CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2019-0137807 filed on Oct. 31, 2019, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties.

BACKGROUND

Embodiments of the inventive concept described herein relate to a regulator and an operating method thereof, and more particularly, relate to a time-based digital low-dropout (LDO) regulator and an operating method thereof.

A regulator is used to supply a stable power to various electronic circuits (or loads). Compared to an analog regulator, a digital LDO regulator is on the spotlight in terms of the ease of a frequency compensation characteristic and the expandability of process. A conventional digital LDO regulator includes a comparator, a shift register, and a switch array for the purpose of regulating an output voltage. The comparator may compare an output voltage output from the switch array with a reference voltage. The shift register may adjust the number of turned-on switches, depending on a comparison result.

However, in the case of the conventional digital LDO regulator, because the number of turned-on switches is quantized, the accuracy of an output voltage may decrease. Also, because the conventional digital LDO regulator regulates the output voltage by using the comparator, a limit cycle oscillation phenomenon may occur, thereby causing an increase of an output ripple. Also, in the case of the conventional digital LDO regulator, because the number of turned-on switches is adjusted one by one every rising edge of a clock, a transient response speed may be slow.

SUMMARY

Embodiments of the inventive concept provide a regulator capable of improving the accuracy of an output voltage and improving a transient response speed and an operating method thereof.

A regulator according to an embodiment of the inventive concept includes a switch array, a feedback circuit, a first voltage-controlled oscillator, a second voltage-controlled oscillator, and a switch driver. The switch array includes a plurality of switches connected in parallel and generates an output voltage based on a number of enabled switches from among the plurality of switches. The feedback circuit generates a feedback voltage which depends on a level of the output voltage. The first voltage-controlled oscillator generates a first signal having a first frequency which depends on a difference between a reference voltage and the feedback voltage. The second voltage-controlled oscillator generates a second signal having a second frequency which depends on a difference between the feedback voltage and the reference voltage. The switch driver determines a turn-on time point of each of the plurality of switches based on the first signal and determining a turn-off time point of each of the plurality of switches based on the second signal.

For example, when the reference voltage is greater than the feedback voltage, the first frequency is greater than the second frequency, and the number of the enabled switches increases depending on a difference between the first frequency and the second frequency. For example, when the feedback voltage is greater than the reference voltage, the second frequency is greater than the first frequency, and the number of the enabled switches decreases depending on a difference between the second frequency and the first frequency. For example, when the reference voltage is equal to the feedback voltage, the first frequency and the second frequency are equal to a reference frequency, and the turn-on time point and the turn-off time point of each of the plurality of switches are repeated at the reference frequency.

For example the first voltage-controlled oscillator may generate the first signal including a plurality of set signals having different phases and respectively corresponding to the plurality of switches. The second voltage-controlled oscillator may generate the second signal including a plurality of reset signals having different phases and respectively corresponding to the plurality of switches. The switch driver may turn on the plurality of switches respectively at different time points based on the different phases of the plurality of set signals and may turn off the plurality of switches respectively at different time points based on the different phases of the plurality of reset signals.

For example the switch driver may turn on the plurality of switches respectively corresponding to the plurality of set signals in response to rising edges of the different phases of the plurality of set signals and may turn off the plurality of switches respectively corresponding to the plurality of reset signals in response to rising edges of the different phases of the plurality of reset signals.

The regulator further includes a transient detector deactivating the first voltage-controlled oscillator when the level of the output voltage is greater than a first voltage level and deactivating the second voltage-controlled oscillator when the level of the output voltage is smaller than a second voltage level lower than the first voltage level. For example, when the level of the output voltage is greater than the first voltage level, the first voltage-controlled oscillator may delay generation of the first signal until the level of the output voltage is smaller than the first voltage level. The number of the enabled switches may decrease while the generation of the first signal is delayed. For example, when the level of the output voltage is smaller than the second voltage level, the second voltage-controlled oscillator may delay generation of the second signal until the level of the output voltage is greater than the second voltage level. The number of the enabled switches may increase while the generation of the second signal is delayed.

