Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2003-01-13
2004-10-26
Tra, Quan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S538000
Reexamination Certificate
active
06809577
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to semiconductor integrated circuits and particularly to those capable of detection and elimination of oscillation introduced in their internal voltage down conversion circuits.
2. Description of the Background Art
In recent years in LSI (Large Scale Integrated circuit) microfabrication insufficient breakdown voltages associated with transistors' gate oxide film reduced in thickness are complemented by providing a voltage down conversion circuit in semiconductor integrated circuits to down-convert external power supply voltage. The down-converted power supply is used as an operating voltage to ensure reliability.
Generally it is desirable that the down-converted power supply be able to supply a constant voltage however operating conditions may vary. Accordingly, a conventional, internal power supply voltage down conversion circuit generates a constant reference voltage impervious to a variety of external power supply and fabrication process variations and in accordance the reference voltage generates a down converted voltage. This configuration is shown in
FIG. 10
, as standardized.
FIG. 10
is a circuit diagram specifically showing one example of the conventional, internal power supply voltage down conversion circuit.
As shown in
FIG. 10
, the conventional internal power supply voltage down conversion circuit includes a comparator detecting a difference in potential between the level of an internal voltage and the reference voltage and outputting a result of the comparison as a power supply drive signal DRV, and a feedback loop driven by signal DRV to control a drive transistor
17
formed by a p-channel MOS (Metal Oxide Semiconductor) transistor.
The comparator is a current mirror differential amplifier formed of n-channel MOS transistors
16
and
15
having their respective gates receiving internal voltage VDL and reference voltage VREF, respectively, with p-channel MOS transistors
13
and
14
, having their sources connected to an external power supply node
6
, as a load.
P-channel MOS transistors
13
and
14
configure a current mirror circuit, the former's gate connected to the latter's gate and drain.
Transistor
15
has its drain connected to that of transistor
13
and its source grounded.
Transistor
16
has its drain connected to the drain and gate of transistor
14
and the gate of transistor
13
, its gate connected to an internal power supply node
2
and its source grounded.
The comparator has an output node, or the drain of transistor
15
, connected to the gate of drive transistor
17
.
Drive transistor
17
has its source connected to external power supply node
6
, its gate to the comparator's output node or the transistor
15
drain, and its drain connected to internal power supply node
2
.
When drive transistor
17
receives at its gate the power supply drive signal DRV output from the comparator, drive transistor
17
accordingly supplies a current to internal power supply node
2
connected to its source.
If in this configuration a current is supplied to a load (not shown) connected to internal power supply node
2
, drive transistor
17
acts as an impedance and the transistor's drain voltage, or internal voltage VDL, varies negatively. When internal voltage VDL starts to be lower than reference voltage VREF, the comparator outputs power supply drive signal DRV of the logical low level. Drive transistor
17
receiving signal DRV of the low level at its gate turns on and starts to charge internal power supply node
2
while supplying the load (not shown) with a current. When the node has been charged to a level and internal voltage VDL starts to be larger than reference voltage VREF, the comparator outputs power supply drive signal DRV having a logical high level. Drive transistor
17
having received signal DRV of the high level at its gate turns off and stops charging the node.
Thus the internal power supply voltage down conversion circuit eliminates variation in level of internal voltage VDL.
Furthermore a conventional, internal power supply voltage down conversion circuit prevents impaired low power characteristics in a standby state. To achieve this, when a large amount of power is consumed or in an active state a large current is synchronously passed to a load to eliminate variation in internal voltage VDL and when a small amount of current is consumed or in a standby state a current that is supplied is minimized to allow the internal power supply voltage down conversion circuit to be of small power.
Thus the conventional, internal power supply voltage down conversion circuit having an ability to supply a current that alters in the standby or active state of the semiconductor integrated circuit can eliminate variation in internal voltage VDL between modes of operation accompanied by different amounts of power consumption.
However, the current supplying ability in each mode is maintained to be constant throughout the mode.
FIG. 11
is a diagram representing a waveform of internal voltage VDL in the conventional, internal power supply voltage down conversion circuit.
As represented in
FIG. 11
, internal voltage VDL in a normal operation state maintains a constant level in voltage with reference to reference voltage VREF. If power consumption is large and the current supplying ability is excessively increased, however, internal voltage VDL oscillates, having a large variation relative to reference voltage VREF, and this may result in the semiconductor integrated circuit being unable to operate normally.
However, the conventional, internal power supply voltage down conversion circuit provides the current supplying ability that is maintained to be constant throughout each of the active and standby state. As such, if internal voltage VDL oscillates, the current supplying ability does not vary and the oscillation continues disadvantageously.
Furthermore, in estimating a semiconductor integrated circuit including a conventional, internal power supply voltage down conversion circuit, whether internal voltage is in oscillation or not cannot be determined by means other than directly monitoring the level of the internal voltage for example via a tester. As such if the tester for example has an insufficient capacity it can fail to detect that the internal voltage is in oscillation.
SUMMARY OF THE INVENTION
One object of the present invention is therefore to ensure detection of an oscillation introduced by a current excessively supplied in an internal power supply voltage down conversion circuit.
Another object of the present invention is to provide a semiconductor integrated circuit capable of reducing a current supplying ability to spontaneously eliminate an oscillation detected in the internal power supply voltage down conversion circuit.
In accordance with present invention in one aspect a semiconductor integrated circuit operates receiving at an internal circuit an internal voltage from an internal power supply node, the internal voltage being lower than an external power supply voltage, and it includes: an internal power supply voltage down conversion circuit generating the internal voltage at the internal power supply node, the internal voltage being the external power supply voltage decreased to a reference voltage corresponding to a targeted level; and an oscillation detection circuit outputting an oscillation detection signal when a variation of no less than a predetermined variation is observed in the internal voltage relative to the reference voltage a predetermined number of times within a predetermined period of time.
In accordance with the present invention in another aspect when the internal power supply voltage down conversion circuit receives the oscillation detection signal from the oscillation detection circuit the internal power supply voltage down conversion circuit reduces an ability to supply a current to the internal power supply node.
In accordance with the present invention in still another aspect the oscilla
Matsumoto Yasuhiro
Tanaka Kouji
McDermott Will & Emery LLP
Renesas Technology Corp.
Tra Quan
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