Presentation on theme: "Lecture 7 Frequency Response. Review of CS, CG and CD Amplifier."— Presentation transcript:
Lecture 7 Frequency Response
Review of CS, CG and CD Amplifier
Voltage Gain of a CS Amplifier Interpretation: The resistance at the drain Divided by the resistance in the source path
Voltage Gain of a CD Amplifier
Voltage Gain of a CG Amplifier If RS=0 and channel length modulation is ignored, A v is
Resistance into the Drain Terminal
Resistance into the Source Terminal
Typical Application of Miller’s Theorem Miller’s theorem is useful when Z appears in parallel with the main signal (i.e. the amplifier)
Limitation of Miller’s Theorem Limitations: Interaction of poles through R3 and C3.
Association of Poles with Nodes Each pole is determined by the product of 1.Total capacitance seen from each node to ground 2.Total resistance seen at the node to ground “Each node in the circuit contributes one pole to the transfer function”
CS Trade-Off L(um)W(um)GDS (uS)CDB (fF)CGD(fF)CGS(fF) n n n For Same IOUT, L↓→W↓→GDS↑(Ro↓) →CDS ↓ Trade-offs in GDS and parasitic capacitance. Specs: AV=10 Vo,cm=0.6V I(M1)=10 uA g m =AV/RD Gmoverid_1=16.67
CS Trade-Off AVI (uA)L(um)W(um)GDS (uS)CDB (fF)CGD(fF)CGS(fF) ,041.1 For Same IOUT, L↓→W↓→GDS↑(Ro↓) →CDS ↓ Difficult to achieve high gain and high speed at the same time! Specs: Vo,cm=0.6V g m =AV/RD
Output Impedance Only Valid if Rs is large!
Input Impedance Exclude CGS High frequency approximation (First order model)
Input Impedance (KCL) Exclude CGS High frequency approximation (In parallel with CGS)
“Nodal Method”(Miller Approximation) Numerical example: RS=50 Ohms L=2.0 um AV=15 f in =4.65 GHz f out =69.9 MHz fF 16(10.40fF) CDB=27.51 fF, RD=60 KOhm It is important to identify the high impedance node!
“Nodal Method”(Refined Miller Approximation) (Resistive) (Capacitive) (If RS is large!)
Equivalent Circuit Analysis
Comparison to Miller Approximation
Dominant Pole Approximation
Transmission Zero Finding a transmission zero in effective Gm.
Source Follower (Strong interaction between XY, making it difficult to associate each pole with each node)
Analysis of Input Impedance Miller Approximation: Av: (Negative Resistance) Can be used to oscillators.
Equivalent Output Impedance
Cascode (Gain from A to X)
DC Input Resistance Will a large Rin increase the miller effect of CS dramatically ?
Input Resistance of Common Gate Note that ZL is not infinity if RD is replaced by a current source because ZL is in parallel with CD.