Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
1999-10-12
2001-02-27
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S538000, C323S316000
Reexamination Certificate
active
06194957
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority of European Patent Application No. 98308428.6, which was filed on Oct. 15, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to current mirrors.
2. Description of the Related Art
A conventional current mirror has an input or reference device, which is usually diode-connected, and an output device. For increased accuracy the diode connection may be replaced by an amplifier which senses the voltages on the output electrodes of the reference and output devices and provides an output to the control electrodes of the devices. Under some circumstances the output current may be incorrect because the circuit that feeds the reference device is usually imperfect. The output current of such a circuit may change if the voltage across it becomes too small. The amplifier attempts to force almost identical voltages on the output electrodes of the reference and output devices. If the output voltage of the current mirror approaches an extreme of the output voltage range, the current feeding the reference device may change substantially, and the output current will be incorrect. Furthermore, if at start-up the output voltage approaches the said extreme, the amplifier may force the output electrode of the reference device to a similar voltage, and the circuit may “lock-up” in this undesired state with no current flow.
SUMMARY OF THE INVENTION
According to this invention a current mirror comprises a reference device, an output device, each said device having first and second controlled electrodes and a control electrode, the control electrodes of the devices being connected together, an amplifier having an input connected to the first controlled terminal of the reference device and another input connected to the first controlled electrode of the output device, means for connecting output from the amplifier to the control electrodes of the devices, and means for connecting the first controlled and control electrodes of the reference device together in response to the voltage at the first controlled electrode of the output device exceeding a predetermined level.
The connecting means may comprise a comparator having an input connected to the first controlled electrode of the output device and another input for receiving a reference voltage, and a switch for connecting the first controlled and control electrodes of the reference device together in response to a predetermined output from the comparator. The means for connecting the amplifier output to the control electrodes of the devices may comprise a switch which opens in response to the predetermined output of the comparator.
REFERENCES:
patent: 5412348 (1995-05-01), Kasha et al.
patent: 5867012 (1999-02-01), Tuthill
patent: 6075407 (2000-06-01), Doyle
patent: 6091287 (2000-07-01), Salter et al.
patent: 6107789 (2000-08-01), Fryer et al.
patent: 0 403 195 A1 (1990-06-01), None
patent: 0 647 894 A2 (1994-10-01), None
patent: 0 715 239 A1 (1994-11-01), None
Fryer Martin A.
Royce Dominic Charles
Callahan Timothy P.
Englund Terry L.
Lucent Technologies - Inc.
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