A regulator according to an embodiment of the inventive concept includes a switch array, a feedback circuit, a bias generator, a first voltage-controlled oscillator, a second voltage-controlled oscillator, a switch driver, and a transient detector. The switch array includes a plurality of switches connected in parallel between an input terminal and an output terminal. The feedback circuit generates a feedback voltage which depends on a voltage level of the output terminal. The bias generator generates a first input signal based on a difference between a reference voltage and the feedback voltage and generates a second input signal based on a difference between the feedback voltage and the reference voltage. The first voltage-controlled oscillator generates a plurality of set signals having different phases and respectively corresponding to the plurality of switches, based on the first input signal. The second voltage-controlled oscillator generates a plurality of reset signals having different phases and respectively corresponding to the plurality of switches, based on the second input signal. The switch driver sequentially turns on the plurality of switches based on respective phases of the plurality of set signals and sequentially turns off the plurality of switches based on respective phases of the plurality of reset signals. The transient detector controls a transfer of the first input signal to the second voltage-controlled oscillator and a transfer of the second input signal to the second voltage-controlled oscillator, based on the voltage level of the output terminal.

For example, the bias generator may generate the first input signal of a level proportional to a difference between the reference voltage and the feedback voltage and may generate the second input signal of a level proportional to a difference between the feedback voltage and the reference voltage. For example, the first voltage-controlled oscillator may include a first ring oscillator sequentially outputting the plurality of set signals at a time interval which depends on a level of the first input signal. For example, the second voltage-controlled oscillator may include a second ring oscillator sequentially outputting the plurality of reset signals at a time interval which depends on a level of the second input signal.

For example, during a time when the reference voltage and the feedback voltage are equal, a time interval when each of the plurality of switches is enabled may be uniformly maintained, and time intervals when the plurality of switches are enabled may be equal. For example, during a time when the reference voltage is greater than the feedback voltage, a time interval when each of the plurality of switches is enabled may increase. For example, during a time when the feedback voltage is greater than the reference voltage, a time interval when each of the plurality of switches is enabled may decrease.

For example, the transient detector may include a first comparator and a second comparator. The first comparator may generate a first enable signal when the voltage level of the output terminal is smaller than a first voltage level and may generate a first disable signal when the voltage level of the output terminal is greater than the first voltage level. The second comparator may generate a second enable signal when the voltage level of the output terminal is smaller than a second voltage level lower than the first voltage level and may generate a second disable signal when the voltage level of the output terminal is smaller than the second voltage level. The first voltage-controlled oscillator may receive the first input signal based on the first enable signal. The second voltage-controlled oscillator may receive the second input signal based on the second enable signal.

For example the regulator may further include a network circuit electrically connecting the bias generator and the first voltage-controlled oscillator based on the first enable signal, electrically disconnecting the bias generator from the first voltage-controlled oscillator based on the first disable signal, electrically connecting the bias generator and the second voltage-controlled oscillator based on the second enable signal, and electrically disconnecting the bias generator from the second voltage-controlled oscillator based on the second disable signal.

An operating method of a regulator according to an embodiment of the inventive concept includes generating an output voltage based on a number of enabled switches from among a plurality of switches included in a switch array, generating a feedback voltage which depends on a level of the output voltage, generating a plurality of set signals having a first frequency, which depends on a difference between a reference voltage and the feedback voltage, and having different phases, generating a plurality of reset signals having a second frequency, which depends on a difference between the feedback voltage and the reference voltage, and having different phases, sequentially turning on the plurality of switches, depending on respective phases of the plurality of set signals, and sequentially turning off the plurality of switches, depending on respective phases of the plurality of reset signals.

When the reference voltage is greater than the feedback voltage, the first frequency may be greater than the second frequency, and a number of enabled switches from among the plurality of switches may increase depending on a difference between the first frequency and the second frequency. When the feedback voltage is greater than the reference voltage, the second frequency may be greater than the first frequency, and the number of the enabled switches may decrease depending on a difference between the second frequency and the first frequency.

The operating method may further include delaying generation of the plurality of set signals until the level of the output voltage is smaller than a first voltage level, when the level of the output voltage is greater than the first voltage level, and delaying generation of the plurality of reset signals until the level of the output voltage is greater than a second voltage level, when the level of the output voltage is smaller than the second voltage level.

