Electric power conversion systems – Current conversion – Constant current to constant voltage or vice versa
Reexamination Certificate
2000-07-24
2001-11-27
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Constant current to constant voltage or vice versa
C327S103000
Reexamination Certificate
active
06324083
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of and an arrangement for converting a first electrical quantity to a second electrical quantity. The present invention particularly relates to the conversion of voltage to current and more specifically to a voltage/current converter implemented in a chip.
Such converters are generally known. Generally speaking, converters may be divided into two different types, such as for example a type in which the conversion is based on a transconductance, or a type in which the conversion is based on an electrical resistance. A converter of the first-mentioned type is described, for example, by Geert A. de Veirman and Richard G. Yamasaki in 1992 IEEE International Solid State Circuits Conference, ISSCC92/Session 4/Signal processing/Paper WP4.2/“27 MHz Programmable Bipolar 0.05° Equiripple Linear-Phase Lowpass Filter”. However, a drawback of a transconductance is its comparatively low linearity.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a converter with a linearity better than the linearity of a transconductance-based converter.
Converters of the second type, i.e. in which the conversion is based on an electrical resistance, generally have a better linearity. This means that the variation in output current (dI) in the case of a variation in input voltage (dV) is constant over a satisfactorily wide range. Hereinafter, a conversion coefficient &lgr; will be defined as &lgr;=dI/dV. It is desirable to be able to fabricate a converter in such a manner that the conversion coefficient &lgr; is precisely known in advance. In general, this conversion coefficient &lgr; depends on the resistance value of a conversion resistor. If a correction converter is constructed from discrete components a conversion resistor may be selected whose resistance value corresponds to a desired conversion resistance value. However, if the converter forms part of an on-chip circuit, where the conversion resistor is integrated on this chip, it is very difficult to ensure that the resistance value of the conversion resistor accurately corresponds to the resistance value required for the conversion. The deviation which generally occurs and which is caused by variations in process conditions during the fabrication of the chip, will also be termed “tolerance” &agr;. It is to be noted that this tolerance may have a considerable value, which is not known in advance and generally differs from wafer to wafer. On-chip integrated resistors may specifically have a tolerance of 30%.
Therefore, it is an object of the present invention to provide compensation for such a tolerance.
The invention is based on the insight that if a plurality of resistors are fabricated on a chip all these resistors will be fabricated by means of the same process steps and therefore all these resistors will have substantially the same inaccuracy or tolerance.
On the basis of this insight the present invention provides a converter having a conversion resistor and a compensation resistor, said conversion resistor and said compensation resistor being formed in the same process steps.
The invention further provides a chip including a plurality of converters which each have an associated conversion resistor and which have a single compensation resistor common to all said converters, all said conversion resistors and the compensation resistor being formed in the same process steps.
In accordance with a further important aspect of the present invention an accurate reference current is provided on a chip, which reference current is based on, for example, an external reference resistor, and a current derived from said accurate reference current is supplied as output current of a V/I converter, the ratio between the output current and the reference current being defined by the ratio between, on the one hand, a current determined by a conversion resistor and, on the other hand, by the current determined by the compensation resistor.
REFERENCES:
patent: 4100433 (1978-07-01), Duffy et al.
patent: 5463309 (1995-10-01), Kawano
patent: 5815012 (1998-09-01), Rivoir et al.
“A 27MHz Programmable Bipolar 0.05 Equiripple Linear-Phase Lowpass Filter”, by Geert A. De Veirman et al., IEEE International Solid-State Circuits Conference 1992, pp. 64,65, 244.
Derks Henk
Thus Franciscus Johannes Maria
Biren Steven R.
Nguyen Matthew
U.S. Philips Corporation
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