EEE598D: Analog Filter & Signal Processing Circuits Instructor: Dr. Hongjiang Song Department of Electrical Engineering Arizona State University
Thursday January 24, 2002 Today: Active RC & MOS-C Circuits Basic LSI Passive & Active Components Tuning of Integrated CT Filters CR Structures Basic Active RC and MOS-C Circuit Blocks
Typical Filter Design Problems Filter Realization: Schematic SFG Block diagram etc. Analysis Design Filter Specification: Responses Dynamic range etc. Math: Diff. Equations Transformations TF etc.
Desired Features for LSI Filters Compatible with LSI process Immunity to parasitic effects, fabrication tolerances, and environment variations Large dynamic range Good power supply rejection Low power and small chip area
Typical Operation Region of LSI Filters SC/SI Filters CT Active Filters Passive LC Filters Distributed Filters f (Hz)
LSI Active RC and MOS-C Filters Direct mapping of discrete active RC filters to LSI active RC filters with CMOS compatible R, C, and Opamp realization. For MOS-C filters, resistors are mapped to MOS CRs. Tuning is usually required due to parameter variation of the LSI components.
2-stage Opamp CMOS Opamp Structures - - out
CMOS Opamp Structures OTA - - out
2-stage Cascode Opamp CMOS Opamp Structures - - out
Folded Cascode Opamp CMOS Opamp Structures - - out
Telescopic Opamp CMOS Opamp Structures - - out
Rail-to-rail Opamp CMOS Opamp Structures - - out
Fully Differential Opamp CMOS Opamp Structures - o - - o- cm
CMOS Opamp Structures Differntial Difference Amplifer (DDA)
Typical Opamp Responses
LSI Capacitor Structures Gate capacitors high density, but Nonlinear Junction capacitors Highly nonlinear Poly(metal)-to-poly (metal) capacitors Good linearity and high Q Fractal capacitor High density and good linearity More complicated structure
Double-Poly Capacitor LSI Capacitor Structures n p-substrate
MOS Capacitor LSI Capacitor Structures n n Heavy n implant (bottom plate) p-substrate
LSI Capacitor Structures Metal-Polycide Capacitor
LSI Capacitor Structures Metal-Polycide Capacitor
LSI Capacitor Structures Metal-Insulator-Metal (MIM) Capacitor
MIM Capacitor Structure
Fractal capacitor LSI Capacitor Structures Enhancement (~ 2.3x) of capacitance/area with lateral coupling
LSI Resistor Structures Diffusion Resistors Poly Resistors Well Resistors Pinch Resistors
LSI Resistor Structures Diffusion Resistor P-diffusion n-well P-substrate
LSI Resistor Structures Poly Resistor n P-substrate
LSI Resistor Structures Well Resistor n n n-well P-substrate
LSI Resistor Structures Pinch Resistor p n n n-well P-substrate P connected to p -
Example of Passive Element Accuracy
Tuning of LSI CT Filters Tuning required for CT integrated filters to account for capacitance and resistance/transconductance variations 30% time-constant variations Must account for process, temperature, aging, etc. While absolute tolerances high, ratio of two like components can be matched to under 1% Tuning can often be the MOST difficult part of a CT integrated filter design Note that SC/SI filters do not need tuning as their transfer-function accuracy set by ratio of capacitors (or transistors) and a clock-frequency
Tuning of LSI CT Filters Example:
Dr Dr. Hongjiang Hongjiang Song, Arizona State University Song, Arizona State University LSI CR Structures Basic MOS voltage controlled resistor (CR) ) 2 ( 1 ) )( 2 ( s d T G s d s d T G R I = = β β Nonlinear term Control voltage
LSI CR Structures Linear MOS CR - 1st approach c 1/2 1/2 d s I Let Then G = R = d β s 2 1 ( ) C Control voltage T C
Dr Dr. Hongjiang Hongjiang Song, Arizona State University Song, Arizona State University LSI CR Structures Linear MOS CR - 2nd approach c c d s ) ( 2 1 ) )( ( 2 ) )( 2 ( ) )( 2 ( T G s d T c s s d s d T s c s d s d T d c R I = = = β β β β I
LSI CR Structures Linear MOS CR - 3rd approach I c s - I- s s - s c c [ I R = I β ( ] = β ( C 1 T C ) T )[( s ) ( s )]
LSI CR Structures Linear MOS CR - 4th approach c1 d d I s d- s s c2 c d- I- c1 s [ I R = I β ( ] = β ( C 2 1 C 2 C 2 ) C 2 )[( d s ) ( d s )]
Dr Dr. Hongjiang Hongjiang Song, Arizona State University Song, Arizona State University LSI CR Structures Grounded Linear MOS CR d I c 2 2 ) ( 2 ) 2 ( ) 2 ( ) ( 2 T d T c d d T c T d I β β β β = = ) 2 ( 1 ) ( 1 T c d d di R = = β
LSI Resistor Structures MOS CR Implementation
LSI Resistor Structures MOS CR Implementation
LSI Resistor Structures MOS CR Implementation
LSI Resistor Structures MOS CR Implementation
Basic Active RC Circuits Fully differential gain stage R2 i -i R1 R1 - - o -o o i = R R 2 1 R2
Basic MOS-C Circuits Fully differential gain stage c2 i -i β1 c1 - β2 - β2 c2 o -o o i β = β 1 2 ( ( c1 c2 T T ) )
Basic Active RC Circuits i2 Fully differential adder stage R1 R2 i1 -i1 -i2 R1 R1 - - o -o R2 ( ) o = i 1 i 2 R 1 R1 R2
Basic MOS-C Circuits Fully differential adder c2 i2 β2 i1 o - -i1 β1 - -o β2 -i2 c1 c2 β1( c 1 T ) o = ( i 1 β ( ) 2 c2 T i2 )
Basic Active RC Circuits Fully differential integrator C i -i R R - - o -o i ( s) = o 1 RCs C
Basic MOS-C Circuits Fully differential integrator i -i c β c - - C C o -o o i ( s) = 1 Cs β ( c T )
Basic Active RC Circuits i -i Fully differential lossy integrator R1 C R o - - R -o C o i 1 ( s) = RCs R R 1 R1
Basic MOS-C Circuits i -i Fully differential lossy integrator c1 β1 C c o - β - -o C c o i ( s) = Cs β ( c T ) 1 β1( β ( c1 c T T ) ) β1 c1