526IEEE JOURNAL OF SOLID-STATE CIRCUITS,VOL.37,NO.4,APRIL 2002
A Sub-1-V
15-ppm/
thn thp
00.9
002
.
先行词I n d e x T e r m s —C M O S b a n d g a p v o l t a g e r e f e r e n c e ,l o w v o l t a g e ,t e m p e r a t u r e .
I .I N T R O D U C T I O N L
O W V O L T A G E a n d l o w p o w e r a r e t w o i m p o r t a n t d s i g n c r i t e r i a i n b o t h t h e a n a l o g a n d d i g i t a l s y s t e m .I t i s e x -p e c t e d t h a t t h e w h o l e s y s t e m w i l l b e a b l e t o o p e r e d o w n t o
a s i n g l e 1-V s u p p l y i n t h e n e a r f u t u r e .A v o l t a g e r e f e r e n c e ,a s o n e o f t h e c o r e f u n c t i o n a l
b l o
c k s i n b o t h a n a l o g a n
d d i g i t a l s y s -t
e m s ,s h o u l d b e a b l e t o o p e r a t e
f r o m a s i n
g l e 1-V s u p p l y f o r
b o t h s y s t e m s .I n C M O S t e
c h n o l o g y ,a p a r a s i t i c v e r t i c a l b i p o l a r j u n c t i o n t r a n s i s t o r (B J T )f o r m e
d i n a p -o r n -w
e l l i s c o m m o n l y u s e d t o
i m p l e m e n t a b a n d g a p r e f e r e n c e [1]–[3].T h e m i n i m u m s u p p l ylittle red riding hood
v o l t a g e n e e d s t o b e g r e a t e r t h a n 1V d u e t o t w o f a c t o r s :1)t h e
r e f e r e n c e v o l t a g e i s a r o u n d 1.25V w h i c h e x c e e d s 1-V s u p p l y
[4],[5]a n d 2)l o w -v o l t a g e d e s i g n o f t h e p r o p o r t i o n a l -t o -a b s o -l u t e -t e m p e r a t u r e (P T A T )c u r r e n t g e n e r a t i o n l o o p i s l i m i t e d b y
t h e c o m m o n -c o l l e c t o r s t r u c t u r e o f t h e p a r a s i t i c v e r t i c a l B J T [2]a n d t h e i n p u t c o m m o n -m o d e v o l t a g e o f t h e a m p l i f i e r [4],[6].T h e f i r s t p r o b l e m c a n b e s o l v e d b y r e s i s t i v e s u b d i v i s i o n m e t h o d s [7],[8]t o s c a l e d o w n t h e 1.25-V r e f e r e n c e v o l t a g e .T h e s e c o n d p r o b l e m c a n b e s o l v e d b y u s i n g B i C M O S p r o c e s s
[6]o r b y u s i n g l o w t h r e s h o l d v o l t a g e d e v i c e s [7],[8].A s s h o w n i n F i g .1(a ),t h e m i n i m u m i n p u t c o m m o n -m o d e v o l t a g e o f a n
a m p l i f i e r w i t h a n n M O S i n p u t s t a g e m u s t
b e l e s s t h a n o n
e
V i s r e q u i r e d (a s s u m i n g V a n
d
V c a n b e e a s i l y f o u n d i n m a n
los angeles
y t e c h n o l o -g i e s .H o w e v e r ,t h e t e m p e r a t u r e e f f e c t o n t h e b a s e –e m i t t e r v o l t a g e a n d t h r e s h o l d v o l t a g e s h o u l d b e c o n s i d e r e d .T h e t e m p e r a t u r e c o e f f i c i e n t (T C )o f t h e b a s e –e m i t t e r v o l t a g e i s
a p p r o x i m a t e l y 2m V /K ,f o r
M a n u s c r i p t r e c e i v e d A p r i l 13,2001;r e v i s e d N o v e m b e r 16,2001.T h i s w o r k w a s s u p p o r t e d b y t h e R e s e a r c h G r a n t C o u n c i l o f H o n g K o n g S A R ,C h i n a u n d e r P r o j e c t n o .H K U S T 6022/01E .
