JPS60257631A - Optical reception circuit - Google Patents

Abstract

PURPOSE:To prevent an output voltage from being affected by temperature and power supply voltage by connecting a current-voltage conversion preamplifier circuit to a photodetector and connecting a main amplifier circuit to the preamplifier circuit via a resistor. CONSTITUTION:The current-voltage converting preamplifier circuit 1 feeds back an output of a transistor (TR)Q2 to an input side of a TR circuit via a resistor R1. Similarly, an output of a TRQ7 is fed back to the input of a TRQ6 via a resistor R4 in a main amplifier circuit 2. The preamplifier circuit 1 and the main amplifier circuit 2 are connected via a resistor R3. A reference voltage generating circuit 3 decides the operating current of TRs Q5, Q10. In setting the value of resistors R1, R3, R5 and R7 so as to establish the relation of R3R7=R1R5 and selecting the ratio of the resistor R3 to the R4 to a prescribed value, the output voltage is made independent of the temperature and power voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background and Objectives of the Invention] The present invention relates to an optical receiving circuit, and particularly to an optical receiving circuit suitable for making the output voltage stable regardless of temperature and voltage.

The first example of an amplifier used in a conventional optical receiver circuit is
As shown in the figure. The emitter of transistor Q is diode D.
The transistor Q1, including the load resistor &, is designed to operate as a common emitter circuit. Transistor Q2 constitutes a common collector (committee follower) circuit, and lowers the output impedance to reduce the influence of resistor 1 (, F) on the feedback loop.
The amplifier section consisting of resistors Rb, R, F, and RE constitutes a so-called lance impedance type amplifier circuit, and has a low input impedance, so it can be used as an efficient current-to-voltage conversion circuit with the light receiving element PI). The combination is used as an optical receiver circuit. Note that the diode D has the function of reducing the output type problem and making it easier to connect to the next stage.

Now, the output voltage V1 when there is no optical input is expressed by the following equation.

VI= VBEI + Vp + In+Rp ・=(
1) Here, ■BE1; Base-emitter voltage IB+ of transistor Ql: t□Collector current of transistor Q, ■F;
Voltage drop RF of diode D; resistance value of resistor Rp Next, when collector current ■cl of transistor Q1 is subtracted, RI.

Here, vcc is the resistance value of power supply voltage Vngz: l and the voltage between the base and emitter of transistor Q2 1=r resistance 几■. By the way, considering that IC1-IB・hFE (hFE is the current amplification factor of a transistor or a transistor), (IL
Subtracting ■1 from equation (2) yields the following equation.

Here, VBEI, Vngz, VF are generally about -
In addition to having a large negative temperature coefficient of 2 mV/deg, as can be seen from equation (3), 'Vl is the power supply voltage V. Since it depends on the basic characteristics of 0 and hFE of the transistor, if it is connected to the next stage amplifier in a direct current manner, the characteristics will fluctuate greatly and stable operation will be difficult.

The present invention has been made in view of the above, and an object of the present invention is to provide an optical receiving circuit whose characteristics are stable with respect to temperature and power supply voltage.

[Summary of the invention]

The feature of the present invention is that a diode is connected to a photodetector that inputs an optical signal and converts it into a current, an emitter that converts the output current of this photodetector to a voltage, and a collector of a PNPI transistor is connected to the collector. A common emitter circuit consisting of a transistor with a PNP transistor as an active load is connected to a common collector circuit consisting of another transistor, and the output of the common collector circuit is fed back to the input side of the common emitter circuit via a feedback circuit. A current-to-voltage conversion preamplifier circuit formed by the above, a main amplifier circuit having the same circuit configuration as the preamplifier circuit connected to the output terminal of the preamplifier circuit via a resistor, the preamplifier circuit and The present invention has a circuit configuration including a reference voltage generation circuit that determines the operating current of the PNP transistor of the main amplifier circuit.

〔Example〕

The present invention will be explained in detail below using the embodiment shown in FIG.

FIG. 2 is a circuit diagram showing an embodiment of the optical receiving circuit of the present invention. In FIG. 2, transistors Q+ to Q4. A circuit section 1 including resistors Rt and R2 is a current-to-voltage conversion preamplifier circuit that functions to convert an optical signal received by the light receiving element PD into a voltage. Transistors Q6 to Qlo, resistor R
The circuit section 2 consisting of 4 and R5 is a main amplifier circuit and is connected to the circuit section 1 via a resistor R3.

Further, the circuit section 3 consisting of the transistor Qllj and the resistors R6 and R7 is a reference voltage generation circuit that determines the operating current of the l-transistor Q5p Qlo.

Transistors Qs and Qlo are PNP transistors, used as constant current sources, and operate as active loads for transistors Q+ and Q6, respectively.

