Sin ttulo de diapositiva

1
Mixed-Mode IC Designfrom subhertz till RF
Jose Silva-MartinezAnalog and Mixed-Signal
CenterTexas AM UniversityBarcelona, June
2005
2
Mixed-Mode IC Designfrom subhertz till RF
Outline

• Filters A fundamental building block for
  front-ends and ADCs.
• Continuous-Time filters from subhertz till GHz
• Analog Built-in Testing
• Low frequency spectrum analizer
• RF Testing Approach based on power detection
• Software (defined) radio Challenges and
  opportunities
• System applications
• RF circuits and transceivers
• UWB
• Digital TV-Tuner front-end

3
CONTINUOUS-TIME FILTERS FROM SUBHERTZ TO
GIGAHERTZJose Silva-MartinezAnalog and
Mixed-Signal CenterTexas AM UniversityBarcelo
na, June 2005
4
Part I. CONTINUOUS-TIME CMOS FILTERS FROM
SUBHERTZ TO GIGAHERTZOutline

• Very Low frequency techniques
• Video, DVD, and Power-Line Filters 1 MHz - lt 100
  MHz
• Extremely linear filters
• Linear phase filter hard-disk Drives 100 Mhz-
  550 MHz
• RF Continuous-Time Filters gt 1 GHz
• Bandpass Sigma-Delta Modulator 100MHz-2 GHz
• Open Problems

5
Typical applications of OTA-C filters and
frequency ranges

• Hard disk drivers filters
• XDSL Sigma-delta ADC
• IF Receiver filters

• Medical
• Seismic
• Built-in generators

RF Filters, oscillators data Communications and
equalizers
Applications
Frequency (Hz)
6
CIRCUITS FOR VERY LOW FREQUENCY
APPLICATIONSAnalog Integrated Circuits 1999,
TCAS-II-Dec 2000, Journal of Solid-State
Circuits-Aug-2002
7
Output Signal
Block Diagram of a general purpose bioelectric
signal acquisition system
Vout
Typical configuration for the measurement of
bio-potentials
8

• Issues about the OTA
• Operated in open loop conditions
• High-Frequency Operation
• Poor Linearity Range
• Power efficiency is bad

iout
Source degeneration
Vin
Linearity Range from 50mV to 200 mV
9
VERY LOW FREQUENCY FILTERS

• The Design of Analog Circuits below 100 Hz is not
  trivial
• RC gt 0.001 sec
• if C 10 pF then R gt 100 MOHMS
• For a 1 Hz filter (pacemakers and other
  applications)
• C 10 pF, R 628 GOHMS (Gm 2 pA/V)
• C 1000 pF, R 6.28 GOHMS (Gm 2 nA/V)

10
IMPEDANCE SCALERS for realization of very large
time constants
Single capacitor
Voltage amplifier
Current amplifier
iin
vi
vi
vi
iC
iin
C
iC
C
NiC
C
-AV vi

• Remarks
• Voltage amplification is useless for low-voltage
  continuous-time applications.
• Impedance scaler based on currrent amplification
  is precise for moderated N.

11
CAPACITOR MULTIPLIER CIRCUIT IMPLEMENTATION

• The following conditions must be satisfied
• Low impedance at node A
• Transistor output resistance might be neglected
• Current gain is precise

12
IMPROVING ITS FREQUENCY RESPONSE
Cascode transistor improves frequency response
1 N
ii
vi
C
Design procedure MP is optimized for
frequency. N-type transistors are optimized for
precision. The loop must be stable
iC
NiC
MP
VB
1 N
13
DESIGN EXAMPLE Capacitor Multiplier
100 pF capacitor. Scaled capacitor is 5 pF and
N19.
14
Chip microphotograph of a sub-hertz
filter/oscillator (JSSC-Aug-2002).
CMFB
Multiplier OTA
Capacitor multiplier
Capacitor multiplier
Comparators
15
Experimental results for a 0.8 Hz BPF (0.5 mm
CMOS technology).
16
CURRENT DIVISION PRINCIPLE PLUS SOURCE
DEGENERATION TRANSCONDUCTANCE
17
CURRENT CANCELLATION PRINCIPLE
PARTIAL POSITIVE FEEDBACK ! LINEAR RANGE IS
LIMITED! GOOD NOISE PERFORMANCE
18
OTA for Low-Frequency Applications with Current
cancellation techniques
The basic circuit is an analog multiplier
19
OTA with current splitting and cancellation
techniques
Basic circuit is an analog multiplier
20
OTA FOR VERY LOW-FREQUENCY APPLICATIONS
3 techniques are used Source degeneration Curre
nt splitting Current cancellation
21
Floating Gate plus Current Division OTA
Floating gates improve linearity but DC-offset
might be an issue Signal attenuation noise might
be an issue as well
VSS
22
Bulk Driven plus Current Deviation OTA
Input impedance is not very large important
issue for low frequency applications. Gm-bulk is
4-5 times smaller than normal gm. Large
parasitic capacitors (well-substrate) PSRR might
be limited
iout
Bulk-Driven Current splitting
23
EXPERIMENTAL RESULTS FOR THE DIFFERENT OTA
DESIGNS
Key SD source degeneration CD current
division FG floating gate BD bulk driven
SNR is almost the same for all cases!
WHY? Integrated noise is determined by
KT/C! Noise due to the current sources?
24
DESIGN ISSUES FOR UHF OTA-C FILTER
REALIZATIONS IEEE-Dallas Workshop Invited Talk
(2001) Jose Silva-Martinez Texas AM University
25
BASIC INTEGRATOR Crude approximations
gm
vin
vout
C1
Mobility degradation Vertical electric field
v
v
ip
in
NOISE
IB
VSS
26
FOLDED-CASCODE OTA
VDD
POWER
2IB
2IB
NOISE
i0p
i0n
TRANSCONDUCTANCE
v
v
ip
in
IB
IB
2IB
VSS
OUTPUT RESISTANCE
INPUT SWING
OUTPUT SWING
27
TYPICAL OTA ARCHITECTURES WITH SOURCE DEGENERATION
28
SECOND-ORDER FILTER
Bandpass output
29
SECOND-ORDER FILTER
v
v
v
BP
LP
in
-g
g
g
m1
m1
min
C1
C1
RQ
INTEGRATED NOISE
Tradeoff Large gain reduces the noise level but
increases the harmonic distortions.
30
Output resistance effects
CENTER FREQUENCY IS LITTLE SENSITIVE TO AV BW
IS QUITE SENSITIVE TO AV
Avgm1R1 (R1R2 OTA output resistance)
31
EFFECTS OF THE NON-DOMINANT POLE
Sensitive
Single pole
Quite sensitive!!
32
PARASITIC CAPACITORS
C1 and C2 are affected by the grounded parasitic
capacitors (partially corrected by the automatic
tuning system) Cin introduces a high frequency
zero
33
SMALL SIGNAL ANALYSIS High-Q filters are quite
sensitive!

• Little sensitve to OTA output resistances
• Quite sensitive to parasitic poles
• Parasitic capacitors should be accounted in the
  ATS (matching)
• Tune the filter itself (??)

34
OTA based on Complementary Differential Pairs
TRANSCONDUCTANCE
DISTORTION
OUTPUT RESISTANCE
OUTPUT SWING IS LIMITED
DC GAIN
35
Simulated results
36
OTA Results
For f 100M-1GHz Phase error lt 10
37
CMFB is required for Differential Structures
CMFB Requirements Fixes the OTA output (low
offset) gt High dc loop gain
Reduction of common-mode noisegt
Large Bandwidth
IBicmfb
IB
IBicmfb
IBicmfb
IB
IB
CMFB
CMFB
GND
GND
VC
VC
R
R
2 IB
IB
IB
icmfb gcmfb(v01v02-2Vref)
CMFB
GND
38
Efficient CMFB for Differential Pair Based OTAs
Common-mode loop gain AV Gm RL 3 poles in the
CMFB loop. Loop stability requires AV Gm / CL lt
wp1 _at_ VC, wp2 _at_ VB1
39
Pseudo-Differential OTAs with Source Degeneration
Sensitive to supply noise and common-mode input
signals
Little sensitive to supply noise
40
Efficient CMFB for Pseudo-Differential OTAs
Actual OTA Next OTA
VDD
IB
IB
IB
IB
R1
R1
M1
M1
common-mode detector
IB
IB
IB
IB
VSS
CMFB
41
THANKS! If you are interested in the Analog and
Mixed Signal Center, visit our website http//ams
c.tamu