JPS63104548A - Bias circuit - Google Patents

Abstract

PURPOSE:To prevent the aperture efficiency of the eye parttern of a modulation signal from being deteriorated and also a transition state just after transmission begins from being generated constituting a bias circuit only with resistances and a switch and not using a capacitor which obstructs a direct current. CONSTITUTION:A titled circuit has the resistances 3-6 and the switch 7 and in case of reception the switch 7 is made in ON state so as to keep an input terminal 1 in the same electric potential as a second reference voltage terminal(earth) and meanwhile in case of transmission the switch 7 is turned OFF so as to input the modulation signal in the input terminal 1 and obtain the outputs from connection point of first and second registances 3 and 4. Thus the aperture efficiency of the eye pattern of the modulation signal inputted in a modulator 9 is not deteriorated and the transition state does not occur just after the transmission begins, since the capacitor is not used, which obstructs the direct current and causes time constant.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a bias circuit that can be used in a modulator of a communication device.

BACKGROUND OF THE INVENTION In recent years, data communications have rapidly become widespread, and modulators, which play a key role in communication quality, are required to have higher performance.

An example of a conventional bias circuit will be described below with reference to the drawings. FIG. 3 is a block diagram of a conventional bias circuit, in which 11 is an input terminal for inputting a modulation signal;
2 is a power supply terminal, 13 is a capacitor that blocks the DC component of the modulation signal input to the input terminal 11, 14 and 15 are resistors that provide a bias voltage to the subsequent circuit, and 16 is the capacitor 13 that removes the DC component. A modulator 17 is an output terminal of the modulator 16 which inputs a modulation signal and performs modulation.

The operation of the bias circuit configured as described above will be explained assuming that NRZ signals of ethics "1" and "0" are input as modulation signals. Here, it is assumed that the voltage applied to the power supply terminal is 2, and that the resistors 14 and 15 are equal. As shown in the waveform diagram in Figure 4, ethics “1” and “0”
A modulated signal (a) consisting of the following is input to the input terminal 11. The input modulation signal (a) is transformed into a modulation signal (
The waveform becomes as shown in b) and is input to the modulator 16. The modulator 16 modulates the input signal (b) and outputs it from the output terminal 17.

Problems to be Solved by the Invention However, in the above configuration, since the modulator 16 performs modulation using the signal fb) corresponding to the time constants of the capacitor 13 and the resistors 14 and 15, the capacitance value of the capacitor 13 is If it is small, the aperture ratio of the eye pattern will deteriorate when the ethics "1" or "0" are consecutive as seen from time t2 to t3 of signal (b), and to prevent this, the capacitance value If the value is increased, the transient state immediately after the transmission start time t1 takes a long time, and significant distortion occurs during demodulation in this portion, making it difficult to determine the ethical level.

In view of the above-mentioned problems, the present invention provides a bias circuit that does not deteriorate the aperture ratio of the eye pattern of the modulated signal input to the modulator and does not cause a transient state immediately after the start of transmission.

Means for Solving the Problems In order to solve the above problems, the bias circuit of the present invention has first and second reference voltage terminals that provide two reference voltages, and an input terminal for inputting a modulation signal that changes around a midpoint voltage; and first and second resistors connected in series between the first and second reference voltage terminals;
a third resistor connected between the connection point between the first and second resistors and the input terminal; and between the connection point between the first and second resistances and the first reference voltage terminal. 4th connected in series
The switch is equipped with a resistor and a switch, and when receiving, the switch is turned on and the input terminal is kept at the same potential as the second reference voltage terminal, and when transmitting, the switch is turned off and the input terminal is kept at the same potential as the second reference voltage terminal. The modulation signal is input to a terminal, and an output is obtained from a connection point between the first and second resistors.

Effect of the Invention With the above-described configuration, the present invention does not use a capacitor to block the direct current that causes the time constant, so the aperture ratio of the eye pattern of the modulated signal input to the modulator does not deteriorate, and the aperture ratio of the eye pattern of the modulated signal input to the modulator does not deteriorate immediately after the start of transmission. This means that no transient state occurs.

Example Below, regarding a bias circuit which is an example of the present invention,
This will be explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the bias circuit of the present invention. In FIG. 1, 1 is an input terminal for inputting a modulation signal, 2 is a power supply terminal, 3 and 4 are resistors that apply a bias voltage to the subsequent circuit, 5 and 6 are resistors that apply a bias voltage during reception, 7 is a switch, 8 is a control terminal for controlling the switch 7; 9 is a modulator for inputting a modulation signal applied with a bias voltage through resistors 3 and 4 for modulation; 1;
0 is the output terminal of the modulator 9.

