Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
1999-05-10
2001-09-18
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S112000, C326S083000, C326S087000
Reexamination Certificate
active
06292035
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a signal transmission device that is used to transmit a signal from a logic circuit through a transformer to another device.
2. Description of the Prior Art
Such a signal transmission device is used in a circuit that needs to meet strict requirements as to the overshoots and undershoots occurring in the circuits succeeding thereto, for example in a terminal adapter that is used to connect terminal equipment to an ISDN (integrated services digital network) line. As shown in
FIG. 4
, a conventional signal transmission device has, in its output stage, two pairs of serially connected P-channel and N-channel MOS transistors, QH
1
and QL
1
forming one pair and QH
2
and QL
2
forming the other pair, and an inverter circuit I for inverting the signal fed to the MOS transistors QH
2
and QL
2
. The two ends of the primary coil L
1
of a transformer are connected individually to the nodes K
1
and K
2
between the two transistors in those pairs. In a case where the primary coil L
1
is driven so that a square wave will appear between the two ends of the secondary coil L
2
, the gate voltages A, B, C, and D of the individual transistors are varied as shown at (a) in
FIG. 5
; that is, all the transistors are turned on or off simultaneously.
In this conventional circuit configuration, however, since all the transistors are turned on or off simultaneously, large transient variations occur in the current flowing through the coil L
1
, and thus large back electromotive forces are induced by the inductance of the coil L
1
. As a result, as shown at (b) in
FIG. 5
, overshoots OS and undershoots US occur in the square wave E that appears between the two ends of the coil L
2
.
In particular, at the node (generally called the S/T point) between a terminal adapter, which is used to connect terminal equipment to an ISDN line, and a DSU (digital service unit), where an interface employing a coil is customarily used, the ISDN standards set a very strict requirements that overshoot and undershoot be within approximately 10 mV. This requirement, however, is very difficult to meet as long as the conventional circuit configuration is used.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a signal transmission device that operates with reduced overshoots and undershoots.
To achieve the above object, according to one aspect of the present invention, in a signal transmission device for transmitting a signal from a logic circuit through a transformer to another device, two ends of a primary coil of the transformer are individually connected to coil driving circuits each having switching devices connected in series between a supplied voltage and a reference voltage so that the primary coil is driven by the coil driving circuits complementarily from both ends thereof, and the switching devices are turned on or off in such a way that those switching devices into which a current has thus far been flowing are turned from on to off with a delay with respect to the time point when the other switching devices are turned on or off.
According to another aspect of the present invention, a signal transmission device is provided with: logic circuits that produce a binary output on first and second lines respectively; first and second current sources; first and second delay means; a first transistor having its control electrode connected to the first line and having its first electrode connected to the first current source; a second transistor having its control electrode connected through the first delay means to the second line, having its first electrode connected to the second electrode of the first transistor, and having its second electrode connected to a predetermined voltage point; a third transistor having its control electrode connected to the second line and having its first electrode connected to the second current source; a fourth transistor having its control electrode connected through the second delay means to the first line, having its first electrode connected to the second electrode of the third transistor, and having its second electrode connected to the predetermined voltage point; a primary coil having one end connected to the second electrode of the first transistor and to the first electrode of the second transistor and having the other end connected to the second electrode of the third transistor and to the first electrode of the fourth transistor; and a secondary coil that together with the primary coil constitute a transformer. In this signal transmission device, switching of the transistors is so performed that, from the state in which the first and fourth transistors are on and the second and third transistors are off, first the second and third transistors are turned on and then, with a delay, the first and fourth transistors are turned off and that, from the state in which the second and third transistors are on and the first and fourth transistors are off, first the first and fourth transistors are turned on and then, with a delay, the second and third transistors are turned off.
REFERENCES:
patent: 5019719 (1991-05-01), King
patent: 5285477 (1994-02-01), Leonowich
patent: 5506522 (1996-04-01), Lee
patent: 5514921 (1996-05-01), Steigerwald
patent: 5521531 (1996-05-01), Okuzumi
patent: 5583451 (1996-12-01), Sharpe-Geisler
Arent Fox Kintner & Plotkin & Kahn, PLLC
Cunningham Terry D.
Nguyen Long
Rohm & Co., Ltd.
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