CN113760031A

CN113760031A - Low quiescent current NMOS type fully integrated LDO circuit

Info

Publication number: CN113760031A
Application number: CN202111069200.9A
Authority: CN
Inventors: 白春风; 张开
Original assignee: Suzhou University
Current assignee: Suzhou University
Priority date: 2021-09-13
Filing date: 2021-09-13
Publication date: 2021-12-07
Anticipated expiration: 2041-09-13
Also published as: CN113760031B

Abstract

The invention discloses a low quiescent current NMOS type fully integrated LDO circuit, which comprises an error amplifier circuit, a self-adaptive bias current source circuit, an NMOS tube N5, resistors R1 and R2, a frequency compensation circuit, an upper overshoot detection circuit for self-adaptively controlling the opening and closing of the NMOS tube N6 and a lower overshoot detection circuit for self-adaptively controlling the opening and closing of a PMOS tube P5; the overshoot detection circuit turns on the NMOS transistor N6 when the overshoot is detected to provide additional bias current to the error amplifier circuit; the undershoot detection circuit turns on PMOS transistor P5 when the undershoot is detected to provide additional bias current to the error amplifier circuit. The invention can realize the quick response of the fully integrated LDO facing the load current switching rate of dozens of A/mu s with very low static current.

Description

Low quiescent current NMOS type fully integrated LDO circuit

Technical Field

The invention relates to the technical field of integrated circuit design, in particular to a low-static-current NMOS (N-channel metal oxide semiconductor) type fully-integrated LDO (low dropout regulator) circuit.

Background

Low Drop Out (LDO) linear regulators, commonly used for short as LDOs, are circuit modules that provide a clean, stable voltage source. Full integration requires that all of its components be implemented on-chip to power modules in a system on chip (SoC). The SoC often requires multiple fully integrated LDOs to power it, such as one analog module, one rf module, and another LDO for other modules. The simulation module has small interference on an input power supply of the LDO, and the load current changes slowly; the radio frequency module is easy to interfere with an input power supply of the LDO, a full-band high Power Supply Rejection Ratio (PSRR) is needed, load current changes rapidly, but the change amplitude of the load current is not large; other digital circuit blocks and mixed signal circuit blocks may cause a sudden load current change due to momentary sleep or turning on some or all of the digital blocks, in which case especially the undershoot voltage of the LDO may cause the circuit to restart or affect the normal operation of other blocks if the magnitude is too large or the recovery time is too long.

Fig. 1 to 3 show 3 basic structures of a fully integrated LDO, in which:

referring to fig. 1, the PMOS transistor is used as a power transmission transistor in the first structure, which is easy to obtain an extremely low dominant pole through miller compensation to ensure the stability of a loop, and has the advantages of large load current range, good linear regulation rate and load regulation rate, and the like; but also suitable for working under lower power supply voltage. However, the gate-drain parasitic capacitance of the power transfer tube can limit the loop bandwidth; and the power supply rejection ratio is poor because the source of the power transmission tube is connected with the input power supply.

Referring to fig. 2, in the second structure, an NMOS transistor is used as a power transmission transistor, and a loop bandwidth changes little with a load, so that loop stability is good; the parasitic effect is small, and the broadband is easy to realize; the drain electrode of the NMOS power transmission tube is connected with an input power supply, so that the power supply rejection capability is better. However, since the gate of the power pass transistor is higher than the output voltage by a VGS, the error amplifier is required to have a higher operating voltage, but this is not a problem in most electronic systems, because the standard supply voltage of the I/O is 2.5/3.3V, and the bandgap reference is generally supplied with a voltage of 2.5/3.3V, which is much higher than the voltage of 1-1.2V required by the SoC core. The bias current of the error amplifier is typically very small and does not affect the interface circuit.

Referring to fig. 3, the third structure adopts the FVF structure, which is actually a variation of the first structure, and is compact and suitable for fully integrated implementation and fast response occasions; but the loop response is complex, which results in a small output current adjustment range.

