TIDUEU6B September 2020 – December 2021 OPA810

- Description
- Resources
- Features
- Applications
- 5
- 1System Description
- 2System Overview
- 3Hardware, Software, Testing Requirements, and Test Results
- 4Design Files
- 5Software Files
- 6Related Documentation
- 7Revision History

When the unknown impedance to be measured is capacitive i.e. C_{X}, it forms the circuit shown in Figure 2-3. The transfer function of V_{F} is given in Equation 4.

Equation 4.

In comparison with Equation 2, Equation 4 shows that due to presence of R_{G}, there is a pole-zero combination in the feedback path. The zero and pole frequencies in 1/β are given by,

Equation 5.

Equation 6.

The pole and zero frequencies hold the relation ω_{P} = 2*ω_{Z} because R_{G} is equal to R_{F} in every R_{G} - R_{F} setting.

This provides the advantage of an inherent pole to
cancel the zero. Figure 2-8 shows that the rate of closure of Aolβ is 20 dB/dec for almost all the
C_{X}. The exception for this fact is when f_{CL} lies between
f_{Z} and f_{P}. The R_{G} - R_{F} settings are
selected such that this situation is avoided. This allows for a key factor of this
design where ω_{P} = 2*ω_{Z} is independent of the value of
C_{X}. The measurement can be done in two ways as explained below,