JP2001144683A - I-v conversion circuit for optical transmission reception circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an I-V conversion circuit that can enhance output waveform distortion and configure a reception IC with low power consumption. SOLUTION: The I-V conversion circuit receives a light emitting output of an LED, uses a photoelectric conversion element PIN-PD to convert the received light into a current, uses a resistor R1 to convert the current into a voltage and an amplifier 2 amplifies the converted voltage signal through a coupling capacitor C. The amplified signal is fed back via a clamp circuit 1 to a gate of an N-channel transistor(TR) M1 connected in parallel with the resistor R1. An output of the amplifier 2 (point C) is given to a comparator 3, in which the waveform is shaped and which provides an output of an output signal VO. According to this control, an excess current from the photoelectric conversion element PD is quickly discharged when the input signal level is high so as to quicken the trailing of the I-V conversion output waveform thereby suppressing distortion (thickened waveform) in the output waveform. Furthermore, configuring the circuit by CMOS TRs suppresses waveform distortion and a reception circuit can be manufactured monolithically.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an IV conversion circuit for an optical transmission / reception circuit, and more particularly to an I / V conversion circuit for an optical transmission / reception module.
The present invention relates to an IV conversion circuit for an optical transmission / reception circuit that performs current-voltage conversion in a C receiving circuit.

[0002]

2. Description of the Related Art Hitherto, an IV conversion circuit for an optical transmitting / receiving circuit has been generally applied to an IC receiving circuit of an optical transmitting / receiving module, and has been adopted for an infrared communication system called IrDA. The characteristics required for the receiving circuit specified in the present communication system are 2.4 Kbit / s to 4 Mbit / s,
The output must be in the range of the optical communication distance of 0 cm to 1 m and the waveform is properly shaped from the first pulse.

In recent years, IrDA applications have been changed from notebook personal computers to portable terminals such as PDAs,
Its application range is expanding to mobile phones and the like. Under such circumstances, the optical transceiver module is also required to be driven at a low voltage and consume low power.

An optical transmission / reception circuit (IC) to which a conventional IV conversion circuit is applied usually has a block circuit configuration as shown in FIG. 6, and an IV conversion unit is as shown in FIG. .

FIG. 6 shows a configuration example of a conventional IV conversion circuit for an optical transmission / reception circuit. FIGS. 8 and 9 show examples of IV conversion output waveforms in the circuit of FIG. Conventionally, for the reasons described above, the I-I / O
A V conversion circuit is generally used. In FIG. 6, a resistor R1 is an IV conversion resistor having a resistance value of 1 to 5 KΩ, and a diode Di4 has a clamp voltage VF (0.7
V) for clamping.

The above-mentioned conventional IV conversion circuit is applied to, for example, an optical transceiver module shown in FIG. An optical transceiver module in which the above-described conventional IV conversion circuit is applied as the IV conversion amplifier shown in FIG.
-It is configured to include a PD, an IV conversion amplifier, a capacitor, a signal amplification amplifier, and a comparator. The IV conversion amplifier is a circuit corresponding to the above-described IV conversion circuit for the optical transmission / reception circuit.

[0007] The IV conversion circuit for an optical transmission / reception circuit of the present configuration receives the light emission output of the LED, and outputs the photoelectric conversion element PIN.
-Converts to a current by PD, voltage-converts by an IV converter for an optical transmitting and receiving circuit, further amplifies the converted voltage signal by an amplifier through C-coupling, shapes the waveform by a comparator and outputs it as an output signal VO. Output. Here, the C-bonded state is a constant external light (background light).
This is to remove the signal of the above and stop the operation with the extraneous light.

The receiving IC circuit having the above configuration has a photocurrent of about 10 mA at the time of 0 cm (at the time of close proximity), about 100 nA at a distance of 1 m, and must operate normally with a dynamic range of about 100 dB. Further, an amplifier is inserted after C-coupling for the purpose of minimum signal amplification. However, if the gain of this amplifier is too high, the amplifier is susceptible to oscillation and noise. Therefore, the IV conversion amplifier is designed to gain as much as possible.

Conventionally, for the above reasons, the configuration of an IV conversion circuit for an optical transmitting / receiving circuit as shown in FIG. 6 is a general form. The resistor R1 is an IV conversion resistor having a resistance value of 1
The diode Di1 is used to clamp at a clamp voltage VF (0.7 V) at the time of a large signal.

