JP4048819B2 - Photoelectric conversion device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photoelectric conversion device incorporating a limiter circuit suitable for a semiconductor integrated circuit.
[0002]
[Prior art]
FIG. 4 shows a circuit example of a conventional photoelectric conversion device. The photodiode 401 has an anode grounded and a cathode connected to the limiter circuit 412. The limiter circuit 412 is connected to the inverting input terminal of the operational amplifier 402, the resistor 403, and the cathode of the diode 404, the anode of the diode 404 is connected to the output terminal of the operational amplifier 402, and the resistor 403 and the diode 404 are connected in parallel. It becomes the composition.
[0003]
The operation of this photoelectric conversion device is described below. A voltage drop is caused by the current Ipd generated by the light incident on the photodiode 401 flowing through the resistor 403, and the current Ipd with respect to the reference voltage supplied by the reference voltage source 405 connected to the non-inverting input terminal of the operational amplifier 402 is generated. A voltage of × R is generated at the output terminal 410. However, since the diode 404 is connected in parallel with the resistor 403, when the output voltage becomes a diode voltage of about 0.7V with respect to the reference voltage (hereinafter referred to as “VD”), the diode 404 is turned on, and more than that Even if a current is generated in the diode 401, the current flows through the diode 404. Therefore, the resistor 403 does not flow beyond the current value at which the output voltage becomes VD with respect to the reference voltage. Therefore, the output voltage is limited by VD with respect to the reference voltage. By adopting such a structure, it is possible to limit the output voltage with VD even for a large-amplitude optical input signal that saturates the operational amplifier 402. Since the operational amplifier 402 is not saturated, a high-speed response characteristic is obtained. It is done.
[0004]
[Problems to be solved by the invention]
Although the conventional photoelectric conversion device is configured as described above, since the output voltage can be set only with VD or an integer multiple of VD with respect to the reference voltage, the degree of freedom is very low. When there is a limiter circuit as shown in FIG. 5C, the output voltage can be set to a voltage determined by the limiter circuit (hereinafter referred to as a limiter voltage). In this case, the limiter voltage is VD or a value that is an integral multiple of VD with respect to the reference voltage. Furthermore, by setting this voltage lower than the saturation voltage of the operational amplifier, the high-speed response characteristic described above can be obtained. However, in the configuration of the limiter circuit 412, the limiter voltage also fluctuates when the reference voltage changes. For this reason, the limiter voltage may become larger than the saturation voltage of the operational amplifier due to the fluctuation of the reference voltage. Once the operational amplifier is saturated, it takes a certain time to return from the saturated state to the normal state, and there is a problem that the response characteristic to the optical input signal deteriorates.
[0005]
In general, the saturation voltage of an operational amplifier is determined with a constant voltage based on a voltage for driving the operational amplifier (hereinafter referred to as a power supply voltage). Therefore, when the power supply voltage decreases, the saturation voltage also decreases. . For this reason, when the limiter voltage exceeds the saturation voltage, there is a problem that the response characteristic with respect to a large-amplitude optical input signal is deteriorated.
[0006]
Furthermore, even when measures such as lowering the reference voltage or increasing the power supply voltage are taken to secure the dynamic range, there is a problem that the dynamic range does not exceed VD.
[0007]
The present invention is intended to solve the above-described problems. The limiter voltage of the photoelectric conversion device can be freely set, and even if the reference voltage or the power supply voltage fluctuates, a large-amplitude optical input is possible. A stable and high-speed response characteristic can be obtained with respect to a signal.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, in the photoelectric conversion device of the present invention, a photodiode is connected to an inverting input terminal of an operational amplifier and an output terminal via a resistor, and an output of the operational amplifier is a base of an NPN transistor and a PNP transistor. The collector of the NPN transistor is connected to a voltage source, the emitter is connected to a current source and an output terminal, the base of the PNP transistor is connected to a limiter voltage source, and the collector is connected to GND. .
[0009]
According to this configuration, the voltage at the output terminal can be the voltage of the limiter voltage source. Since the voltage of the limiter voltage source can be set freely and can be set independently of the reference voltage source, a stable response characteristic can be obtained even when the reference voltage varies.
[0010]
Further, by using a bias circuit that changes the voltage while maintaining a constant voltage with respect to the voltage change of the voltage source as the limiter voltage source, a stable response characteristic can be obtained even with respect to fluctuations in the power supply voltage.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments according to the present invention will be described below with reference to the drawings.
