CN214583654U

CN214583654U - Device for improving dynamic range of photodiode

Info

Publication number: CN214583654U
Application number: CN202120706532.2U
Authority: CN
Inventors: 崔建国; 宁永香; 崔燚
Original assignee: Shanxi Institute of Technology
Current assignee: Shanxi Institute of Technology
Priority date: 2021-04-08
Filing date: 2021-04-08
Publication date: 2021-11-02
Anticipated expiration: 2031-04-08

Abstract

The utility model discloses a device for improving the dynamic range of a photodiode, which comprises a +12V power supply circuit, a photodiode circuit, a common emitter amplifier circuit, a base bias circuit, an integrating circuit and an in-phase proportional operation circuit; the common emitter amplifier circuit is composed of a transistor T1, resistors R1 and R2, a +12V power supply circuit is connected and operated sequentially through C-E poles of phototubes D1 and T1, a collector of T1 is connected and operated sequentially through resistors R1 and R2 to a base of T1, an integrating circuit is composed of a resistor R1 and a capacitor C1, a collector of T1 is connected and operated sequentially through R1 and C1, a same-phase proportional operational circuit is composed of an operational amplifier N1, resistors R4 and R5, a collector of T1 is connected and operated sequentially through a resistor R3 to a pin 2 of an operational amplifier N1, an output end of the operational amplifier N1 is connected and operated sequentially through R4 to a pin 3 of an operational amplifier N1, a pin 3 of the operational amplifier N1 is connected and operated sequentially through R5, and an output end of the operational amplifier N1 is an effective signal after amplification.

Description

Device for improving dynamic range of photodiode

Technical Field

The utility model relates to an improve photodiode work dynamic range's technique, especially one kind can increase photodiode's dynamic range, does not sacrifice its amplification again, and both sides are taken into account, and this kind of circuit can also the filtering slowly become (low frequency) light intensity's influence moreover to the various problems that the messenger arouses because of light changes on every side reduce widely.

Background

Photodiodes are commonly used as photodetectors, such devices comprising a p-n junction and usually an intrinsic layer between the n and p layers, the devices with an intrinsic layer being called PIN photodiodes, the depletion layer or intrinsic layer generating, upon absorption of light, electron-hole pairs which contribute to the photocurrent which is strictly proportional to the intensity of the absorbed light over a large power range.

The current-voltage characteristic of a photodiode is shown in fig. 1, and the photodiode can operate in two different modes: 1) photovoltaic mode: similar to solar cells, the voltage produced by a photodiode exposed to light can be measured, however, the relationship between voltage and optical power is non-linear and has a relatively small dynamic range and also does not reach peak velocity, as in the first quadrant of the curve of fig. 1.

2) Photoconductive mode: when a reverse voltage is applied to the diode (i.e. the diode is not conducting in the absence of incident light at a voltage in that direction), and the resulting photocurrent, which is sufficient if the voltage at the cell end remains close to 0, is measured, the photocurrent depends very linearly on the optical power and has a magnitude six orders of magnitude or more greater than the optical power, for example, for an active region of a few mm²The latter from a few nanowatts to a few tens of milliwatts, the magnitude of the reverse voltage has little effect on photocurrent and little effect on dark current (without light), but the higher the voltage, the faster the response and the faster the device heats up, as shown in the third quadrant of fig. 1.

Common negative impedance amplifiers are typically used for pre-amplification of the photo-current of the photodiode, such amplifiers holding the voltage constant (e.g. close to 0, or some adjustable negative number) so that the photodiode operates in photoconductive mode, typically with a large gain of the negative impedance amplifier.

Many modular circuits for optical communication, which are currently in use or commercially available, transmit information by modulating optical signals and then transmit the information to a terminal via optical fibers or direct infrared rays, and an optical receiver used in the terminal generally consists of one or more photodiodes.