The fully integrated LDO does not rely on an off-chip large capacitor to maintain a low output impedance as in a conventional LDO, and therefore, the overshoot voltage during load switching is generally large. Improving the output slew rate of the error amplifier to accelerate the recovery of the overshoot voltage is a basic approach for suppressing the overshoot amplitude. At the same time, the quiescent current of the LDO must be very small to ensure high current efficiency.

In order to reduce the overshoot amplitude during sudden load change, the conventional LDO circuit architecture is generally connected with a large off-chip capacitor of the μ F stage at the output terminal. In the SoC system, for convenience of on-chip integration, output capacitors of the LDO are all built-in, and the capacitance values of the capacitors which can be realized on the chip are generally not large, and the capacitance values are generally at pF level; furthermore, chip area is also an important design constraint, sometimes not even adding any extra output capacitance. This can cause a problem of large overshoot amplitude of the LDO during load switching, especially the overshoot, which if too large may cause an unexpected restart of the circuit.

In order to improve the transient response performance of the load, suppress the overshoot voltage at the output end and select a reasonable frequency compensation scheme to stabilize the loop, the LDO circuit usually needs additional complex circuits to control the charging and discharging of the gate of the output power transistor, and these additional circuits usually mean more current branches, which inevitably increases the quiescent current of the LDO.

Low quiescent current is a basic requirement of a linear regulator, and refers to the current consumed by the LDO itself when the external load current is zero. The device comprises a reference voltage source, an error amplifier, an output divider resistor and other circuits. The quiescent current is determined by the topology, input voltage and temperature.

In order to extend the service time of a battery-powered system, SoC systems generally require low power consumption in standby mode, and how to achieve fast response of a fully integrated LDO facing a load current switching rate of several tens of a/μ s with very low quiescent current is a problem to be solved by those skilled in the art.

Disclosure of Invention

The invention aims to provide a low-static-current NMOS type fully-integrated LDO circuit, which realizes the quick response of the fully-integrated LDO facing the load current switching rate of dozens of A/mu s at very low static current.

The technical scheme of the invention is as follows: a low quiescent current NMOS type fully integrated LDO circuit comprises an error amplifier circuit, a self-adaptive bias current source circuit, an NMOS tube N5 serving as a power transmission tube, resistors R1 and R2 serving as load resistors, a frequency compensation circuit, an upper overshoot detection circuit and a lower overshoot detection circuit, wherein the upper overshoot detection circuit is used for adaptively controlling the opening and closing of the NMOS tube N6, and the lower overshoot detection circuit is used for adaptively controlling the opening and closing of a PMOS tube P5;

the overshoot detection circuit is configured to turn on NMOS transistor N6 upon detection of an overshoot to provide additional bias current to the error amplifier circuit, and turn off NMOS transistor N6 when the overshoot voltage on the output returns to near steady state;

the overshoot detection circuit is configured to turn on the PMOS transistor P5 when overshoot is detected, and to provide additional bias current to the error amplifier circuit through a current mirror formed by NMOS transistors N7-N8, and to turn off the PMOS transistor P5 when the output overshoot voltage returns to a value close to a steady state;

the drain of the NMOS transistor N5 is electrically connected to the voltage source VDD1 and the first input terminal of the lower overshoot detection circuit, the source of the NMOS transistor N5 is electrically connected to one end of the resistor R1, the first input terminal of the upper overshoot detection circuit and the second input terminal of the lower overshoot detection circuit, respectively, and serves as the output power source terminal VP of the LDO circuit, and the other end of the resistor R1 is electrically connected to one end of the resistor R2, the second input terminal of the upper overshoot detection circuit and the bias voltage source VB, respectively;

the other end of the resistor R2 is grounded.