[0012]
(Embodiment 1)
FIG. 1 is a circuit diagram of the photoelectric conversion apparatus according to Embodiment 1 of the present invention. The photodiode 101 has an anode connected to GND and a cathode connected to a limiter circuit 112. In the limiter circuit 112, the inverting input terminal of the operational amplifier 102 is connected to the output terminal 110 via the resistor 103. The base of the NPN transistor 106 is connected to the output terminal of the operational amplifier 102 and the emitter of the PNP transistor 107, the collector is connected to the power supply voltage source 108, and the emitter is connected to the current source 109 and the output terminal 110. Further, the base of the PNP transistor 107 is connected to the limiter voltage source 111 and the collector is connected to GND.
[0013]
Next, the circuit operation in the present embodiment will be described in detail.
[0014]
Since the input current of the operational amplifier 102 is negligibly small among the current I generated in the photodiode 101 when light is incident, most of the current flows through the resistor 103. Therefore, a voltage obtained by multiplying the current I by the resistance value R of the resistor 3 with respect to the voltage of the reference voltage source 105 is further generated at the output terminal 110. When the input current increases and the voltage at the output terminal 110 increases, the base voltage of the NPN transistor 106 increases while maintaining the base-emitter voltage (hereinafter referred to as “VBE”) of the transistor with respect to the emitter voltage. VBE is about 0.7V.
[0015]
Since the VBE of the NPN transistor 106 and the VBE of the PNP transistor 107 are designed to be substantially equal, the PNP transistor 107 is turned on when the voltage at the output terminal 110 reaches the voltage of the limiter voltage source 111, and the emitter of the PNP transistor 107. The voltage is fixed to a voltage of VBE with respect to the voltage of the limiter voltage source 111 which is a base voltage. Since the VBE of the NPN transistor 106 and the VBE of the PNP transistor 107 are substantially equal, the emitter voltage of the NPN transistor 106, that is, the voltage of the output terminal 110 is fixed by the voltage of the limiter voltage source 111, and does not increase further. Therefore, even when a large amplitude optical signal is incident by setting the voltage of the limiter voltage source 111 to a voltage that does not saturate the operational amplifier 102, the output voltage is limited by the limiter voltage before the operational amplifier 102 saturates. High-speed response characteristics can be obtained for input signals.
[0016]
Even when the voltage of the reference voltage source 105 changes, the limiter voltage can be set independently of the voltage of the reference voltage source 105 according to the present embodiment. In other words, the limiter voltage can be easily set so as not to exceed the saturation voltage of the operational amplifier 2 as shown in FIG.
[0017]
Even if the collector of the PNP transistor 107 is connected to the inverting input terminal of the operational amplifier 102, the same effect as described above can be obtained.
[0018]
(Embodiment 2)
FIG. 3 is a circuit diagram of the photoelectric conversion apparatus according to Embodiment 2 of the present invention.
[0019]
The present embodiment differs from the configuration shown in FIG. 1 in that the limiter voltage source is configured as a bias circuit 312 that changes while maintaining a constant voltage with respect to the power supply voltage source 308. Has the same configuration as FIG.
[0020]
In this embodiment, the saturation voltage of the operational amplifier 302 is determined to be a constant value with respect to the voltage of the power supply voltage source 308. This is the same as in the first embodiment, and the saturation voltage of the operational amplifier 102 changes while maintaining a constant value with respect to the voltage of the power supply voltage source 108.
[0021]
In the present embodiment, the output voltage of the bias circuit 312 also changes while maintaining a constant voltage with respect to the power supply voltage source 308. Therefore, as shown in FIG. 2D, even when the voltage of the power supply voltage source 308 changes, the relationship between the voltage of the output terminal 310 where the operational amplifier 302 is saturated and the output voltage of the bias circuit 312 is always kept constant. Since the limiter voltage can always be limited by the output voltage of the bias circuit 312, a high-speed response characteristic can be obtained with respect to a large amplitude optical input signal.
[0022]
This will be described in more detail.
[0023]
First, a circuit example of the bias circuit 312 is as shown in FIG. The emitter of the PNP transistor 313 is connected to the power supply voltage source 308, the collector and base are connected to the emitter of the PNP transistor 314, the collector and base are connected to GND via the base of the PNP transistor 318 and the resistor 315, and the collector of the PNP transistor 318. Is connected to GND via a resistor 319, the emitter is connected to a power supply voltage source 308 via a resistor 317 and a resistor 316, the base of the NPN transistor 320 is connected to the resistor 317 and the resistor 319, and the collector is connected to the power supply voltage source 308. The emitter is connected to GND via a terminal 321 and a resistor 322. In this circuit, since the voltage across the terminals 321 and 317 is always constant at VBE in this circuit, the values of the terminal 321, power supply voltage source 308, resistor 316, and resistor 317 are V1, V2, R1, and R2, respectively. Then, it is expressed by the following formula.
