Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
2000-02-24
2001-11-13
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
Reexamination Certificate
active
06316984
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to an interface circuit. More specifically, the present invention pertains to an interface circuit which is used for a switchboard, etc. to transmit signals at high speed.
BACKGROUND OF THE INVENTION
A backplane application is a system which can transmit a large volume of data in parallel. It is used in many types of industrial equipment (large-scale hard disk, switchboard, transmission device, measurement equipment, etc.).
Reference number
101
in
FIG. 6
represents a conventional backplane application. Said backplane application
101
comprises back board
102
and multiple cards
105
.
Back board
102
is made of a thin rectangular substrate. Multiple transmission lines
103
are formed on the back board. Said multiple transmission lines
103
are arranged in the longitudinal direction of back board
102
. The transmission lines are arranged in parallel to each other at prescribed intervals. Socket
104
is arranged on back board
102
in such a way that it crosses each transmission line
103
. There are multiple sockets
104
which are arranged at prescribed intervals.
Each card
105
has an internal circuit
106
, an input/output circuit
110
, wiring
121
, and a connection part (not shown in the figure). Internal circuit
106
is electrically connected to the connection part via input/output circuit
110
and wiring
121
.
Input/output circuit
110
has output circuit
108
and input circuit
109
which are connected back to back. Either output circuit
108
or input circuit
109
is operated under the control of internal circuit
106
.
Each card
105
has a signal line group
107
and a connector
118
. Internal circuit
106
is connected to an external device (not shown in the figure) via signal line group
107
and connector
118
.
In said backplane application
101
, one card
105
is inserted into one socket
104
. As shown in
FIG. 6
, each of three cards
105
1
-
105
3
are inserted into each of three sockets
104
1
-
104
3
, respectively.
In this case, the internal circuits
106
1
-
106
3
of cards
105
1
-
105
3
are electrically connected to each other via the connection parts of cards
105
1
-
105
3
and the transmission lines
103
on back board
102
.
In said plane application
101
, to transfer a signal from internal circuit
106
, of card
105
, on the output side to internal circuit
106
2
of card
105
2
on the input side, only output circuit
108
1
is switched into the active state in the input/output circuit
110
1
on the output side, and only input circuit
109
2
is switched into the active state in the input/output circuit
110
2
on the input side. When a high-voltage (high-level) signal or low-voltage (low-level) signal is output from output circuit
108
1
on the output side corresponding to the output signal of internal circuit
106
1
on the output side, the signal is output to transmission line
103
via wiring
121
1
on the output side and socket
104
1
. The signal is then input from transmission line
103
to internal circuit
106
2
on the input side via socket
104
2
of card
105
2
on the input side, wiring
121
2
, and input circuit
109
2
.
As described above, the signal is transferred from internal circuit
106
1
on the output side to internal circuit
106
2
on the input side.
In said backplane application
101
, one input/output circuit
110
on one card is connected to one transmission line
103
. Since multiple input/output circuits
110
are arranged on each card
105
, data with the same number of bits as the number of the input/output circuits
110
on a card can be transmitted in parallel among multiple internal circuits
106
in said backplane application
101
.
In said backplane application
101
, it is required that signals be transmitted as fast as possible between cards
105
. As shown in the equivalent circuit diagram illustrated in
FIG. 7
, terminal resistors
115
1
,
115
2
,
116
1
, and
116
2
are connected in series and arranged at the two ends of transmission line
103
.
However, parasitic capacitance is present in said back board
102
and in the wiring of each card
105
. Specifically, there is a large parasitic capacitance between input/output circuit
110
of each card
105
and wiring
121
of the socket. Since many cards
105
are installed on back board
102
, the total parasitic capacitance of backplane application
101
is very large.
Due to the aforementioned large parasitic capacitance, signals will vary significantly while being transmitted, and the potential of each wiring
121
also varies significantly. Since the potential of each wiring
121
is not stable over a long period of time, it will take a long time for the output of input circuit
109
to settle to either a high level or a low level. As a result, signals cannot be transmitted between output circuit
108
and input circuit
109
at high speed.
To suppress changes in the signal, the resistance values of terminal resistors
115
1
,
115
2
,
116
1
, and
116
2
are reduced. In this case, however, power consumption becomes very high. This is a problem.
The purpose of this invention is to solve the aforementioned problems of the conventional technology by providing a technology which can transmit signals at high speed.
SUMMARY OF THE INVENTION
In order to realize the aforementioned purpose, Claim
1
of the present invention provides an interface circuit having an input circuit whose input terminal is electrically connected to a signal line, and a clamping circuit, which is electrically connected between the aforementioned signal line and a reference voltage supply terminal and has such a configuration that it is able to maintain the voltage of the aforementioned signal line at a first clamping voltage, which is higher than the aforementioned reference voltage by a prescribed amount, or at a second clamping voltage which is lower than the aforementioned reference voltage by a prescribed amount.
According to Claim
2
of the present invention, in the interface circuit described in Claim
1
, the aforementioned clamping circuit has first and second diode circuits which are electrically connected in parallel with each other between the aforementioned signal line and reference voltage supply terminal, and the aforementioned first and second diode circuits are connected in opposite directions.
According to Claim
3
of the present invention, in the interface circuit described in Claim
2
, the aforementioned first or second diode circuit comprises two diodes which are connected in series.
According to Claim
4
of the present invention, in the interface circuit described in Claim
1
,
2
, or
3
, there is a switch circuit which is electrically connected between the aforementioned clamping circuit and reference voltage supply terminal.
As described above, in the present invention, the clamping circuit is connected to the signal line (wiring) connected to the input terminal (input side) of the input circuit.
Consequently, even when the input voltage of the input circuit varies significantly, since it is clamped to the first or second clamping voltage, the change in the input voltage will not exceed the voltage range between the first and second clamping voltages.
Therefore, compared with the conventional circuit in which the variation in the input voltage is not limited, the time that it takes for the input voltage of the input circuit to settle down and converge to a certain level can be shortened significantly. As a result, it becomes possible to transmit signals between the transmission lines and the circuit substrate at high speed.
The clamping circuit is connected to wiring. However, if the clamping circuit is connected to wiring far away from the input circuit, even if the input voltage is clamped to the first or second clamping voltage using the clamping circuit, it is still unable to stabilize the input voltage of the input circuit under the influence of the parasitic capacitance that exists between the input of the input circuit and the place where the clamping circuit is conn
Petersen Bret J.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
Zweizig Jeffrey
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