Question

2. (30 pts) Frequency Response Voo R3 R2 R5 + C4 HE C2 HH C3 R4 M WE Ri C1 RO Vo VA R1 -VOD A. (2 pts) What cutoff frequency is influenced by C1, C2, C3, and C4? (circle one) OL OH B. (3 pts) Write the expression to estimate this cutoff frequency in expanded form (i.e. there should not be a summation symbol in your expression). C. (25 pts) Write an expression (in terms of the small signal parameters and the resistors in the circuit) for each resistance used in the estimate of the cutoff frequency expression in part B. Draw ALL circuits for full credit and write circuit equations to justify or explain your answer. Assume ro is infinite for the BJT, but include ro for the MOSFET.

Answer 1

Sol A are - C1, C2, (3,84 these coupling capaitors. coupling capacitors are responsible for low cut off frequeny wi WH 3 small signal model L₂ IH + HAI + VT more R2 Ral 1R3 vgs igmugs C44 li -3 wa Ro R & {{{- figure o 1 + I ha + 2X LICRITRI) 2162(R2+f411R:) DAC3(Rotfello) + IN CARS

F C 11- + 171 gmbre ਨ R2/1R3 mugs r। ST 44 Ri 있 H3 Ro 63 figure 1

from figure ① using open time constant methoch frequency th due to a capacitor flia تار- T = 20 G(Ri+R) ful 2XL (Ritra - frequency due to cz capacitor fl2 = 1 4 22 TL2 = 29 C2( Rz7R411 R3) $12 = I'acz (Retralia) frequency due to (3 capacitor 423 = 1 h TL3 1 τι και 2 2XL3R6 6 + rollel) fL3 2763(R6 + 8011 RL) frequely due to ea f24a ti TL 4 f L4 2 29 C4 R5 2 R C 4 R5 111 CARS