Fast Transient Response Low Drop-Out Voltage Regulator

International Journal of Embedded Systems and Applications (IJESA) Vol.4, No.2/3, September 2014
DOI : 10.5121/ijesa.2014.4301 1
FAST TRANSIENT RESPONSE LOW DROP-
OUT VOLTAGE REGULATOR
[
Hicham Akhamal1
, Mostafa Chakir 2
and Hassan Qjidaa3
1
Laboratoire d’Electronique Signaux – Systèmes et Informatique(LESSI), Sidi Mohamed Ben
Abdellah University, Dhar El Mehraz sciences Faculty, Fez, Morocco
ABSTRACT
This paper presents the design of Low Drop-Out (LDO) voltage regulator has fast transient response and
which exploits a few current else low quiescent current in the operational amplifier PMOS type. We use
band-gap reference for eliminate the temperature dependence. The proposed LDO voltage regulator
implemented in 0.18-µm CMOS technology, we use Folded cascode CMOS amplifiers high performance in
the stability , provide fast transient response which explains a fast settling, the LDO itself should provide in
the output regulator voltages at ∆t equal 2ps with transient variation of the voltage less than 170mV. High
accuracy in the DC response terms, the simulation results show that the accuracy of the output regulator
voltages is 1.54±0.009V, and power consumption of 1.51 mW.
KEYWORDS
Low-dropout (LDO ) voltage regulator, Band-gap reference, Fast transient response, Current efficiency,
Figure of merit & Layout.
1.INTRODUCTION
The power management systems is importance and increased much in the electronics industry
elsewhere the integrated circuits is exist in the last few years, The rationale is that LDO yields a
good line and load regulation while maintaining a stable, constant and accuracy output voltage.
Those battery-powered and handheld devices require advanced power management techniques to
extend the life cycle of the battery and consequently the operation cycle of the device. I have
chosen this architecture of a LDO linear regulator works for a frame made this set of
specifications and find my position in the study of other integrated circuit with very high
performance. All times power management in integrated circuits has been gaining a high-
efficiency power management module is necessary such as low-power power converter or low
dropout regulator to integrate circuit more attention because it allows for drastic reduction in the
consumption of battery-powered portable equipment, such as cellular phones, pagers, laptops,
camera recorders, and PDAs. The regulator is divided into two types, voltage mode LDO and
current mode LDO, the regulator which uses the voltage mode is named linear regulator,
therefore, the regulator which uses the current-mode is named shunt regulator. The power
transistor of the voltage-mode linear regulator is series with the load resistant, an error amplifier
and the power transistor are supplied by the same power supply (VIN), the series combination
forms a voltage divider to reduce the unregulated input source to a regulated output one.

2
Vin
Error
amplifier
Cc
Vout
Gnd
Rb1
Rb2
RL
CL
EA
VREF
This paper is organized as follows. In section II, description of circuit and the theoretical study of
the characteristics proposed LDO voltage regulator are discussed. In section III, the static-state
and dynamic-state characteristics are simulated and corresponding simulation results are
summarized. The conclusion is derived in section IV.
2. LDO ARCHITECTURE
The top level structure of the proposed LDO shown in Fig. 1 It includes the following modules as
error amplifier, band-gap reference, Equivalent Series Resistance (ESR), Power Transistor (PM)
and Feedback Network (FN≡≡PD). This work presents a design of a LDO regulator in a 0.18-
µm CMOS technology.
2.1. Description Of Circuit
Fig. 1. Structure of the Regulator LDO Circuit.
The (Fig. 1) enclose a schematic of a regulators LDO voltage based on a PMOS, the structure of
LDO implemented in CMOS 0.18µm technology. This transistor PMOS with common source
connection as the pass element transistor between the input and output voltages. A part of the
output voltage is fed back through R1 and R2 to the input of the amplifier and is compared to the
voltage reference VREF. Capacitor CL stands for the capacitive load. The current Load (IL)
represents the load whose current is supplied by the power transistor [1], [2], [4], [5].
An EA signal is fed back to the gate of the pass transistor through the feedback loop to respond
to the load current while keeping the output voltage constant. The Voltage Control regulator
which is an electrical regulator is designed to maintain a constant voltage level, the Voltage
Control regulator regulates the Voltage supply to the load by adjusting the load current. It consists
of an error amplifier, a power transistor, and the load elements.
Bias
Circuit
Voltage
Reference Pass
Element