In this type of device, it is very important to guarantee the dynamic range of the photodiode, however, the increase of the dynamic range of the photodiode reduces its sensitivity a lot, and another disadvantage of the photodiode is that it is very sensitive to the variations of the light intensity of the surrounding environment.

For example, when detecting input light with small optical power, the signal is submerged in noise due to low signal-to-noise ratio, and a useful signal cannot be accurately detected; or when detecting input light with high optical power, saturation distortion of the signal may be caused due to a large transimpedance gain.

As another example, infrared communication is a communication method using infrared to transmit information, but an incandescent light bulb can also be called an infrared light source, and an incandescent light bulb can convert 75% of its electric energy into infrared radiation light, so it can also be called an infrared light source, but because the infrared radiation emitted by the incandescent light bulb is absorbed by its outer glass shell, it presents a small amount of infrared light, so it is a light source close to infrared light, and the intensity of the infrared light is not small compared with the useful infrared light signal received by the photoelectric tube of the terminal, and the sensitivity of the optical receiver is greatly affected by the light beam.

Therefore, the influence of the illumination light on the photoelectric tube cannot be ignored, and how to filter the infrared signals is also a problem to be solved.

A circuit is designed, which can increase the dynamic range of the photodiode without sacrificing its amplification, and can filter the influence of slowly-varying (low-frequency) light intensity, thereby greatly reducing various problems caused by ambient light variation.

Disclosure of Invention

The utility model aims to solve the technical problem that a technique that simple structure, low in cost, use are reliable can improve photodiode work dynamic range is provided.

In order to achieve the above object, the present invention provides a device for increasing the dynamic range of a photodiode, which comprises a +12V power supply circuit, a photodiode circuit, a common emitter amplifier circuit, a base bias circuit, an integrating circuit, and a same-phase proportional operation circuit; the common emitter amplifier circuit is composed of a transistor T1, the base bias circuit resistors R1 and R2, the +12V power supply circuit is connected with the photodiode circuit D1 and the C-E pole of the transistor T1 in turn to work, the collector of the transistor T1 is connected with the base of the T1 in turn through the resistors R1 and R2, the integrating circuit is composed of a resistor R1 and an electrolytic capacitor C1, the collector of the transistor T1 is connected with the working ground through the resistor R1 and the forward electrolytic capacitor C1 in turn, the in-phase proportional operation circuit is composed of an ideal operational amplifier N1, resistors R4 and R5, a collector of a transistor T1 is connected with an inverting input end of an operational amplifier N1 through an input resistor R3, an output end of an operational amplifier N1 is connected with an in-phase input end of the operational amplifier N1 through a resistor R4, an in-phase input end of an operational amplifier N1 is connected with a working place through a resistor R5, and an output end of the operational amplifier N1 is an amplified effective signal.

Drawings

Fig. 1, 2, and 3 are provided to provide a further understanding of the present invention and form a part of the present application, and fig. 1 is a current-voltage characteristic of a photodiode; FIG. 2 is an electrical schematic diagram for increasing the dynamic range of a photodiode; fig. 3 is a graph showing the average light intensity signal entering the photocell.

Detailed Description

Electrical principle for improving dynamic range of photodiode

In order to increase the dynamic range of the photodiode, a circuit as shown in fig. 2 may be adopted, which increases the dynamic range of the photodiode by introducing negative feedback, and due to the existence of the low frequency filter, the voltage signal generated by the slowly varying light intensity (such as the illumination light) passing through the photocell may be filtered by the filter, and the voltage signal generated by the normal light signal (higher frequency) passing through the photocell may directly pass through the amplifier without being affected by the filter and the feedback circuit, as shown in fig. 2.

As can be seen from FIG. 2, the design comprises a +12V power supply circuit, a photodiode circuit, a common emitter amplifier circuit, a base bias circuit, an integrating circuit and an in-phase proportional operation circuit.