The "photocurrent conversion circuit" of Japanese Patent Application Laid-Open No. 6-29754 of the prior art 2 discloses a current conversion circuit for converting an optical signal incident on a light receiving element into a current for voltage conversion, and a diode for converting the photoelectric conversion current. And a current-voltage conversion circuit for current-voltage conversion.

[0011]

However, in the circuit configuration in the above-mentioned prior art, as shown in FIG. 9, the output waveform is distorted (fatter) as a large input signal. In addition, there is a problem that low power consumption is disadvantageous due to the bipolar process.

The present invention improves the output waveform distortion, and
It is an object of the present invention to provide an IV conversion circuit capable of configuring a reception IC with low power consumption.

[0013]

To achieve the above object, an IV conversion circuit according to the present invention is an IV conversion circuit for an optical transmission / reception circuit applied to an IC reception circuit of an optical transmission / reception module. In the circuit, the photoelectric conversion element PIN-PD
An amplifier that amplifies the converted output signal from the amplifier, a clamp circuit that controls the discharge characteristic of the converted output signal by the output signal of the amplifier, and a transistor M1 that controls the discharge of the converted output signal by the control signal of the clamp circuit. It is characterized by having been constituted.

A capacitor is further inserted between the output of the photoelectric conversion element PIN-PD and the input of the amplifier. This capacitor eliminates a steady conversion output signal from the photoelectric conversion element PIN-PD. Furthermore, it is preferable that the photoelectric conversion element PIN-PD and the resistor R1 are connected in series between the drive power supply VCC and the ground GND, and the resistor R1 and the transistor M1 are connected in parallel.

Note that the resistance value of the resistor R1 is 1 to 5
It is preferable to further include a comparator for comparing the output of the amplifier with a predetermined reference, and to use the output whose waveform is shaped by the comparator as the output signal VO.

According to a sixth aspect of the present invention, there is provided an I / O circuit for an optical transmitting / receiving circuit.
The -V conversion circuit is a built-in PD that converts an optical signal to an electrical signal.
A built-in dummy PD whose optical signal is shielded by a light shielding material,
A first IV conversion amplifier for amplifying the output signal of the built-in PD, and a second IV amplifying the output signal of the built-in dummy PD
A conversion amplifier, and a comparator that receives an output signal of the first IV conversion amplifier and an output signal of the second IV conversion amplifier and outputs a comparison signal VO. And

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an IV conversion circuit according to the present invention will be described in detail with reference to the accompanying drawings.
1 to 5, there is shown an embodiment of an IV conversion circuit according to the present invention.

First, the outline of the present embodiment will be described below based on comparison with a conventional example. As shown in FIGS. 1 and 2, the IV conversion circuit of the present embodiment includes
The feature is that it is composed of S. This is shown in FIG.
This corresponds to FIG.

Here, the problems of the prior art will be searched for in more detail. A conventional signal diagram will be described with reference to FIGS. 6, 7, 8, and 9. FIG. At the time of a small signal, the optical signal received from the photoelectric conversion element PIN-PD is converted into a current and the resistor R
The voltage is converted at 1 (point E). At this time, since this output voltage is equal to or lower than the clamp voltage VF (0.7 V), the diode Di1 does not turn on. Next, through the C bond (F
Point) Amplified by the amplifier and reaches the comparator (point G).
The comparator shapes and outputs the waveform according to the threshold value determined by the reference voltage.

At the time of a large signal, the output waveform at the point E exceeds the clamp voltage VF.
The waveform is more clamped. At this time, when the input signal is large and the speed is high as shown in FIG. 9, the fall of the front pulse approaches the rear pulse. Due to such a phenomenon, the final output waveform is more distorted (fatter) than in the case of a small signal.

Next, a signal diagram of the circuit according to the present invention will be described with reference to FIGS. 1, 2, 3 and 4. For small signals,
The operation is the same as in the prior art as shown in FIG.

At the time of a large signal (FIG. 4), since the potential at the point B turns on the transistor M1, the excess current from the photoelectric conversion element PD passes through the transistor M1. Here, in order to quickly discharge carriers remaining in the photoelectric conversion element PD when the signal is cut off, the constants of C1 and the resistors R2 and R3 are changed so that the transistor M1 is turned off (T1) with a slight delay. Set it.

Since the transistor M1 is turned off with a delay, the falling of the IV conversion output waveform (point A) becomes faster than in the prior art, and the distortion (thickness) of the output waveform can be suppressed.

(Embodiment) FIGS. 1 and 2 show an embodiment of the present invention. FIG. 1 is a block diagram, which includes an IV conversion circuit section, a small signal amplification amplifier section, a comparator section, and a clamp circuit section. Specifically, a photoelectric conversion element PIN-PD that converts LED light into an electric signal, a clamp circuit 1, an amplifier 2, a comparator 3, an N-channel transistor M1,
It comprises a resistor R1 and a capacitor C.

The photoelectric conversion element PIN-PD and the resistor R1 are connected in series, connected between the driving power supply VCC and the ground GND, and further, an N-channel transistor M1 is connected in parallel with the resistor R1. Here, the IV conversion circuit section and the small signal amplifier 2 are C-coupled by a capacitor C. Note that, except for the photoelectric conversion element PIN-PD, C-
The circuit can be configured as an IC by a standard MOS process.

The IV conversion circuit for the optical transmission / reception circuit of this configuration receives the light emission output of the LED and outputs the light to the photoelectric conversion element PIN.
-Convert to current with PD, convert voltage with resistor R1,
The converted voltage signal is further amplified by the amplifier 2 through C-coupling. The amplified signal is fed back via the clamp circuit 1 and connected to the gate of the N-channel transistor M1 connected in parallel with the resistor R1. The output (point C) of the amplifier 2 is output as an output signal VO after waveform shaping by the comparator 3. Here, the C-coupling is performed in order to remove a signal of stationary extraneous light (background light) so as not to operate with the extraneous light.

FIG. 2 is a circuit diagram showing a configuration example of the clamp circuit 1 of FIG. The clamp circuit applied to the IV conversion circuit of the present invention includes P-channel transistors M2, N
Channel type transistor M3, P channel type transistor M4, N channel type transistor M5, capacitor C
1. It is configured to include resistors R2 and R3.

The clamp circuit according to the present embodiment includes a resistor R2,
Each of P-channel transistor M2, N-channel transistor M3, resistor R3, and P-channel transistor M4 and N-channel transistor M5 is connected in series between power supply VCC and GND. The base terminals of the P-channel transistor M2 and the N-channel transistor M3 and the base terminals of the P-channel transistor M4 and the N-channel transistor M5 are connected. Further, the base connection point of the transistor M2 and the transistor M3 is connected to the connection point of the drain of the transistor M4 and the source of the transistor M5. Note that a connection point between the drain of the transistor M2 and the source of the transistor M3 is connected to the base of the N-channel transistor M1, and a connection point between the base of the transistor M4 and the base of the transistor M5 is an output terminal (point C).

The clamp circuit composed of the above components adjusts the timing of the gate voltage of the N-channel transistor M1 so that the IV conversion output waveform (point A) is not distorted.

(Explanation of Operation) An embodiment of the present invention will be described with reference to FIG. 1, FIG. 2, FIG. 3, and FIG. As described above, the photocurrent input from the photoelectric conversion element PIN-PD is IV-converted by the resistor R1. Usually a resistor R
Since the response speed is limited by 1 and the capacitance of the photoelectric conversion element PIN-PD, the resistor R1 is usually set to 1 to 5 KΩ.

When the input signal becomes large (IPD = 100 μA) and the output (point C) exceeds about 2 V, the gate potential (point B) of the transistor M1 becomes 1.5 V or more,
The transistor M1 turns on, and the excess current
Flow 1

Next, when the signal is cut off, the resistor R3
(5 to 10 KΩ), and due to the discharging time of the capacitor C1 (1 to 5PF), the transistor M1 is still in the ON state during the time T1 (several tens of nanoseconds).

While the transistor M1 is ON, the carrier of the photoelectric conversion element PIN-PD is discharged through the transistor M1, so that the IV conversion output waveform falls faster than the discharge by the resistor R1. Can be. Therefore, distortion (thickening) of the VO output waveform is suppressed to a small value.

(Explanation of Effect) By constructing the circuit configuration as shown in FIGS. 1 and 2 with C-MOS, it is possible to suppress the waveform distortion and to manufacture a receiving circuit monolithically by C-MOS. Low power consumption is also facilitated.

(Other Embodiment) FIG. 5 shows another embodiment of the present invention. The basic configuration of the IV converter is composed of the clamp circuit using the resistor R1 and the transistor M1 as described above.

Here, the present IC has a built-in photoelectric conversion element PD and determines the threshold value by making the reference voltage have the same circuit configuration as the signal side. At this time, a dummy PD is placed on the reference side, and light is shielded by aluminum so that light does not enter. The state of signal transmission is almost the same as in FIGS. 3 and 4, and it may be considered that the signal is transmitted directly from the output of point A to point B.

The advantage of this configuration is that the reference side has exactly the same configuration as the signal side, so that the relative accuracy is good and the variation in threshold value can be reduced.

The above embodiment is an example of a preferred embodiment of the present invention. However, it is not limited to this.
Various modifications can be made without departing from the spirit of the present invention.

[0039]

As is apparent from the above description, the IV conversion circuit according to the first aspect of the present invention includes a photoelectric conversion element PIN.
Control the discharge characteristics of the converted output signal from the PD, and control the discharge of the converted output signal by this control signal. With this control, at the time of a large signal, the surplus current from the photoelectric conversion element PD is discharged quickly, the falling of the IV conversion output waveform is made faster, and the distortion (thickness) of the output waveform can be suppressed. . In addition, by configuring the circuit configuration with a C-MOS, it is possible to suppress the waveform distortion and to manufacture the receiving circuit monolithically.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing a configuration example of a clamp circuit 1 of FIG.

FIG. 3 is a diagram showing an example of a pulse response at the time of a small signal.

FIG. 4 is a diagram showing an example of a pulse response at the time of a large signal.

FIG. 5 is a block diagram showing a second embodiment of the IV conversion circuit of the present invention.

FIG. 6 is a circuit diagram showing a configuration example of a conventional IV conversion circuit.

FIG. 7 is a block diagram of a conventional optical transceiver IC circuit.

FIG. 8 is a diagram showing an example of a conventional pulse response at the time of a small signal.

FIG. 9 is a diagram showing an example of a conventional pulse response at the time of a large signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Clamp circuit 2 Amplifier 3 Comparator C, C1 Capacitor M1, M3, M5 N-channel transistor M2, M4 P-channel transistor PIN-PD (PD) Photoelectric conversion element R1, R2, R3 Resistor VCC Power supply

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/26 10/14 10/04 10/06 F term (Reference) 5J090 AA01 AA56 CA21 CA36 FA10 FA17 GN01 GN06 HA10 HA17 HA19 HA25 HA29 HA39 HA44 KA17 KA21 MA11 TA06 5J092 AA01 AA56 CA21 CA36 FA10 FA17 HA10 HA17 HA19 HA25 HA29 HA39 HA44 KA17 KA21 MA11 TA06 UL02 5K002 AA03 BA07 CA01 DA07

Claims (6)

[Claims] 1. An IV conversion circuit for an optical transmission / reception circuit applied to an IC reception circuit of an optical transmission / reception module, comprising: an amplifier for amplifying a conversion output signal from a photoelectric conversion element PIN-PD; and an output signal of the amplifier. And a transistor M1 for controlling discharge of the converted output signal by a control signal of the clamp circuit. Conversion circuit. 2. A capacitor is further inserted between the output of the photoelectric conversion element PIN-PD and the input of the amplifier, and the capacitor converts the input of the photoelectric conversion element PIN-PD.
2. An IV conversion circuit for an optical transmission / reception circuit according to claim 1, wherein said stationary conversion output signal from said optical transmission and reception circuit is excluded. 3. A configuration in which the photoelectric conversion element PIN-PD and a resistor R1 are connected in series between a driving power supply VCC and a ground GND, and the resistor R1 and the transistor M1 are connected in parallel. 3. A method according to claim 1, wherein
An IV conversion circuit for an optical transmission / reception circuit according to claim 1. 4. The IV conversion circuit for an optical transmission / reception circuit according to claim 1, wherein the resistance value of said resistor R1 is 1 to 5 KΩ. 5. The circuit according to claim 1, further comprising a comparator for comparing an output of said amplifier with a predetermined reference, and an output whose waveform has been shaped by said comparator is used as an output signal VO. An IV conversion circuit for an optical transmission / reception circuit according to claim 1. 6. A built-in PD for converting an optical signal into an electric signal
A built-in dummy PD whose light signal is shielded by a light-blocking material, a first IV conversion amplifier for amplifying an output signal of the built-in PD, and a second amplifying the output signal of the built-in dummy PD. IV
A conversion amplifier; an output signal of the first IV conversion amplifier;
And a comparator that receives the output signal of the -V conversion amplifier and outputs a comparison signal VO; and an IV conversion circuit for an optical transmission / reception circuit, comprising: