note7 - Handout 7 ECE 315, Cornell University 1 First-Order...

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Unformatted text preview: Handout 7 ECE 315, Cornell University 1 First-Order Frequency Analyses of Transistors What you will learn: The Bode plot and the frequency analyses MOSFET capacitances and non-quasi-static models The cutoff and corner frequencies BJT capacitances and high-frequency models Frequency response of CS/CE and CG/CB amplifiers Frequency response of diff pairs Handout 7 Handout 7 ECE 315, Cornell University 2 7.1 First-Order Circuits with Single-Time Constant (STC) The small-signal capacitance in MOSFET and BJT. The generalized Bode plot and the relation to the dominant pole in the first-order circuits. Use Miller theorem and open-circuit time constant to find the dominant pole and corner frequency. Textbook reading: App. D/E Handout 7 ECE 315, Cornell University 3 CMOS Capacitances in Geometry LOCOS or shallow- trench isolation Junction isolation 1 1 2 2 body contact well contact C OV WLC ox Handout 7 ECE 315, Cornell University 4 Layout-Corresponding CMOS Capacitances in Small-Signal Circuit Models Body effect with source and drain not connected: C sb >> C db Fig. 4.47 Handout 7 ECE 315, Cornell University 5 Simplified CMOS Capacitances in Small-Signal Circuit Models No body effect with source and drain shorted: C sb folded into C gs C db usually much smaller in saturation Handout 7 ECE 315, Cornell University 6 Source Drain Channel Gate inversion region L V DS MOSFET Capacitance In Linear Region C ox WL C ox WL ov L ov C ox WL ov L ov ov ox gd gs C WLC C C + = 2 1 C db C sb Handout 7 ECE 315, Cornell University 7 Pinchoff or velocity saturation region Source Drain Channel Gate inversion region L L L L V DS V Dsat V Dsat V DS MOSFET Capacitance In Saturation C ox WL L ov L ov C ox WL ov C ox WL ov ox ov ov gd ox gs C WL C C WLC C = 3 2 Handout 7 ECE 315, Cornell University 8 MOSFET Capacitance Components ov ox gd gs C WLC C C + = 2 1 In the linear region ov gd ox gs C C WLC C 3 2 In the saturation region ox gb ov gd gs WLC C C C C = In the cutoff region L L C WL C ov ox ov ov 1 . 05 . = bi DB db db bi SB sb sb V V C C V V C C + + 1 1 These are very crude approximations, and even for quasi-static operations, fitting parameters are necessary. For non-quasi-static operations (when devices operated higher than its f C , then device simulation is needed) Handout 7 ECE 315, Cornell University 9 The Bode Plot for Low Pass = 2 / 1 ( ) ( ) ( ) ( ) RC j K j T s K s T / 1 / 1 / 1 / 1 = = + = + = ( ) ( ) 2 / 1 + = K j T ( ) ( ) 1 / tan = normalized gain in dB Fig. D.6 Handout 7 ECE 315, Cornell University 10 The Bode Plot for Real Zero 2 / 1 ( ) ( ) ( ) / 1 / 1 j s s s T + = + = + = This is the mirror inverse of the Low Pass or Real Poles Fig. E.1 Handout 7 ECE 315, Cornell University 11 The Bode Plot for High Pass = 2 / 1 ( ) ( ) ( ) RC j K j T s Ks s T / 1 / 1 / 1 = = = + =...
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note7 - Handout 7 ECE 315, Cornell University 1 First-Order...

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