JPH02274111A - Reception level monitoring circuit - Google Patents

Abstract

PURPOSE:To obtain a reception level with an excellent temperature characteristic by keeping a multiple factor control voltage of an APD to a constant value while applying temperature compensation thereto in a normal reception level range, varying a gain control voltage of an AGC amplifier, and monitoring the gain control voltage when a prescribed pulse amplitude is outputted as a reception level. CONSTITUTION:A multiple factor M of an APD 1 is fixed at a normal state where a reception light level is low, temperature compensation is applied by a temperature compensation circuit 6 and a prescribed pulse amplitude of a reception data to an identification circuit is kept by applying variable control to the gain G of an AGC amplifier 2. In such a case, the gain G to the AGC amplifier 2 to be monitored or a DC voltage corresponding to the pulse amplitude outputted from a pulse amplitude detection circuit 3 come from an electric AGC loop, then an accurate reception level is provided without affected by temperature fluctuation. Thus, a reception level not subject to temperature fluctuation at a conventional reception level is monitored.

Description

[Detailed Description of the Invention] [Summary] With regard to a circuit that monitors the reception level in an optical repeater or optical receiving circuit, the purpose of this invention is to convert the predecessor's capulse into an electric pulse, with the aim of making it unaffected by temperature changes. A, a PD that inputs the electric pulse, an AGC amplifier that inputs the electric pulse, a pulse amplitude detection circuit that generates a DC voltage corresponding to the amplitude of the output pulse of the amplifier, and a normal application range where the DC voltage is below a predetermined threshold. Then, the variable gain control voltage for the AGC amplifier,
an AGC switching circuit that generates a constant gain control voltage for the APD, and above the threshold, a constant gain control voltage for the AGC amplifier and a variable gain control voltage for the APO; A circuit that temperature-compensates a control voltage in accordance with the breakdown voltage of the APD, and a circuit that converts the temperature-compensated multiplication factor control voltage into a voltage for the APD, and controls the gain as a reception level. Configured to monitor voltage or nuclear DC voltage.

[Industrial Field of Application] The present invention relates to a reception level monitoring circuit, and particularly to a circuit for monitoring reception level in an optical repeater or an optical receiving circuit.

In order to always perform optical communication in an optimal state, it is necessary to monitor the reception level of an optical repeater or an optical receiving circuit at a terminal station or the like.

[Conventional technology]

Figure 5 shows a conventionally used reception level monitor circuit.
), 2 is A that inputs the electric pulse of APDl.
a GC amplifier, 3 a pulse amplitude detection circuit that generates a DC voltage corresponding to the amplitude of the output pulse of the AGC amplifier 2, and 4 a pulse amplitude detection circuit that generates a DC voltage corresponding to the amplitude of the output pulse of the AGC amplifier 2;
Constant gain control voltage for GC amplifier 2 and APDI
A variable control voltage is generated above the threshold value.
Variable gain control voltage for GC amplifier 2 and APDI
an AGC switching circuit that generates a constant control voltage for
5 is a D/D (direct current/direct current) converter circuit that converts the actual control voltage (approximately lOOν) to APDI. The input voltage of the D/D converter is used as the reception level. In addition, 2a and 2b are AG
These are a preamplifier and a postamplifier of C amplifier 2.

FIG. 6 specifically shows the AGC switching circuit 4 of FIG. 5, which is composed of transistors Q1 to Q8, a constant current source], and a resistor r.
5 and Q6, Q7 and Q8 respectively constitute a differential pair, and transistors Q6 and Q7 constitute a differential pair transistor Ql-Q2.
have common bases connected to common emitters of transistors Q5 and Q8, and each base of transistors Q4 and Q3
The transistor Q3 has a common base with the transistor Ql and is always turned on by the input voltage Vin, and the transistor Q4 has a common base with the transistor Q2 and is always turned on by the voltage threshold Vth. There is. In addition, there are two output voltages ■. 1%v
OX is the gain (G) control voltage of AGC amplifier 2, respectively;
This is the APDI multiplication factor (M) control voltage.

The operation shown in FIG. 5 when such an AGC switching circuit is used will be explained.

