Linear regulator with low overshooting in transient state

Details Linear regulator with low overshooting in transient state Linear regulator with low overshooting in transient state

2001-04-05

2002-05-14

Nguyen, Matthew (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

C323S274000

Reexamination Certificate

active

06388433

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of electronic circuits, and, more particularly, to low drop-out (LDO) type linear voltage regulators, namely low serial voltage drop-out regulators.
BACKGROUND OF THE INVENTION
Low drop-out (LDO) type linear voltage regulators, such as low serial voltage drop-out regulators, are used in a variety of applications. In particular, these regulators may be used in mobile telephones to deliver a regulated voltage from a battery power supply voltage to radio transmission/reception circuits.
By way of example, a standard linear regulator
10
is illustrated in FIG.
1
. An output of the regulator
10
delivers a regulated voltage Vout to a load Z. The load Z represents, for example, several radio circuits present in a mobile telephone. The regulator
10
is powered by a voltage Vbat delivered by a battery
1
and comprises a differential amplifier
2
whose output drives the gate G of a P-channel metal oxide semiconductor (PMOS) regulation transistor
3
. The output stage of the amplifier
2
has an internal resistance Rg (or gate resistance), shown in dashes, that determines the gain of the amplifier
2
and the maximum current that it can deliver at the output.
The transistor
3
receives the voltage Vbat at its source S. Its drain D, connected to the output of the regulator
10
, is connected to the anode of a capacitor Cst for filtering and stabilizing the voltage Vout. This capacitor Cst is parallel-connected with the load Z. The amplifier
2
receives a reference voltage Vref at its negative input and a feedback voltage Vfb at its positive output. The voltage Vfb is, for example, a fraction of the voltage Vout provided to the input of the amplifier
2
by a divider bridge including two resistors R
1
, R
2
.
Operation of a regulator of this kind, which is well known to those skilled in the art, includes modulating the gate voltage Vg of the transistor
3
using the amplifier
2
. This is done as a function of the difference between the voltage Vfb and the reference voltage Vref. When the voltage Vg is substantially smaller than Vbat−Vtp, the transistor
3
is on because its gate-source voltage Vgs is substantially higher than the threshold voltage Vtp. When the voltage Vg is higher than Vbat−Vtp, the transistor
3
is off. In a stabilized state, the voltage Vout is regulated in the neighborhood of its nominal valve Voutnom, which is equal to [(R
1
+R
2
)Vref/R
2
].
In an application such as supplying power to the radio circuits of a mobile telephone, it is important that the amplifier
2
consume as little electricity as possible to maintain the charge stored in the battery. To this end, the gate resistance Rg of the output stage of the amplifier
2
should be chosen so that it has a high value (e.g., 100 K&OHgr;) to limit the maximum current flowing in the output stage to the high state.
Furthermore, the regulation transistor
3
must have a low serial resistance RdsON in the on state (drain-source resistance) so that it can deliver high current without any prohibitive voltage drop-out at its terminals. Thus, the transistor
3
conventionally has a high gate width-to-length ratio. For example, the transistor
3
may have a gate width W of 2×10
5
micrometers for a gate length L of 0.6 micrometers, giving a W/L ratio in the range of 3×10
5
micrometers and a very great transistor width. Due to its size and its high W/L ratio, the transistor
3
also has a high gate capacitance Cg (shown in dashes in FIG.
1
), in the range of 100 to 200 picofarads.
These various characteristics are indispensable for obtaining a regulator with low consumption and low serial voltage drop-out. Yet, driving a regulation transistor that has high gate capacitance Cg with an amplifier with a limited maximum output current causes an undesirable overshooting phenomena, in certain conditions, at the output of the regulator.
By way of an example,
FIGS. 2A
,
2
B,
2
C illustrate a phenomena of voltage overshooting that appears at the output of the voltage regulator of a mobile telephone when the telephone sends data bursts or “GSM bursts” at regular intervals (e.g., every 4 milliseconds).
FIG. 2A
shows the battery voltage Vbat for which the nominal value Vbatnom is 3.5 V.
FIG. 2B
shows the gate voltage Vg whose value oscillates in the vicinity of a voltage Vgnom equal to Vbat−Vtp when the regulator is stabilized. In this case, this voltage is about 2.8 V if the threshold voltage Vtp of the transistor is 0.7 V. Finally,
FIG. 2C
shows the output voltage Vout whose rated value Voutnom is 2.8 V when the regulator is stabilized.
At a time t
1
, the radio circuits of the telephone go into operation to send a burst. The current consumed is very great and the voltage Vbat drops sharply below the rated value Voutnom (
FIG. 2A
) due to the internal resistance of the battery. The amplifier
2
is unbalanced, the voltage Vg goes to 0 (FIG.
2
B), the gate capacitance Cg is entirely discharged, and the transistor
3
is on. The regulator
10
thus works in follower mode, i.e., where the output voltage Vout is substantially equal to the voltage Vbat (FIG.
2
C).
At a time t
2
, the burst is terminated and the power consumed diminishes. The battery voltage Vbat rises again sharply (e.g., in one microsecond) (see
FIG. 2A
) until it reaches its nominal value Vbatnom. The output voltage Vout follows the voltage Vbat until, at a time t
3
, it reaches its nominal voltage Voutnom. At this time, the amplifier
2
releases its output from the low state towards the high state and the gate of the transistor
3
is connected to the voltage Vbat by the gate resistance Rg.
This would normally have led to the transistor
3
being immediately turned off. However, as shown in
FIG. 2B
, the gate voltage Vg increases very slowly due to the high value of the gate resistor Rg, which limits the current delivered, and the high value of the gate capacitance Cg. The output stage of the amplifier
2
is therefore unable to instantaneously charge the gate capacitor Cg and turn off the transistor
3
. The transistor
3
continues to be on and the voltage Vout continues to follow the voltage Vbat. As shown in
FIG. 2C
, a voltage peak OS thus appears at the output of the regulator. This voltage peak cannot dissipate until an instant t
4
when the gate voltage Vg crosses the value Vbat−Vtp that turns the transistor
3
off, provided the load Z consumes current.
SUMMARY OF THE INVENTION
It is an object of the present invention to limit the effect of overshooting at the output of a voltage regulator in a transient state without the need to modify the structure of a regulation transistor thereof to diminish its gate capacitance.
Another object of the present invention is to limit the effect of overshooting in the transient state without the need to increase the maximum current that can be delivered by the output of the regulation amplifier.
These and other objects, features, and advantages are provided by a voltage regulator including a regulation MOS transistor with low serial resistance and an amplifier whose output drives a gate of the transistor based upon a difference between a reference voltage and a feedback voltage. The regulation MOS transistor has a terminal which receives a supply voltage and another terminal connected to the output of the regulator. The regulator further includes a switch having one of its terminals connected to the gate of the regulation MOS transistor while its other terminal is taken to a potential for turning the regulation transistor off. Also, a switch controller or switch control means monitors the output of the regulator and controls the switch. The switch control means closes the switch when the output voltage of the regulator is higher than a first threshold, where the first threshold is higher than a nominal value of the output voltage.
More specifically, the switch control means are laid out to compare the output voltage of the regulator or a voltage proportional to the output voltage wit

Affiliated with

Also associated with

Rating

Linear regulator with low overshooting in transient state does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Linear regulator with low overshooting in transient state, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Linear regulator with low overshooting in transient state will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2853887