[0024]
V1 = V2−VBE × R1 / (R1 + R2) −VBE (Formula 1)
Equation 1 means that the voltage value V1 of the terminal 321 is always kept at a constant voltage with respect to the voltage value V2 of the power supply voltage source 308. Further, the voltage of the terminal 321 can be freely set by changing the ratio of the resistor 316 and the resistor 317.
[0025]
【The invention's effect】
With the configuration shown in the present invention, the limiter voltage can be freely set by an external voltage source, and even if the power supply voltage or the reference voltage varies, the limiter voltage may exceed the output voltage at which the operational amplifier saturates. Therefore, there is an effect that a high-speed response is possible for a large amplitude optical input signal.
[0026]
In addition, the power supply voltage and the reference voltage can be set regardless of the limiter voltage, the dynamic range of the operational amplifier can be expanded, and a photoelectric conversion device with a wide operation margin can be obtained.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a photoelectric conversion device according to Embodiment 1 of the present invention. FIG. 2 is a response waveform of the photoelectric conversion device according to Embodiments 1 and 2 of the present invention.
(A) A diagram showing an input signal (b) A diagram showing an output voltage when there is no limiter circuit (c) A diagram showing an output voltage when a limiter circuit is provided (d) A case where a limiter circuit is provided, and FIG. 3 is a circuit diagram of a photoelectric conversion device according to a second embodiment of the present invention. FIG. 4 is a circuit diagram of a conventional photoelectric conversion device. The response waveform of the photoelectric conversion device of
(A) A diagram showing an input signal (b) A diagram showing an output voltage when there is no limiter circuit (c) A diagram showing an output voltage when a limiter circuit is provided (d) A case where a limiter circuit is provided, and Diagram showing output voltage when reference voltage rises [Explanation of symbols]
101, 301, 401 Photodiode 102, 302, 402 Operational amplifier 103, 303, 315, 317, 319, 322, 403 Resistor 105, 305, 405 Reference voltage source 106, 306 NPN transistor 107, 307, 313, 314, 318 PNP Transistors 108 and 308 Power supply voltage sources 109 and 309 Current sources 110, 310 and 410 Output terminal 111 Limiter voltage source 112 and 412 Limiter circuit 312 Bias circuit 321 Output terminal 404 of bias circuit 312 Diode

Claims (4)

A photodiode that converts an optical signal into a current signal is connected to an inverting input terminal of the operational amplifier and an output terminal through a resistor that converts the current signal into a voltage signal. The output of the operational amplifier is connected to the base of the NPN transistor and the PNP transistor. The NPN transistor has a collector connected to a power supply voltage source, an emitter connected to a current source and an output terminal, a base of the PNP transistor connected to a limiter voltage source, and a collector connected to GND. Photoelectric conversion device. 2. The photoelectric conversion device according to claim 1, wherein the voltage of the limiter voltage source is set lower than a saturation voltage of the operational amplifier. 3. The photoelectric conversion apparatus according to claim 1, wherein the limiter voltage source is a bias circuit whose output changes depending on the voltage of the power supply voltage source. The bias circuit includes:
An emitter of a first PNP transistor is connected to the power supply voltage source, a collector of the first transistor is connected to a base of the first transistor and an emitter of a second PNP transistor, and the second PNP A collector of the transistor is connected to a base of the second PNP transistor and one end of the first resistor, and the other end of the first resistor is connected to GND;
One end of the second resistor is connected to the power supply voltage source, the other end of the second resistor is connected to one end of the third resistor and the base of the first NPN transistor, and the other of the third resistor The end is connected to the emitter of the third PNP transistor, the base of the third PNP transistor is connected to the base and collector of the second PNP transistor, and the collector of the third PNP transistor is connected to the fourth resistor. Connected to one end, and the other end of the fourth resistor is connected to GND,
The collector of the first NPN transistor is connected to the power supply voltage source, the emitter is connected to one end of a fourth resistor, and the other end of the fourth resistor is connected to GND,
4. The photoelectric conversion device according to claim 3, wherein an emitter voltage of the first NPN transistor is used as an output voltage of the bias circuit.

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