First, the received light power Pin is the threshold value P of the normal reception level range.
a (which corresponds to the voltage threshold vth mentioned above), the DC voltage Vin indicating the amplitude of the output pulse of the amplifier 2b is lower than vth, so the transistor Q2 is turned on and the transistors Q6 and Q7 are turned on. An N voltage approximately equal to the voltage threshold vth (lower by about 0.7 V as the base-emitter voltage of the transistor) is applied to the common base.

Therefore, as shown in FIG. 7, the differential pair transistor Q5
- Both base inputs of Q6 are equal and output V. 1 becomes constant, and the electric AGC III that controls the gain C of A G C1 @radiator 2? II voltage becomes constant, but between the base inputs of the differential pair transistors Q7 and QB becomes 1n-Vth, and the voltage Vinvth according to the change in Vin becomes V. 2, and this output voltage ■. 2 is a multiplication factor AGC control voltage that controls the multiplication factor M of APDl.

On the other hand, if the received light power Pin>Pa, A
Since the PDI multiplication factor M becomes too low and the reception dynamic range becomes narrow, in order to prevent this, the sixth
In the circuit shown in the figure, transistor Q1 is turned on this time, and the output is V, contrary to the above case. 2 becomes constant and the multiplication factor A
GC becomes constant and output ■. , is made variable so that electric AGC is applied to AGC amplifier 2 (
(See Figure 7).

Therefore, under normal conditions when the light receiving level is low, the multiplication factor M of APDl is controlled to keep the output of APDI constant, and the gain G of AGC amplifier 2 is kept constant, so that the identification circuit (
(not shown) also maintains a constant pulse amplitude. Then, when the light receiving level becomes high, the APDI
Keeping the multiplication factor M constant, this time AGC amplifier 2
A constant received pulse amplitude is obtained by controlling the gain G of .

In these cases, the reception level is output ■.

By monitoring the AGC voltage with a multiplication factor of 2, it is possible to know at a terminal station, for example, what the reception level of an optical repeater in which this circuit is installed is.

[Problem B to be solved by the invention] In the conventional reception level monitor circuit as described above,
As shown in Figure 8 (a), the breakdown voltage of APDI changes depending on the temperature, so the control voltage of APDI also changes as shown in Figure 8 (5), and if this is monitored as the reception level, the monitor accuracy There was a problem that it deteriorated.

9 Therefore, it is an object of the present invention to make such a reception level monitor circuit unaffected by temperature changes.

[Means to solve the problem]

In order to achieve the above object, the reception level monitor circuit according to the present invention, as conceptually shown in FIG. , a pulse amplitude detection circuit 3 that generates a DC voltage corresponding to the amplitude of the output pulse of the amplifier 2, and a variable gain control for the an AGC switching circuit that generates a constant gain control voltage for the AGC amplifier 2 and a constant multiplication factor control voltage for the APDI, and above the threshold, generates a constant gain control voltage for the AGC amplifier 2 and a variable multiplication factor control voltage for the APD I; 4, a circuit 6 for temperature-compensating the multiplication factor control voltage corresponding to the breakdown voltage of the APD 1, and a circuit for converting the temperature-compensated multiplication factor side'<nI lightning voltage into a voltage for the APDI. 5. Then, the gain control voltage or the DC voltage is monitored as the reception level.

[For production]

In the present invention shown in FIG. 1, the two outputs of the AGC switching circuit 4 are reversed from those in the conventional example shown in FIG. This is different from the conventional example.

Therefore, as shown in the graph of FIG. 2, when the light reception level is always low, the APDI multiplication factor M is fixed, the temperature is compensated by the temperature compensation circuit 6, and the gain G of the AGC amplifier 2 is variably controlled. Therefore, the received data to the identification circuit (not shown) also maintains a constant pulse amplitude. In this case, the gain G to the AGC amplifier 2 monitored or the DC voltage corresponding to the pulse amplitude output from the pulse amplitude detection circuit 3 is that of the electrical AGC loop, so it is not subject to temperature fluctuations and has a positive value. When the received light level becomes high, the gain G of the amplifier 2
is fixed and the APDI multiplication factor M is variably controlled via the temperature compensation circuit 6 to maintain a constant received pulse amplitude.

In this case, the reception level monitored by the gain control voltage is constant, so it is not particularly used.

