JPH0247907A - Optical receiving circuit - Google Patents

Abstract

PURPOSE:To convert an optical signal into an electric signal accurately by connecting a base of a common base amplifier in a trans-impedance optical reception circuit of prescribed constitution to ground in terms of AC through a parallel circuit comprising a Zener diode of reverse bias connection and a capacitor. CONSTITUTION:With an optical input signal Vin given to a photodetector 1, the level of a base potential Vb of the common base amplifier 10 is almost unchanged even with the input of a burst optical signal through the action of a Zener diode DZ. Thus, a low level for a period of the reception of the burst signal in the collector voltage Vc is nearly equal to the level for a period without any signal. Thus, the burst optical signal being the input signal is converted into an electric signal accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical receiving circuit, particularly a transimpedance type optical receiving circuit.

[Conventional technology]

Optical receiver circuits can be roughly divided into two types: no impedance type and transimpedance type.The transimpedance type has a wider band, compared to the high impedance type.
It is excellent in that it has a wide dynamic range.

FIG. 4 is a circuit diagram showing a conventional transimpedance type optical receiving circuit. This optical receiving circuit includes a light receiving element 1,
It is composed of a common source amplifier 2, a common base amplifier 3, an emitter follower circuit 4.5, and a feedback resistor 6, and the base of the common base amplifier 3 is grounded by a resistor R6 and a capacitor C in an alternating current manner. In addition, in the same figure, Vl.

v , v , v , v are bias voltages, Ql
is FET, Q is pnp transistor, Q, Q
is npn) transistor, R-R6 is resistor, C is ■ capacitor, Pln is input burst optical signal, ■
is the output electrical signal, ■ is the base potential, ■ out

c is the collector potential.

[Problem to be solved by the invention]

However, in this conventional optical receiving circuit, as mentioned above, the base of the common base amplifier 3 is AC-grounded through the resistor R6 and the capacitor C, so the low level of the output signal V varies depending on the presence or absence of the signal. There was a problem with this. This problem will be explained in more detail using the waveform diagram in FIG. For example, when the light receiving element 1 receives a burst signal period T as shown in FIG. 5(A),
When an optical signal P1n having a signal P1n is received, the base potential Vb of the common base amplifier 3 rises during that time as shown in FIG.

Therefore, the collector potential V of the common base amplifier 3 is
As shown in the same figure (C), the low level of the burst signal section T becomes higher than the level of the no-signal section by Vl, and this state is caused by the final output of this circuit as shown in the same figure (D). This is carried over to the output of the emitter follower circuit 5. In other words, although the low level of the manually input optical signal P1n is constant regardless of whether it is a burst signal section or a no-signal section, the output signal V
The low level of ut differs depending on the presence or absence of a burst signal. Therefore, with this conventional circuit, it was impossible to accurately convert the burst optical signal into an electrical signal.

An object of the present invention is to solve these problems.

[Means to solve the problem]

In order to solve the above problems, in the optical receiving circuit of the present invention, the base of a common base amplifier is grounded in an alternating current manner through a parallel circuit consisting of a reverse-biased Zener diode and a capacitor.

[Effect]

The base potential of the common base amplifier is held approximately constant regardless of the state of the human input signal. For this purpose, signal amplification is performed accurately in the common base amplifier.

〔Example〕

FIG. 1 is a circuit diagram showing one embodiment of the present invention. The basic configuration is the same as a conventional optical receiver circuit, with the light receiving element 1
, a common source amplifier 2, a common base amplifier 10, an emitter follower circuit 4.5, and a feedback resistor 6. The configuration of the common base amplifier 10 is different from the conventional circuit shown in FIG.

That is, in this embodiment, a Zener diode Dz, a resistor R3, and a capacitor C are connected to the base of the common base amplifier 10, the cathode of the Zener diode Dz and the other terminal of the capacitor C are grounded, and the The other terminal is connected to bias voltage v3. Note that the same reference numerals are given to the same or equivalent elements as in FIG. 4, and the explanation of each element will be omitted.

Next, the operation of the optical receiver circuit of this embodiment will be explained using the waveform diagram of FIG. The signal waveform shown in FIG. 2(A) is the same as the human-powered optical signal PIn shown in FIG. 5(A), and is the same regardless of whether the low level is in the burst signal section T or not. FIG. 2(B) shows the base potential V of the common base amplifier 10 when the optical signals P and n are applied to the light receiving element 1, and even if a burst optical signal is input, the base potential V is very small. It only increases, and its level remains almost unchanged throughout. This is based on the low voltage characteristics of the Zener diode Dz.

As described above, since the base potential ■, of the common base amplifier 10 hardly changes regardless of changes in the human input signal, the collector potential ■ of the common base amplifier 10 is
), the low level of the burst signal section T is approximately equal to the level of the no-signal section. Therefore, even in the output voltage V outputted after impedance conversion in the emitter follower circuit 4.5, the low level of the period T of the burst signal ut is almost equal to the level of the no-signal period, and the burst optical signal, which is a human input signal, can be accurately detected. It can be converted into an electrical signal.

FIG. 3 is a circuit diagram showing a more specific example of this embodiment, in which the bias voltage v-V5 is shared.

〔Effect of the invention〕

As explained above, according to the optical receiver circuit of the present invention, the base potential of the common base amplifier is held almost constant regardless of the state of the input signal, so that signal amplification can be performed accurately in the common base amplifier. , the entire circuit can accurately convert optical signals into electrical signals.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a circuit diagram showing a more specific example of this embodiment, FIG. 4 is a circuit diagram showing a conventional optical receiver circuit, and FIG. 5 is an operating waveform diagram thereof. . 1... Light receiving element, 2... Source common amplifier, 4.5
...Emitter follower circuit, 6...Feedback resistor, 10.
... Grounded base amplifier, Dz... Zener diode. R-cho conventional circuit diagram

Claims (1)

[Claims] a common source amplifier having a gate connected to the output terminal of the light receiving element; a common base amplifier having an emitter connected to the drain of the common source amplifier; and a base connected to the collector of the common base amplifier. In the transimpedance optical receiving circuit, the base of the common base amplifier is reverse-biased and has a feedback resistor connected between the emitter of the emitter follower circuit and the gate of the common source amplifier. An optical receiving circuit characterized in that the optical receiving circuit is grounded through a parallel circuit including a Zener diode and a capacitor.