US 6,486,727 B1Granted

Low-power substrate bias generator disabled by comparators for supply over-voltage protection and bias target voltage

AssigneePericom Semiconductor Corp.

InventorDavid Kwong

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Abstract

A substrate bias generator has a ring oscillator disabled when a supply over-voltage condition is detected by a supply comparator, or when a target substrate voltage is reached. A substrate comparator compares the substrate voltage to a reference generated by a p-channel sense transistor that is independent of the substrate voltage. The substrate is sensed by an n-channel sense transistor with only its bulk connected to the substrate voltage. Current sources for the sense transistors and comparator are controlled by bias voltages generated by a voltage divider that switches from a high-power state to a low-power state once the substrate target is reached. Feedback turns off a high-current resistor, limiting current to that passing through a low-current resistor. The bias voltages are adjusted to reduce current to the sense transistors and comparator, reducing power. High current and power are used for fast sensing before the substrate target is reached.

Claims18

Dependent claims

A low-power substrate bias generator comprising:

an oscillator for generating pumping signals when activated, but being in a low-power state when disabled;
a charge pump, receiving the pumping signals from the oscillator, for pumping charge from a substrate to reduce a substrate voltage to a target;
a substrate comparator, sensing the substrate voltage and comparing the substrate voltage to a target, for disabling the oscillator when the substrate voltage has reached the target;
wherein the substrate comparator further comprises:
a reference-voltage generator for generating a current-reference voltage;
a current switch, coupled to the reference-voltage generator, for switching a large current through the reference-voltage generator when the substrate comparator is in the higher-power state, but for switching a smaller current through the reference-voltage generator when the substrate comparator is in the lower-power state;
wherein the reference-voltage generator switches the current-reference voltage between a first level for the higher-power state, and a second level for the lower-power state;
a sensing transistor, receiving the substrate voltage, for modulating a larger current when the current-reference voltage is at the first level, but for modulating a smaller current when the current-reference voltage is at the second level, the sensing transistor modulating a current in response to changes in the substrate voltage;
wherein the substrate comparator senses the substrate voltage more quickly when in the higher-power state than when in the lower-power state, and
a supply comparator, sensing a supply voltage and comparing a supply-independent reference voltage, for disabling the oscillator when the supply voltage is above a limit determined by the supply-independent reference voltage,
whereby the oscillator is disabled, entering the low-power state, when the substrate reaches the target or when the supply voltage is above the limit and whereby rapid substrate sensing is provided before the substrate voltage reaches the target, but the lower-power state is entered after the target is reached.

8 more elements

A power-reducing bias generator comprising:

ring oscillator means for generating an oscillating voltage;
charge pump means, receiving the oscillating voltage through a capacitor, for pumping charge from a pumped node;
supply-voltage comparator means for detecting when a supply voltage is over a limit;
a pumped-voltage detector means for detecting when the pumped node has reached a target voltage;
disable means, coupled to the supply-voltage comparator means and to the pumped-voltage detector means, for disabling the ring oscillator means when the supply-voltage comparator means detects that the supply voltage is over the limit, and for disabling the ring oscillator means when the pumped-voltage detector means detects that the pumped node has reached the target voltage;
wherein the ring oscillator means draws less current when disabled than when generating the oscillating voltage;
and
current-switching means, in the pumped-voltage detector means, for switching a detection current from a high current to a low current when the pumped-voltage. detector means determines that the pumped node has reached the target voltage;
wherein the current-switching means comprises:
boost switch means for switching on a boost current to increase a reference current;
voltage-reference means for generating a voltage reference that determines the detection current generated by the current-switching means, the voltage reference being generated in response to the reference current;
and
feedback means for driving an output of the pumped-voltage detector means to the boost switch means,
wherein the pumped-voltage detector means draws less current when the current-switching means switches the detection current to the low current when the pumped-voltage detector means determines that the pumped node has reached the target voltage,
whereby power is reduced in both the ring oscillator means and in the pumped-voltage detector means when the pumped node reaches the target voltage and whereby current is switched to increase the detection current.

12 more elements

A substrate-bias generator comprising:

an oscillator that is disabled and enters a lower-power mode in response to a disable signal;
a charge pump, driven by the oscillator, for generating a substrate bias below a ground;
a substrate comparator that generates a substrate-target signal that causes the disable signal to be activated when the substrate bias reaches a target, the substrate comparator having a high-power mode and a low-power mode wherein the substrate comparator more quickly senses the substrate bias when in the high-power mode than when in the low-power mode;
and
a feedback switch, activated by the substrate-target signal, for reducing current in the substrate comparator when the substrate-target signal is active to place the substrate comparator into the low-power mode, but for increasing current in the substrate comparator when the substrate-target signal is inactive to place the substrate comparator into the high-power mode,
whereby current is reduced in both the oscillator and the substrate comparator when the substrate bias reaches the target.

3 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/682,736Filed 11 Oct 2001
Granted: 26 Nov 2002
Term ends: Not estimatedThe source records don’t support an estimate.

Classification4 codes

H02M 3/073
Using capacitors charged and discharged alternately by semiconductor devices with control electrode , e.g. charge pumps: charge pumps of the…
H02M 1/0022
Control circuits providing compensation of output voltage deviations using feedforward of disturbance parameters: the disturbance parameters being…
H02M 1/0041
Details of control, feedback or regulation circuits: control circuits in which a clock signal is selectively enabled or disabled
H02M
Apparatus for conversion between ac and ac, between ac and dc, or