ho20.l17_multi_stage

# ho20.l17_multi_stage - Lecture 17 Multi-Stage...

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1 Lecture 17 Multi-Stage Amplifiers (Single-Ended) R. Dutton, B. Murmann R. Dutton, B. Murmann 1 EE114 (HO #20) Stanford University Multi-stages--getting started So, what do we need to think about? •What are constraints? •Source signal/impedance + Load •Gain and Bandwidth requirements •Power budget and Biasing •What is the right technology? •IC or discrete (we’ve discussed in Lect. 1… dc-coupled IC is our focus) R. Dutton, B. Murmann 2 dc coupled, IC is our focus) •Other systems issues: •Power supplies (what’s available; head room) •Noise (both intrinsic [see EE214] and chip/board level) EE114 (HO #20)

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2 Reminders about Basics What have we learned (so far) about Stages? •CS, CD: =High Impedance (R in ); A v (some vs. ~1); BW (Miller vs.none) •CG: =Low Impedance (R in ); current buffer; BW(no Miller) Cascode, our first multi-stage: •Way to exploit CG and overcome CS limit (BW); requires extra bias/headroom Biasing R. Dutton, B. Murmann 3 •Replicated current-source biasing--both to set gain-stage biasing and for loads--is the best plan. Matching! Ratioed W values EE114 (HO #20) Cascading (and for what purpose) Purpose : handle impedances… with appropriate gain CS-CD--A V + Output Buffer: CS-CS--Lots of A V : •High R in ; moderate/high R out •Gain! •Limits for cascading CG-CS--Trans-Impedance: Low R ; moderate/high R R. Dutton, B. Murmann 4 •High R in ; Low R out •Modest Gain •Low R in ; moderate/high R out •I-to-V Gain (trans-resist.) EE114 (HO #20)
3 An Example--A Multi-Stage Amplifier Assume a 1 μ A (ac) source (I.e. coming from a photo- diode) that needs to be amplified across a wide bandwidth to a 1V level with a load of 10pF. (A case study directly related to the Design Project) Observations: Input Current (need a good input buffer for current, that does not load the source very much) How about a unity current gain buffer --very low input impedance and very high output impedance with A I ~1 Output Voltage into a rather small impedance; this again sounds like a buffer is needed For example a unity R. Dutton, B. Murmann 5 sounds like a buffer is needed.

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ho20.l17_multi_stage - Lecture 17 Multi-Stage...

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