed by the transistors Q43 and Q44. This makes it possible to process a larger photocurrent.

In FIG. 4, (4-16) is a power supply terminal and (4-15) is a ground terminal. Also, Q41
Is a first transistor forming the Wilson current mirror (4-2), Ic41 is its collector current, and P41 is a photodiode. Furthermore, R4
1 is a resistor connected between the emitter (4-7) of the second transistor 42 and the ground terminal (4-15), and R4
3 is the collector resistance of the fourth transistor Q44, Vo
Is the output terminal voltage.

(Other Embodiment 2) FIG. 5 is a circuit configuration diagram of a photocurrent input circuit which is still another embodiment of the present invention.

In the circuit of FIG. 5, a constant current source It is provided between the collector (5-3) of the first transistor Q51 forming the Wilson current mirror (5-2) and the power supply terminal (5-16). It is connected. In the circuit system of the present invention, unlike the conventional circuit (FIG. 2), the photodiode P5
When the photocurrent from 1 is not input, almost no current flows in each transistor. When light is applied to the photodiode P51 in this state and a photocurrent flows through the collector (5-3) of the transistor Q51, the parasitic capacitance of each transistor is charged first, resulting in loss of response. At this time, if the speed of the optical signal applied to the photodiode P51 is slow, there is no problem so much,
When handling a high-speed signal in optical communication or the like, there is a problem that the signal is not transmitted due to the waveform rounding due to the loss of the response time. Therefore, by adding the above-mentioned constant current source, a current is constantly supplied to each transistor to improve the responsiveness.

In FIG. 5, (5-15) is a ground terminal and Q52 is a Wilson type current mirror (5-2).
The second transistor R51 that forms the second transistor Q51 includes an emitter (5-7) of the second transistor Q52 and a ground terminal (5-
15) a first resistor connected between the two, Q53 is the same third transistor, Q54 is the third transistor Q53
A fourth transistor R52 sharing a base with is a second resistor R52 connected between the emitter (5-8) of the fourth transistor Q54 and the emitter (5-10) of the third transistor Q53, and R53 is , The fourth transistor Q54
, And Vo is the output terminal voltage.

[0031]

As described in detail above, the current input circuit of the present invention has the following effects.

(1) By using the Wilson type current mirror method for the (optical) current input circuit, the current consumption during standby can be greatly reduced. In the circuit configurations of FIGS. 3 and 4, the dark current of the photodiode is the only current that flows during standby, which is a current of the order of nA even if the total of the currents that flow through the current mirrors is very small. In addition, the circuit configuration in which the constant current source It shown in FIG.
Even with 10 μA, the current consumption during standby is 270 μA from the graphs of FIGS. 6 and 7, which is much smaller than when the maximum allowable input current value is 10 mA in the circuit configuration of FIG.

(2) By connecting a resistor to the emitter of the Wilson type current mirror and performing logarithmic compression on the input current when the photocurrent is large, the input dynamic range can be greatly increased. In the circuit of Fig. 3, set the power supply voltage to 3
When it is set to V, the collector (3-5) of the transistor Q33 is 1.
Must be 4V or higher. Therefore, the voltage drop across the resistor R33 must be 1.6 V or more. If R33 = 2 kΩ, the maximum current value of Ic33 is 800 μA, and the maximum allowable input current value is 600 μA from the graph of FIG.

(3) According to the current input circuit of the present invention according to claim 2, the output side transistor Q43 of the Wilson type current mirror (4-2) and the transistor Q44 sharing the base are connected, and the transistors are connected to each other. By connecting the emitters with the resistor R42, two-stage logarithmic compression can be applied and a larger input dynamic range can be obtained. In the circuit of FIG. 4, when the power supply voltage is set to 3 V, the transistor Q44 operates in a non-saturated state.
If 3 = 2 kΩ, the maximum current value of the collector current Ic44 of the transistor Q44 is 800 μA, and the maximum allowable input current value is 10 mA or more from the graph of FIG.

(4) According to the current input circuit of the third aspect of the present invention, the constant current source It is connected to the collector (5-3) of the input side transistor Q51 of the Wilson current mirror (5-2). As a result, the influence of the parasitic capacitance of each transistor can be reduced and the response speed can be increased.

(5) According to the current input circuit of the present invention according to claim 4, it is possible to provide a photocurrent input circuit which is extremely suitable for use in high-speed optical communication.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a (photo) current input circuit of the present invention.

FIG. 2 is a circuit configuration diagram of a conventional photocurrent input circuit.

FIG. 3 is a circuit configuration diagram of a photocurrent input circuit which is an embodiment of a current input circuit of the present invention.

FIG. 4 is a circuit configuration diagram of a photocurrent input circuit which is another embodiment of the current input circuit of the present invention.

FIG. 5 is a circuit configuration diagram of a photocurrent input circuit which is still another embodiment of the current input circuit of the present invention.

6 is a diagram showing a relationship between input and output currents in the circuit of FIG.

7 is a diagram showing a relationship between input and output currents in the circuit of FIG.

[Explanation of symbols]

(1-1) Signal current source (1-2) Wilson type current mirror (1-9) First transistor (1-10) Second transistor (1-11) Third transistor (1-14) Fourth transistor (1-15) Ground terminal (1-16) Power supply terminal (1-17) Constant current source (1-18) Photodiode

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H04B 10/26 10/28 (56) References JP-A-9-130157 (JP, A) JP-A-63-124009 (JP, A) JP-A-1-300607 (JP, A) JP-A-64-18304 (JP, A) JP-A-9-130165 (JP, A) JP-A-9-298429 (JP, A) JP-A-56 −141609 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H03F 1/00-3/72 H04B 1/18 H04B 10/00-10/28

Claims (4)

(57) [Claims] 1. A first transistor, a second transistor sharing a base and a collector and a collector of the first transistor, a collector and a base of the first transistor, and the second transistor. A Wilson type current mirror circuit composed of a base / collector of the transistor and a third transistor sharing the emitter is used, and a signal current source is provided between the power supply terminal and the collector of the first transistor of the Wilson type current mirror. A current input circuit connected to a first resistor connected between an emitter of the second transistor of the Wilson current mirror and a ground terminal, and a second resistor connected to the first transistor. By increasing the transistor size of the transistor, the input current output from the signal current source When it is open, the amount of current flowing through the collector of the third transistor is increased, and conversely, when the input current output from the signal current source is large, the current is compressed to flow through the collector of the third transistor. A current input circuit characterized in that the input dynamic range is increased by limiting the amount of current. 2. The current input circuit according to claim 1, further comprising a fourth transistor sharing a base with the third transistor of the Wilson current mirror, and the emitter of the fourth transistor and the fourth transistor. The second resistor is connected between the emitter of the third transistor and the transistor size of the fourth transistor is made larger than that of the third transistor, thereby improving the current compression capability and inputting the current. A current input circuit with a wider dynamic range. 3. The current input circuit according to claim 1 or 2, wherein when the amount of current output from the signal current source is small, the effect of parasitic capacitance of each element is suppressed.
A current input circuit characterized in that a constant current source is connected between the collector of the transistor and the power supply terminal. 4. The photocurrent input circuit according to claim 1, 2, or 3, wherein a photodiode, which is an optoelectric conversion element, is used as the signal current source. .