In the above technical solution, the error amplifier circuit adopts a telescopic cascode structure, which includes NMOS transistors N1-N4, PMOS transistors P1-P4, and a bias current source IB 1,

the source electrode of the PMOS tube P1 is electrically connected to a voltage source VDD2, the grid electrodes are respectively and electrically connected to the grid electrode of the PMOS tube P2, the drain electrode of the PMOS tube P3 and the drain electrode of the NMOS tube N3, and the drain electrode is electrically connected to the source electrode of the PMOS tube P3;

the source electrode of the PMOS transistor P2 is electrically connected to a voltage source VDD2, and the drain electrode is electrically connected to the source electrode of the PMOS transistor P4;

the grid electrode of the PMOS tube P3 is electrically connected to a bias voltage source VB2 and the grid electrode of the PMOS tube P4 respectively;

the drain electrode of the PMOS tube P4 is respectively and electrically connected to the grid electrode of the NMOS tube N5 and the drain electrode of the NMOS tube N4;

the grid electrode of the NMOS transistor N3 is respectively and electrically connected to a bias voltage source VB 1 and the grid electrode of the NMOS transistor N4, and the source electrode is electrically connected to the drain electrode of the NMOS transistor N1;

the source electrode of the NMOS transistor N4 is electrically connected to the drain electrode of the NMOS transistor N2;

the gate of the NMOS transistor N1 is electrically connected to a reference voltage source VR, and the sources are respectively electrically connected to the source of the NMOS transistor N2 and grounded via a bias current source IB 1;

the gate of the NMOS transistor N2 is electrically connected to the output power source terminal VP.

In the above technical solution, the adaptive bias current source circuit includes NMOS transistors N6-N8 and a PMOS transistor P5, wherein,

the source electrode of the PMOS tube P5 is electrically connected to a voltage source VDD2, the grid electrode of the PMOS tube P5 is electrically connected to the output end of the overshoot detection circuit, and the drain electrode of the PMOS tube P5 is respectively and electrically connected to the grid electrode and the drain electrode of the NMOS tube N7 and the grid electrode of the NMOS tube N8;

the source electrode of the NMOS transistor N6 is grounded, the grid electrode is electrically connected to the output end of the overshoot detection circuit, and the drain electrode is respectively and electrically connected to the source electrode of the NMOS transistor N1 and the source electrode of the NMOS transistor N2;

the source electrode of the NMOS transistor N7 is grounded;

the source of the NMOS transistor N8 is grounded, and the drain is electrically connected to the drain of the NMOS transistor N6.

In the above technical solution, the overshoot detection circuit includes a PMOS transistor P7, an NMOS transistor N9, an NMOS transistor N10, a bias current source IB2, and a capacitor C1;

the source electrode of the PMOS tube P7 is electrically connected to a voltage source VDD2 and is respectively and electrically connected to the gate electrode of the PMOS tube P7, the gate electrode of the NMOS tube N9 and the drain electrode of the NMOS tube N10 through a bias current source IB2, and the drain electrode is respectively and electrically connected to the gate electrode of the NMOS tube N6 and the drain electrode of the NMOS tube N9;

the source electrode of the NMOS transistor N9 is grounded;

the grid electrode of the NMOS transistor N10 is respectively and electrically connected to one end of a capacitor C1 and a bias voltage source VB, and the source electrode is grounded;

the other end of the capacitor C1 is electrically connected to the output power source terminal VP.

In the above technical solution, the overshoot detection circuit includes a PMOS transistor P8, a PMOS transistor P9, an NMOS transistor N11, and a bias current source IB 3;

the source electrode of the PMOS tube P8 is electrically connected to a voltage source VDD1, the gate electrode is electrically connected to an output power supply end VP, and the drain electrode is respectively electrically connected to the gate electrode of the PMOS tube P9 and the gate electrode of the NMOS tube N11 and grounded through a bias current source IB 3;

the source electrode of the PMOS tube P9 is electrically connected to a voltage source VDD2, and the drain electrode is respectively and electrically connected to the grid electrode of the PMOS tube P5 and the drain electrode of the NMOS tube N11;

the source of the NMOS transistor N11 is grounded.

In the technical scheme, the device further comprises a PMOS tube P6 and a resistor R3;

the source and the drain of the PMOS transistor P6 are both electrically connected to the gate of the NMOS transistor N5, and the gate is electrically connected to one end of a resistor R3;

the other end of the resistor R3 is grounded.

In the above technical solution, the device size ratio of the NMOS transistor N7 to the NMOS transistor N8 is 1: 4.