In this way, it is possible to monitor a reception level that is not affected by temperature fluctuations at a normal reception level.

〔Example〕

FIG. 3 shows an embodiment of the reception level monitor circuit according to the present invention. In this embodiment, the outputs 01 and 2 of the AGC switching circuit 4 shown in FIGS. 5 and 6. 2 is simply replaced as is, and a preamplifier 2a and a rear amplifier 2b are also provided before and after the AGC amplifier 2, and the pulse amplitude detection circuit 3 is A peak detection circuit 31 that detects a peak; a differential amplifier 32 that receives the output voltage of the peak detection circuit 31 and an AGC reference voltage corresponding to a voltage approximately at the center of this peak voltage and generates a differential voltage; It consists of

As a result, the pulse amplitude detection circuit 3 generates a DC voltage corresponding to the amplitude of the output pulse of the amplifier 2b and supplies it to the GC switching circuit 4.

FIG. 4 shows an embodiment of the temperature compensation circuit 6 for breakdown voltage of APDI, which includes a thermistor, posistor,
Or a voltage dividing circuit of a temperature sensing element A such as a diode and a resistor 61, a voltage dividing circuit of resistors 62 and 63, an inverting differential amplifier 66,
Input resistance 64.65 and feedback resistance 67 of amplifier 66, and transistors 68.69 forming a current mirror
and resistors 70-72. In addition, transistor 6
A collector 8 inputs a control voltage from the AGC switching circuit 4 to the D/D converter 5.

In this temperature compensation circuit 6, a temperature sensing element A and a resistor 61
The divided voltage between the resistors 62 and 63 is compared with the reference divided voltage between the resistors 62 and 63 in the differential amplifier 66, and the difference voltage is applied to the transistor 69 forming a current mirror, so that the same current is applied to the transistor 68. By flowing, the control voltage to the D/D converter 5 changes according to the collector current of the transistor 68,
Temperature compensation is performed for the breakdown voltage of APDI.

In this way, the APDI multiplication factor side '4B voltage is always temperature compensated.

〔Effect of the invention〕

As described above, according to the reception level monitor circuit of the present invention, in the normal reception level range, the APDO multiplication factor control voltage is kept constant while being temperature-compensated, and the gain control voltage of the AGC amplifier is varied to generate a constant pulse. Since the amplitude is output and the gain control voltage at that time is monitored as the reception level, a reception level with good temperature characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is a principle diagram of a reception level monitor circuit according to the present invention, FIG. 2 is a graph diagram showing AGC switching characteristics of the reception level monitor circuit according to the present invention, and FIG. 3 is a diagram of the reception level monitor circuit according to the present invention. FIG. 4 is a circuit diagram showing an embodiment of the temperature compensation circuit used in the reception level monitor circuit according to the present invention; FIG. 5 is a configuration diagram of a conventional example; FIG. A circuit diagram showing a specific example of the AGC switching circuit used in the invention and the conventional example, FIG. 7 is a graph diagram showing the AGC switching characteristics of the conventional example, FIG. 8 is a characteristic diagram for explaining the problems of the conventional example, It is. In Figure 1, l... Avalanche photo diode (APD)
, 2... AGC amplifier, 3... Pulse amplitude detection circuit, 4... AGC switching circuit, 5... Voltage conversion circuit, 6... Temperature compensation circuit. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] An APD (1) that converts an optical input pulse into an electric pulse, an AGC amplifier (2) that inputs the electric pulse, and a DC voltage corresponding to the amplitude of the output pulse of the amplifier (2). the generated pulse amplitude detection circuit (3) and, in normal application ranges where the DC voltage is below a predetermined threshold, the AGC amplifier (2);
A variable gain control voltage for the APD (1) and a constant multiplication factor control voltage for the APD (1) are generated;
A constant gain control voltage for the GC amplifier (2) and the A
an AGC switching circuit (4) that generates a variable multiplication factor control voltage for the PD (1); and a circuit (6) that temperature compensates the multiplication factor control voltage in accordance with the breakdown voltage of the APD (1). , a circuit (5) that converts the temperature compensated multiplication factor control voltage into a voltage for the APD (1), and monitors the gain control voltage or the DC voltage as a reception level. received level monitor circuit.