JPS60248009A - Wide bank amplifier - Google Patents

Abstract

PURPOSE:To form a wide bank amplifier with an excellent temperature characteristic by using a transistor (TR) for microwave so as to apply DC feedback and high frequency feedback at the same time from the collector to the base. CONSTITUTION:The characteristic having a flat gain from low to high frequencies is obtained by using a resistor 17 and a capacitor 22 for high frequency signal feedback. When a collector current flowing to a collector resistor 20 is increased because of temperature fluctuation, the collector potential of a transistor (TR)16 is lowered by the collector resistor 20 and a DC feedback resistor 19, the base potential is decreased through a resistor 19, thereby preventing the collector current from being increased. On the other hand, when the collector current is decreased, the base potential rises conversely so as not to decrease the collector current. Since the fluctuation of the collector current due to temperature fluctuation is suppressed, the gain characteristic is hardly changed. Thus, a wide band amplifier with an excellent temperature characteristic is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a wideband amplifier used in an optical receiver or the like that receives digital optical signals.

Conventional Structure and Problems Therebelow, the conventional structure of an optical receiver for receiving digital optical signals will be explained with reference to FIG. In Fig. 1, 1 is a photodiode for optical reception, 2 is a preamplifier with low noise characteristics, 3 and 5 are high gain wideband amplifiers, and 4 is a preamplifier with low noise characteristics.
is an AGC that changes the amount of attenuation of the input signal depending on the input voltage.
(automatic gain control) circuit, 6 is a DC regeneration circuit, 7 is an identification circuit, 8 is a peak value detection circuit, 9 is a voltage that controls the bias voltage of the photodiode 1 and the bias voltage of the AGC circuit 4. It is a control circuit.

In the above configuration, an input optical signal is first converted into an electrical signal by the photodiode 1. The converted signal is sent to preamplifier 2. After being amplified by the high-gain broadband amplifier 3.5 and subjected to DC regeneration by the DC regeneration circuit 6, it is identified by the identification circuit 7 at a predetermined identification level, and then an identification output is output to the output terminal.

On the other hand, as the AGC loop of the receiving circuit, the DC regeneration circuit 6
The peak value of the output signal is detected by the peak value detection circuit 8, and the bias voltage of the photodiode 1 and the bias voltage of the AGC circuit 4 are supplied from the voltage control circuit 9 so that the peak value is constant. .

The AGC loop changes the amplification gain by changing the bias voltage of the photodiode 1 sent from the voltage control circuit 9 when the optical reception level fluctuates, and also changes the bias voltage of the AGC circuit 4. By changing the input electric signal level of the identification circuit 7, the input electric signal level is kept constant.

In the above configuration, we have explained an optical receiver circuit that obtains a constant electrical output by controlling the multiplication gain of photodiode 1 and the gain of the amplifier, but as another method, it is possible to control only the multiplication gain of photodiode 1. There are optical receiving circuits that control the gain of the amplifier and others that control only the gain of the amplifier.

Now, in the optical receiving circuit described above, in order to improve the operation of the identification circuit 7, the input level of the DC regeneration circuit 60 is set to 0.
．． A voltage of about 5 to 1.0V is required. On the other hand, the photodetection current of the photodiode 1 is very small, and the output of the preamplifier 2 is several mV to several TrLv. Therefore, the voltage gain of broadband amplifiers 3 and 6 is 40 to 5 od
B is necessary. In addition, in an optical receiver that receives a digital optical signal, if the amplification gain of the low frequency range is different from that of the high frequency range, the shear pattern deteriorates due to the pattern effect and the error rate deteriorates.

Therefore, there is a need for an amplifier with a flat gain and a wide band from low frequencies (several tens of times) to the pit rate frequency or higher of the digital optical signal.

Conventionally, a negative feedback amplifier is often used as an amplifier with a flat gain from low frequencies to high frequencies.

FIG. 2 shows a circuit of such a conventional negative feedback amplifier.

In FIG. 2, 1o is a bipolar transistor, 1
1. 12 is a resistor for setting the base bias of the transistor, 13 is a collector resistor, 14 is a feedback resistor, and 15 is a feedback capacitor.

In the circuit configured as described above, the feedback resistor 14 is normally used with a value of several hundred ohms in order to flatten the gain from a low frequency range (several tens of MHz) to a high frequency range of several hundred MHz.

