CS256146B1 - Photodetector with photodiode capacity compensation - Google Patents

Abstract

The wiring solves the increase in the photodetector bandwidth when using large-scale, photodiodes with PN transition. The photodetector consists of a photodiode connected the anode to the non-inverting input and the cathode to the op amp output, then from the first resistors and capacitors whose parallel the combination is attached between noninverting input and ground terminal. Negative backward the binding is formed by a second resistor connected between the inverting input and the ground terminal and a third resistor connected between the inverting ones operational amplifier input and output. Appropriate selection of capacitor value and setting operational amplifier voltage amplification by changing the ratio of the values of the third resistor and a second resistor, may be in the transmission to compensate for the photodetector function dependent members, thereby increasing the bandwidth of the photodetector. Said engagement can be utilized at Application of photodetectors in industrial facilities eg in non-electric sensors quantities, for robotics, machine guidance for earthworks, etc.

Description

BACKGROUND OF THE INVENTION The present invention relates to a photodiode capacitance compensation photodetector, which generally allows the frequency range of the photodector to be expanded, particularly when using large-area photodiodes.

Photodetector circuits using photodiodes in various operating modes are known: photodiode, short-circuit photodiode, photovoltaic and open-circuit photovoltaic. The first two are most commonly used, either in terms of low photodiode capacitance in the reverse direction or due to the linear dependence of the photocurrent on the radiant flux in the short-circuit mode. The basic limiting factor in terms of the frequency range of the photodetector made up of the photodiode and the amplifier is the photodiode capacity, which together with the input capacitance of the amplifier and the load resistor forms the resulting time constant of the photodetector determining its frequency characteristics.

In practice, requirements arise for the implementation of photodetectors with large-area photodiodes, whether in linear or quadrant arrangements, for solving various guidance tasks. The considerable capacity of these diodes limits the frequency range of their use.

It is an object of the present invention to provide a photodetector which allows for greater bandwidth using photodiodes of conventional construction, e.g. PN junction silicon.

The principle of a photodiode capacitance compensation photodiode according to the invention comprising one photodiode, one operational amplifier, one auxiliary resistor and one capacitor and two resistors for adjusting the voltage amplification of the operational amplifier is that the photodiode capacity is compensated by the sum of capacitors connected to the operational amplifier input. the constant for achieving equality is the voltage amplification of the operational amplifier.

Stability of the photodetector is achieved by selecting the value of the resistor connected between the input terminal of the operational amplifier and ground.

The circuitry according to the invention makes it possible to achieve a larger bandwidth of a photodetector with a large-area photodiode with a PN junction, than the conventional photodetector connections have in practice. The increase in bandwidth is caused by compensating for the photodiode capacity, which significantly contributes to the inertia of the photodiode. Other components involved in the inertia of the photodiode, in particular the diffusion of the supports and the time required to empty the depleted layer of the photodiode after irradiation, are not affected.

In the accompanying drawings, a photodetector connection is shown, wherein Fig. 1 is a wiring diagram of a photodetector according to the invention, and Fig. 2 is a wiring diagram of a photodetector according to the invention with a spare photodiode circuit for deriving an output voltage.

FIG. 1 shows a circuit diagram of a photodetector composed of photodiode S, connected by an anode to non-inverting input 2 ^and cathode to output 2 of operational amplifier 10, first resistor 2 ^and capacitors 6 in parallel and connected between the non-inverting input 2 and ground terminal 4. The second resistor connected between the inverting input 2 ^{and the} ground terminal 6 and the third resistor connected between the inverting input 2 ^{and the} output 2 of the operational amplifier 10 form a negative feedback circuit.

Depending on the incident flux, the photoelectric current generating a voltage drop across the input resistor of the operational amplifier 10, in parallel with the first resistor 7, is passed through the photodiode. The output voltage is drawn between output 2 ^and ground terminal 4. the amplifiers 10 together with the capacitance of the capacitors 6 depending on the amplification of the operational amplifier 10, which can be adjusted by the negative feedback formed by the second resistor 2 ^{and the} third resistor 2.

Here, the stability of the whole circuit is maintained by appropriately selecting the value of the first resistor T.

In Fig. 2, the photodiode 5 is replaced by a model consisting of a current source 1, the conductivity of the photodiode G (j) and the capacitance of the photodiode C1.

Output voltage υ _θ is given by:

-AI

U - -G -G _d -p / C + C _d / _d + ApC AG + _d

If voltage amplification A is chosen appropriately and capacitance C is used, frequency-dependent terms can be removed from the denominator of the expression:

ApC _d - p (C + C _d ) = 0

C

A = - + 1 ^{° C} d

For the amplifier to be stable, the remainder of the denominator must be non-zero:

-G -G _d + AG _d / 0

After substituting for A, the previous condition requires that G be greater than G _d . C / C _d - For a given type of photodiode 5 and operational amplifier 10, both conditions can be satisfied by selecting C, G and A. The voltage gain A is adjusted by feedback in the inverting input by the ratio of the third resistor a to the second resistor 88, where A = R _B / R _A + 1 ·

In the opposite polarity of the photodiode 5, the output voltage polarity changes with the same function of the other elements.

Claims (2)

SUBJECT OF THE INVENTION A photodiode capacitance compensated detector, characterized in that the photodiode (5) is connected by an anode to the non-inverting input (1) and the cathode to the output (3) of the operational amplifier (10), the first resistor (7) and the capacitor (6) are together. connected in parallel and connected between the non-inverting input (1) and the ground terminal (4), the second resistor (8) being connected between the inverting input (2) and the ground terminal (4) and the third resistor (9) being connected between the inverting input and the output (3) of the operational amplifier (10). Photodetector according to claim 1, characterized in that the photodiode (5) is connected by its cathode to the non-inverting input (1) and by the anode to the output (3) of the operational amplifier (10).