Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
1999-09-15
2001-04-17
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S541000, C327S542000, C327S543000, C327S312000, C327S315000
Reexamination Certificate
active
06218894
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electronic circuit with a voltage and/or current reference circuit.
2. Description of Related Art
Such a circuit is known from an article titled “New class of high-performance PTAT current sources”, by H. C.Nauta and E. H.Nordholt, published in Electronics letters Vol. 21 No. 9 pages 384 to 386, April 1985 (the Nauta article).
FIG. 1
shows a PTAT reference circuit disclosed in the Nauta article.
At the core of this PTAT reference circuit are two transistors and a resistor. Furthermore, the circuit disclosed in the Nauta article uses two (high impedance) current sources. The current sources on the one hand and the transistors and the resistor on the other hand are connected to opposite power supply poles. Thus the current sources are able to supply proportionally adjustable currents I to the transistors and the resistor (that is, the currents are adjusted so that the proportion between these currents remains fixed).
The PTAT reference circuit makes use of the logarithmic relation between base emitter voltage Vbe and junction current density i of bipolar transistors:
Vbe=kT/q
log
i/i
0
Here “log” is the natural logarithm and i0 is a standard current density which is substantially the same for any transistor. In the known PTAT reference circuit unequal current densities i1, i2 (where i1=n*i2) are supplied to two transistors by supplying the same current I to two transistors whose junction area differs by a factor n. As a result, there is a fixed difference dV between the base emitter voltages in the two transistors:
dV=kT/q
log
n
At the same time, the current I is fed through a resistor R, so that a voltage drop IR occurs through the resistor. A feedback loop adjusts the current supplied by the current sources so that the voltage drop compensates the dV difference between the junction. i.e. so that
IR=kT/q
log
n
Thus a reference current I is obtained.
The circuit disclosed in the Nauta article uses two (high impedance) current sources to supply the current I to the two transistors. This is in contrast to more conventional reference circuit designs, which use the (low impedance) input and (high impedance) output of a current mirror to supply the current I to respective ones of the transistors. By the use of two high impedance current sources, the Nauta article achieves high accuracy because it overcomes the detrimental consequences (e.g. supply voltage dependence) of the Early effect on the accuracy of the reference circuit.
However, it has been found that the reference circuit disclosed in the Nauta article has a potential instability problem, which can be overcome only by cumbersome additional circuits such as adding a relatively large capacitor between point A and Vnn. This capacitor undoes the elimination of the detrimental consequences of the Early effect at higher frequencies, because it causes an imbalance between the loads of the current sources; moreover the capacitor takes up circuit space.
BRIEF SUMMARY OF THE INVENTION
Amongst others, it is an object of the invention to provide for a circuit with a voltage and/or current reference circuit that achieves high accuracy and is stable even without a relatively large capacitor.
In the Nauta article, the feedback loop adjusts the currents from the current sources to obtain the desired current. This means that a voltage must be sensed on the transistors. This voltage is defined relative to the power supply pole of the transistors and the resistor. The sensed voltage must then be used to generate a control voltage for the current sources. This control voltage is defined relative to power supply pole of the current sources. Thus a shift of voltage reference is needed. It has been found that the circuits needed to shift from the one reference to the other give rise to the instability if no cumbersome measures are taken.
The need for this shift of voltage reference is removed by adjusting the current flowing the transistors by deviation of current through a deviation circuit which is connected to the same power supply pole as the transistors and the resistor. Thus stability is improved without a capacitor, at the price of a slightly increased current consumption, whereas the high accuracy may be retained. As a further advantage, the circuit does not need an additional startup circuit, as is the case for conventional PTAT current reference circuits.
These and other advantageous aspects of the invention will be described using the attached figures.
REFERENCES:
patent: 3962592 (1976-06-01), Tommen et al.
patent: 4435678 (1984-03-01), Joseph et al.
patent: 5304918 (1994-04-01), Khieu
patent: 5471132 (1995-11-01), Ryat
patent: 5481180 (1996-01-01), Ryat
patent: 5631600 (1997-05-01), Akioka et al.
patent: 5696440 (1997-12-01), Harada
patent: 6002245 (1999-12-01), Sauer
H.C. Nauta et al, “New Class of High-Performance PTAT Current Sources”, Electronics Letters Apr. 25, 1985, vol. 21, No. 9, pp. 384-386.
De Langen Klaas-Jan
Huijsing Johan H.
Cunningham Terry D.
U.S. Philips Corporation
Wieghaus Brian J.
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