Riso with Dual Feedback Op Amp Stability
18
Riso with Dual Feedback Op Amp Stability Collin Wells Tim Green Precision Linear Analog Applications November 21, 2013 1
description
Riso with Dual Feedback Op Amp Stability. Collin Wells Tim Green Precision Linear Analog Applications November 21, 2013. Riso with Dual FB Topology (OPA330 Example). Zo Test. Zo Test. Modified Aol. Zo and CL. - PowerPoint PPT Presentation
Transcript of Riso with Dual Feedback Op Amp Stability
Riso with Dual FeedbackOp Amp Stability
Collin Wells
Tim Green
Precision Linear Analog Applications
November 21, 20131
2
Riso with Dual FB Topology (OPA330 Example)
Vcc 5 CL
R1
10
kR
2 1
0k
Riso
RF 10k
CF
VOUT
VOA
+
-
+
U1 OPA330V2 5
VFB
FB#1
FB#2
2.500004V
2.500005V
2.500005V
Riso Dual FB Topology.TSC
3
Zo Test
V1 2.5V
V2 2.5V
VOUT
L1 1GH
C1 1GF
IG1 0
+
-
+U1 OPA330
AC Current Generator
AC = 1
Zo(dB) = VOUT
Zo(ohms) = VOUT on Logarithmic scale
OPA330 Zo Test.TSC
4
Zo TestT
Frequency (Hz)
1.00m 316.23 100.00M
Ga
in (
dB
)
3.89
130.34
4.37k
OPA330 Zo
5
Modified Aol
J1
J1
+
-
+
U1 OPA330
Vdd 2.5 CL
V2 2.5
R1
76.8
kR
2 76
.8k
Cdi
ff 2p
Ccm 4pL1 1T
Riso
RF 10k
C2 2.2n
Vout
VOA
+
VG1
C3 1T
VOA = ModAol (Modif ied Aol)
ModAol.TSC
6
T
Zo
ZM1[5]: 1u[F]
ZM1[4]: 100n[F]
ZM1[3]: 10n[F]
ZM1[2]: 1n[F]
ZM1[1]: 100p[F]
Frequency (Hz)
1m 10m 100m 1 10 100 1k 10k 100k 1M 10M 100M
Ga
in (
dB
)
1.59m
50.33k
1.59T
ZM1[5]: 1u[F]
ZM1[4]: 100n[F]
ZM1[3]: 10n[F]
ZM1[2]: 1n[F]
ZM1[1]: 100p[F]OPA330 Zo and CL
Zo
Zo and CL
Modified Aol will have Complex Poles with sharp phase shifts anywhere CLCrosses Zo in Zo “Inductive” region.
7
Modified Aol with CL
J1
J1
+
-
+
U1 OPA330
Vdd 5 CL 150n
V2 5
R1
76.8
kR
2 76
.8k
Cdi
ff 2p
Ccm 4pL1 1T
RF 10k
C2 2.2n
Vout
VOA
+
VG1
C3 1T
VOA = ModAol (Modif ied Aol)
2.500009V
2.500009V
ModAol CL.TSC
Modified Aol with CL
8
T
Vout[15]: 10n[F]
Vout[20]: 100n[F]
Vout[25]: 1u[F] Vout[5]: 100p[F]
Vout[9]: 1n[F]
Vout[15]: 10n[F]
Vout[20]: 100n[F]
Vout[25]:1u[F]
Vout[5]: 100p[F]
Vout[9]: 1n[F]
Ga
in (
dB
)
-100
-80
-60
-40
-20
0
20
40
60
80
100
120
140
Frequency (Hz)
1.00m 316.23 100.00M
Ph
ase
[de
g]
-135
-90
-45
0
45
90
135
180
Modified Aol with CL
Vout[9]: 1n[F]
Vout[5]: 100p[F]
Vout[15]: 10n[F]
Vout[20]: 100n[F]
Vout[25]:1u[F]
Vout[20]: 100n[F]
Vout[25]: 1u[F]
Vout[15]: 10n[F]
Vout[9]: 1n[F]
Vout[5]: 100p[F]
9
Zo, CL, RisoT
Zo
ZM1[5]: 1u[F]
ZM1[4]: 100n[F]
ZM1[3]: 10n[F]
ZM1[2]: 1n[F]
ZM1[1]: 100p[F]
ZM1[1]: 100[Ohm]ZM1[2]: 200[Ohm] ZM1[3]: 400[Ohm]
ZM1[4]: 600[Ohm]
ZM1[5]: 800[Ohm]
ZM1[6]: 1k[Ohm]
Frequency (Hz)
1m 10m 100m 1 10 100 1k 10k 100k 1M 10M 100M
Ga
in (
dB
)
1.59m
50.33k
1.59T
ZM1[1]: 100[Ohm]ZM1[2]: 200[Ohm] ZM1[3]: 400[Ohm]
ZM1[4]: 600[Ohm]
ZM1[5]: 800[Ohm]
ZM1[6]: 1k[Ohm]
ZM1[5]: 1u[F]
ZM1[4]: 100n[F]
ZM1[3]: 10n[F]
ZM1[2]: 1n[F]
