ampdesign - ECE145A/ECE218A AMPLIFIER DESIGN In other...

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ECE145A/ECE218A AMPLIFIER DESIGN12/14/071 Prof. Stephen Long, ECE/UCSBIn other courses, you have learned to design amplifiers using small signal models for devices. This works reasonably well at lower frequencies, but at high frequencies often the device S.S. model is not accurate enough. Then, measured s-parameters can be used to accurately design the amplifier. The s-parameter design technique employs relationships between input and output powers, forward and reflected powers that look scary at first but can easily be derived using the signal flow graph method and Mason’s gain rules. (Gonzalez, Sec. 2.6) Our sequence of topics will include: 1.Signal flow graph method (homework) 2.Power gain definitions 3.Stability of amplifiers 4.Unilateral approximation (S12=0) 5.Bilateral design 6.Bias circuits and wideband stability Goal: Learn to design stable narrowband amplifiers using S parameters
ECE145A/ECE218A AMPLIFIER DESIGN12/14/072 Prof. Stephen Long, ECE/UCSBRecall the definition of the S parameters: 11111222211222bS aS abS aS a=+=+Consider the forward transmission and calculate the transducer power gain: 2221102outgenaVbSVa===In general, for an arbitrary RSand RL, 2282genoutAVSLSLVVPPRR==The definition of transducer power gain: LTAVSPGP=So, for the special case where RS= RL= ZO, 222212248||2outoutOTgenOgenVVZSGVZV===a1a2b2b1A transistora1a2b2b1Sa1a2b2b1A transistor
3 Prof. Stephen Long, ECE/UCSB. ´ ³ Γ´ ³ SMN
4 Prof. Stephen Long, ECE/UCSB
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ECE145A/ECE218A AMPLIFIER DESIGN12/14/075 Prof. Stephen Long, ECE/UCSBOther gain definitions can also be used for specific purposes Operating Power Gain=GP=Power delivered to loadPower input to network2221222211 ||||1 |||1|LPINLGSS− Γ=− ΓΓThis can be useful because it eliminates the dependence of gain on ΓS- helpful when the device is bilateral

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