9/27/11 1 Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Semiconductors and operational amplifiers (Op Amps) 1- Semiconductors 2- Op Amp definitions 3- Circuits – comparator, voltage follower, current follower 4- Mathematical operations with Op Amps -Sections 2C, 3A to 3E Suggested exercises: 3-3, 3-6, 3-8, 3-10, 3-13, 3-16 Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Figures 2-15, 2-16, Section 2C symbol Forward biased reverse biased (see photodiode) Current-voltage plot A pn-junction diode (semiconductor) Forward bias Reverse bias Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Equivalent circuit representation of an Op Amp Figure 3-1, Section 3A Made with many integrated circuits, semiconductors Zi = Input impedance Zo = Output inpedance PS = Power supply (± 15 V) A = Amplification (Gain)9/27/11 2 Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Various Op Amp Representations Figure 3-2, Section 3A Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Comparator Mode Figure 3-4, Section 3B vs : (-13 µV to +13 µV) , if A = 106 vo = A vs = A (v+ - v-) (+ 13V) (- 13V) (+ 15V) (- 15V) A = - slope Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Current Follower Circuit Prevents loading error, accurate current measurement Figure 3-6, Section 3B (Equation 3-8, current-to-voltage converter) vo = - ii (Rf) Summing point S ii = if + ib Eq 3-3 i b ~ 10-11 – 10-15 A9/27/11 3 Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Current follower in a photometer Figure 3-10, Section 3C Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Voltage Follower Circuit Prevents loading error, high power gain Figure 3-5, Section 3B (Equation 3-2, open loop gain) € Vo= ViAA + 1Voltage Loop vo = vi + vs Eq 3-1 € Power gain =PoPi=iovoiivi=ZoZi (See Equation 2-3Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Inverting Voltage Amplifier Circuit Prevents loading error, accurate measurement of Vi Figure 3-7, Section 3B (Equation 3-8, closed loop gain) € Vo= −ViRfRiOn your own, calculate the power gain9/27/11 4 Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Voltage follower in voltage measurements Figure 3-11, Section 3C V-=? Vo=? 1 2 V-=? Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Difference Amplifiers analyte signal minus reference signal, rejects drift and noise Figures 3-13, Section 3C = - (Equation 3-15) Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Multiplication or division Figure 3-16, Section 3E9/27/11 5 Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Addition or Subtraction Figure 3-16, Section 3E (Equation 3-17) Lecture 10 – Sep 28 Chem 4101 – Fall 2011 Integration Figure 3-16, Section 3E (Equation
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