The invention has the advantages that:

1. the tail current of the error amplifier circuit consists of a bias current source IB 1, an NMOS tube N6 and a dynamic current provided by an NMOS tube N8, wherein the bias current source IB 1 is determined and is determined by bias voltage, the dynamic current is almost zero in a steady state, and the NMOS tube N6 and the NMOS tube N8 are not started at the same time;

2. the PMOS transistor P6 of the present invention has multiple utilities: a. the reverse voltage-stabilizing characteristic of a PN junction between the N-type substrate of the undershoot transient PMOS pipe P6 and the two ends of the P-type source drain provides transient current between the N5 gate and the source of the NMOS pipe, so that undershoot voltage is greatly attenuated, and the undershoot recovery is accelerated; b. frequency compensation is carried out to improve the stability in no-load, so that the quiescent current is further reduced; c. in addition, the gate-source capacitance of the PMOS tube P6 can effectively inhibit power supply noise coupled to the gate of the NMOS tube N5, and the PSRR is favorably improved;

3. the low-power-consumption overshoot detection circuit works only when the load current is instantly reduced, the voltage at two ends of an overshoot instant capacitor C1 is pulled high, the gate-source voltage of an NMOS tube N10 is increased, a current source works, a phase inverter detects the voltage drop of an input end, so that the voltage of an output end is raised, the NMOS tube N6 works, the current is injected into an error amplifier circuit through the NMOS tube N6, and the static current of the output circuit is almost zero when the output is in a steady state;

4. the overshoot detection circuit under low power consumption works when the load current is increased instantly, the gate-source voltage of the PMOS pipe P8 is increased at the moment of undershoot, the current source works, the inverter detects the voltage rise of the input end, the voltage of the output end is reduced, the PMOS pipe P5 is conducted, then the current is injected into the tail current of the error amplifier circuit through the mirror current source, and the quiescent current of the output error amplifier circuit is almost zero when the output is in a steady state.

Drawings

The invention is further described with reference to the following figures and examples:

fig. 1 is a basic circuit diagram of a prior art LDO linear regulator using a PMOS transistor as a power transfer transistor.

Fig. 2 is a basic circuit diagram of a prior art LDO linear regulator using an NMOS transistor as a power transfer transistor.

Fig. 3 is a basic circuit configuration diagram of an LDO linear regulator employing an FVF structure in the related art.

Fig. 4 is a main circuit diagram of the linear regulator of the present invention.

Fig. 5 is a circuit configuration diagram of the upper overshoot detection circuit of the present invention.

Fig. 6 is a circuit configuration diagram of the overshoot detection circuit of the present invention.

Fig. 7 is a load transient response diagram of the present invention.

FIG. 8 is a graph of the undershoot response of the present invention when the load current is switched from 200 μ A to 50mA for 1ns versus a normal NMOS type.

Fig. 9 is a comparison of the overshoot response of the present invention when the load current is switched from 50mA to 200 ua at 1ns, compared to a conventional NMOS type LDO.

FIG. 10 is a schematic diagram of the loop gain and stability of the present invention (the loop gain and stability in the range of 1 Hz-100 MHz when the load currents are 0, 0.2mA, 2mA, 20mA, and 60 mA).

Fig. 11 is a diagram of linear adjustment rate of the present invention (the input voltage changes from 1.25V to 1.5V corresponding to the load currents of 0, 0.2mA, 2mA, 20mA, and 50mA, respectively).

Fig. 12 is a schematic diagram of the load regulation rate of the present invention (the output voltage changes corresponding to the load current changes from 0 to 60mA when Vdropout is 40mV, 150mV, 200mV, and 400mV, respectively).

FIG. 13 is a diagram illustrating PSRR without load capacitance according to the present invention.

FIG. 14 is a diagram of PSRR with 100pF load capacitance applied in accordance with the present invention.

Detailed Description

Example (b):

referring to fig. 4, the present invention provides a low quiescent current NMOS type fully integrated LDO circuit, which includes an error amplifier circuit, an adaptive bias current source circuit, an NMOS transistor N5 as a power transfer transistor, resistors R1 and R2 as load resistors, a frequency compensation circuit, an upper overshoot detection circuit and a lower overshoot detection circuit, wherein the upper overshoot detection circuit adaptively controls the on and off of the NMOS transistor N6, and the lower overshoot detection circuit adaptively controls the on and off of the PMOS transistor P5;

the other end of the resistor R2 is grounded.

