01_15 computers _ signal processing

01_15 computers _ signal processing - Electronics in...

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Electronics in Chemical Measurements (part 2) Chapters 2, 3&4
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Transistors (diode sandwich) Most common uses: amplifiers and low-noise switches Bipolar junction type (shown here) has three electrodes Current flows (in or out) on the base lead to initiate conduction from input (collector) to output (emitter) More current (signal) goes out than came in (i.e. amplified) pnp npn
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Transistor Amplification In this example emitter-base circuit is forward- biased (free current flow) The base-collector is reverse-biased (depletion zone) In pnp transistors p-zones have 100x more M III than the n-zones have M V (excess +-holes) The n-zone is a very thin layer (microns) so that the +-holes can migrate through relatively easily Leads to 100x amplification of current between collector and emitter
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Operational Amplifiers ( Chapter 3 ) The simplest example of a real device Made up of 10-100’s of transistors and resistors actual package length 1 cm or less two input voltages- one output voltage possible setup (in a detector) V is raw signal V + could be used to trigger data acquisition V O is amplified output signal
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) ( 0 + - - - = - = v v A Av v s A v v v 0 - = + - + - = v v i i i R v v i - - = f f R v v i 0 - = - f i i R v v R v v 0 - = - - - f i i R v A v v R A v v v 0 0 0 ) ( ) ( - - = - - + + i f i R R v v - 0
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Op-Amp Detector transducer meter circuit the whole thing is the detector I x = I f + I s I f V 0 = -I f R f = -I x R f I x = -V 0 /R f = kV 0
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Op-Amps that Do Math
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12 15 6 32 5 4 v 12 = -15 × ( v 1 /3+ v 2 /5)=-5 v 1 -3 v 2 v 0 = -12 × ( v 12 /6+ v 3 /4+ v 4 /6) = -2 v 12 -3 v 3 -2 v 4 = 10 v 1 +6 v 2 -3 v 3 -2 v 4 Design a circuit having an output given by - v 0 = 2 v 1 +3 v 2 Show the algebraic relationship between the voltage input and output for the above circuit: Example circuit calculations
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2 0 1 2 1 2 2
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01_15 computers _ signal processing - Electronics in...

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