1. CHAPTER 5: FREQUENCY RESPONSE DR. PHẠM NGUYỄN THANH LOAN
Hà Nội, 9/24/2014

2. Frequency Response Introduction Models Low frequency response
Miller effect
High frequency response

3. Introduction
Relation of gain and input frequency: Bode diagram

4. Introduction Cut-off frequency (fc): gain decrease of 3dB (0.707)
f1 : fc at low frequency region
f2: fc at high frequency region
A=ao/(1+jf/ft)
|A|f=ft=ao/sqrt(2)  log|A|=log ao – 3dB ( )

5. Filter models
…. pass filter

6. Filter models
Low pass filter
High pass filter

7. High pass filter Equivalent capacitor short circuit at high frequency
open circuit at low frequency

8. Model - High pass filter
Low frequency
Open-circuit equivalent Capacitor
=> Vo=0, Av=0
High frequency
Short - circuit equivalent Capacitor
=> Vo=Vi, Av=1

9. short circuit at high frequency open circuit at low frequency
Model - Low pass filter
Equivalent capacitor
short circuit at high frequency
open circuit at low frequency

10. Open-circuit eq. capacitor => Vo= Vi , Av= 1
Model - Low pass filter
Low frequency,
Open-circuit eq. capacitor
=> Vo= Vi , Av= 1
High frequency,
Short-circuit eq. capacitor
=> Vo= 0 , Av=0

11. Model - Cut-off frequency

12. Model - Cut-off frequency
fc: gain reduces 0,707 times (3dB)

13. Low frequency response EC amplifier
Low frequency can be determined from:
Cin (fLs) at input
Cout (fLo) at output
Cemitter (fLe)
f1 = fL = Max( fLs, fLo, fLe )

14. fc introduced by input capacitor
with

15. fc introduced by output capacitor
with

16. fc introduced by emitter capacitor
with

17. FET amplifier Similar to BJT amplifier 3 capacitors: mCG, CC, CS
fLG=1/[2π(Rsig+Ri)CG] with Ri=RG
fLC=1/[2π(Ro+RL)CC] with Ro=RD//rd
fLs=1/[2π(ReqCs] with Req=Rs/[1+Rs(1+gmrd)/(rd+R D//RL)]

18. Miller effect Cf: feedback capacitor Inverting amplifier
Equivalent of Input and output capacitance
CMin = (1-Av)Cf
CMout = (1-1/Av)Cf ≈ Cf when Av is very big

19. High frequency response EC amplifier
Vùng tần số cao bị giới hạn bởi các khâu lọc thông thấp do các tụ kí sinh Cbc, Cce, Cbe, Cwi, Cwo

20. High frequency response EC amplifier
Ci=CWi+Cbe+CMi Co=CWo+Cce+CMo

21. High frequency response EC amplifier

22. How to choose cutoff frequency?

23. High frequency response FET amplifier
Tham khảo trang 546, Electronic devices and circuit theory

24. Determine ao, ao(dB) bandwidth, fc?
Given Bode diagram

25. Example A)Determine voltage gain B) Determine fLs, flC, FlE
C) Determine fHi, fH0
D) Plot Bode diagram

26. Homework
Chapter 11: 10, 11, 15, 17, 18, 19, 22, 26, 28, 29, 32