In FIG. 2, a photodiode D₁The photoelectric tube is reversely connected between a power supply and an amplifying circuit, so that the photoelectric tube works in a photoconductive mode, in the mode, as can be seen from figure 1, the current generated by the photoelectric tube under the condition of reverse pressure and being illuminated is called photocurrent, the photocurrent is controlled by incident illumination, when the illumination is constant, the photodiode can be equivalent to a constant current source, the greater the illumination is, the greater the photocurrent is, and when the photocurrent is more than dozens of microamperes, the linear relation with the illumination is formed, and the characteristic can be widely applied to remote control, alarming and photoelectric sensors.

Improving dynamic range of photodiodes using common emitter amplifiers

The circuit of fig. 2 operates on a simpler principle, with the photocells D connected in opposition if there is no illumination₁A reverse current, called dark current, is generated, typically less than 0.2uA, with the current-voltage characteristic in the first quadrant shown in fig. 1, a dark current of 0.2uA being unlikely to make the transistor T₁Generating a turn-on voltage, T₁Cut-off, T₁The collector of (a) has no electrical signal output.

In fact, due to the transistor T₁Has no AC signal input at the base, and therefore is composed of T₁The formed common emitter amplifier can be regarded as a direct current common emitter amplifier which is powered by the photocurrent generated by the phototube.

When the modulated weak light enters the photodiode D₁The photoelectric tube generates a weak photocurrent, the magnitude of the current is in direct proportion to the intensity of the light, and the photocurrent passes through the resistor R₁To electrolytic capacitor C₁Charging, the charging voltage passing through the resistor R₂In the transistor T₁The base electrode of the transistor generates a starting voltage to form a starting current for the ground, and if the photocurrent is relatively small, the transistor T₁Near saturation.

Meanwhile, the weak current can pass through an integrating circuit R₁/C₁The changed current is converted into the change of voltage, so that the weak voltage signal formed by the weak optical signal can still be converted from T₁Is finally output by an operational amplifier N₁And a feedback resistor R₄The output of the in-phase proportional operation circuit is amplified, and the external appearance is that the dynamic range of the photoelectric tube is ideal at the low end, and the sensitivity is not reduced.

When the intensity of light entering the photodiode gradually increases, the photocurrent increases, and the current-voltage characteristic curves shown in fig. 1 gradually move down, they are distributed in the third and fourth quadrants, and in a certain range of the reverse voltage, i.e., in the third quadrant, the characteristic curves are parallel lines of a set of horizontal axes.

With increasing light intensity, T₁Gradually increases the base voltage of the transistor at a certain instant T₁In a fully saturated conducting state, the light continues to be enhanced and passes through T₁The excessive photocurrent generated by the optical signal with excessive intensity is saturated by the T-state of saturation since the intensity of the modulated optical signal has no direct relation to the fidelity of the signal₁By shunting a part of the signal, the circuit structure can not affect the accurate demodulation of the modulated signal, and can not cause the saturation distortion of a post-stage amplifying circuit.

The external performance is that the dynamic range of the photoelectric tube is still ideal at the higher end, and the sensitivity is not reduced.

In optical fiber communication, a 10 Gbit/s optical transmission system adopts an intensity modulation and direct detection mode, wherein the intensity modulation is to change the intensity of an optical signal by using a transmitted electric signal at a transmitting end, and the direct detection is to change an optical wave into an original electric signal by using an optical detector at a receiving end; the 40 Gbit/s wavelength division multiplexing system adopts a DQPSK modulation mode of a phase modulation mode and a differential detection mode, which can improve the utilization rate of frequency spectrum,

if entering the photoelectric tube D₁The light intensity of the light signal is rapidly fluctuated (the frequency of the lighting lamp light is 50 Hz), and the light signal isEffective signal modulated by the transmitting end, by resistor R₁And a capacitor C₁Forming an integrating circuit in which the capacitance C₁The transistor T has too fast a fluctuation of the photocurrent to reach or be insufficiently charged₁At this time, a high impedance is presented, and the effective photocurrent signal passes through the resistor R₁Converting a change in current into a change in voltage U_XDirectly output at X point, and amplified and output by in-phase proportional operation circuit.