In this embodiment, the error amplifier circuit is a telescopic cascode structure, which includes NMOS transistors N1-N4, PMOS transistors P1-P4, and a bias current source IB 1,

In this embodiment, the adaptive bias current source circuit includes NMOS transistors N6-N8 and a PMOS transistor P5, wherein,

the source electrode of the NMOS transistor N7 is grounded;

Referring to fig. 5, in the present embodiment, the overshoot detection circuit includes a PMOS transistor P7, an NMOS transistor N9, an NMOS transistor N10, a bias current source IB2, and a capacitor C1;

the source electrode of the NMOS transistor N9 is grounded;

Referring to fig. 6, in the present embodiment, the overshoot detection circuit includes a PMOS transistor P8, a PMOS transistor P9, an NMOS transistor N11, and a bias current source IB 3;

the source of the NMOS transistor N11 is grounded.

In the embodiment, the transistor further comprises a PMOS tube P6 and a resistor R3;

the other end of the resistor R3 is grounded.

In this embodiment, the device size ratio of the NMOS transistor N7 to the NMOS transistor N8 is 1: 4.

In order to ensure the gain, the bandwidth and the output slew rate of the error amplifier circuit, the invention adopts the NMOS tube as the circuit structure of the LDO linear voltage stabilizer of the power transmission tube, and in order to ensure that the transient recovery speed can meet the requirement of the establishment time, the invention adopts the method that the bias current of the error amplifier circuit is increased in a self-adaptive manner at the moment of load switching, and the output slew rate of the error amplifier circuit is improved to accelerate the recovery speed.

In order to solve the problem of low power consumption of the LDO, the low-power-consumption upper overshoot detection circuit and the low-power-consumption lower overshoot detection circuit adopted by the invention only work when the load changes in a transient state, and are in a closed state in a steady state, namely, only the error amplifier circuit and the power transmission tube work in the steady state, and no redundant circuit branch consumes current, so that low quiescent current is realized, and further low quiescent power consumption is realized.

With continued reference to fig. 4, the basic approach of the present invention to reduce the settling time is to increase the output slew rate of the error amplifier circuit by adaptive biasing, i.e., turning on the NMOS transistor N6(NMOS transistor N8) during the up (down) overshoot to provide extra large bias current for the error amplifier circuit. In addition, the PMOS transistor P6 has two functions: (1) the PN junction between the source and drain and the N well substrate plays a role in stabilizing voltage when overshoot is caused by the forward rapid change of load current; (2) the gate source and gate drain parasitic capacitance and the resistor R3 form a phase lead compensation structure for frequency compensation, and the frequency compensation is also beneficial to reducing the static power consumption of the system, because the zero point introduced by the frequency compensation can be used for compensating the influence of the output pole moving to the lowest value in the low frequency direction in no-load.

With continued reference to fig. 5 and 6, a circuit diagram of the low power consumption overshoot detection circuit is provided, which is characterized in that almost no static current is generated during steady state output, and the static power consumption of the whole LDO is greatly reduced. When the output voltage is in a steady state, the NMOS transistor N10 and the PMOS transistor P8 both work in a cut-off region, bias current sources IB2 and IB3 in the low-power-consumption overshoot detection circuit and the low-power-consumption overshoot detection circuit both work in a linear region, and the currents are very small.

When the overshoot occurs, the NMOS transistor N10 is turned on, the voltage at the drain of the NMOS transistor N10 is pulled down, and the NMOS transistor N6 is turned on through the inverter (the PMOS transistor P7 and the NMOS transistor N9), so as to provide extra bias current for the error amplifier circuit to improve the output slew rate and accelerate the recovery speed of the overshoot.