3
2.2. Regulator Schematic And Parameters
The circuit of the proposed voltage -mode shunt regulator is shown in Fig. 2. Transistors M1 to
M11 form the first-stage amplifier, while M12 to M1 form the bias amplifier. R1 and R2 are the
resistive feedback network, the power transistor is labeled as MP. The error amplifier detects two
input signal regarding the reference voltage VREF and the feedback signal Voltage between R1
and R2 . M32,M33 and M34 are the Simple current mirror in the band gap. from M22 to M31
form the two-stage operational amplifier utilized in this design is shown in Fig. 2, the band-gap
circuit consists of two loops; one with negative feedback (through M23) and one with positive
feedback (through M22), and since it consists of a nMOS differential pair operating, this may lead
to stability especially if the positive feedback dominates over the negative feedback.
Fig. 2. Schematic of the proposed LDO voltage regulator.
From a equivalent small signal model of the proposed LDO. The small signal loop gain at low
frequency can be given as bellow
_
op amp MP
G A A
= ×
Where
_
sg s g out op amp
V V V V V
= − = −
_ 7 9 7 9 7 7 3 1 5 3 1 5 3 3
[( (1 ))// ] [( // ) ( // ) (1 )]
outop amp ds ds ds ds m ds ds ds ds ds ds m
R r r r r g r r r r r r g
η η
= + + − + + +

4
And
_ m1 7 9 7 9 7 7 3 1 5 3 1 5 3 3
= g [( (1 ))/ / ] [( / / ) ( / / ) (1 )]
op amp ds ds ds ds m ds ds ds ds ds ds m
A r r r r g r r r r r r g
η η
+ + − + + +
( ) 1
1 2
1 2
1 / /
MP MP
dsP
R
A g R R
g R R
  
= +  
  +
 
 
The dominant and non-dominant poles of the feedback loop can be given as
( ) ( )
1 gsMP gdp8 gdp10 gdn4 gdn6
C = C + C + C // C + C
 
 
2 gdMP _ _
C = C + Cc out op amp
C
+
3 Load
C =C
1
_ _ gdMP _ _
1
2 C C +
out op amp c out op amp
f
R C
π
=
+
2
1 2
1
2 ( ( / /( ))
mMP dsMP L
f
g r R R C
π
=
+
0
1
2 ( )
ESR L
Z
R C
π
=
2.2.1. Error Amplifier
The folded cascode operational amplifier (error amplifier) (EA) itself should provide very low
power dissipation (especially in stand-by mode), and its bias currents must be kept as low as
possible. It is apparent that a speed/dissipation trade-off arises, and the main limitation is
manifested in terms of slew-rate of the error amplifier.
As an example, if the EA can deliver to a 5-pF power-MOS gate no more than 2µA of current,
producing a 1.54 -V step will take 2ps of slewing interval. This allows improvement to the
transient response without increasing the DC consumption.
Considering that during this time the control loop of the LDO is interrupted and that the output
voltage is out of control, it is apparent that such a long slewing period may negatively impact on
the LDO performance, especially in terms of output voltage overshoots which may become
unacceptable for many applications.
2.2.2. Band-Gap
A CMOS band-gap reference circuit shown in Fig. 2 operates in a current-mode. A temperature
independent current is first generated by summing the proportional to absolute temperature
(PTAT) current IR7 and the complementary to absolute temperature (CTAT) current IR6.
Assuming M32, M33 and M34 have the same size [4],[5], the proposed band-gap reference uses
the Simple current mirror to decrease the surface layout of the Band-gap.
I = I1 +I2