The operation of the bias circuit configured as described above will be described assuming that NRZ signals of ethics "1" and "0" are input as modulation signals. Here, the voltage applied to power supply terminal 2 is assumed to be 1, and resistors 3 and 4 are equal in resistance value R.
It is assumed that resistors 5 and 6 have the same resistance value R2. Further, it is assumed that the switch 7 is in an ON state when the control terminal 8 is in the logic "1" and in an OFF state when the logic is in "0".

It is also assumed that ethics "1" is input to the control terminal 8 during reception and ethics "O" is input during transmission. First, as shown in the waveform diagram of FIG. 2, reception is received after time t1 and t4, and
During the period from I to t4, transmission is performed, and a modulated signal consisting of ethical "1" and "0" as shown in the waveform diagram (a) is input to the input terminal l. The control signal (b) is input to the control terminal 8 as described above. First, at the time of reception, the logic level "0" is input to the input terminal 1 and the switch 7 is turned on, so that the input signal (C) of the modulator 9 becomes Vl/2. Next, at the time of transmission, a modulation signal is input to the input terminal 1 and the switch 7 is turned off, so the modulator 9 receives a signal ( C) will be input.

As described above, according to this embodiment, the bias circuit is configured with only resistors and switches, and no DC blocking capacitor is used, so there is no time constant, and the ethical problem seen between time t2 and t3 is avoided. Even when "1" or "0" is continuous, the aperture ratio of the eye pattern does not deteriorate at all. Also, transmission start time 1. No transient state occurs immediately after. Further, since the amplitude of the input signal to the modulator 9 is determined by the resistance values of the resistors 3.4 and 6, the degree of modulation of the modulator 9 can be arbitrarily set by changing these values. Also, during reception, the input signal to the modulator 9 is V
Since it is fixed at +/2 and no modulation is applied to the output of the modulator 9, this output can also be used as a local oscillation signal of the receiver.

Note that in this embodiment, the switch 7 is a transistor,
It can be easily constructed using a gate IC or the like.

Furthermore, the control signal (b) applied to the control terminal 8 is also controlled by the microcomputer.
This can be easily generated using a gate IC or the like.

In this embodiment, the power supply voltage (2) is applied to the power supply terminal 2, and one end of the resistor 4 is grounded, but any voltage may be used as long as these two voltages serve as a reference voltage.

In addition, although the modulation signal is a rectangular wave with ethics "1" being 1 and ethics "0" being O, any signal may be used as long as it changes around the midpoint voltage of the two reference voltages.

Further, although the resistors 3 and 4 are assumed to be equal, they may vary as long as the amplitude fluctuations of the modulator input signal are within the permissible range when designing the system. In addition, resistors 5 and 6 are also assumed to be equal, but when designing the system, if the amplitude fluctuation of the modulator input signal is within the tolerance range, there will be variations, and as described above, the present invention can be applied only to the resistors and switches. Since the bias circuit is configured with , and no DC blocking capacitor is used, there is no underfire of the eye pattern aperture ratio even if the ethics "1" or "o" are repeated.
Further, an excellent effect can be obtained in that no transient state occurs immediately after the start of transmission. Furthermore, by changing the resistance value, the modulation degree of the modulator can be set arbitrarily, and the output of the modulator can also be used as a local oscillation signal of the receiver during reception.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2(a)
(b) (C) is a waveform diagram of each part of an embodiment of the present invention, FIG. 3 is a block diagram of a conventional bias circuit, and FIG.
(bl is a waveform diagram of each part of a conventional bias circuit. 1... Input terminal for modulation signal, 2... Power supply terminal, 3 and 4... For subsequent circuit Resistors that provide bias voltage, 5 and 6... Resistor that provides bias voltage during reception, 7... Switch, 8
・Old...Switch control terminal, 9...Modulator,
10... Output terminal of modulator. Name of agent: Patent attorney Toshio Nakao Figure 1 tt tz Otsu s t
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Claims (1)

[Claims] first and second reference voltage terminals providing two reference voltages;
an input terminal for inputting a modulation signal that changes around the midpoint voltage of the first and second reference voltages; and first and second terminals connected in series between the first and second reference voltage terminals. a resistor, a third resistor connected between a connection point between the first and second resistors and the input terminal, a connection point between the first and second resistances and the first reference voltage terminal; A fourth resistor and a switch are connected in series between the switch and the switch.
N state, and the input terminal is kept at the same potential as the second reference voltage terminal, and at the time of transmission, the switch is turned OFF, and the modulation signal is input to the input terminal, and the first and second reference voltage terminals are kept in the N state. A bias circuit characterized in that an output is obtained from a connection point of a second resistor.