When undershoot occurs, the PMOS tube P8 is opened, the voltage of the drain electrode of the PMOS tube P8 is pulled high, the PMOS tube P5 is further opened through the phase inverter (the PMOS tube P9 and the NMOS tube N11), and then extra bias current is provided for the error amplifier circuit through a current mirror formed by the NMOS tube N7 and the NMOS tube N8, so that the output slew rate is improved, and the undershoot recovery speed is accelerated.

Embodiments of the present invention are implemented in a 180nm CMOS process with the goal of providing a supply voltage of 1.2V to the core and a maximum load current of 50 mA. The working voltage of the error amplifier circuit can be 2.5-5V, and the power supply voltage of the NMOS tube N5 can be 1.25-1.6V. The no-load quiescent current of the invention is only 3.6 muA, and the aim of low quiescent current is realized.

The advantages of the present invention will be described in detail with reference to the accompanying drawings

Referring to fig. 7, the present invention has a significant effect of increasing the overshoot recovery speed when the load current is switched between 200 μ a and 50mA in 1ns, which is particularly significant.

Referring to fig. 8, the lower overshoot voltage can return to within 10% of the final value (i.e., 1.15V) in 160 ns.

Referring to fig. 9, the upper overshoot voltage can be restored to within 10% of the final value (i.e., 1.22V) within 240 ns.

As shown in FIG. 10, the invention has good stability within 0-60 mA of load current.

Referring to FIG. 11, the linear adjustment rates were 0.018mV/V,0.01mV/V, 0.014mV/V, 0.096mV/V, and 0.32mV/V at no-load, 0.2mA, 2mA, 20mA, and 60mA load currents, respectively.

Referring to FIG. 12, when Vdropout is 40mV, 150mV, 200mV, 400mV, respectively, the load adjustment rates are 5.67mV/A, 4.1mV/A, 4.05mV/A, 4mV/A, respectively.

Referring to fig. 13 and 14, the present invention has good PSRR characteristics, and can maintain a power supply rejection of more than 10dB at high frequencies.

It should be understood that the above-mentioned embodiments are only illustrative of the technical concepts and features of the present invention, and are intended to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the scope of the present invention. All modifications made according to the spirit of the main technical scheme of the invention are covered in the protection scope of the invention.

Claims

1. A low quiescent current NMOS type fully integrated LDO circuit comprises an error amplifier circuit, an adaptive bias current source circuit, an NMOS tube N5 as a power transmission tube, resistors R1 and R2 as load resistors, a frequency compensation circuit, an upper overshoot detection circuit and a lower overshoot detection circuit, and is characterized in that: the upper overshoot detection circuit adaptively controls the on and off of an NMOS transistor N6, and the lower overshoot detection circuit adaptively controls the on and off of a PMOS transistor P5;

the other end of the resistor R2 is grounded.

2. The low quiescent current NMOS-type fully integrated LDO circuit of claim 1, wherein: the error amplifier circuit adopts a sleeve type cascode structure and comprises NMOS transistors N1-N4, PMOS transistors P1-P4 and a bias current source IB 1, wherein,

3. The low quiescent current NMOS-type fully integrated LDO circuit of claim 1, wherein: the self-adaptive bias current source circuit comprises NMOS transistors N6-N8 and a PMOS transistor P5, wherein,

the source electrode of the NMOS transistor N7 is grounded;

4. The low quiescent current NMOS-type fully integrated LDO circuit of claim 1, wherein: the upper overshoot detection circuit comprises a PMOS tube P7, an NMOS tube N9, an NMOS tube N10, a bias current source IB2 and a capacitor C1;

the source electrode of the NMOS transistor N9 is grounded;

5. The low quiescent current NMOS-type fully integrated LDO circuit of claim 1, wherein: the lower overshoot detection circuit comprises a PMOS tube P8, a PMOS tube P9, an NMOS tube N11 and a bias current source IB 3;

the source of the NMOS transistor N11 is grounded.

6. The low quiescent current NMOS-type fully integrated LDO circuit of claim 1, wherein: the PMOS transistor P6 and the resistor R3 are also included;

the other end of the resistor R3 is grounded.

7. The low quiescent current NMOS-type fully integrated LDO circuit of claim 1, wherein: the device size ratio of the NMOS transistor N7 to the NMOS transistor N8 is 1: 4.