Note that the circuit section 1 has a diode (a transistor Q3 is used in FIG. 2, and a diode D in FIG. 1 is used as an emitter).
The collector of PNP transistor Q5 is connected to the collector of transistor Q5, and the common emitter circuit consisting of transistor Q1 with transistor Q5 as an active load is connected to the common collector circuit consisting of transistor Q2. The output of this common collector circuit is fed back to the input side of the common emitter circuit via a feedback circuit consisting of a resistor R+. Circuit section 2 is similar, with a diode (transistor Qs in Figure 2) connected to the emitter, and a transistor QIo connected to the collector.
Connect the collector of PNP) transistor Q! A common emitter circuit consisting of a transistor Q6 with o as an active load is connected to a common collector circuit consisting of a transistor Q7, and the output of this common collector circuit is connected to the input side of the common emitter circuit via a feedback circuit consisting of a resistor R4. I am planning to return.

Next, the operation of the circuit shown in FIG. 2 will be explained using equations. However, in subtraction, assume the following. It is assumed that the current amplification factor of each transistor is the same, and this is referred to as hFF. Assume that each resistor has no temperature dependence. These conditions are easily satisfied within an integrated circuit and are appropriate. Note that the base current of transistor Q+-Qo is I
As n+ to IBII, the collector current is ■. 1
~IC11, and the base-emitter voltage is V! IE
It is displayed as I to VBEI+. 1. The resistance value of each resistor is indicated by the symbol representing each resistor.

First, the operating current Io of the transistor Qu is expressed by the following equation.

Therefore, the collector currents of the PNP transistors Qs and Qlo 5. Ic+o is expressed by the following formula.

Ic 5-IBI-I. 2-I. 3=I. 4 = Io
X &/R2...(51'C+o = Ice = IC7°I(s = IC
9-Io X &/R5-(6) Next, since the base current IB6 of the transistor Q6 is the difference between the current 2 and I+ shown in FIG. 2, it is expressed by the following equation.

Here, V+=Vt+r++VnE3+IBg+R1= 2VI
]EI+IBI Rt...(8)Vz=Vnp:
6+Vr+ag= 2VBE6 - (9) Dimensions, V8゜6 Vn+:+=to=-6・±C6,,,(.

q Ic1 (8)~t! Substituting DJ into equation (7) and subtracting v3, we get
V3=2V++. 6+R4 (In2-Machi■8.)3 By the way, z Ioa (= Ice / hpF,) and I old (-Ic+ / hpg) are +5L As is clear from equation (6), you can freely choose R2 and Rs. Can be set. Now, if we choose In2 =----IBI 几3, that is, l R7----・R5 3, the zero sword type is expressed as follows. By differentiating V3 with respect to temperature T and subtracting the temperature coefficient of ■3, the following is obtained. The first term of equation (I3) has a negative temperature coefficient (approximately -
2 mv/deg), whereas the second term is a positive temperature coefficient, and if Vnge R7 is chosen, then the following equation is satisfied: (3), that is, the output voltage does not vary with temperature.

In addition, if VI]E'6 of the (supporting) equation is replaced here with ■s: reverse saturation current, then ■3 has power supply voltage dependence. but,
The value is extremely small, and when Ic6 is 100/A, the change in ■3 is even if vcc changes by 10% from 5■.
The variation of 3 is within 20 mv, which is a value that does not pose any problem at all. Therefore, according to the circuit shown in FIG. 2, the output voltage (3) is independent of temperature and power supply voltage and operates stably.

Note that the output voltage when light is input to the light receiving element PDKPIN of the circuit shown in FIG. 2 is expressed as PIN・几1・R4/R3.

And +1r+w t7- of the transistor, 7>
Even if 11+r fluctuates, as long as the ratio is constant, the output voltage v3 is stable regardless of temperature and power source Ichikawa, so it is easy to implement as an integrated circuit.

〔Effect of the invention〕

As explained above, according to the present invention, the output voltage does not depend on temperature or power supply voltage, and the characteristics can be made stable with respect to temperature and power supply voltage.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of an amplifier of a conventional optical receiving circuit, and FIG. 2 is a circuit diagram showing an embodiment of the optical receiving circuit of the present invention. 1. Current-voltage conversion preamplifier circuit, 2. Main amplifier circuit, 3.
Reference voltage generation circuit, Q+-Q4. Q6~Q91Q
l+...Tranogista+Qs, Q+o...PN
P transistor. R1~I(,7・Resistance. Figure 1 + 2 3

Claims (1)

[Claims] ② Connect a diode to a photodetector that manually converts an optical signal into a current and an emitter that converts the output current of the photodetector to a voltage, connect the collector of a PNP transistor to the collector, and use the PNP transistor as an active load. I did it.
An esota grounded circuit consisting of a transistor and a collector grounded circuit consisting of another transistor are connected (1) to a current-voltage such that the output of the collector grounded circuit is fed back to the input side of the emitter grounded circuit via a feedback circuit. a conversion preamplifier circuit, a main amplifier circuit connected to the output terminal of the preamplifier circuit via a resistor and having the same circuit configuration as the preamplifier circuit, and P N P of the preamplifier circuit and the main amplifier circuit. )
An optical receiving circuit comprising a reference voltage generating circuit that determines the operating current of a transistor.