"Chapter 1 - The Op Amp's Place in the World" - HTL Wien 10

11.3.6 Large Signal Differential Voltage Amplification
Additional Parameter Information
Large signal differential voltage amplification, AVD, is similar to the open loop gain of the
amplifier except open loop is usually measured without any load. This parameter is usually
measured with an output load. Figure 11–11 shows a typical graph of AVD vs. frequency.
AVD is a design issue when precise gain is required. The gain equation of a noninverting
amplifier:
Gain 1
1
1 1
AVD
Understanding Op Amp Parameters
(11–2)
is a feedback factor, determined by the feedback resistors. The term 1
in the equa-
AVD
tion is an error term. As long as AVD is large in comparison with 1
, it will not greatly affect
the gain of the circuit.
11.3.7 Input Parasitic Elements
Both inputs have parasitic impedance associated with them. Figure 11–5 shows a model
of the resistance and capacitance between each input terminal and ground and between
the two terminals. There is also parasitic inductance, but the effects are negligible at low
frequency.
Input impedance is a design issue when the source impedance is high. The input loads
the source.
Vn
Vp
+
_
Cd
Figure 11–5.Input Parasitic Elements
Rd
Cn
Cp
Rn
Rp
11-13