These various behaviors mean that the dynamic range of the photodiode is increased without a reduction in amplification.

In addition, it can be understood that the signal U of the Y point of FIG. 2_YNamely the capacitor C₁Is not proportional to the intensity of the light, but can be used to verify the incoming photocell D₁The average light intensity of the light source changes, as can be seen from the comparison of the X signal and the Y signal shown in FIG. 3, when the light enters D₁When the light intensity of the light exceeds the average light intensity (corresponding to the intensity of the modulated effective light signal), the Y signal U is outputted_YAt a high level, the transistor T₁Conduction, U_XThe part of the signal exceeding the average light intensity is T₁Short-circuiting to ground; if the light intensity entering the photoelectric tube is less than or equal to the average light intensity, U_YThe signal being low, transistor T₁Cut-off is high resistance U_XThe signal is high.

In-phase proportional operation circuit with high input impedance

Operational amplifier N₁Model number CA3140, a high input impedance operational amplifier, which combines the advantages of piezoelectric PMOS transistor technology and high voltage double-pass transistor.

By a transistor T₁And the integrating circuit converts the change of the photocurrent into the change of the voltage U_XA signal, the weak electric signal passing through the input resistor R₃Enter into operational amplifier N₁Non-inverting input of, N₁Is passed through a resistor R₄The voltage is introduced to be connected in series with negative feedback, so that the input resistance can be considered to be infinite, and the operational amplifier N₁And a feedback resistor R₄An in-phase proportional operation circuit is formed, and the amplified output signal is obtained by the following formula:

2 debug and notes

In practical applications, the function of the circuit of fig. 2 is to filter out the influence of slowly varying (low frequency) light intensity, so as to greatly reduce the problems of demodulation caused by ambient light variation, it is understood that, for example, the power frequency lighting lamp light is frequency-modulated at 50Hz, but it cannot be regarded as an effective modulation signal, and should be used as an interference signal to try to eliminate it.

The circuit parameters can be designed such that the capacitor C₁Should be at least 1.5uF, and when the capacity takes this value, the switching point of the circuit from high-pass to low-pass is about 50Hz, just the frequency of the illumination light; if the capacitance C₁Taking 10uF as shown in FIG. 2, the switching frequency is about 7 Hz.

In the actual optical communication design, the structure is too simple, but at least an idea is provided, and the idea is reasonable, effective and accurate, and still has a certain value in circuit teaching or optical communication teaching in colleges and universities.

Claims

1. An apparatus for increasing the dynamic range of a photodiode, comprising: the device comprises a +12V power supply circuit, a photodiode circuit, a common emitter amplifier circuit, a base electrode bias circuit, an integrating circuit and an in-phase proportional operation circuit; the common emitter amplifier circuit is composed of a transistor T1, the base bias circuit resistors R1 and R2, the +12V power supply circuit is connected with the photodiode circuit D1 and the C-E pole of the transistor T1 in turn to work, the collector of the transistor T1 is connected with the base of the T1 in turn through the resistors R1 and R2, the integrating circuit is composed of a resistor R1 and an electrolytic capacitor C1, the collector of the transistor T1 is connected with the working ground through the resistor R1 and the forward electrolytic capacitor C1 in turn, the in-phase proportional operation circuit is composed of an ideal operational amplifier N1, resistors R4 and R5, a collector of a transistor T1 is connected with an inverting input end of an operational amplifier N1 through an input resistor R3, an output end of an operational amplifier N1 is connected with an in-phase input end of the operational amplifier N1 through a resistor R4, an in-phase input end of an operational amplifier N1 is connected with a working place through a resistor R5, and an output end of the operational amplifier N1 is an amplified effective signal.