T h e a u t h o r s a r e w i t h t h e D e p a r t m e n t o f E l e c t r i c a l a n d E l e c t r o n i c E n g i n e e r i n g ,T h e H o n g K o n g U n i v e r s i t y o f S c i e n c e a n d T e c h n o l o g y ,C l e a r W a t e r B a y ,H o n g K o n g S A R (e -m a i l :e e m o k @e e .u s t .h k ).
P u b l i s h e r I t e m I d e n t i f i e r S 0018-9200(02)02563-5.
e x a m p l e ,m n -w e l l C M O S t e c h -n o l o g y [10].A t h i g h t e m p e r a t u r e s
,
,a n d t h e r e f e r e n c e c i r c u i t w i l l n o
p r o p e r l y .T h u s ,e i t h e r n a t i v e n M O S t r a n s i s t r a n s i s t o r s w i t
h
l e s s t h a n 0.2V
i s r e q u i r e d t o i m p l e m e n t a 1-V r e f e r e n c e .
T o a d d r e s s t h e a b o v e -m e n t i o n e d d e s i g n p r o
b a n d g a p r e f e r e n
c e c i r c u i t i n a s t a n
d a r d C M O s
e n t e d i n t h i s p a p e r .T h e k e y
f e a t u r e o f t h e p c i r c u i t i s t h a t n o l o w t h r e s h o l d v o l t a
g e d e v d e s i g n t e c
h n
i q u e s f o r a c h i e v i n g a g o o d p e r p r e s e n t e d i n e t a i l .I I .P
R O P O S E D S U B -1-V B A N D G A P V OLTAGE R EFERENCE IN CMOS T ECHNOLOGY The structure and the complete schematic of the propod
sub-1-V bandgap voltage reference are shown in Figs.2and 3,
respectively.The reference core circuitry is modified from the
one propod by Banba et al.[7].The main differences are that
an amplifier with a pMOS input stage is ud and the inputs
of the amplifier are connected to
nodes
and
given
by
is the emitter area ratio,
is injected
to
IEEE JOURNAL OF SOLID-STA TE CIRCUITS,VOL.37,NO.4,APRIL 2002
527
Fig.1.Bandgap voltage references in CMOS technology using an amplifier with (a)nMOS input stage,and (b)pMOS input
stage.
元音字母和辅音字母Fig.2.Propod sub-1-V bandgap voltage reference.
on the resistor ratio (ratio
of
hearfrom
.There-fore,the minimum supply
voltage
is t to a small value.This
structure is suitable for any CMOS technology to implement low-voltage bandgap reference.Moreover,there is no increa on the total resistance compared to the one propod by Banba et al.
A.Operation in High-Gain Region by Forward Biasing the Source–Bulk Junctions of pMOS Transistors
A high-gain amplifier with ultralow offt voltage is very im-portant in the propod bandgap reference to ensure that the
nodes
(4)
where
is the body bias coefficient,
and
(region B in Fig.4),and this allows the amplifiers to operate in the high-gain region.
In [12],the forward-biad junction is defined by the voltage drop across a Schottky diode.In order to eliminate the u of the Schottky diode and allow the reference circuit to be compat-ible to any CMOS process,a temperature-independent voltage
across
is ud to forward bias the source–bulk junc-tions of all pMOS transistors.The temperature-dependent bulk
528IEEE JOURNAL OF SOLID-STATE CIRCUITS,VOL.37,NO.4,APRIL
2002
Fig.3.Complete schematic of the propod sub-1-V bandgap voltage reference (the source–bulk junctions of all pMOS transistors are forward biad by
V
V B.Low-Voltage Amplifier With DC Level-Shifting Current Mirror
A dc level-shifting current mirror [5]must be ud in order to make the low-voltage amplifier function properly,especially
for some technologies
with
.The circuit shown in Fig.5(a)is part of the amplifier in Fig.3without dc level-shifting current mirror.The drain–source voltage of MA08is given
by
.