5
And yet
V+
= VA = R5 I1 + Vbe1
V-
= VB = Vbe1= R6 I2
Then
V+
≈ V-
Else R5 I1 + Vbe1 = Vbe2
So he said to
2 1
1
2 2
be be be
V V V
I
R R
− ∆
= =
ln( )
be t
V V n
∆ =
1
5
ln( )
t
V n
I
R
=
2
2
6
be
V
I
R
=
Then 2
4
5 6
ln( )
t be
REF
V n V
V R
R R
 
= +
 
 
3. SIMULATED AND EXPERIMENTAL RESULTS
The LDO Circuit has been implemented in 0.18-µm CMOS technology. This work is improved
by the use of CMOs capacity (CT) so the advantage of reducing the area in the Layout is
shown in (Fig. 3) in which the effective die area is 10.853x10-3
mm2
Fig. 3. Layout of this work (LDO).

6
For testing the LDO and external current mirror was used, and its output impedance is heavily
dependent of the amount of current. The LDO regulator is tested for R1 =0.5 kΩ, R2 = 1.5 kΩ
,VDD = 1.8 V, VREF = 1.2 V and multilayer ceramic output CMOS capacitor 500 pF with
several bypass CMOS capacitors in the f F range placed in parallel to reduce high-frequency
noise. The dc output voltage of the regulator is 1.54V. The ground current consumed by the LDO
regulator is 52 µA.
3.1. Gain , Phase And Stability Considerations
From the simulation results in Fig.4, the proposed LDO regulator is stable for load current values
ranging from 0 to 50 mA with a gain of the pass band is 85 dB. The phase margin is better than
60° for all cases then the LDO with the compensation is stable showing that the phase margin is
good enough.
Fig. 4 : Frequency response of the proposed LOO
3.2. Static-State Regulation Characteristics
The current mass is the sum of all currents polarization including in the regulator: the current
feedback, the current error amplifier and the drive current of the power transistor [2], [7].The
current mass is 52µA. The simulation results of different corners are as follows: The
characteristic of input voltage (Vin) and the output voltage (Vout) for our LDO voltage regulator
shown in Fig. 5. The drop-out voltage is 260 mV. The DC line regulation is 0.642%. The output
voltage of the proposed LDO voltage regulator with the load current swept from 100µA to 50mA
is given in Fig.6 the load regulation is 0.18x10-3
mV/mA. The current efficiency is 99.8% and
the power efficiency is 86%. The figure of merit (FOM) is 2.8ps.

7
Fig. 5. The DC sweep of the LDO
Fig. 6. DC Load regulation of the LDO.
Fig.7. Transient output voltage of the LDO regulator.
∆t

8
Fig.8. Simulated Temperature Variation of the proposed bandgap reference
circuit shown in Fig2.
The simulation results of the transient response shown in Fig.8. The transient response increases
further with different voltage input VIN from 2 V to 1.8 V and increasing the capacity CL, if ∆t
= 2ps so he said to fast transient response [2],[3], [8]. Fig. 9 shows the simulated temperature
variation of the generated bias voltage 1.2 V that has a 30 mV variation in a temperature range of
-40°C to 80 °C .
4. CONCLUSIONS
LDO dropout is minimized to guarantee high power supply rejection at optimized efficiency. In
the meanwhile, current efficiency is enhanced up to 99.8 % because of low quiescent current
operation. The design procedure for obtaining the proper accuracy in the DC response low
quiescent current and fast transient output for to integrate with other circuit, involving a high
result of the figure of merit equal 2ps. Table I provides a performance comparison between this
work and recently published designs.

