AC-coupled emitter follower design example

Art of Electronics 3rd ed. 2.2.5/A Input frequency range is 20Hz-20KHz Vcc is 15V Quiescent current: 1mA Step1: Choose Ve Ve=0.5Vcc (for the largest swing without clipping) Step2: Choose Re. For 1mA quiescent current, Re=7.5K Step3: Choose R1 and R2 (base bias resistors) Vb=Ve+0.6V for this R1:R2=1:1.17 Loading criterion: R1||R2<<βRe For 7.5K*β: R1=130K, R2:150K Step4: Chose C1(base decoupling capacitor) Zin ≈ βRe ≈ 750K || 70K (bias divider) ≈ 63K f3db << 20Hz 20Hz<<1/2πRC C>0.15uF Step5: Choose C2 (output decoupling capacitor) Assume Zload >> Re, so C2>1uF To avoid excessive attenuation of lower frequencies the capacitor values should be increased, so C1=0.47uF, C2=3.3uF

published 9 years ago