Bandgap and current reference circuits

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Transcript of Bandgap and current reference circuits

Microsoft PowerPoint - N16-Bandgap-10-05.pptWilly Sansen
Ref.: B.Gilbert, G.Meijer, ACD , Kluwer 1995
Willy Sansen 10-05 165
kT/q
and Tr = 323 K
- 2 mV/oC
- 2 µV/oC
Vg00 = Vg0 + (η-m) kTr/q
Tr
T
Vg0
VBE
Vg0 = 1156 mV η= 4 Tr = 300 K VBE(Tr) = 700 mV
Willy Sansen 10-05 167
The curvature c(T)
m = 1 IC ~ T gm constant m = 0 IC constant gm ~ T-1
m = - IC ~ VBE gm ~ T-x
VBE (V)
T (K)
IC ~ T
IC constant
IC ~ VBE
m = 1
m = 0
Willy Sansen 10-05 168
≈ 0.6 V
-
kT qR2
R1 R2
-
VC = n ln nr = n A = nR1IC2 ≈ 0.6 V kT q
R1 R2
R1 >> 1/gm1 R1IC1 ≈ 0.5 V gm1R1 ≈ 20
R2 >> 1/gm2 R2IC2 ≈ 0.06 V gm2R2 ≈ 2.3
Noise sources : R1 R2 gm3,4 negligible for large VGS -VT or RE !!
A = ln nr ≈ 0.12 V kT q
IC2
-
VC = n ln nr = n A = nR1IC2 ≈ 0.6 V kT q
R1 R2
dVRef 2 = 4kT R1 df + R1
2n2 4kT/R2 df
n2 = R1n = R1 R2
R1 R2
IC2 VBE =R1
VC ≈ 0.6 V : >> Large IC2 : small R’s >> Large r : large VBE
Q4 Q3
Ref.: B. Gilbert, G.Meijer, ACD , Kluwer 1995
Willy Sansen 10-05 1615
-
VBE = ln nr kT q IC = ln nr
kT qR2
1 R2
Willy Sansen 10-05 1616
R2 1 : r
IC
Willy Sansen 10-05 1620
+ -
+ -
dVBE = ( - ) dIS IS
= ( - - ) dRPT RPT
dIS IS
dn n
= 26 mV (0.46 2% - 30 % - 20%) ≈ 13 mV (if n = 10)
is PTAT !
Vref = VBE + A (VBE1 - VBE2)
d(VBE1 - VBE2) =
kT q
= A ln n ( + ) dn n
= 600 mV (1 % + 0.46 2% ) ≈ 11 mV 24 mV or 2%
is PTAT !
kT q
dn n
dA A
R1
VBE (V)
m=1 PTAT current ratio η/(η-1) or 1/a2 η = 3.5 a2 ≈ 0.714
m=0 constant current stronger curvature
Vref ≈ 210 mV
+
-
R1 R2
- R1(I (const) + I (PTAT))
-
R2 R1
translinear circuit
Ref.: B.Gilbert, G.Meijer, ACD , Kluwer 1995
Willy Sansen 10-05 1628
+ -
Ref. MIETEC; Meijer, ACD, Kluwer 1995
2.7 ... 5.5 V
4000 ppm -50 oC
1 : 1 : N
kT q
300 µA
Willy Sansen 10-05 1632
Floating CMOS bandgap reference
2.48 V ± 24 mV 21 ppm/oC
5 V 1.2 mA
Willy Sansen 10-05 1633
CMOS Bandgap without resistors
VD = VD2 - VD1
VOUT = VD2 + AG VD
VOUT ≈ 1.12 V 9 mV 0 …70 oC 3.7 V; 0.4 mA
A = 1.5 B = 4 G = 6 AD1/AD2 = 8
Willy Sansen 10-05 1634
Single-junction CMOS Bandgap reference
IB2
t1: closed : Vout = VBE1 t2: open t3: openC1 C2 + VBE21C2
C1+C2
Willy Sansen 10-05 1635
MOST in weak inversion ?
nkT/q
Ref.: B. Gilbert, G.Meijer, ACD , Kluwer 1995
Willy Sansen 10-05 1637
Vref = VBE + R4 R2
+ -
R0
Vout
Vin-Vin+
VB
Cc
+ -
1 : 11 : 1
Ref.: B. Gilbert, G.Meijer, ACD , Kluwer 1995
Willy Sansen 10-05 1644
Willy Sansen 10-05 1645
Temperature coefficient of resistors
Ref. Op ‘t Eynde, JSSC June 88, pp. 821-824
K’n ~ T -1.5 V2 ~ T Iref ~ T -0.5 Vcc > 3.5 V 2 µA 0.774 ± 0.02 µA 3 % 0o ... 80oC
V2 ≈ 0.32 V
Current reference
Ref. Op ‘t Eynde, JSSC June 88, pp. 821-824Ref. Vittoz, JSSC June 79, pp. 573-577
Vo
Sa
V2 ≈ 0.32 V Vcc > 3.5 V 2 µA 0.774 ± 0.02 µA 3 % 0o ... 80oC
Sb/Sa = 5 Vo ≈ 64 mV
Willy Sansen 10-05 1649
Ref. H.Klein, W. Engl, ESSCIRC 83, pp. 119-122
C1 = C2 = 3 pF fc = 270 kHz ±5 V 4 µA
Vref C1 = Iref Tc/2
Ref.: B. Gilbert, G.Meijer, ACD , Kluwer 1995
Willy Sansen 10-05 1651
Low drop-out regulator : principle
Vout = Vref R1 + R2
R1
R2
Ref.: B. Gilbert, G.Meijer, ACD , Kluwer 1995
Willy Sansen 10-05 1653
References
P. Brokaw, “A simple three-terminal IC bandgap reference” JSSC Dec.74, pp.388-393
M. Degrauwe, etal, “CMOS voltage references using lateral bipolar transistors”, JSSC Dec.85, pp.1151-1157
K. Kuijk, “A presicion reference voltage source” JSSC June 1973, pp.222-226 G. Meijer etal “An integrated bandgap reference”, JSSC June ‘76, pp.403-406 G. Meijer etal “A new curvature-corrected bandgap reference”
JSSC Dec.82, pp.1139-143 G. Meijer, “Bandgap references”, ACD Kluwer, 1995 B. Song, P.Gray, “A precision curvature-compensated CMOS bandgap
reference” JSSC Dec.83, pp.634-643 A. van Staveren etal “An integratible second-order compensated