Environmental Engineering Reference
In-Depth Information
7.3 HARMONIC DISTORTION AND COMPENSATION
In this paragraph we will study the effect of the different types of
frequency compensation on harmonic distortion. To this end, we will first
apply the above results to two-stage amplifiers and then a typical single-
stage amplifier will be considered. Dominant-pole and Miller techniques for
a two-stage amplifier are treated in sections 7.3.1 and 7.3.2, respectively.
Under the assumption that the second stage is the principal responsible for
nonlinear behaviour, we will demonstrate the better linearity performance of
Miller-compensated amplifiers. Linearity performance of a single-stage
architecture with dominant-pole compensation will be treated in section
7.3.3.
Linear and, unless specified, frequency-independent feedback is thorough
considered for simplicity.
7.3.1 Two-stage Amplifier with Dominant-Pole Compensation
The analysis carried out in the previous paragraph can be now directly
applied to two-stage amplifiers
compensated
with the dominant-pole
technique.
We can use the same model in Fig. 7.8, and assume and
to be a single-pole transfer function given by (7.43) and here reported again
This means that the nonlinearity is caused by the second stage. Assume also
for simplicity the nonlinear coefficients
being independent of frequency.
From (7.50) and (7.51), being
and
we get
immediately
