ANALOG INTEGRATED CIRCUITS Summary of the Lectures by Prof. Dr. Q. Huang Lukas Cavigelli, December 2011 [email protected] 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: