Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2000-02-23
2001-08-28
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
Reexamination Certificate
active
06281745
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an internal power supply voltage generating circuit and to reducing overshoot caused when a feedback control responds to a drop in the internal power supply voltage.
2. Description of the Related Art
High-capacity semiconductor memory devices such as DRAMs having storage capacity greater than 64 Mbits commonly use a low supply voltage (typically 3.3 V or less) to reduce power consumption. However, other DRAMs, integrated circuits and systems use a higher supply voltage (typically about 5 V). Accordingly, a flexible semiconductor memory device should be able to utilize either power supply.
Conventionally, a semiconductor memory device includes an internal power supply voltage generating circuit that generates a stable internal supply voltage from the external supply voltage. When a word line is enabled, the semiconductor memory device consumes a relatively large amount of power, which can cause the voltage level of the internal power supply voltage to drop. This is commonly called as a DIP. If a DIP causes the internal supply voltage to remain low, the low supply voltage can create a fatal error in the circuit.
To improve response to a DIP, an internal power supply voltage generating circuit can use a feedback system. When a DIP occurs, the feedback system detects a voltage drop and increases the driving ability of the internal power supply to rapidly recover a normal voltage level. However, the conventional method, which increases the driving ability to improve response to a DIP, can cause an overshoot where the internal voltage rises above the desired level. The overshoot can be serious enough to cause a fatal error in the internal circuit. Specially, with a low external supply voltage of 3.3 V, the overshoot is typically small and does cause serious errors, but an overshoot with a high external supply voltage of 5 V can causes a fatal error.
One way to decrease the problems with overshoot is to improve the current capacity of the internal power supply to reduce DIP and the need for a feedback response. Increasing current capacity typically requires enlarging the capacitance of the power supply circuit to improve response to a DIP. Accordingly, the capacitance for the power supply circuit occupies a large area in a chip and increases the total IC area and cost. Another way to decrease problems with overshoot is to reduce or eliminate occurrences of DIP. This method increases recovery time and reduces the current charging word lines, but this method changes the operating speed of the chip.
Another concern in the internal supply voltage generating circuit is that the circuits that solve the problem of overshoot for a high external supply voltage of 5 V can have detrimental consequences when used with a low external supply voltage of 3.3 V.
SUMMARY OF THE INVENTION
In accordance with an aspect of the present invention, an internal supply voltage generator of a semiconductor memory device provides a selectable driver with a set-down circuit to reduce overshoot caused by a high external supply voltage. For a low external supply voltage, the driver directly drives an internal supply voltage without doing anything. For a high external supply voltage, the driver provides the high external supply voltage through the step-down circuit.
One embodiment of the invention is a device that includes a control circuit, a selection circuit, a step-down circuit, and a driver. The control circuit generates a control signal having a first voltage in a normal mode and a second voltage when controlling a DIP of an internal supply voltage. The control circuit compares the internal power supply voltage with a reference voltage when a word line is driven. The selection circuit includes a common node connected to the power supply terminal, a high voltage node and a low voltage node. The selection circuit selectively connects the high voltage node or the low voltage node to the common node according to the level of the external supply voltage. The step-down circuit, which typically includes a resistor or a MOS diode, connects to the high voltage node and serves to step down the external power supply voltage. The driver is between an internal circuit and a common connection point of the step-down circuit and the low voltage node. The driver provides the power supply voltage to the internal circuit in response to the control signal.
REFERENCES:
patent: 5298807 (1994-03-01), Salmon et al.
patent: 5321653 (1994-06-01), Suh et al.
patent: 5982162 (1999-11-01), Yamauchi
patent: 6097113 (2000-08-01), Teraoka et al.
Jang Hyun Soon
Kim Jae Hoon
Ryu Hoon
Heid David W.
Samsung Electronics Co,. Ltd.
Skjerven Morrill & MacPherson LLP
Zweizig Jeffrey
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