Docstoc

Operational Amplifiers _Op Amps_

Document Sample
Operational Amplifiers _Op Amps_ Powered By Docstoc
					Operational Amplifiers (Op Amps)

         Discussion D3.1
    Operational Amplifiers (Op Amps)

•   Ideal Op Amp
•   Non-inverting Amplifier
•   Unity-Gain Buffer
•   Inverting Amplifier
•   Differential Amplifier
•   Current-to-Voltage Converter
•   Non-ideal Op Amp
                   Ideal Op Amp
                                 VDD
                  i    v                         VSS  v0  VDD
                             +
                             -                vo
                   i   v
                                 VSS


1)   v0  Av  v  v 
     The open-loop gain, Av, is very large, approaching infinity.

2)   i  i  0
     The current into the inputs are zero.
Ideal Op Amp with Negative Feedback
                v            +
                                             vo
                v             -


                             Network



 Golden Rules of Op Amps:

   1. The output attempts to do whatever is necessary to
      make the voltage difference between the inputs zero.

   2. The inputs draw no current.
Operational Amplifiers (Op Amps)
•   Ideal Op Amp
•   Non-inverting Amplifier
•   Unity-Gain Buffer
•   Inverting Amplifier
•   Differential Amplifier
•   Current-to-Voltage Converter
•   Non-ideal Op Amp
               Non-inverting Amplifier
vi        v                 Closed-loop voltage gain
               +        vo
          v                                vo
               -                     AF 
                                            vi
                   R2
     R1                                           R1
                              vi  v  v            vo
                                               R1  R2


                                   vo     R2
                               AF   1 
                                   vi     R1
Operational Amplifiers (Op Amps)
•   Ideal Op Amp
•   Non-inverting Amplifier
•   Unity-Gain Buffer
•   Inverting Amplifier
•   Differential Amplifier
•   Current-to-Voltage Converter
•   Non-ideal Op Amp
                    Unity-Gain Buffer
vi         v                     Closed-loop voltage gain
                +
           v                vo                 vo
                -                        AF 
                                                vi

                                      vi  v  v  vo


                                              vo
                                       AF       1
                                              vi


Used as a "line driver" that transforms a high input impedance
(resistance) to a low output impedance. Can provide substantial
current gain.
Operational Amplifiers (Op Amps)
•   Ideal Op Amp
•   Non-inverting Amplifier
•   Unity-Gain Buffer
•   Inverting Amplifier
•   Differential Amplifier
•   Current-to-Voltage Converter
•   Non-ideal Op Amp
            Inverting Amplifier
Current into op amp is zero                            R2
                                         ii
      v  v  0              ii             v
                          vi                       -        vo
                                    R1        v
             v  0 vi                              +
         ii  i    
                R1   R1

             0  v0 v0
        ii                          vi v0
               R2    R2                 
                                      R1 R2

                                           vo   R
                                    AF        2
                                           vi   R1
Operational Amplifiers (Op Amps)
•   Ideal Op Amp
•   Non-inverting Amplifier
•   Unity-Gain Buffer
•   Inverting Amplifier
•   Differential Amplifier
•   Current-to-Voltage Converter
•   Non-ideal Op Amp
          Differential Amplifier
                                                             R2   i1
Current into op amp is zero
                                       i1   R1     v
                                  v1                     -
        v  v                                    v                  vo
                                  v2                     +
                                            R1
                  v1  v
           i1                                          R2
                     R1
               v  v0
          i1 
                 R2                     v1  v v  v0
                                               
              R2                           R1     R2
       v          v2
            R1  R2                  R2           R2
                              v1          v2           v2  v0
                                   R1  R2      R1  R2
                                              
                                    R1                R2
              Differential Amplifier
                                                                   R2   i1
       R2           R2
v1          v2           v2  v0
     R1  R2      R1  R2                    i1
                                       v1
                                                  R1     v
      R1                R2                                     -             vo
                                                         v
                                        v2                     +
                                    2
                                                  R1
      R2      R2               R                              R2
v0   v1          v2             2
                                        v2
      R1    R1  R2      R1  R1  R2 

        R2      R2  R2 
  v0   v1          1   v2
        R1    R1  R2  R1 
                                                       R2
                                                  v0      v2  v1 
                                                       R1
Operational Amplifiers (Op Amps)
•   Ideal Op Amp
•   Non-inverting Amplifier
•   Unity-Gain Buffer
•   Inverting Amplifier
•   Differential Amplifier
•   Current-to-Voltage Converter
•   Non-ideal Op Amp
Current-to-Voltage Converter
       v
            +
                           vo
       v   -                       ii  i f
 ii
                                 v  v  0
            RF     if
                                0  v0  i f RF
                 v0  ii RF

      Transresistance  v0 ii   RF
                Photodiode Circuit
     ii  25 A per milliwatt of incident radiation
           v
                +
           v             vo
                -
      ii                       At 50 mW
h

                     if    ii  50  25 106  1.25mA
                RF
                           Assume RF  3.2k

      v0  ii RF  1.25 103  3.2  103  4V
Operational Amplifiers (Op Amps)
•   Ideal Op Amp
•   Non-inverting Amplifier
•   Unity-Gain Buffer
•   Inverting Amplifier
•   Differential Amplifier
•   Current-to-Voltage Converter
•   Non-ideal Op Amp
             Non-ideal Op Amp
•   Output voltage is limited by supply voltage(s)
•   Finite gain (~105)
•   Limited frequency response
•   Finite input resistance (not infinite)
•   Finite output resistance (not zero)
•   Finite slew rate      slew rate  dv0 (t ) dtMAX
•   Input bias currents
•   Input bias current offset
•   Input offset voltage
•   Finite common mode rejection ratio (CMRR)

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:2
posted:10/9/2011
language:Dutch
pages:18