Computer-aided design and analysis of circuits and semiconductor – Nanotechnology related integrated circuit design
Reexamination Certificate
2000-04-18
2003-04-08
Smith, Matthew (Department: 2825)
Computer-aided design and analysis of circuits and semiconductor
Nanotechnology related integrated circuit design
C716S030000, C716S030000
Reexamination Certificate
active
06546528
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to systems and methods that perform evaluation on electric characteristics of printed-circuit boards in accordance with numerical analysis. In addition, this invention also relates to storage media storing programs and data that actualize evaluation of the electric characteristics of the printed-circuit boards.
Conventionally, engineers propose a variety of techniques that perform evaluation using numerical analysis as to whether printed-circuit boards operate normally or not. One of those techniques generally known corresponds to a circuit simulator called “PSPICE” (where “SPICE” is an abbreviation for “Simulation Program with Integrated Circuit Emphasis”, which is developed by the University of California at Berkeley), an example of which is described on pp. 25-27 of RF Design published on January of 1993. Another example of the circuit simulator is disclosed by Japanese Unexamined Patent Publication No. Hei 9-274623, which aims at improvement of accuracy and reduction of number of steps for simulation of transmission lines in upstream stages of designs of electric circuits fabricated on boards.
The content of the aforementioned publication will be described in detail with reference to
FIG. 23
, which is a block diagram showing a configuration of a transmission-line simulator.
The transmission-line simulator of
FIG. 23
operates as follows:
At first, there are provided components of electric circuits, which are being symbolized. The symbolized components (or component symbols) and their connection (or wiring pattern) are input to a display controller
101
, so that a display
102
shows on a screen a physical shape and wiring topology with regard to a board on which the components are interconnected together in accordance with the connection. The display controller
101
urges a human operator to select an appropriate property for the connection by means of an input device
103
. The property is forwarded to an electromagnetic field simulator
106
, which calculates line constants of the connection. Through calculations, the electromagnetic field simulator
106
creates a line model. A substitution block
105
receives the component symbols so as to extract a corresponding device model from a component library
105
a
. A combination block
107
combines the line model and device model together to form an equivalent circuit, which is a subject being evaluated. Thus, a circuit simulator
108
performs transmission-line analysis on the equivalent circuit with respect to its transmission-line delay characteristic and transmission-line reflection characteristic.
FIG. 24
shows an example of a circuit model in which a driver IC
201
and a receiver IC
202
are mounted (or fabricated) on a printed-circuit board
200
. The aforementioned simulator is capable of evaluating electric characteristics of signals, which are transmitted from the driver IC
201
to the receiver IC
202
by way of a line
203
.
That is, it is possible to produce an analysis model and its analysis result with respect to the circuit model formed on the board
200
shown in FIG.
24
. Namely,
FIG. 25A
shows an example of the analysis model, and
FIG. 25B
shows an example of the analysis result.
The analysis model of
FIG. 25A
simply shows the circuit model in which the driver IC
201
and the receiver IC
202
are connected together by way of the line
203
. Herein, an equivalent circuit being formed using a voltage source (or current source) and a certain value of impedance is substituted for the driver IC
201
, while an equivalent circuit being formed using a certain value of impedance is substituted for the receiver IC
202
. In addition, the line
203
is replaced with a simple equipotential line or a transmission line which is constructed by combining resistors, inductors and capacitors, for example.
The analysis results of
FIG. 25B
show a voltage waveshape, which is being measured at an input of the receiver IC
202
. This voltage waveshape includes relatively large “overshoot” in a rise portion, and it also includes “undershoot” in a decay portion. Such voltage waveshape cannot guarantee a normal operation of a subject circuit which is a subject being evaluated. Hence, it can be said that a printed-circuit board having such a subject circuit is inappropriate for manufacturing.
To improve electric characteristics, it is possible to propose another analysis model shown in
FIG. 26A
, in which a filter circuit
204
is inserted between the driver IC
201
and the line
203
. By insertion of such a filter circuit
204
, it is possible to suppress the overshoot and undershoot in the voltage waveshape, which is shown in FIG.
26
B.
Using the aforementioned operations of the transmission-line simulator, it is possible to change circuit parameters with ease. Thus, it is possible to optimize circuit design with ease. In addition, it is possible for engineers to grasp a signal waveshape of the circuit before actual manufacture of the printed-circuit board having the circuit. This reduces reprints of printed-circuit boards due to errors in circuit design. So, it is possible to reduce an amount of cost in manufacture of the printed-circuit boards.
In some cases, the printed-circuit boards are designed to have power supply circuits, which supply active components such as ICs and LSI devices with stable direct-current voltages, other than the aforementioned circuits that perform transmission and reception of signals.
FIG. 27
shows an example of an equivalent circuit which is created in connection with the power supply circuit. That is, the equivalent circuit of
FIG. 27
contains a power supply circuit
210
, which corresponds to an area encompassed by a dotted line.
Specifically, the equivalent circuit of
FIG. 27
contains an IC
205
being connected with a power terminal
206
and a ground terminal
207
, between which a capacitor
208
and a DC power source
209
are connected. Herein, the capacitor
208
acts as the power supply circuit
210
, while the DC power source
209
is provided outside of the board. In addition, the capacitor
208
is connected in proximity to the IC
205
. This provides replacement of the DC power source
209
. That is, the capacitor
208
supplies the IC
205
with electric charges, which are required for the IC
205
to perform switching operations. Incidentally, it is possible to use a low-impedance capacitor as the capacitor
208
. In that case, no variations are caused to occur in voltage between the power terminal
206
and ground terminal
207
even when the IC
205
performs the switching operations.
The aforementioned capacitor
208
is called a decoupling capacitor. Until recently, it is believed that the conventional circuit simulators do not have to analyze high frequency characteristics of the power source circuits, which are assumed as DC circuits by being coupled with the decoupling capacitors.
Recently, however, active components such as ICs and LSI devices are rapidly developed in operating frequencies to become higher and higher. This indicates necessity of evaluation being performed on the power supply circuits with respect to their high frequency characteristics. Until now, however, no engineers actually propose techniques for evaluation of the high frequency characteristics of the power supply circuit by numerical analysis. As a result, the engineers related to technologies of printed-circuit boards suffer from problems, as follows:
(1) It is impossible to sufficiently guarantee quality in circuit operations of the printed-circuit boards.
(2) The printed-circuit boards radiate unwanted electromagnetic waves. Now, a description will be given in detail with respect to the problem
(1). With respect to the decoupling capacitor, there are provided two kinds of impedance due to parasitic inductance, i.e., first impedance being caused by parasitic inductance of a decoupling capacitor itself and second impedance being caused by other parasitic inductance due to pads and via hole(s) for in
Harada Takashi
Sasaki Hideki
LandOfFree
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