Lecture 12. Transistor Bias Section 5.1-5.2. K-30/AK-710 FM Wireless Microphone. Radio Frequency Oscillator. Radio Frequency Amplifier. Audio Amplifier. Operating Point Analysis and Design. Simple Biasing. Assumed VBE and β → IB→IC →VC. Comments: IB is sensitive to VBE.
Assumed VBE and β → IB→IC →VC
IB is sensitive to VBE.
IC is very sensitive to β.
(Kick off iteration with VBE=0.7)
Variation of gm implies that the gain of the amplifier
will vary significantly as a function of beta.
Assume the base current is negligible,
i.e. negligible compared to the current
IC does not depend on Beta!
1% error in R2 leads to 14 % error in IC.
5% error in R2 leads to 85 % in IC.
If R2↑→VP↑→IE↑→VRE↑→small ∆VBE
An error in VX due to inaccuracies in R1, R2 and VCC is absorbed by RE, leading to a smaller change in VBE.
VRE should be > 100 mV.
1% error in R2 leads to 1.05 % error in IC.
5% error in R2 leads to 5.7 % error in IC.
Initial assumption: VBE=0.7 V