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Reduction of Steady-State Error by Positive Feedback for Minimization Of Reactances

IP.com Disclosure Number: IPCOM000100481D
Original Publication Date: 1990-Apr-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 78K

Publishing Venue

IBM

Related People

Jove, SA: AUTHOR [+5]

Abstract

Disclosed is a positive feedback circuit used within the negative feedback loop of an amplifier with a high-pass frequency characteristic. The objective of this circuit is to lower the steady-state error of the amplifier without changing the frequency response and without increasing the size of the reactances or the resistance values within the feedback loop.

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Reduction of Steady-State Error by Positive Feedback for Minimization Of Reactances

       Disclosed is a positive feedback circuit used within the
negative feedback loop of an amplifier with a high-pass frequency
characteristic.  The objective of this circuit is to lower the
steady-state error of the amplifier without changing the frequency
response and without increasing the size of the reactances or the
resistance values within the feedback loop.

      A generalized configuration for an amplifier with a high-pass
frequency characteristic is shown in Fig. 1. Ve(s) is calculated as:
         (s B R1 C1 + 1)
Ve(s) = ----------------------- Vi,
       s B R1 C1 + 1 + go B Ro
with go B Ro >> 1, the steady state error Ve(0) is Vi/(go B Ro)
and the -3 dB frequency is go Ro/(2 pi R1 C1).

      An improvement over the system of Fig. 1 is shown in Fig. 2.
Ve(s) is calculated now as:
         (s B R1 C1 + 1 - g1 B R1)
Ve(s) = --------------------------------- Vi.
        s B R1 C1 + 1 - g1 B R1 + go B Ro
By choosing g1 B R1 = 1, the steady-state error Ve(0) is reduced to
zero, while the -3 dB frequency is unchanged: the extra degree of
freedom g1 provides, allows a reduced steady-state error without
sacrificing frequency response and without increases of power
dissipation, capacitor size or power supply voltage.

      The disclosed circuitry which performs the function of the
added transconductance stage in Fig. 2 is shown in Fig. 3...