ZM1[1]: 100p[F]OPA330 Zo, CL, Riso
Zo
CL
CL
CL
CL
CL
Riso
Riso
Riso
RisoRiso
Riso
Riso=400ohms, CL=1uFSeries Combination -Highest Z wins -Intersects Zo as Resistive Impedance
Riso and Zo.TSC CL and Zo.TSC
10
Modified Aol with CL=1uF, Riso=400ohms
J1
J1
+
-
+
U1 OPA330
Vdd 5
V2 5
R1
10k
R2
10k
Cdi
ff 2p
Ccm 4pL1 1T
RF 10k
C2 2.2n
Vout
VOA
+
VG1
C3 1T
Riso 400
CL 1u
VOA = ModAol (Modif ied Aol)
2.499999V
2.499999V
ModAol Riso CL.TSC
11
Modified Aol with CL=1uF, Riso=400ohmsT
VOA
-80
-60
-40
-20
0
20
40
60
80
100
120
140
Frequency (Hz)
1m 10m 100m 1 10 100 1k 10k 100k 1M 10M 100M
VOA
-90
-45
0
45
90
135
180
Modified AolCL=1uF, Riso=400ohms
VOA:
VOA A:(56.508587k; 8.881784E-16) B:(3.244457k; 36.430298)
VOA:
VOA A:(56.508587k; 72.338331) B:(3.244457k; 29.488718)
a
b
Note:1) Modified Aol looks like an Aol with a second pole around 1kHz and a zero at about 20kHz2) No abrupt phase shifts and minimum phase is 29.488 degrees away from 180 degree total phase shift3) Modified Aol UGBW=56.5kHz with phase margin at 72.33 degrees
12
FB#1 with CL=1uF, Riso=400ohms
J1
J1
+
-
+
U1 OPA330
Vdd 5
V2 5
R1
10k
R2
10k
Cdi
ff 2p
Ccm 4pL1 1T
RF 10k
C2 2.2n
Vout
VOA
+
VG1
C3 1T
Riso 400
CL 1u
VOA = ModAol (Modif ied Aol)
2.499999V
2.499999V
FB_1.TSC
13
FB#1 with CL=1uF, Riso=400ohmsT
FB#1
Modified Aol
Frequency (Hz)
1m 10m 100m 1 10 100 1k 10k 100k 1M 10M 100M
Ga
in (
dB
)
-80
-60
-40
-20
0
20
40
60
80
100
120
140
fcl
FB#1
FB#1 CL=1uF, Riso=400ohmsModified Aol
Note:1) At fcl, where loop gain goes to zero, there is a 40dB/decade rate-of-closure indicating INSTABILITY for FB#1 alone2) We will add FB#2 s shown for a Net 1/Beta which will be stable at new fcl
FB#2
Net 1/BetaLowest FB Wins!
New fcl
fz2
14
FB#2 with CL=1uF, Riso=400ohms, RF=100k, CF=82nF
J1
J1
+
-
+
U1 OPA330
Vdd 5
V2 5
R1
10k
R2
10k
RF 100k
Vout
VOA
+
VG1
C3 1T
Riso 400
VFB
CF 82n
CL 1u
L1 1
T
L2 1T
C1
1T
FB#2=1/VFB
fz2=1/(2piCFRF)
FB_2 Rev A.TSC
15
FB#2 with CL=1uF, Riso=400ohms, RF=100k, CF=82nF
T
FB2
fz219.46Hz
Frequency (Hz)
1m 10m 100m 1 10 100 1k 10k 100k 1M 10M 100M
Ga
in (
dB
)
-20
0
20
40
60
80
100
fz219.46Hz
FB2
16
Loop Gain for CL=1uF, Riso=400ohms Final Compensation
J1
J1
+
-
+
U1 OPA330
Vdd 5
V2 5
R1
10k
R2
10k
Cdi
ff 2p
Ccm 4pL1 1T
RF 100k
C2 2.2n
Vout
VOA
+
VG1
C3 1T
Riso 400
CL 1u
C1 82n
VFB
VFB=Loop Gain
2.500004V
2.500015V
2.500015V
Loop Final.TSC
17
Loop Gain for CL=1uF, Riso=400ohms Final Compensation
T
29deg
VFB
-80
-60
-40
-20
0
20
40
60
80
100
120
140
Frequency (Hz)
1m 10m 100m 1 10 100 1k 10k 100k 1M 10M 100M
VFB
-90
-45
0
45
90
135
180
29deg
Loop Gain
CL=1uF, Riso=400ohms
Final Compensation
fcl
VFB:
VFB A:(56.310625k; 9.325873f)
VFB:
VFB A:(56.310625k; 72.239224)
a
Phase Margin
18
Riso with Dual Feedback curves
Riso Dual FB CW_TG RevA.tdr