9
Table 1. Performance summary and comparison.
Parameter [1] [2] [3] [6] This
Work
Technology
(µm)
0. 18 µm 0.11µm 0.18 µm 0. 18 µm 0. 18 µm
Drop out
voltage
(mV)
300 385 200 190 260
Ground
Current
(IQ)
28µA 41.5µA 40 µA 120µA 52 µA
Band-gap
included
YES NO NO NO YES
Settling
time
1.6 µs 77ps 1.172µs/ 1.055
µs
1400ns/
1100ns
2ps
Active
Area
104400 mm2 210000 µm2 43940
µm2
- 10853
µm2
REFERENCES
[1] Vahid Majidzadeh, Alexandre Schmid, and YusufLeblebici, " A Fully On-Chip LDO Voltage
Regulator for Remotely Powered Cortical Implants ", IEEE Transactions 978-1-4244-4353-6 /09
/$25 .00 ©2 0 0 9 IEEE.
[2] Young-il Kim and Sang-sun Lee, " A Capacitorless LDO Regulator With Fast Feedback Technique
and Low-Quiescent Current Error Amplifier", IEEE TRANSACTIONS ON CIRCUITS AND
SYSTEMS—II: EXPRESS BRIEFS, VOL. 60, NO. 6, JUNE 2013.
[3] Cheekala Lovaraju, Ashis Maity, and Amit Patra, " A Capacitor-less Low Drop-out (LDO) Regulator
with Improved Transient Response for System-on-Chip Applications", 2013 26th International
Conference on VLSI Design and the 12th International Conference on Embedded Systems.
[4] Andrea Boni, Member, IEEE, “Op-Amps and Startup Circuits for CMOS Bandgap References” IEEE
JOURNAL OF SOLID-STATE CIRCUITS, VOL 37, NO. 10, OCTOBER 2002.
[5] Chia-Chun Tsai, Tsung-Ming Liu, and Trong-Yen Lee “Micro Fuel Cell Power Management Circuit
Design for Portable Devices” 2012 9th International Conference on Fuzzy Systems and Knowledge
Discovery (FSKD 2012).
[6] J.H.Wang,C.H.Tsai, and S. W.Lai, “A low-dropout regulator with tail current control for DPWM
clock correction”IEEE Trans. Circuits Syst. II, Exp.Briefs,vol. 59, no.1, pp.4549, Jan. 2012.
[7] Dongpo Chen, Lenian He and Xiaolang Yan, “A Low-dropout Regulator with Unconditional Stability
and Low Quiescent Current”, IEEE Transactions on Power electronics, 0-7803-9584-
0/06/$20.00O2006 IEEE.
[8] W. Chen, W.H. Ki, and P.K.T. Mok, “Dual-Loop Feedback for Fast Low Dropout Regulators,” Proc.
IEEE PESC, vol. 3, Jun.2001, pp.1265-1269.

10
AUTHORS
Hicham Akhamal was born in Fez, Morocco in 1978. He received B.S. and
M.S. degrees in Faculty of Sciences from Sidi Mouhamed Ben Abdellah
University in2009 and 20011, respectively. Since 20011, he has been working
toward a Ph. Ddegree at the same university. His current research interests
include design of regulator LDO boost up gain and fast response ,
power-management integrated-circuit designs for telecommunication
applications, and G -C filter designs for biomedical applications.
Mostafa Chakir was born in Taounate, Morocco in 1986. He received
B.S. and M.S. degrees in Faculty of Sciences from Sidi Mouhamed Ben
Abdellah University in 2009 and 2011, respectively. Since 2011, he has been
working toward a Ph. D degree at the same university. His current interests are
in high speed mixed-signal integrated circuit designs, including active filters,
A/D andD/A converters.
Hassan Qjidaa received his M.S. and PhD in Applied Physics from Claude
Bernard University of Lyon France in 1983 and 1987 respectively. He got the
Pr.Degree in Faculty of Sciences from Sidi Mohammed Ben Abdellah
University, Fez, Morocco 1999. He is now an Professor in the Dept. of Physics
in Sidi Research interests include Very-large-scale integration (VLSI) solution,
Image Manuscripts Recognition,Cognitive Science, Image Processing,Computer
Graphics, Pattern Recognition, Neural Networks, Human machine Interface,
Artificial Intelligence and Robotics.

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