Method of emulating an ideal transformer valid from DC to...

Details Method of emulating an ideal transformer valid from DC to... Method of emulating an ideal transformer valid from DC to...

2000-01-31

2004-06-22

Thomson, W. (Department: 2128)

Data processing: structural design, modeling, simulation, and em

Simulating electronic device or electrical system

C703S014000, C703S018000, C703S023000, C716S030000, C716S030000

Reexamination Certificate

active

06754616

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods of simulating the behavior of circuit components to assist with the design of semiconductor devices, and more specifically, to a method of emulating an ideal transformer which is valid over a frequency range from DC to infinity.
2. Description of the Prior Art
Circuit simulation techniques are used in the semiconductor industry as an alternative to breadboarding the actual circuit designs. In many instances, the computer models used to emulate integrated circuit components have been found to accurately model device behavior that could not be duplicated using breadboard based versions of the components. This is because the breadboard parasitics dominate the characteristics of the microcircuit geometries, making it difficult to isolate the behavior of the actual circuit components from the effects of the breadboard. A well known circuit simulation program currently available is the SPICE program. This program is used for analyzing the operation of circuit elements and combinations of such elements.
One of the circuit elements which it is advantageous to be able to model is an ideal transformer. An ideal transformer can be used to perform an impedance transformation between two sub-circuits of an electrical circuit. An impedance transformation conserves the power transferred between the primary and secondary windings (i.e., the input and output sides) of the transformer, but takes into account that the two windings present different impedances to their respective sub-circuits by scaling the impedance. An ideal transformer may also be used in situations in which the inductance and losses of a real transformer can be neglected. Typically, an ideal transformer is represented as a pair of inductors which are coupled together with a magnetic coupling coefficient of unity, i.e., “perfect”coupling. The inductors represent the primary and secondary windings, respectively, of the ideal transformer.
FIG. 1
is a schematic diagram showing a representation of an ideal transformer
10
according to the prior art. Transformer
10
is represented as an input sub-circuit having two inputs (labeled “IN” in the figure) and an output sub-circuit having two outputs (labeled “OUT”in the figure). As shown in the figure, the sub-circuits of transformer
10
are represented or modeled as a first inductor
12
and a second inductor
14
, with the two inductors being magnetically coupled together. Inductor
12
contains N
1
turns, while inductor
14
contains N
2
turns. If the turn ratio (i.e., N
2
/N
1
) between the two inductors is defined as (n), then the voltage across the ideal transformer increases from the input side to the output side by a factor of n, while the current across the transformer decreases by a factor of n. Thus, for the ideal transformer of
FIG. 1
, V
out
=(n) V
in
and I
out
=−(1
) I
in
. This scaling of the voltage and current across the transformer conserves power between the transformer input and output. The impedance across the transformer increases by a factor of n
2
and produces no phase shift in the input signal.
However, the ideal transformer of
FIG. 1
has limitations. It does not properly represent the behavior of an actual transformer at DC since the impedance of an inductor at DC is zero. In addition, representing a transformer using inductors is computationally time consuming for low frequency calculations. This is because of the computer time needed to solve the cross-coupled differential equations which result from the
FIG. 1
representation of a transformer.
What is desired is a method of emulating the behavior of an ideal transformer which is valid over the frequency range from DC to an infinite frequency.
SUMMARY OF THE INVENTION
The present invention is directed to methods of representing an ideal transformer and simulating the behavior of an electrical circuit of which the ideal transformer is a part. The ideal transformer representation may be used to represent a transformer serving as a circuit element or to perform an impedance transformation between two parts of a circuit. In the broadest embodiments of the invention, the ideal transformer representations are frequency independent and can be used to emulate the behavior of a transformer over the frequency range from DC to infinity. In one embodiment, the ideal transformer is modeled as having an input sub-circuit and an output sub-circuit. Each sub-circuit comprises a resistor coupled in parallel with a current controlled current source. The current sources provide the current scaling and the resistors provide the impedance scaling. The input current, output current, current source currents, and resistances are scaled with the turns ratio between the primary and secondary windings of the ideal transformer. The circuit elements of each inventive representation of an ideal transformer can be used as the basis for generating a set of input parameters (or input deck) for a circuit emulation program.


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