JPH03198414A - Waveform shaping circuit for interface circuit - Google Patents

Abstract

PURPOSE:To reduce the undershoot of a transmission pulse waveform to hold the transmission pulse waveform within a prescribed pulse mask by using a pair of specific diodes to shape the waveform of the pulse outputted to a transmission line. CONSTITUTION:Not only resistances R1 and R2 but also respective cathodes of diodes D1 and D2 constituting a waveform shaping circuit 20 are connected to terminals X1 and X2 of a driver 10, and anodes connected in common of diodes D1 and D2 are connected to the connection point of resistances R3 and R4. The pair of diodes D1 and D2 are connected to one pair of terminals X1 and X2 respectively, and they are pulled up to potentials near the high level of this pair of terminals. Thus, the undershoot of the transmission pulse waveform is reduced to hold the transmission pulse waveform within the preliminarily prescribed pulse mask.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a waveform shaping circuit for an interface circuit.
5DN (Integrated Service Digital Network) The waveform shaping circuit of the interface circuit shapes the output pulse waveform of the basic interface.

15DN has rapidly become popular in recent years, and the number of compatible devices is gradually increasing. However, in 15DN, strict interface regulations are prescribed regarding output pulse waveforms, etc. in order to connect various devices on the same interface.

[Conventional technology]

FIG. 3 shows a circuit configuration diagram of an example of a conventional interface circuit. In the figure, terminals X1. of the driver 10. Each of X2 is connected to both ends of the primary winding of the transformer T via current limiting resistors R+ and R2 (150 each). A 10m cable 11 is connected to both ends of the secondary winding of the transformer T, and the end of this cable 11 is connected to a 50Ω resistor R[
is shorted.

In this circuit configuration, the interface rules are determined so that the output pulse waveform is within the pulse mask shown by diagonal lines in FIG.

[Means to solve the problem]

Conventionally, it has been possible to fit the output pulse waveform within the pulse mask by using a special cable with low impedance as the cable 11, but the special cable is expensive. If a normal cable with an impedance exceeding 100Ω is used, the transmission pulse waveform at both ends of resistor R4 will be
As shown by the solid line in the figure, the undershoe 1~ that occurs due to the delay in the switching timing of terminal X2 when terminal x1 switches from H level to high impedance and terminal x2 switches from L level to high impedance is large. However, there was a problem in that the pulses would go outside the pulse mask.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a waveform shaping circuit for an interface circuit that reduces undershoot of a transmitted pulse waveform and fits the transmitted pulse waveform within a prescribed pulse mask.

[Means to solve the problem]

The waveform shaping circuit of the interface circuit of the present invention is provided in a differential driver type interface circuit that outputs pulses from a pair of terminals that perform tri-state output to a transmission line via a transformer, and a waveform shaping circuit that outputs pulses from a pair of terminals to an anode. It has a pair of diodes whose potential is close to high level and whose cathodes are connected to a pair of terminals, respectively, and shapes the waveform of the pulses output to the transmission line.

[Effect]

In the present invention, a pair of diodes are connected to each of the pair of terminals and pulled up to a potential near the high level of the pair of terminals, so that the pair of terminals are both disconnected from the high level and low level to high impedance. The undershoot of the transmission pulse waveform caused by the timing shift is reduced.

〔Example〕

FIG. 1 shows a circuit diagram of an embodiment of the circuit of the present invention. In the figure, the same parts as in FIG. 3 are given the same reference numerals, and their explanations will be omitted.

In Figure 1, the driver 10 is connected to the output terminal X to the tri-stay 1.
1 to H level (3v) output, trice date output terminal
2 is set to a positive polarity pulse output state by outputting L level (OV), and terminals X1. Differential output is performed in which both terminals X2 are in a high impedance state, and terminal x1 is output at a 1-level, and terminal x2 is output at an H level, resulting in a negative pulse output state. End FX1 of driver 10. To X2: is the resistance R+,
R2 is connected, and the cathodes of diodes D+ and D2 forming the waveform shaping circuit 20 are also connected. The commonly connected anodes of diodes D+ and D2 are connected to the connection point of resistors R3 and R4.

For example, a resistor R3 of 1Ω and a resistor R4 of 1.5Ω
is connected in series between the voltage mVcc (5V) and GND (OV), and the potential at the connection point of resistors R3 and R4 is, for example, 3
■And driver 10 is the end? H output from X1 or ×2
The potential is approximately equal to the level potential.

Here, when the terminal X1 is at H level (30) and the terminal X2 is at L level (OV), the diode D+.

Since the anode of D2 is 3v, the diode D1 is
A is disconnected, and diode D2 is conductive. However, since the resistance value of the resistor R3 is 1Ω, which is larger than the resistors R+ and R2, the current flowing through the diode D2 is quite small.

After this, terminal X1. When both terminals X2 switch to high impedance, terminals X1. Both X2 are clamped to 3.times. by the waveform shaping circuit 20. In this case, a normal cable with an impedance exceeding 100Ω is used as the cable 11, and even if the switching timing of the terminal FX2 is delayed, the diode D2 is conductive until the terminal x2 becomes high impedance, so the transmission at both ends of the resistor RL is As for the pulse waveform, as shown by the solid line in FIG. 2, the undershoot of the pulse is reduced compared to the conventional method, and the transmitted pulse falls within the pulse mask shown by the diagonal line in FIG. This eliminates the need to use an expensive special cable with low impedance as the cable 11.

[Effects of the Invention] According to the waveform shaping circuit of the interface circuit of the present invention,
This is extremely useful in practice as it reduces the undershoot of the transmitted pulse waveform and allows the transmitted pulse waveform to fall within a predefined pulse mask.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an embodiment of the circuit of the present invention, Fig. 2 is a transmission pulse waveform diagram of the circuit of the present invention, Fig. 3 is a circuit diagram of an example of a conventional circuit, and Fig. 4 is a transmission diagram of the conventional circuit. It is a pulse waveform diagram. In the figure, 10 is a driver, 11 is a cable, 20 is a waveform shaping circuit, D+ and D2 are diodes, and R1-R4 are resistors.

Claims (1)

[Claims] A pair of terminals (X1, X2) that perform tri-state output
It is provided in a differential driver type interface circuit that outputs pulses to the transmission path via a transformer, and the anode is set to a potential close to the high level output from the pair of terminals (X1, X2), and the cathode is set to Terminal (X
1, X2) A pair of diodes (D_1
, D_2), and performs waveform shaping of pulses output to the transmission line.