JPH0242813A - driver circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an AMI signal driver circuit for a terminal device connected to an ISDN network.

[Prior art] As a specification for the l5DN user network interface, CCI
TT 1.430 and TTT standard JT-1,43G
There is. The above recommendation specifies the AMI signal as the transmission signal.

In this specification, the AMI signal is
It is an abbreviation for ark inversion, and it is a mark signal (
It is a ternary signal whose polarity is inverted every binary O).

Further, the recommendations include pulse mask regulations and output impedance regulations when there is no signal (space signal), and the pulse mask regulations relate to the amplitude, undershoot, and overshoot of the transmission signal.

In addition, the output impedance specification when there is no signal is set to a high output impedance so as not to affect the signal transmission of other terminals on the bus.
The content is to make it into a dance.

Figure 3 shows a conventional driver circuit in which +5 is applied to the terminal At.
When v is applied, Tri and Tr2 become conductive, and a ten-polarity signal is output to the output C1 of the transformer T1. Similarly, when +5V is applied to terminal B1, terminals r3 and terminals r4 become conductive, and a unipolar signal is output to output C1 of transformer Tl. For this, both 1.81 and (
At the time of IV, transistors Tri, Tr2, Tr
3 and Tr4 are cut off, and the transformer T1 enters a high output impedance state with no signal.

[Problems to be Solved by the Invention] In the conventional example, when the mark signal is sent out and the space signal sent out, that is, when the transition is made to the no-signal sending state, the third
The transformer T1 in the figure is in an oven state, and the CCIT
Although it satisfies the output impedance specifications of the TI-430 when there is no signal, it has the disadvantage that it is difficult to meet the pulse mask specifications of the I-430 due to the occurrence of waveform undershoot as shown in FIG.

[Means for Solving the Problems] According to the present invention, by inserting a resistor in parallel to the input of the driver circuit transformer, it is possible to reduce the undershoot of the AMI output signal.

[Example] FIG. 1 shows a driver circuit showing an example of the present invention.
I is a pulse transformer, Tri, Tr2. Tr3. T
r4 is a switching transistor, R1-R8 are resistors for operating the transistors, IC and IC2 are inverters that invert the human input signals of AI and Ill, respectively, AI is an input terminal for generating a positive pulse of the AMI signal, 81 is an input terminal for generating a negative pulse of the AMi signal, C1 is an output terminal, and RIO is ^MI
A resistor according to the invention for suppressing signal undershoot.

Figure 2 is a time chart of the driver circuit, and the AI
and B1 are input signals, and CI is the ^MI output signal.

Next, in the above configuration, logic 1 (5v) is applied to the input terminal ^l.
When is applied, Tri and Tr2 become conductive, current flows through the line transformer T1, and a positive pulse is generated at the output terminal c1.

Furthermore, when logic 1 (5V) is applied to the input terminal Bl next, Tr3 and Tr4 become conductive, and the line transformer T
A current flows through I in the opposite direction to the above direction, and a negative pulse is generated at the output terminal C1.

In this circuit, input terminal ^1 and AI are both logic o
(ov), Tri, Tr2. Tr3 and Tr4 are cut off, and the line transformer T1 is disconnected from the transistor ↓
It is left open and input terminated by a resistor RIO.

First, from a state where logic 1 (5V) is applied to input terminal A1 and logic O (OV) is applied to input terminal Bl, logic 0 (OV) is applied to input terminal A1, and logic O (OV) is applied to input terminal B1.
Considering the case of transitioning to a state where V) is applied, initially the transistors Tri and Tr2 are conductive, so
A current flows through the line transformer Tl, and a positive pulse of AMI is generated at the output terminal C1.

Next, when both input terminals ^1.81 become logic O (OV),
Transistor Tr1. By changing Tr2 from the conductive state to the cutoff state in 6 lines, the current flowing through the line transformer T1 is stopped and a back electromotive force is generated.

Although an overshoot occurs at the output terminal C1 due to the back electromotive force, the overshoot can be reduced by the resistor R10 acting as a braking resistor.

It can be said that the signal waveform and output impedance are mainly determined by the specifications of the transformer. The amplitude is the turns ratio, the rising and falling waveforms are the leakage inductance, and the output impedance is determined by the stray capacitance and inductance.

Even if these were optimized, waveform undershoot was a problem, but according to the embodiment described above, the resistor RIO
solved this problem.

[Effects of the Invention] As described above, according to the present invention, waveform undershoot can be easily reduced by inserting a resistor in parallel on the drive side of the line transformer.

[Brief Description of the Drawings] Figure 1 is a circuit diagram of a driver circuit implementing the present invention, Figure 2 is a time chart of signals of the circuit in Figure 1, Figure 3 is a circuit diagram of a conventional driver circuit, and Figure 3 is a circuit diagram of a conventional driver circuit. FIG. 4 shows the AMI signal waveform generated by the circuit of FIG. In the figure, AI, Bl...input terminal, CI...output terminal, R1゜R2, R3, R4, R5, R6, R7, RB
---Transistors Trl, Tr2, Tr3
, resistance for operating Tr4, Tri, Tr2
, Tr3, Tr4- transistor, T I
... Line transformer, ICI, IC2... Inverter. −〇1〇

Claims (1)

[Claims] In a driver circuit that generates an AMI signal from the output of a pass transformer and has a high output impedance when sending out a space signal, by providing a braking resistor in parallel to the input of the pulse transformer, the signal applied to the input is separated from the mark signal by the space signal. A driver circuit that reduces undershoot of an AMI signal obtained from the output when changing to a signal.