If ,the drain–source
voltage of MA08is less
than
fly的过去式
.The drain–source voltage of MA08may be less than the saturation voltage
if
阿黛尔好听的歌is small.
Since
in the propod sub-1-V bandgap reference,MA08may operate in triode region and this reduce the gain of the amplifier.
A dc level-shifting current mirror using the parasitic vertical BJTs,shown in Fig.5(b),can solve this problem.The drain–source voltage of MA08is now given
by
grassroots.This ensures that MA08
will operate in the saturation region even
when
V ,providing
that
is not greater英文名句
than by more than 0.6V .
C.Startup Circuitry
The startup circuit of the propod reference circuit is formed by MS1–MS4.MS1and MS2form a function of inverter.
The
ratio of MS2is chon to be much less than one,and
the
.
The drain voltages of MS1and MS2are pulled low,and this turns on MS3and MS4to inject current to the bandgap core circuitry (by MS3)and to the amplifier (by MS4).The drain voltage of M2increas,and the amplifier also starts to operate.Then,the amplifier forces the drain voltage of M1to increa by pulling down the gate voltages of M1–M3to inject current.Once the gate voltage of MS1decreas,the drain voltages of MS1and MS2pull high and cut off MS3and MS4.
The
ratio of MS2is critical since the loop of the refer-ence core is destroyed if MS3and MS4cannot be completely cut off after startup.To ensure a complete cutoff of MS3and
MS4,
the
should be chon at maximum supply voltage and operating temperature.Since accuracy is not important,it is suggested to choo 1.2times the simulated channel length to avoid the effect of process variations.D.Effect of Offt Voltage and Noi
Bandgap voltage reference in MOS technology suffers from the effect of MOS transistor offt due to
the mismatches of tran-sistor size and threshold voltage.This leads to drifts of the ab-solute value of the reference voltage and also its temperature
IEEE JOURNAL OF SOLID-STA TE CIRCUITS,VOL.37,NO.4,APRIL2002
529
Fig.5.Current mirror in the amplifier.(a)Without dc level shifting(b)With dc level shifting. dependence even after trimming.In the propod bandgap ref-
erence,the effect of the offt
voltage
is amplified by the resistor
ratio.
However,this can be reduced by increasing the emitter area ratio
(is ud in this design),and thus the required resistor
ratio求职信模板
of
[13],[14].Moreover,the systematic offt can be minimized by
transistor size and bias current in ratio,while the random offt
can be reduced by symmetrical and compact layout[3].
The noi of the propod reference,which is similar to the
offt voltage,is incread by the resistor
ratio.How-
ever,most of the noi is wide-band thermal noi and can be
reduced by an RC low-pass filter.
The degradation of the noi performance and the effect of
offt voltage is a tradeoff that enables the reference circuit to
operate at a lower supply voltage.
III.E XPERIMENTAL R ESULTS
The propod sub-1-V bandgap voltage reference shown
in Fig.3was successfully fabricated in AMS
0.6-
/sq.)is ud to reduce
the chip area,and the circuit occupies0.24mm
2.2mV at room temperature when the supply voltage changes
from0.98to1.5V.The measured TCs from0C
at different supply voltages
(
C and increas slightly to25
ppm/
A is drawn
when
C.
At
C.This is due to larger threshold voltages at lower
temperatures,thereby forcing the amplifier to operate out of the
high-gain region.The reduction of the gain of amplifier caus
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TABLE I
C OMPARISON OF L OW-V OLTAGE B ANDGAP R EFERENCES
the rapid drop of the reference voltage at low temperatures.
Therefore,the measured minimum supply voltage is0.98V.
At the lowest supply ,
44dB and that at
10MHz is
C CMOS bandgap voltage reference,
which consumes a maximum of18
C,has been prented.The main features are that no
low threshold voltage device is needed and thus the circuit
is reproducible in any CMOS technology.If low threshold
voltage pMOS transistors(