In a feedback amplifier as shown in FIG. 2, as the temperature rises, the collector current with respect to the base-emitter voltage changes as shown in FIG.

In FIG. 3, the horizontal axis is temperature, the vertical axis is collector current, and A shows the change in collector current with respect to temperature when the base-emitter voltage is constant.

As is clear from FIG. 3, when a temperature change occurs, the collector current changes, so in the conventional negative feedback amplifier as shown in FIG. 2, the amplification gain changes with respect to the temperature change.

For example, to explain the characteristics of this example, in a single-stage feedback amplifier configured as shown in FIG. 2, the gain changes by about 2 dB from temperature -6°C to +60°C.

As mentioned earlier, a wideband amplifier used in an optical receiver that receives digital optical signals has a gain of 40 to 6o.
dB is required. For this reason, it is necessary to connect feedback amplifiers in multiple stages as shown in FIG. 2, and as a whole, a gain variation of nearly 10 dB occurs with respect to temperature changes in the broadband amplifier.

On the other hand, since the AGC loop needs to obtain a flat gain from low frequencies to high frequencies, it can only operate as an AGC within a certain range. However, temperature fluctuations in the gain of the broadband amplifier do not narrow the AGC tolerance range, but have the drawback of narrowing the input tolerance range of an optical receiver using digital optical signals.

For this reason, it is necessary to take measures for temperature compensation to reduce gain fluctuations due to temperature changes in the wideband amplifier as a whole.

Therefore, various methods have been considered and implemented as temperature compensation measures, such as adding a temperature compensation diode, but these methods have disadvantages such as increasing the number of circuit components and making the circuit complicated.

OBJECTS OF THE INVENTION In view of these conventional drawbacks, it is an object of the present invention to provide a broadband amplifier with a simple circuit configuration and good temperature characteristics.

Structure of the Invention The present invention uses a microwave transistor, and simultaneously performs DC feedback and high frequency feedback from the collector side to the base side of the transistor.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 shows a circuit diagram of a broadband amplifier according to an embodiment of the present invention using transistors.

In FIG. 4, 16 is a microwave transistor, 17
is a resistor for high frequency signal feedback, 18 is a capacitor for current coupling, 19 is a resistor for DC feedback, 20 is a collector resistor, 21 is an emitter resistor, and 22 is a capacitor for correcting the gain in the high frequency band. .

In the following, the circuit having the configuration described in "2" will be explained.

According to the above configuration, the high frequency signal feedback resistor 1 and the capacitor 22 can provide a flat gain characteristic from low frequencies (several tens of +-[z) to high frequencies.

Furthermore, when the collector current flowing through the collector resistor 2o increases due to temperature fluctuations, the collector potential of the transistor 16 decreases due to the collector resistor 2o and the DC feedback resistor 19, and the base potential decreases through the DC feedback resistor 19, preventing the collector current from increasing. It works like this. When the collector current decreases, the base potential rises to -, contrary to the above, and operates so as not to decrease the collector current.

As described above, since the device operates to suppress fluctuations in the collector current due to greenhouse fluctuations, etc., the gain characteristics also hardly change.

As described above, according to this embodiment, the resistor 19 for DC feedback and the resistor 17 for high frequency signal feedback are connected in parallel between the collector and base of the transistor 16, and the collector resistor 20 and the DC feedback resistor 19 are appropriately selected. This makes it possible to minimize changes in gain due to temperature fluctuations.

Effects of the Invention As is clear from the above explanation, the wideband amplifier of the present invention can provide an amplifier with good temperature characteristics with a simple circuit configuration, and is particularly suitable for optical receivers for digital optical signals. .

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional optical receiver circuit, Fig. 2 is a circuit diagram of a conventional negative feedback type wideband amplifier, and Fig. 3 is a characteristic diagram showing changes in collector current with respect to temperature changes in a conventional wideband amplifier. FIG. 4 is a circuit diagram of a wideband amplifier in one embodiment of the present invention. 16...Microwave transistor, 17...
Resistor for high frequency signal feedback, 18... Capacitor for DC cut, 19... Resistor for DC feedback, 20-
... Collector resistance, 21 ... Emitter resistance,
22-...Capacitor for gain correction. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
figure

Claims (1)

[Claims] 1. A wideband amplifier comprising: a series circuit comprising a first resistor and a capacitor connected between a base and an emitter of a transistor; and a second resistor connected in parallel with the series circuit.