ELECTRONIC DEVICES. Assist. prof. Laura-Nicoleta IVANCIU, Ph.D. C10 Applications with OpAmp - 2

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1 ELECNC DEVCE Assist. prof. Laura-Nicoleta VANCU, Ph.D. C10 Applications with pamp - 2

2 Contents Half-wae and full-wae precision rectifiers Precision peak detectors Current sources Logarithmic and exponential amplifiers Circuits for multiplication and diision Laura-Nicoleta VANCU, Electronic deices 2

3 Basic applications of pamps with negatie feedback nerting/non-inerting amplifier (C7, L11) Differential amplifier (C8, L11) umming amplifier (inerting/non-inerting) (C8) ther applications of pamps with negatie feedback: Voltage domain conersion circuits (C9) Capacitiely coupled amplifiers (C9) p-amp amplifiers operated from a single power supply (C9, L12) ntegrators and differentiators actie filters (C9) Half-wae and full-wae precision rectifiers (C10) Precision peak detectors (C10) Current sources (C10) Logarithmic and exponential amplifiers (C10) Circuits for multiplication and diision (C10) Laura-Nicoleta VANCU, Electronic deices 3

4 Half-wae and full-wae precision rectifiers Preiously on ED (C3) Half-wae rectifier Problems: small signals can t be rectfied (D - off) some oltage (0.7 V) is wasted across the conducting diode olution: Precision rectifier: uperdiode (almost) zero oltage drop across the conducting superdiode Circuit? Laura-Nicoleta VANCU, Electronic deices 4

5 Half-wae and full-wae precision rectifiers Half-wae precision rectifier i D cannot become negatie 0 perating principle: > 0,oa > 0.6 V, (D) on, NF Circuit for rectifying the for > 0 negatie half-wae? < 0,oa < 0, (D) off No NF -> pamp works as a simple comparator, non-inerting,oa V L, 0 (no current through L ) for < 0 Laura-Nicoleta VANCU, Electronic deices 5

6 Half-wae and full-wae precision rectifiers nerting half-wae precision rectifier aoiding saturation PNAL VC < 0; D2 ( on); D1 ( off ) NF through D2 and 2;, oa + 0.7V pamp actie region > 0; D ( off ); D1 ( on) NF through D1;, 0.7V pamp actie region + 2 oa Laura-Nicoleta VANCU, Electronic deices 0; 0 6

7 Half-wae and full-wae precision rectifiers Full-wae precision rectifier superdiodes perating principle > 0, D 1 -(on), D 2 (off) < 0, D 1 -(off), D 2 (on) - Circuit? Laura-Nicoleta VANCU, Electronic deices 7

8 Half-wae and full-wae precision rectifiers Full-wae precision rectifier A1 > 0, D 1 - (on), D 2 (off) NF only for A1, A2 < 0, D 1 -(off), D 2 (on) NF only for A2, -(/) - Laura-Nicoleta VANCU, Electronic deices 8

9 Precision peak detectors Precision positie peak detector PNAL he diode from the common peak detector is replaced with a superdiode. Laura-Nicoleta VANCU, Electronic deices 9

10 Precision peak detectors Precision positie peak detector PNAL Precision positie peak detector that holds the oltage - D 2 preents negatie saturation of A1 - A2 oltage follower (buffer) - A1 local NF, when D 2 - (on),, A1 is limited to 0.7 V - proides a small current through D 2 Laura-Nicoleta VANCU, Electronic deices 10

11 Current sources Voltage controlled current source PNAL i i does not depend on the alue of L adjustable i - replace with ( + P) Circuit? Why can t be replaced only with P? alue of i is controlled by the alue of L is not connected to ground -> floating load?circuit with non-floating load? Laura-Nicoleta VANCU, Electronic deices 11

12 Current sources Current source with non-floating load PNAL Howland source NF and PF, NF is dominant K K L 4 1 L + 1 ince L <, K - > K + -> NF + Laura-Nicoleta VANCU, Electronic deices 1 2 L + L + i i 1 + i o, A o, A o, A i o, A i 0 L

13 Current sources PNAL For i 1 he pairing of the resistors should be ery accurate, in order to obtain a perfect current source (infinite output resistance). Practical solution: current source using pamp and BJ/M Laura-Nicoleta VANCU, Electronic deices 13

14 Current sources Current follower PNAL he current source does not generate power he power in the load resistor, L, is obtained from the power supplies of the pamp ale A Laura-Nicoleta VANCU, Electronic deices 14

15 Logarithmic and exponential amplifiers Logarithmic amplifier PNAL BE V ln 1 i i C C 1 e V BE For < 0 - use pnp transistor BE V ln i C Limitations of the circuit: - the range of the output oltage is narrow, hundreds of mv ( is a base to emitter oltage); - temperature dependence of the output oltage (V and ) Laura-Nicoleta VANCU, Electronic deices 15

16 Logarithmic and exponential amplifiers Exponential amplifier PNAL i C 1i C BE e V BE e V 1 e V Laura-Nicoleta VANCU, Electronic deices 16

17 Circuits for multiplication and diision Multiplication circuit PNAL BE1 BE 2 V V 1 ln 11 ln 2 12 BE4 BE1 + BE2 14 e V BE e ln ( ) ( ln + ) e ln Laura-Nicoleta VANCU, Electronic deices 17

18 Circuits for multiplication and diision Multiplication and diision circuit BE1 BE2 V BE3 V ln PNAL V 1 ln 11 2 ln BE4 BE1 BE2 BE3 14 e V BE For equal resistances: No temperature dependence! Laura-Nicoleta VANCU, Electronic deices 18

19 ummary ur last encounter with the pamp (this semester) showed us how it can be used to obtain: Half-wae and full-wae precision rectifiers Precision peak detectors Current sources Logarithmic and exponential amplifiers Circuits for multiplication and diision Although it s quite sad to see it wae Goodbye with all its terminals, our journey must continue. New challenges await. Next week: ransistors. BJs. o do: Homework 8 Laura-Nicoleta VANCU, Electronic deices 19