Summary Analog Integrated Circuits ITET Lukas Cavigelli.pdf
-
Upload
lukas-cavigelli -
Category
Documents
-
view
80 -
download
5
description
Transcript of Summary Analog Integrated Circuits ITET Lukas Cavigelli.pdf
ANALOG INTEGRATED CIRCUITS
Summary of the Lectures by Prof. Dr. Q. Huang
Lukas Cavigelli, December 2011
BASIC EQUATIONS & SMALL SIGNAL CIRCUITS
Small Signal Model: Only model differential behavior, use derivatives for all currents and voltages many ground-connections & short circuits. Use small letters.
BIPOLAR
Collector current: (
) ⁄
⁄
Transconductance:
⁄
Amplification: ⁄ for this lecture Hybrid- (small signal) model: at a certain operation point
for low frequencies:
|
[ ]
|
[ ]
|
[ ]
: bias current, : thermal voltage, : Early voltage Frequency Response: for low frequencies, -10dB/dec after ⁄ , | ( )| , more on foils
MOSFET (HERE: N-TYPE)
Triode/lin./ohmic region: if and (NMOS)
then ⏞
[ ( )
]
Active/saturation region: if and (NMOS)
( )
( )⏟
condition for saturation with PMOS: !! Cut-off/subth./weak-inversion region:
if
Pinch-Off point: and
[ ] [ ]
[ ] [ ] [ ] (√| [ ] | √| [ ]|)
[ ]
( [ ])⏟
√ [ ]
[ ]
[ ]
,
,
TYPICAL VALUES
MOS-TECHNOLOGY
for AMS C35 FETs: ( ): for and
3.3V NFET 3.3V PFET Unit
⁄
( ) ( )
⁄
⁄
⁄ ,
Reasonable values: BJT: , MOS: ⁄ , ⁄ , ,
Capacitors: MOS Capacitor: 5-12 fF/, , cheap MIM Cap: 1-5 fF/, highly linear, ±20%, 1µm
Resistors: Silicided Poly-Si Resistor 5-20 Ω/ (cheap) , ±20% Unsilicided Poly-Si Resistor 50-400 Ω/, ±20% but more accurate relations can be used
ANALOG SUBCIRCUITS
CURRENT MIRRORS
Simple CM:
→ √
( ⁄ )
MOS:
( ⁄ )
( ⁄ ) (
)
⏟
BJT:
and
⁄ if
from ⁄
COMMON-EMITTER & COMMON-SOURCE AMPLIFIERS
C-E, C-S Amplifier with resistive load:
, ⁄ ⁄
√
C-E, C-S Amplifier with Active Load: ideal current source instead of resistor
Common-Emitter Amplifier with non-ideal current source:
( )
(
)
→
( √ ⁄ )
√
( )
⁄
⁄ ⁄
( ) ( )
EMITTER & SOURCE DEGENERATION
Emitter Degeneration: increases input & output resistance, but reduces input resistance:
|
( ) ( ), if
output resistance:
|
(
(
))
→
( )
( )
Source Degeneration: same setup with MOSFET instead of BJT. increases output resistance, but reduces .
CASCODE STRUCTURE
Basic Cascode: Cascode = cascade to cathode
For FET:
For BJT: ( ) ( )
Regulated Cascode:
REFERENCES
Simple Current Source:
Widlar Current Source: for very small currents (µA) using only moderate resistor sizes
for BJT:
( ⁄ )
for FET: (not widely used)
√
( ⁄ )
,
√
( ⁄ )
√ √
Wilson Current Source:
Simple Voltage Source:
The bulk off all PFETs are connected to .
TRICKS
STUFF FROM THE EXERC ISE
High Swing Cascode Current Mirror:
usually , blabla
BASIC AMPIFIERS
UNSORTED
PMOS: , small-signal model accordingly flipped
ADMINISTRATIVE
Testing:
start: icdesign ams-hk3.70 -tech c35b3 & user: aic04 pass: 7qf-D3Lr user: aic20 pass: afto1]Xb
IMAGE ARCHIVE
sophisticated small-signal bjt
MOSFET hybrid-pi
MOSFET physical model
supply independent biasing
Single-Ended Amplifier
Emitter-Coupled pair
Source-Coupled pair
Differential Input to Single-Ended Output
SINGLE-STAGE OTA
AC ANALYSIS
mit ( ) , :
⏞
( ) [ (
)]
( ) [
( )⏟
]
Basic Idea: Stability problem in feedback conf., if gain>1 where 180°, because
DESIGN CONSTRAINTS
DC Gain:
| ( ) √
( ⁄ )
Output Swing:
√
( ⁄ )
, √
( ⁄ )
Slew Rate:
∫
GBP: (gain-BW-prod)
| |
UGBW: (unity-gain-BW)
|| | ( )
( )
Phase Margin: (
| |)
( )
SINGLE-STAGE CASCODE OTA
Comparison to non-cascode OTA: higher gain, higher output resistance, smaller output swing Additional pole of M9/M10-cascode at much higher frequency Gain Function:
( ) (
) (
)
with
DESIGN CONSTRAINTS
( ) ( )
( | |) ( | |)
mit
( ) und
:
o
( ), if | | | |
o (
| |)
⏟
(
| |)
⏟
⁄ Noise consideration: , because noise-power
, PMOS less noisy Typical performance of single-stage cascade OTA in 0.5µm CMOS process:
FOLDED CASCODE CMOS OTA
⁄ ⁄
( ) (
)
( ( ) )
Folded Cascode BiCMOS OTA: Difference: Replace M3,M4,M5,M6 with npn Q3,Q4,Q5,Q6 Comparison: improves by 6 dB, higher for npn BJTs, can be higher fastre OpAmp TODO: 2
nd Order Amplifier Model
REGULATED CASCODE
Principle:
NORTON-EQUIVALENT
( ) |
( ( ) ( )⁄ )
( ) ( ) | ( )
( )
SMALL-SIGNAL ANALYSIS
Applying KCL and simplifying with and and | | | | | |:
( ) (
)
FULLY DIFFERENTIAL O TA
SIMPLE FULLY DIFFERE NTIAL OTA
COMMON-MODE (CM) FEEDBACK
FULLY DIFFERENTIAL T ELESCOPIC CASCODE OTA
SWITCHED CM FEEDBACK
Example:
FULLY DIFFERENTIAL V S. SINGLE ENDED
Adv. of fully differential Amps Adv. of single ended Amps
Better PSRR (power supply rejection) Better CMRR (common mode reject.)
= diff. gain / common mode gain Double output swing for low volt. Higher SNR No extra diff. to single ended conv.
Less area consumption No extra common-mode feedback Requires less effort to design
TWO STAGE AMPLIFIERS
COMPARATORS